Implement enough wrappers to start the WiFi task

Work in progress. Does not work yet.

Some notes:

  - This requires some changes to TinyGo, look at the espnet branch.
  - The  next step is probably defining all the functions in
    g_wifi_osi_funcs (see espnet.c). Right now it hangs in
    esp_wifi_init_internal, probably a NULL pointer dereference.
  - This is only for the ESP32-C3. This will require some work to work
    on other chips from Espressif.

.gitmodules

@@ -0,0 +1,3 @@
+[submodule "espnet/esp-idf"]
+	path = espnet/esp-idf
+	url = https://github.com/espressif/esp-idf.git

Makefile

@@ -2,7 +2,7 @@
 clean:
 	@rm -rf build
 
-FMT_PATHS = ./*.go ./examples/**/*.go
+FMT_PATHS = ./
 
 fmt-check:
 	@unformatted=$$(gofmt -l $(FMT_PATHS)); [ -z "$$unformatted" ] && exit 0; echo "Unformatted:"; for fn in $$unformatted; do echo "  $$fn"; done; exit 1
@@ -75,6 +75,8 @@ smoke-test:
 	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=xiao ./examples/ili9341/scroll
 	@md5sum ./build/test.hex
+	tinygo build -size short -o ./build/test.hex -target=pyportal ./examples/ili9341/slideshow
+	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=circuitplay-express ./examples/lis3dh/main.go
 	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=microbit ./examples/lsm303agr/main.go
@@ -199,12 +201,16 @@ endif
 	@md5sum ./build/test.hex
 	tinygo build -size short -o ./build/test.hex -target=wioterminal ./examples/rtl8720dn/webclient/
 	@md5sum ./build/test.hex
+	tinygo build -size short -o ./build/test.hex -target=wioterminal ./examples/rtl8720dn/webserver/
+	@md5sum ./build/test.hex
+	tinygo build -size short -o ./build/test.hex -target=wioterminal ./examples/rtl8720dn/mqttsub/
+	@md5sum ./build/test.hex
 
 DRIVERS = $(wildcard */)
 NOTESTS = build examples flash semihosting pcd8544 shiftregister st7789 microphone mcp3008 gps microbitmatrix \
 		hcsr04 ssd1331 ws2812 thermistor apa102 easystepper ssd1351 ili9341 wifinina shifter hub75 \
 		hd44780 buzzer ssd1306 espat l9110x st7735 bmi160 l293x dht keypad4x4 max72xx p1am tone tm1637 \
-		pcf8563 mcp2515 servo sdcard rtl8720dn
+		pcf8563 mcp2515 servo sdcard rtl8720dn image cmd
 TESTS = $(filter-out $(addsuffix /%,$(NOTESTS)),$(DRIVERS))
 
 unit-test:

cmd/convert2bin/convert2bin.go

@@ -0,0 +1,49 @@
+package main
+
+import (
+	"fmt"
+	"io/ioutil"
+	"log"
+	"os"
+	"strings"
+)
+
+// See ../../image/README.md for the usage.
+
+func main() {
+	err := run(os.Args)
+	if err != nil {
+		log.Fatal(err)
+	}
+}
+
+func run(args []string) error {
+	if len(args) < 2 {
+		return fmt.Errorf("usage: %s FILE")
+	}
+
+	b, err := ioutil.ReadFile(args[1])
+	if err != nil {
+		return err
+	}
+
+	fmt.Printf("const %s = \"\" +\n", strings.Replace(args[1], ".", "_", -1))
+
+	i := 0
+	max := 32
+	for i = 0; i < len(b); i++ {
+		bb := b[i]
+		if (i % max) == 0 {
+			fmt.Printf("	\"")
+		}
+		fmt.Printf("\\x%02X", bb)
+		if (i%max) == max-1 && i != len(b)-1 {
+			fmt.Printf("\" + \n")
+		}
+	}
+	if (i % max) < max-1 {
+		fmt.Printf("\"\n")
+	}
+
+	return nil
+}

dht/highfreq.go

@@ -1,4 +1,5 @@
-// +build mimxrt1062  stm32f405  atsamd51  stm32f103xx  k210  stm32f407
+//go:build mimxrt1062 || stm32f405 || atsamd51 || stm32f103xx || k210 || stm32f407
+// +build mimxrt1062 stm32f405 atsamd51 stm32f103xx k210 stm32f407
 
 package dht // import "tinygo.org/x/drivers/dht"
 

dht/lowfreq.go

@@ -1,4 +1,5 @@
-// +build arduino atmega1284p nrf52840 digispark nrf52 arduino_nano nrf51 atsamd21 fe310 arduino_nano33 circuitplay_express arduino_mega2560
+//go:build !mimxrt1062 && !stm32f405 && !atsamd51 && !stm32f103xx && !k210 && !stm32f407
+// +build !mimxrt1062,!stm32f405,!atsamd51,!stm32f103xx,!k210,!stm32f407
 
 package dht // import "tinygo.org/x/drivers/dht"
 

espnet/ap.go

@@ -0,0 +1,49 @@
+package espnet
+
+/*
+#cgo CFLAGS: -DCONFIG_IDF_TARGET_ESP32C3
+#cgo CFLAGS: -Iinclude
+#cgo CFLAGS: -Iesp-idf/components/esp_common/include
+#cgo CFLAGS: -Iesp-idf/components/esp_event/include
+#cgo CFLAGS: -Iesp-idf/components/esp_netif/include
+#cgo CFLAGS: -Iesp-idf/components/esp_wifi/include
+
+#cgo LDFLAGS: -Lesp-idf/components/esp_wifi/lib/esp32c3 -lnet80211 -lpp -lphy -lmesh -lcore
+#cgo LDFLAGS: -Tesp-idf/components/esp_rom/esp32c3/ld/esp32c3.rom.ld
+
+#include "esp_private/wifi.h"
+#include "esp_wifi_types.h"
+#include "espnet.h"
+*/
+import "C"
+
+import _ "compat/freertos"
+
+type ESPWiFi struct {
+}
+
+var WiFi = &ESPWiFi{}
+
+type Config struct {
+}
+
+var internalConfig = C.wifi_init_config_t{
+	osi_funcs:           &C.g_wifi_osi_funcs,
+	wpa_crypto_funcs:    C.g_wifi_default_wpa_crypto_funcs,
+	static_rx_buf_num:   10,
+	static_tx_buf_num:   10,
+	mgmt_sbuf_num:       6,
+	sta_disconnected_pm: true,
+	magic:               C.WIFI_INIT_CONFIG_MAGIC,
+}
+
+func (wifi ESPWiFi) Configure(config Config) error {
+	C.esp_wifi_internal_set_log_level(5)
+	return makeError(C.esp_wifi_init_internal(&internalConfig))
+}
+
+func (wifi ESPWiFi) AccessPointMAC() ([6]byte, error) {
+	var mac [6]byte
+	errCode := C.esp_wifi_get_mac(C.ESP_IF_WIFI_AP, &mac[0])
+	return mac, makeError(errCode)
+}

espnet/error.go

@@ -0,0 +1,103 @@
+package espnet
+
+// #include <esp_err.h>
+// #include <esp_wifi.h>
+import "C"
+
+// Wrapper for C.esp_err_t. Don't convert a C.esp_err_t to an Error type,
+// instead use makeError to handle ESP_OK.
+type Error C.esp_err_t
+
+// makeError converts a C.esp_err_t into an error or nil depending on whether
+// errCode indicates an error or not.
+func makeError(errCode C.esp_err_t) error {
+	if errCode == C.ESP_OK {
+		return nil
+	}
+	return Error(errCode)
+}
+
+func (e Error) Error() string {
+	switch {
+	case e < C.ESP_ERR_WIFI_BASE:
+		// esp-idf/components/esp_common/include/esp_err.h
+		switch e {
+		case C.ESP_OK:
+			return "OK" // not an error
+		case C.ESP_FAIL:
+			return "ESP FAIL"
+		case C.ESP_ERR_NO_MEM:
+			return "Out of memory"
+		case C.ESP_ERR_INVALID_ARG:
+			return "Invalid argument"
+		case C.ESP_ERR_INVALID_STATE:
+			return "Invalid state"
+		case C.ESP_ERR_INVALID_SIZE:
+			return "Invalid size"
+		case C.ESP_ERR_NOT_FOUND:
+			return "Requested resource not found"
+		case C.ESP_ERR_NOT_SUPPORTED:
+			return "Operation or feature not supported"
+		case C.ESP_ERR_TIMEOUT:
+			return "Operation timed out"
+		case C.ESP_ERR_INVALID_RESPONSE:
+			return "Received response was invalid"
+		case C.ESP_ERR_INVALID_CRC:
+			return "CRC or checksum was invalid"
+		case C.ESP_ERR_INVALID_VERSION:
+			return "Version was invalid"
+		case C.ESP_ERR_INVALID_MAC:
+			return "MAC address was invalid"
+		default:
+			return "Unknown error"
+		}
+	case e >= C.ESP_ERR_WIFI_BASE && e < C.ESP_ERR_MESH_BASE:
+		// esp-idf/components/esp_wifi/include/esp_wifi.h
+		switch e {
+		case C.ESP_ERR_WIFI_NOT_INIT:
+			return "WiFi driver was not installed by esp_wifi_init"
+		case C.ESP_ERR_WIFI_NOT_STARTED:
+			return "WiFi driver was not started by esp_wifi_start"
+		case C.ESP_ERR_WIFI_NOT_STOPPED:
+			return "WiFi driver was not stopped by esp_wifi_stop"
+		case C.ESP_ERR_WIFI_IF:
+			return "WiFi interface error"
+		case C.ESP_ERR_WIFI_MODE:
+			return "WiFi mode error"
+		case C.ESP_ERR_WIFI_STATE:
+			return "WiFi internal state error"
+		case C.ESP_ERR_WIFI_CONN:
+			return "WiFi internal control block of station or soft-AP error"
+		case C.ESP_ERR_WIFI_NVS:
+			return "WiFi internal NVS module error"
+		case C.ESP_ERR_WIFI_MAC:
+			return "MAC address is invalid"
+		case C.ESP_ERR_WIFI_SSID:
+			return " SSID is invalid"
+		case C.ESP_ERR_WIFI_PASSWORD:
+			return "Password is invalid"
+		case C.ESP_ERR_WIFI_TIMEOUT:
+			return "Timeout error"
+		case C.ESP_ERR_WIFI_WAKE_FAIL:
+			return "WiFi is in sleep state(RF closed) and wakeup fail"
+		case C.ESP_ERR_WIFI_WOULD_BLOCK:
+			return "The caller would block"
+		case C.ESP_ERR_WIFI_NOT_CONNECT:
+			return "Station still in disconnect status"
+		case C.ESP_ERR_WIFI_POST:
+			return "Failed to post the event to WiFi task"
+		case C.ESP_ERR_WIFI_INIT_STATE:
+			return "Invalid WiFi state when init/deinit is called"
+		case C.ESP_ERR_WIFI_STOP_STATE:
+			return "Returned when WiFi is stopping"
+		case C.ESP_ERR_WIFI_NOT_ASSOC:
+			return "The WiFi connection is not associated"
+		case C.ESP_ERR_WIFI_TX_DISALLOW:
+			return "The WiFi TX is disallowed"
+		default:
+			return "Other WiFi error"
+		}
+	default:
+		return "Other error"
+	}
+}

espnet/espnet.c

@@ -0,0 +1,829 @@
+#include <stdint.h>
+#include <stddef.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include "espnet.h"
+#include "esp_wifi.h"
+#include "esp_private/wifi.h"
+#include "freertos/FreeRTOS.h"
+#include "freertos/semphr.h"
+#include "freertos/task.h"
+
+
+// Stub functions, to know which functions need to be implemented for OS
+// functionality.
+
+static bool _env_is_chip(void) {
+	printf("called: _env_is_chip\n");
+	return false;
+}
+static void _set_intr(int32_t cpu_no, uint32_t intr_source, uint32_t intr_num, int32_t intr_prio) {
+	printf("called: _set_intr\n");
+}
+static void _clear_intr(uint32_t intr_source, uint32_t intr_num) {
+	printf("called: _clear_intr\n");
+}
+static void _set_isr(int32_t n, void *f, void *arg) {
+	printf("called: _set_isr\n");
+}
+static void _ints_on(uint32_t mask) {
+	printf("called: _ints_on\n");
+}
+static void _ints_off(uint32_t mask) {
+	printf("called: _ints_off\n");
+}
+static bool _is_from_isr(void) {
+	printf("called: _is_from_isr\n");
+	return false;
+}
+
+// Having conflict between when include 
+// #include "freertos/portmacro.h" 
+
+typedef struct {
+	/* owner field values:
+	 * 0				- Uninitialized (invalid)
+	 * portMUX_FREE_VAL - Mux is free, can be locked by either CPU
+	 * CORE_ID_REGVAL_PRO / CORE_ID_REGVAL_APP - Mux is locked to the particular core
+	 *
+	 *
+	 * Any value other than portMUX_FREE_VAL, CORE_ID_REGVAL_PRO, CORE_ID_REGVAL_APP indicates corruption
+	 */
+	uint32_t owner;
+	/* count field:
+	 * If mux is unlocked, count should be zero.
+	 * If mux is locked, count is non-zero & represents the number of recursive locks on the mux.
+	 */
+	uint32_t count;
+} portMUX_TYPE;
+
+#define portMUX_FREE_VAL	SPINLOCK_FREE
+#define SPINLOCK_FREE	   0xB33FFFFF
+
+#define portMUX_INITIALIZER_UNLOCKED {					\
+		.owner = portMUX_FREE_VAL,						\
+		.count = 0,										\
+	}
+
+static void * _spin_lock_create(void) {
+	portMUX_TYPE tmp = portMUX_INITIALIZER_UNLOCKED;
+	void *mux = malloc(sizeof(portMUX_TYPE));
+	if (mux) {
+		memcpy(mux,&tmp,sizeof(portMUX_TYPE));
+		return mux;
+	}
+	return NULL;
+}
+static void _spin_lock_delete(void *lock) {
+	free(lock);
+}
+static uint32_t _wifi_int_disable(void *wifi_int_mux) {
+	printf("called: _wifi_int_disable\n");
+	return 0;
+}
+static void _wifi_int_restore(void *wifi_int_mux, uint32_t tmp) {
+	printf("called: _wifi_int_restore\n");
+}
+static void _task_yield_from_isr(void) {
+	printf("called: _task_yield_from_isr\n");
+}
+static void *_semphr_create(uint32_t max, uint32_t init) {
+	return (void *)xSemaphoreCreateCounting(max, init);
+}
+static void _semphr_delete(void *semphr) {
+	vSemaphoreDelete(semphr);
+}
+static int32_t _semphr_take(void *semphr, uint32_t block_time_tick) {
+	if (block_time_tick == OSI_FUNCS_TIME_BLOCKING) {
+		return (int32_t)xSemaphoreTake(semphr, portMAX_DELAY);
+	} else {
+		return (int32_t)xSemaphoreTake(semphr, block_time_tick);
+	}
+}
+static int32_t _semphr_give(void *semphr) {
+	return (int32_t)xSemaphoreGive(semphr);
+}
+static void *_wifi_thread_semphr_get(void) {
+	static SemaphoreHandle_t sem = NULL;
+	if (!sem) {
+		sem = xSemaphoreCreateCounting(1, 0);
+	}
+	return (void*)sem;
+}
+static void *_mutex_create(void) {
+	printf("called: _mutex_create\n");
+	return NULL;
+}
+
+static void *_recursive_mutex_create(void) {
+	return xSemaphoreCreateRecursiveMutex();
+}
+static void _mutex_delete(void *mutex) {
+	return vSemaphoreDelete(mutex);
+}
+static int32_t _mutex_lock(void *mutex) {
+	return (int32_t)xSemaphoreTakeRecursive(mutex, portMAX_DELAY);
+}
+static int32_t _mutex_unlock(void *mutex) {
+	return (int32_t)xSemaphoreGiveRecursive(mutex);
+}
+static void * _queue_create(uint32_t queue_len, uint32_t item_size) {
+	printf("called: _queue_create\n");
+	return NULL;
+}
+static void _queue_delete(void *queue) {
+	printf("called: _queue_delete\n");
+}
+static int32_t _queue_send(void *queue, void *item, uint32_t block_time_tick) {
+	if (block_time_tick == OSI_FUNCS_TIME_BLOCKING) {
+		return (int32_t)xQueueSend(queue, item, portMAX_DELAY);
+	} else {
+		return (int32_t)xQueueSend(queue, item, block_time_tick);
+	}
+}
+static int32_t _queue_send_from_isr(void *queue, void *item, void *hptw) {
+	printf("called: _queue_send_from_isr\n");
+	return 0;
+}
+static int32_t _queue_send_to_back(void *queue, void *item, uint32_t block_time_tick) {
+	printf("called: _queue_send_to_back\n");
+	return 0;
+}
+static int32_t _queue_send_to_front(void *queue, void *item, uint32_t block_time_tick) {
+	printf("called: _queue_send_to_front\n");
+	return 0;
+}
+static int32_t _queue_recv(void *queue, void *item, uint32_t block_time_tick) {
+	if (block_time_tick == OSI_FUNCS_TIME_BLOCKING) {
+		return (int32_t)xQueueReceive(queue, item, portMAX_DELAY);
+	} else {
+		return (int32_t)xQueueReceive(queue, item, block_time_tick);
+	}
+}
+static void * _event_group_create(void) {
+	printf("called: _event_group_create\n");
+	return NULL;
+}
+static void _event_group_delete(void *event) {
+	printf("called: _event_group_delete\n");
+}
+static uint32_t _event_group_set_bits(void *event, uint32_t bits) {
+	printf("called: _event_group_set_bits\n");
+	return 0;
+}
+static uint32_t _event_group_clear_bits(void *event, uint32_t bits) {
+	printf("called: _event_group_clear_bits\n");
+	return 0;
+}
+static uint32_t _event_group_wait_bits(void *event, uint32_t bits_to_wait_for, int clear_on_exit, int wait_for_all_bits, uint32_t block_time_tick) {
+	printf("called: _event_group_wait_bits\n");
+	return 0;
+}
+
+#define P(x) printf("called: "#x"\n");
+
+static int32_t _task_create_pinned_to_core(void *task_func, const char *name, uint32_t stack_depth, void *param, uint32_t prio, void *task_handle, uint32_t core_id) {
+	// Note: using xTaskCreate instead of xTaskCreatePinnedToCore.
+	return (uint32_t)xTaskCreate(task_func, name, stack_depth, param, prio, task_handle);
+}
+static int32_t _task_create(void *task_func, const char *name, uint32_t stack_depth, void *param, uint32_t prio, void *task_handle) {
+	P(_task_create)
+	return 0;
+}
+static void _task_delete(void *task_handle) {
+	P(_task_delete)
+}
+static int32_t _task_ms_to_tick(uint32_t ms) {
+	return (int32_t)(ms / portTICK_PERIOD_MS);
+}
+static int32_t _task_get_max_priority() {
+	return configMAX_PRIORITIES;
+}
+static int32_t _event_post(const char* event_base, int32_t event_id, void* event_data, size_t event_data_size, uint32_t ticks_to_wait) {
+	P(_event_post)
+	return 0;
+}
+static uint32_t  _get_free_heap_size(void) {
+	P(_get_free_heap_size)
+	return 0;
+}
+static uint32_t  _rand(void) {
+	P(_rand)
+	return 0;
+}
+static void _dport_access_stall_other_cpu_start_wrap(void) {
+	P(_dport_access_stall_other_cpu_start_wrap)
+}
+static void _dport_access_stall_other_cpu_end_wrap(void) {
+	P(_dport_access_stall_other_cpu_end_wrap)
+}
+static void _wifi_apb80m_request(void) {
+	P(_wifi_apb80m_request)
+}
+static void _wifi_apb80m_release(void) {
+	P(_wifi_apb80m_release)
+}
+static void _phy_disable(void) {
+	P(_phy_disable)
+}
+static void _phy_enable(void) {
+	P(_phy_enable)
+}
+static int _phy_update_country_info(const char* country) {
+	P(_phy_update_country_info)
+	return 0;
+}
+static int _read_mac(uint8_t* mac, uint32_t type) {
+	P(_read_mac)
+	return 0;
+}
+static void _timer_arm(void *timer, uint32_t tmout, bool repeat) {
+	P(_timer_arm)
+}
+static void _timer_disarm(void *timer) {
+	P(_timer_disarm)
+}
+static void _timer_done(void *ptimer) {
+	P(_timer_done)
+}
+static void _timer_setfn(void *ptimer, void *pfunction, void *parg) {
+	P(_timer_setfn)
+}
+static void _timer_arm_us(void *ptimer, uint32_t us, bool repeat) {
+	P(_timer_arm_us)
+}
+static void _wifi_reset_mac(void) {
+	P(_wifi_reset_mac)
+}
+static void _wifi_clock_enable(void) {
+	P(_wifi_clock_enable)
+}
+static void _wifi_clock_disable(void) {
+	P(_wifi_clock_disable)
+}
+static void _wifi_rtc_enable_iso(void) {
+	P(_wifi_rtc_enable_iso)
+}
+static void _wifi_rtc_disable_iso(void) {
+	P(_wifi_rtc_disable_iso)
+}
+static int64_t _esp_timer_get_time(void) {
+	P(_esp_timer_get_time)
+	return 0;
+}
+static int _nvs_set_i8(uint32_t handle, const char* key, int8_t value) {
+	P(_nvs_set_i8)
+	return 0;
+}
+static int _nvs_get_i8(uint32_t handle, const char* key, int8_t* out_value) {
+	P(_nvs_get_i8)
+	return 0;
+}
+static int _nvs_set_u8(uint32_t handle, const char* key, uint8_t value) {
+	P(_nvs_set_u8)
+	return 0;
+}
+static int _nvs_get_u8(uint32_t handle, const char* key, uint8_t* out_value) {
+	P(_nvs_get_u8)
+	return 0;
+}
+static int _nvs_set_u16(uint32_t handle, const char* key, uint16_t value) {
+	P(_nvs_set_u16)
+	return 0;
+}
+static int _nvs_get_u16(uint32_t handle, const char* key, uint16_t* out_value) {
+	P(_nvs_get_u16)
+	return 0;
+}
+static int _nvs_open(const char* name, uint32_t open_mode, uint32_t *out_handle) {
+	P(_nvs_open)
+	return 0;
+}
+static void _nvs_close(uint32_t handle) {
+	P(_nvs_close)
+}
+static int _nvs_commit(uint32_t handle) {
+	P(_nvs_commit)
+	return 0;
+}
+static int _nvs_set_blob(uint32_t handle, const char* key, const void* value, size_t length) {
+	P(_nvs_set_blob)
+	return 0;
+}
+static int _nvs_get_blob(uint32_t handle, const char* key, void* out_value, size_t* length) {
+	P(_nvs_get_blob)
+	return 0;
+}
+static int _nvs_erase_key(uint32_t handle, const char* key) {
+	P(_nvs_erase_key)
+	return 0;
+}
+static int _get_random(uint8_t *buf, size_t len) {
+	P(_get_random)
+	return 0;
+}
+static int _get_time(void *t) {
+	P(_get_time)
+	return 0;
+}
+static unsigned long _random(void) {
+	P(_random)
+	return 0;
+}
+// #if CONFIG_IDF_TARGET_ESP32S2 || CONFIG_IDF_TARGET_ESP32S3 || CONFIG_IDF_TARGET_ESP32C3
+//	 uint32_t (* _slowclk_cal_get(void)
+// #endif
+static void _log_write(uint32_t level, const char* tag, const char* format, ...) {
+	va_list argList;
+	printf("[%s] ", tag);
+	va_start(argList, format);
+	vprintf(format, argList);
+	va_end(argList);
+	printf("\n");
+}
+static void _log_writev(uint32_t level, const char* tag, const char* format, va_list args) {
+	printf("[%s] ", tag);
+	vprintf(format, args);
+	printf("\n");
+}
+
+static uint32_t  _log_timestamp(void) {
+	P(_log_timestamp)
+	return 0;
+}
+static void* _malloc_internal(size_t size) {
+	printf("called: _malloc_internal(%d)\n", size);
+	return malloc(size);
+}
+static void* _realloc_internal(void *ptr, size_t size) {
+	printf("called: _realloc_internal(%p,%d)\n", ptr, size);
+	return NULL;
+}
+
+static void* _calloc_internal(size_t n, size_t size) {
+	printf("called: _calloc_internal(%d,%d)\n", n, size);
+	return malloc(n * size);
+}
+static void* _zalloc_internal(size_t size) {
+	printf("called: _zalloc_internal(%d)\n", size);
+	return NULL;
+}
+static void* _wifi_malloc(size_t size) {
+	return malloc(size);
+}
+static void* _wifi_realloc(void *ptr, size_t size) {
+	printf("called: _wifi_realloc(%d)\n", size);
+	return NULL;
+}
+static void* _wifi_calloc(size_t n, size_t size) {
+	return calloc(n, size);
+}
+static void* _wifi_zalloc(size_t size) {
+	return calloc(1, size);
+}
+static void* _wifi_create_queue(int queue_len, int item_size) {
+	wifi_static_queue_t *queue = (wifi_static_queue_t*)malloc(sizeof(wifi_static_queue_t));
+	queue->handle = xQueueCreate( queue_len, item_size);
+	return queue;
+}
+static void _wifi_delete_queue(void * queue) {
+	vQueueDelete(queue);
+}
+static int _coex_init(void) {
+	P(_coex_init)
+	return 0;
+}
+static void _coex_deinit(void) {
+	P(_coex_deinit)
+}
+static int _coex_enable(void) {
+	P(_coex_enable)
+	return 0;
+}
+static void _coex_disable(void) {
+	P(_coex_disable)
+}
+static uint32_t  _coex_status_get(void) {
+	P(_coex_status_get)
+	return 0;
+}
+static void _coex_condition_set(uint32_t type, bool dissatisfy) {
+	P(_coex_condition_set)
+}
+static int _coex_wifi_request(uint32_t event, uint32_t latency, uint32_t duration) {
+	P(_coex_wifi_request)
+	return 0;
+}
+static int _coex_wifi_release(uint32_t event) {
+	P(_coex_wifi_release)
+	return 0;
+}
+static int _coex_wifi_channel_set(uint8_t primary, uint8_t secondary) {
+	P(_coex_wifi_channel_set)
+	return 0;
+}
+static int _coex_event_duration_get(uint32_t event, uint32_t *duration) {
+	P(_coex_event_duration_get)
+	return 0;
+}
+static int _coex_pti_get(uint32_t event, uint8_t *pti) {
+	P(_coex_pti_get)
+	return 0;
+}
+static void _coex_schm_status_bit_clear(uint32_t type, uint32_t status) {
+	P(_coex_schm_status_bit_clear)
+}
+static void _coex_schm_status_bit_set(uint32_t type, uint32_t status) {
+	P(_coex_schm_status_bit_set)
+}
+static int _coex_schm_interval_set(uint32_t interval) {
+	P(_coex_schm_interval_set)
+	return 0;
+}
+static uint32_t  _coex_schm_interval_get(void) {
+	P(_coex_schm_interval_get)
+	return 0;
+}
+static uint8_t _coex_schm_curr_period_get(void) {
+	P(_coex_schm_curr_period_get)
+	return 0;
+}
+static void* _coex_schm_curr_phase_get(void) {
+	P(_coex_schm_curr_phase_get)
+	return NULL;
+}
+static int _coex_schm_curr_phase_idx_set(int idx) {
+	P(_coex_schm_curr_phase_idx_set)
+	return 0;
+}
+static int _coex_schm_curr_phase_idx_get(void) {
+	P(_coex_schm_curr_phase_idx_get)
+	return 0;
+}
+
+
+uint32_t _slowclk_cal_get(void) {
+	return 0;
+}
+
+// OS adapter functions.
+// See: esp-idf/components/esp_wifi/include/esp_private/wifi_os_adapter.h
+wifi_osi_funcs_t g_wifi_osi_funcs = {
+	._version = ESP_WIFI_OS_ADAPTER_VERSION,
+	._env_is_chip = _env_is_chip,
+	._set_intr = _set_intr,
+	._clear_intr = _clear_intr,
+	._set_isr = _set_isr,
+	._ints_on = _ints_on,
+	._ints_off = _ints_off,
+	._is_from_isr = _is_from_isr,
+	._spin_lock_create = _spin_lock_create,
+	._spin_lock_delete = _spin_lock_delete,
+	._wifi_int_disable = _wifi_int_disable,
+	._wifi_int_restore = _wifi_int_restore,
+	._task_yield_from_isr = _task_yield_from_isr,
+	._semphr_create = _semphr_create,
+	._semphr_delete = _semphr_delete,
+	._semphr_take = _semphr_take,
+	._semphr_give = _semphr_give,
+	._wifi_thread_semphr_get = _wifi_thread_semphr_get,
+	._mutex_create = _mutex_create,
+	._recursive_mutex_create = _recursive_mutex_create,
+	._mutex_delete = _mutex_delete,
+	._mutex_lock = _mutex_lock,
+	._mutex_unlock = _mutex_unlock,
+	._queue_create = _queue_create,
+	._queue_delete = _queue_delete,
+	._queue_send = _queue_send,
+	._queue_send_from_isr = _queue_send_from_isr,
+	._queue_send_to_back = _queue_send_to_back,
+	._queue_send_to_front = _queue_send_to_front,
+	._queue_recv = _queue_recv,
+	._queue_msg_waiting = (uint32_t(*)(void *))uxQueueMessagesWaiting,
+	._event_group_create = _event_group_create,
+	._event_group_delete = _event_group_delete,
+	._event_group_set_bits = _event_group_set_bits,
+	._event_group_clear_bits = _event_group_clear_bits,
+	._event_group_wait_bits = _event_group_wait_bits,
+	._task_create_pinned_to_core = _task_create_pinned_to_core,
+	._task_create = _task_create,
+	._task_delete = _task_delete,
+	._task_delay = vTaskDelay,
+	._task_ms_to_tick = _task_ms_to_tick,
+	._task_get_current_task = (void *(*)(void))xTaskGetCurrentTaskHandle,
+	._task_get_max_priority = _task_get_max_priority,
+	._malloc = malloc,
+	._free = free,
+	._event_post = _event_post,
+	._get_free_heap_size = _get_free_heap_size,
+	._rand = _rand,
+	._dport_access_stall_other_cpu_start_wrap = _dport_access_stall_other_cpu_start_wrap,
+	._dport_access_stall_other_cpu_end_wrap = _dport_access_stall_other_cpu_end_wrap,
+	._wifi_apb80m_request = _wifi_apb80m_request,
+	._wifi_apb80m_release = _wifi_apb80m_release,
+	._phy_disable = _phy_disable,
+	._phy_enable = _phy_enable,
+	._phy_update_country_info = _phy_update_country_info,
+	._read_mac = _read_mac,
+	._timer_arm = _timer_arm,
+	._timer_disarm = _timer_disarm,
+	._timer_done = _timer_done,
+	._timer_setfn = _timer_setfn,
+	._timer_arm_us = _timer_arm_us,
+	._wifi_reset_mac = _wifi_reset_mac,
+	._wifi_clock_enable = _wifi_clock_enable,
+	._wifi_clock_disable = _wifi_clock_disable,
+	._wifi_rtc_enable_iso = _wifi_rtc_enable_iso,
+	._wifi_rtc_disable_iso = _wifi_rtc_disable_iso,
+	._esp_timer_get_time = _esp_timer_get_time,
+	._nvs_set_i8 = _nvs_set_i8,
+	._nvs_get_i8 = _nvs_get_i8,
+	._nvs_set_u8 = _nvs_set_u8,
+	._nvs_get_u8 = _nvs_get_u8,
+	._nvs_set_u16 = _nvs_set_u16,
+	._nvs_get_u16 = _nvs_get_u16,
+	._nvs_open = _nvs_open,
+	._nvs_close = _nvs_close,
+	._nvs_commit = _nvs_commit,
+	._nvs_set_blob = _nvs_set_blob,
+	._nvs_get_blob = _nvs_get_blob,
+	._nvs_erase_key = _nvs_erase_key,
+	._get_random = _get_random,
+	._get_time = _get_time,
+	._random = _random,
+#if CONFIG_IDF_TARGET_ESP32S2 || CONFIG_IDF_TARGET_ESP32S3 || CONFIG_IDF_TARGET_ESP32C3
+	._slowclk_cal_get = _slowclk_cal_get,
+#endif
+	._log_write = _log_write,
+	._log_writev = _log_writev,
+	._log_timestamp = _log_timestamp,
+	._malloc_internal = _malloc_internal,
+	._realloc_internal = _realloc_internal,
+	._calloc_internal = _calloc_internal,
+	._zalloc_internal = _zalloc_internal,
+	._wifi_malloc = _wifi_malloc,
+	._wifi_realloc = _wifi_realloc,
+	._wifi_calloc = _wifi_calloc,
+	._wifi_zalloc = _wifi_zalloc,
+	._wifi_create_queue = _wifi_create_queue,
+	._wifi_delete_queue = _wifi_delete_queue,
+	._coex_init = _coex_init,
+	._coex_deinit = _coex_deinit,
+	._coex_enable = _coex_enable,
+	._coex_disable = _coex_disable,
+	._coex_status_get = _coex_status_get,
+	._coex_condition_set = _coex_condition_set,
+	._coex_wifi_request = _coex_wifi_request,
+	._coex_wifi_release = _coex_wifi_release,
+	._coex_wifi_channel_set = _coex_wifi_channel_set,
+	._coex_event_duration_get = _coex_event_duration_get,
+	._coex_pti_get = _coex_pti_get,
+	._coex_schm_status_bit_clear = _coex_schm_status_bit_clear,
+	._coex_schm_status_bit_set = _coex_schm_status_bit_set,
+	._coex_schm_interval_set = _coex_schm_interval_set,
+	._coex_schm_interval_get = _coex_schm_interval_get,
+	._coex_schm_curr_period_get = _coex_schm_curr_period_get,
+	._coex_schm_curr_phase_get = _coex_schm_curr_phase_get,
+	._coex_schm_curr_phase_idx_set = _coex_schm_curr_phase_idx_set,
+	._coex_schm_curr_phase_idx_get = _coex_schm_curr_phase_idx_get,
+
+	._magic = ESP_WIFI_OS_ADAPTER_MAGIC,
+};
+
+static int esp_aes_wrap(const unsigned char *kek, int n, const unsigned char *plain, unsigned char *cipher) {
+	P(aes_wrap)
+	return -1;
+}
+static int esp_aes_unwrap(const unsigned char *kek, int n, const unsigned char *cipher, unsigned char *plain) {
+	P(aes_unwrap)
+	return -1;	
+}
+static int hmac_sha256_vector(const unsigned char *key, int key_len, int num_elem,
+	const unsigned char *addr[], const int *len, unsigned char *mac) {
+	return -1;
+}
+static int sha256_prf(const unsigned char *key, int key_len, const char *label,
+								   const unsigned char *data, int data_len, unsigned char *buf, int buf_len) {
+	P(sha256_prf)
+	return -1;
+}
+static int hmac_md5(const unsigned char *key, unsigned int key_len, const unsigned char *data,
+							  unsigned int data_len, unsigned char *mac) {
+	P(hmac_md5)
+	return -1;
+}
+static int hamc_md5_vector(const unsigned char *key, unsigned int key_len, unsigned int num_elem,
+							  const unsigned char *addr[], const unsigned int *len, unsigned char *mac) {
+	P(hamc_md5_vector)
+	return -1;							
+}
+static int hmac_sha1(const unsigned char *key, unsigned int key_len, const unsigned char *data,
+							  unsigned int data_len, unsigned char *mac) {
+	P(hmac_sha1)
+	return -1;
+}
+static int hmac_sha1_vector(const unsigned char *key, unsigned int key_len, unsigned int num_elem,
+							  const unsigned char *addr[], const unsigned int *len, unsigned char *mac) {
+	P(hmac_sha1_vector)
+	return -1;
+}
+static int sha1_prf(const unsigned char *key, unsigned int key_len, const char *label,
+							  const unsigned char *data, unsigned int data_len, unsigned char *buf, unsigned int buf_len) {
+	P(sha1_prf)
+	return -1;
+}
+static int sha1_vector(unsigned int num_elem, const unsigned char *addr[], const unsigned int *len,
+							  unsigned char *mac) {
+	P(sha1_vector)
+	return -1;
+}
+static int pbkdf2_sha1(const char *passphrase, const char *ssid, unsigned int ssid_len,
+							  int iterations, unsigned char *buf, unsigned int buflen) {
+	P(pbkdf2_sha1)
+	return -1;
+}
+static int rc4_skip(const unsigned char *key, unsigned int keylen, unsigned int skip,
+							  unsigned char *data, unsigned int data_len) {
+	P(rc4_skip)
+	return -1;
+}
+static int md5_vector(unsigned int num_elem, const unsigned char *addr[], const unsigned int *len,
+							  unsigned char *mac) {
+	P(md5_vector)
+	return -1;
+}
+static void aes_encrypt(void *ctx, const unsigned char *plain, unsigned char *crypt) {
+	P(aes_encrypt)
+}
+static void * aes_encrypt_init(const unsigned char *key,  unsigned int len) {
+	P(aes_encrypt_init)
+	return NULL;
+}
+static void aes_encrypt_deinit(void *ctx) {
+	P(aes_encrypt_deinit)
+}
+static void aes_decrypt(void *ctx, const unsigned char *crypt, unsigned char *plain) {
+	P(aes_decrypt)
+}
+static void * aes_decrypt_init(const unsigned char *key, unsigned int len) {
+	P(aes_decrypt_init)
+	return NULL;
+}
+static void aes_decrypt_deinit(void *ctx) {
+	P(aes_decrypt_deinit)
+}
+static int aes_128_decrypt(const unsigned char *key, const unsigned char *iv, unsigned char *data, int data_len) {
+	P(aes_128_decrypt)
+	return -1;
+}
+static int omac1_aes_128(const uint8_t *key, const uint8_t *data, size_t data_len,
+								   uint8_t *mic) {
+	P(omac1_aes_128)
+	return -1;
+}
+static uint8_t * ccmp_decrypt(const uint8_t *tk, const uint8_t *ieee80211_hdr,
+										const uint8_t *data, size_t data_len,
+										size_t *decrypted_len, bool espnow_pkt) {
+	P(ccmp_decrypt)
+	return NULL;
+}
+static uint8_t * ccmp_encrypt(const uint8_t *tk, uint8_t *frame, size_t len, size_t hdrlen,
+										uint8_t *pn, int keyid, size_t *encrypted_len) {
+	P(ccmp_encrypt)
+	return NULL;
+}
+static int hmac_md5_vector(const unsigned char *key, unsigned int key_len, unsigned int num_elem,
+							  const unsigned char *addr[], const unsigned int *len, unsigned char *mac) {
+	P(hmac_md5_vector)
+	return -1;
+}
+static void esp_aes_encrypt(void *ctx, const unsigned char *plain, unsigned char *crypt) {
+	P(esp_aes_encrypt)
+}
+static void esp_aes_decrypt(void *ctx, const unsigned char *crypt, unsigned char *plain) {
+	P(esp_aes_decrypt)
+}
+static int aes_128_cbc_encrypt(const unsigned char *key, const unsigned char *iv, unsigned char *data, int data_len) {
+	P(aes_128_cbc_encrypt)
+	return -1;
+}
+static int aes_128_cbc_decrypt(const unsigned char *key, const unsigned char *iv, unsigned char *data, int data_len) {
+	P(aes_128_cbc_decrypt)
+	return -1;
+}
+
+const wpa_crypto_funcs_t g_wifi_default_wpa_crypto_funcs = {
+	.size = sizeof(wpa_crypto_funcs_t),
+	.version = ESP_WIFI_CRYPTO_VERSION,
+	.aes_wrap = (esp_aes_wrap_t)esp_aes_wrap,
+	.aes_unwrap = (esp_aes_unwrap_t)esp_aes_unwrap,
+	.hmac_sha256_vector = (esp_hmac_sha256_vector_t)hmac_sha256_vector,
+	.sha256_prf = (esp_sha256_prf_t)sha256_prf,
+	.hmac_md5 = (esp_hmac_md5_t)hmac_md5,
+	.hamc_md5_vector = (esp_hmac_md5_vector_t)hmac_md5_vector,
+	.hmac_sha1 = (esp_hmac_sha1_t)hmac_sha1,
+	.hmac_sha1_vector = (esp_hmac_sha1_vector_t)hmac_sha1_vector,
+	.sha1_prf = (esp_sha1_prf_t)sha1_prf,
+	.sha1_vector = (esp_sha1_vector_t)sha1_vector,
+	.pbkdf2_sha1 = (esp_pbkdf2_sha1_t)pbkdf2_sha1,
+	.rc4_skip = (esp_rc4_skip_t)rc4_skip,
+	.md5_vector = (esp_md5_vector_t)md5_vector,
+	.aes_encrypt = (esp_aes_encrypt_t)esp_aes_encrypt,
+	.aes_encrypt_init = (esp_aes_encrypt_init_t)aes_encrypt_init,
+	.aes_encrypt_deinit = (esp_aes_encrypt_deinit_t)aes_encrypt_deinit,
+	.aes_decrypt = (esp_aes_decrypt_t)esp_aes_decrypt,
+	.aes_decrypt_init = (esp_aes_decrypt_init_t)aes_decrypt_init,
+	.aes_decrypt_deinit = (esp_aes_decrypt_deinit_t)aes_decrypt_deinit,
+	.aes_128_encrypt = (esp_aes_128_encrypt_t)aes_128_cbc_encrypt,
+	.aes_128_decrypt = (esp_aes_128_decrypt_t)aes_128_cbc_decrypt,
+	.omac1_aes_128 = (esp_omac1_aes_128_t)omac1_aes_128,
+	.ccmp_decrypt = (esp_ccmp_decrypt_t)ccmp_decrypt,
+	.ccmp_encrypt = (esp_ccmp_encrypt_t)ccmp_encrypt
+};
+
+// This is a string constant that is used all over ESP-IDF and is also used by
+// libnet80211.a. The main purpose is to be a fixed pointer that can be compared
+// against etc.
+const char *WIFI_EVENT = "WIFI_EVENT";
+
+// Required by libphy.a
+int phy_printf(const char *format, ...) {
+	va_list args;
+	va_start(args, format);
+	printf("phy: ");
+	int res = vprintf(format, args);
+	va_end(args);
+	return res;
+}
+
+// Required by libpp.a
+int pp_printf(const char *format, ...) {
+	va_list args;
+	va_start(args, format);
+	printf("pp: ");
+	int res = vprintf(format, args);
+	va_end(args);
+	return res;
+}
+
+// Required by libnet80211.a
+int net80211_printf(const char *format, ...) {
+	va_list args;
+	va_start(args, format);
+	printf("net80211: ");
+	int res = vprintf(format, args);
+	va_end(args);
+	return res;
+}
+
+// Source: esp-idf/components/wpa_supplicant/src/utils/common.c
+static int hex2num(char c)
+{
+	if (c >= '0' && c <= '9')
+		return c - '0';
+	if (c >= 'a' && c <= 'f')
+		return c - 'a' + 10;
+	if (c >= 'A' && c <= 'F')
+		return c - 'A' + 10;
+	return -1;
+}
+
+// Source: esp-idf/components/wpa_supplicant/src/utils/common.c
+int hex2byte(const char *hex)
+{
+	int a, b;
+	a = hex2num(*hex++);
+	if (a < 0)
+		return -1;
+	b = hex2num(*hex++);
+	if (b < 0)
+		return -1;
+	return (a << 4) | b;
+}
+
+// Source: esp-idf/components/wpa_supplicant/src/utils/common.c
+/**
+ * hexstr2bin - Convert ASCII hex string into binary data
+ * @hex: ASCII hex string (e.g., "01ab")
+ * @buf: Buffer for the binary data
+ * @len: Length of the text to convert in bytes (of buf); hex will be double
+ * this size
+ * Returns: 0 on success, -1 on failure (invalid hex string)
+ */
+int hexstr2bin(const char *hex, uint8_t *buf, size_t len)
+{
+	size_t i;
+	int a;
+	const char *ipos = hex;
+	uint8_t *opos = buf;
+
+	for (i = 0; i < len; i++) {
+		a = hex2byte(ipos);
+		if (a < 0)
+			return -1;
+		*opos++ = a;
+		ipos += 2;
+	}
+	return 0;
+}

espnet/espnet.h

@@ -0,0 +1,5 @@
+#include <stdbool.h>
+
+#include "esp_private/wifi_os_adapter.h"
+
+extern wifi_osi_funcs_t g_wifi_osi_funcs;

examples/espnet/main.go

@@ -0,0 +1,20 @@
+package main
+
+import "tinygo.org/x/drivers/espnet"
+
+func main() {
+	err := espnet.WiFi.Configure(espnet.Config{})
+	if err != nil {
+		println("failed to configure:", err.Error())
+	}
+	mac, err := espnet.WiFi.AccessPointMAC()
+	if err != nil {
+		println("failed to read MAC address:", err.Error())
+		return
+	}
+	print("MAC address:")
+	for _, b := range mac {
+		print(" ", b)
+	}
+	println()
+}

examples/ili9341/basic/atsamd21.go

@@ -1,3 +1,4 @@
+//go:build atsamd21
 // +build atsamd21
 
 package main

examples/ili9341/basic/pyportal.go

@@ -1,3 +1,4 @@
+//go:build pyportal
 // +build pyportal
 
 package main

examples/ili9341/basic/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/ili9341/pyportal_boing/pyportal.go

@@ -1,3 +1,4 @@
+//go:build pyportal
 // +build pyportal
 
 package main

examples/ili9341/pyportal_boing/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/ili9341/scroll/atsamd21.go

@@ -1,3 +1,4 @@
+//go:build atsamd21
 // +build atsamd21
 
 package main

examples/ili9341/scroll/pyportal.go

@@ -1,3 +1,4 @@
+//go:build pyportal
 // +build pyportal
 
 package main

examples/ili9341/scroll/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/ili9341/slideshow/README.md

@@ -0,0 +1,18 @@
+# examples/ili9341/slideshow
+
+![](./slideshow.jpg)
+
+This example uses the image package for TinyGo to display png and jpeg images.  
+
+## How to create an image
+
+The following program will output an image binary like the one in [images.go](./images.go).  
+
+```
+go run ./examples/ili9341/slideshow/convert2bin ./path/to/png_or_jpg.png
+```
+
+## Notes
+
+Displaying a 320x240 png or jpeg often requires more than 50KB of memory.  
+The examples include samd21 settings, but if you run them as is, you will get a memory size error.  

examples/ili9341/slideshow/atsamd21.go

@@ -0,0 +1,30 @@
+//go:build atsamd21
+// +build atsamd21
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/ili9341"
+)
+
+var (
+	display = ili9341.NewSPI(
+		machine.SPI0,
+		machine.D0,
+		machine.D1,
+		machine.D2,
+	)
+
+	backlight = machine.D3
+)
+
+func init() {
+	machine.SPI0.Configure(machine.SPIConfig{
+		SCK:       machine.SPI0_SCK_PIN,
+		SDO:       machine.SPI0_SDO_PIN,
+		SDI:       machine.SPI0_SDI_PIN,
+		Frequency: 24000000,
+	})
+}

examples/ili9341/slideshow/main.go

@@ -0,0 +1,94 @@
+package main
+
+import (
+	"fmt"
+	"image/color"
+	"machine"
+	"strings"
+	"time"
+
+	"tinygo.org/x/drivers/ili9341"
+	"tinygo.org/x/drivers/image/jpeg"
+	"tinygo.org/x/drivers/image/png"
+)
+
+var (
+	black = color.RGBA{0, 0, 0, 255}
+	white = color.RGBA{255, 255, 255, 255}
+	red   = color.RGBA{255, 0, 0, 255}
+	blue  = color.RGBA{0, 0, 255, 255}
+	green = color.RGBA{0, 255, 0, 255}
+)
+
+func main() {
+	err := run()
+	for err != nil {
+		errorMessage(err)
+	}
+}
+
+func run() error {
+	backlight.Configure(machine.PinConfig{machine.PinOutput})
+
+	display.Configure(ili9341.Config{})
+
+	width, height := display.Size()
+	if width < 320 || height < 240 {
+		display.SetRotation(ili9341.Rotation270)
+	}
+
+	display.FillScreen(black)
+	backlight.High()
+
+	for {
+		err := drawJpeg(display)
+		if err != nil {
+			return err
+		}
+		time.Sleep(time.Second)
+
+		err = drawPng(display)
+		if err != nil {
+			return err
+		}
+		time.Sleep(time.Second)
+	}
+
+	return nil
+}
+
+// Define the buffer required for the callback. In most cases, this setting
+// should be sufficient.  For jpeg, the callback will always be called every
+// 3*8*8*4 pix. png will be called every line, i.e. every width pix.
+var buffer [3 * 8 * 8 * 4]uint16
+
+func drawPng(display *ili9341.Device) error {
+	p := strings.NewReader(pngImage)
+	png.SetCallback(buffer[:], func(data []uint16, x, y, w, h, width, height int16) {
+		err := display.DrawRGBBitmap(x, y, data[:w*h], w, h)
+		if err != nil {
+			errorMessage(fmt.Errorf("error drawPng: %s", err))
+		}
+	})
+
+	return png.Decode(p)
+}
+
+func drawJpeg(display *ili9341.Device) error {
+	p := strings.NewReader(jpegImage)
+	jpeg.SetCallback(buffer[:], func(data []uint16, x, y, w, h, width, height int16) {
+		err := display.DrawRGBBitmap(x, y, data[:w*h], w, h)
+		if err != nil {
+			errorMessage(fmt.Errorf("error drawJpeg: %s", err))
+		}
+	})
+
+	return jpeg.Decode(p)
+}
+
+func errorMessage(err error) {
+	for {
+		fmt.Printf("%s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}

examples/ili9341/slideshow/pyportal.go

@@ -0,0 +1,23 @@
+//go:build pyportal
+// +build pyportal
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/ili9341"
+)
+
+var (
+	display = ili9341.NewParallel(
+		machine.LCD_DATA0,
+		machine.TFT_WR,
+		machine.TFT_DC,
+		machine.TFT_CS,
+		machine.TFT_RESET,
+		machine.TFT_RD,
+	)
+
+	backlight = machine.TFT_BACKLIGHT
+)

examples/ili9341/slideshow/wioterminal.go

@@ -0,0 +1,30 @@
+//go:build wioterminal
+// +build wioterminal
+
+package main
+
+import (
+	"machine"
+
+	"tinygo.org/x/drivers/ili9341"
+)
+
+var (
+	display = ili9341.NewSPI(
+		machine.SPI3,
+		machine.LCD_DC,
+		machine.LCD_SS_PIN,
+		machine.LCD_RESET,
+	)
+
+	backlight = machine.LCD_BACKLIGHT
+)
+
+func init() {
+	machine.SPI3.Configure(machine.SPIConfig{
+		SCK:       machine.LCD_SCK_PIN,
+		SDO:       machine.LCD_SDO_PIN,
+		SDI:       machine.LCD_SDI_PIN,
+		Frequency: 40000000,
+	})
+}

examples/lsm6dsox/main.go

@@ -0,0 +1,108 @@
+// Connects to an LSM6DSOX I2C a 6 axis Inertial Measurement Unit (IMU)
+package main
+
+import (
+	"fmt"
+	"machine"
+	"time"
+
+	"tinygo.org/x/drivers/lsm6dsox"
+)
+
+const (
+	PLOTTER           = true
+	SHOW_ACCELERATION = false
+	SHOW_ROTATION     = true
+	SHOW_TEMPERATURE  = false
+
+	// calibration is naive, good enough for a demo: do not shake a second after flashing
+	GYRO_CALIBRATION = true
+)
+
+var cal = [...]float32{0, 0, 0}
+
+func main() {
+
+	machine.I2C0.Configure(machine.I2CConfig{})
+
+	device := lsm6dsox.New(machine.I2C0)
+	device.Configure(lsm6dsox.Configuration{
+		AccelRange:      lsm6dsox.ACCEL_2G,
+		AccelSampleRate: lsm6dsox.ACCEL_SR_104,
+		GyroRange:       lsm6dsox.GYRO_250DPS,
+		GyroSampleRate:  lsm6dsox.GYRO_SR_104,
+	})
+
+	for {
+
+		if !device.Connected() {
+			println("LSM6DSOX not connected")
+			time.Sleep(time.Second)
+			continue
+		}
+
+		// heuristic: after successful calibration the value can't be 0
+		if GYRO_CALIBRATION && cal[0] == 0 {
+			calibrateGyro(device)
+		}
+
+		ax, ay, az := device.ReadAcceleration()
+		gx, gy, gz := device.ReadRotation()
+		t, _ := device.ReadTemperature()
+
+		if PLOTTER {
+			printPlotter(ax, ay, az, gx, gy, gz, t)
+			time.Sleep(time.Millisecond * 100)
+		} else {
+			printMonitor(ax, ay, az, gx, gy, gz, t)
+			time.Sleep(time.Millisecond * 1000)
+		}
+
+	}
+
+}
+
+func calibrateGyro(device *lsm6dsox.Device) {
+	for i := 0; i < 100; i++ {
+		gx, gy, gz := device.ReadRotation()
+		cal[0] += float32(gx) / 1000000
+		cal[1] += float32(gy) / 1000000
+		cal[2] += float32(gz) / 1000000
+		time.Sleep(time.Millisecond * 10)
+	}
+	cal[0] /= 100
+	cal[1] /= 100
+	cal[2] /= 100
+}
+
+// Arduino IDE's Serial Plotter
+func printPlotter(ax, ay, az, gx, gy, gz, t int32) {
+	if SHOW_ACCELERATION {
+		fmt.Printf("AX:%f, AY:%f, AZ:%f,", axis(ax, 0), axis(ay, 0), axis(az, 0))
+	}
+	if SHOW_ROTATION {
+		fmt.Printf("GX:%f, GY:%f, GZ:%f,", axis(gx, cal[0]), axis(gy, cal[1]), axis(gz, cal[2]))
+	}
+	if SHOW_TEMPERATURE {
+		fmt.Printf("T:%f", float32(t)/1000)
+	}
+	println()
+}
+
+// Any Serial Monitor
+func printMonitor(ax, ay, az, gx, gy, gz, t int32) {
+	if SHOW_ACCELERATION {
+		fmt.Printf("Acceleration: %f, %f, %f\r\n", axis(ax, 0), axis(ay, 0), axis(az, 0))
+	}
+	if SHOW_ROTATION {
+		fmt.Printf("Rotation: %f, %f, %f\r\n", axis(gx, cal[0]), axis(gy, cal[1]), axis(gz, cal[2]))
+	}
+	if SHOW_TEMPERATURE {
+		fmt.Printf("Temperature C: %f\r\n", float32(t)/1000)
+	}
+	println()
+}
+
+func axis(raw int32, cal float32) float32 {
+	return float32(raw)/1000000 - cal
+}

examples/rtl8720dn/mqttclient/main.go

@@ -0,0 +1,131 @@
+// This is a sensor station that uses a RTL8720DN running on the device UART2.
+// It creates an MQTT connection that publishes a message every second
+// to an MQTT broker.
+//
+// In other words:
+// Your computer <--> USB-CDC <--> MCU <--> UART2 <--> RTL8720DN <--> Internet <--> MQTT broker.
+//
+// You must install the Paho MQTT package to build this program:
+//
+// 		go get -u github.com/eclipse/paho.mqtt.golang
+//
+// You can check that mqttpub is running successfully with the following command.
+//
+// 		mosquitto_sub -h test.mosquitto.org -t tinygo
+//
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+
+	"tinygo.org/x/drivers/net"
+	"tinygo.org/x/drivers/net/mqtt"
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+// You can override the setting with the init() in another source code.
+// func init() {
+//    ssid = "your-ssid"
+//    password = "your-password"
+//    debug = true
+//    server = "tinygo.org"
+// }
+
+var (
+	ssid     string
+	password string
+	server   string = "tcp://test.mosquitto.org:1883"
+	debug           = false
+)
+
+var buf [0x400]byte
+
+var lastRequestTime time.Time
+var conn net.Conn
+var adaptor *rtl8720dn.RTL8720DN
+
+func main() {
+	err := run()
+	for err != nil {
+		fmt.Printf("error: %s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}
+
+var (
+	topic = "tinygo"
+)
+
+func run() error {
+	rtl, err := setupRTL8720DN()
+	if err != nil {
+		return err
+	}
+	net.UseDriver(rtl)
+
+	err = rtl.ConnectToAP(ssid, password)
+	if err != nil {
+		return err
+	}
+
+	ip, subnet, gateway, err := rtl.GetIP()
+	if err != nil {
+		return err
+	}
+	fmt.Printf("IP Address : %s\r\n", ip)
+	fmt.Printf("Mask       : %s\r\n", subnet)
+	fmt.Printf("Gateway    : %s\r\n", gateway)
+
+	rand.Seed(time.Now().UnixNano())
+
+	opts := mqtt.NewClientOptions()
+	opts.AddBroker(server).SetClientID("tinygo-client-" + randomString(10))
+
+	println("Connectng to MQTT...")
+	cl := mqtt.NewClient(opts)
+	if token := cl.Connect(); token.Wait() && token.Error() != nil {
+		failMessage(token.Error().Error())
+	}
+
+	for i := 0; ; i++ {
+		println("Publishing MQTT message...")
+		data := []byte(fmt.Sprintf(`{"e":[{"n":"hello %d","v":101}]}`, i))
+		token := cl.Publish(topic, 0, false, data)
+		token.Wait()
+		if err := token.Error(); err != nil {
+			return err
+		}
+		time.Sleep(100 * time.Millisecond)
+	}
+
+	// Right now this code is never reached. Need a way to trigger it...
+	println("Disconnecting MQTT...")
+	cl.Disconnect(100)
+
+	println("Done.")
+
+	return nil
+}
+
+// Returns an int >= min, < max
+func randomInt(min, max int) int {
+	return min + rand.Intn(max-min)
+}
+
+// Generate a random string of A-Z chars with len = l
+func randomString(len int) string {
+	bytes := make([]byte, len)
+	for i := 0; i < len; i++ {
+		bytes[i] = byte(randomInt(65, 90))
+	}
+	return string(bytes)
+}
+
+func failMessage(msg string) {
+	for {
+		println(msg)
+		time.Sleep(1 * time.Second)
+	}
+}

examples/rtl8720dn/mqttclient/wioterminal.go

@@ -0,0 +1,74 @@
+//go:build wioterminal
+// +build wioterminal
+
+package main
+
+import (
+	"device/sam"
+	"machine"
+	"runtime/interrupt"
+	"time"
+
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+var (
+	uart UARTx
+)
+
+func handleInterrupt(interrupt.Interrupt) {
+	// should reset IRQ
+	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))
+	uart.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INT_INTFLAG_RXC)
+}
+
+func setupRTL8720DN() (*rtl8720dn.RTL8720DN, error) {
+	machine.RTL8720D_CHIP_PU.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	machine.RTL8720D_CHIP_PU.Low()
+	time.Sleep(100 * time.Millisecond)
+	machine.RTL8720D_CHIP_PU.High()
+	time.Sleep(1000 * time.Millisecond)
+	if debug {
+		waitSerial()
+	}
+
+	uart = UARTx{
+		UART: &machine.UART{
+			Buffer: machine.NewRingBuffer(),
+			Bus:    sam.SERCOM0_USART_INT,
+			SERCOM: 0,
+		},
+	}
+
+	uart.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, handleInterrupt)
+	uart.Configure(machine.UARTConfig{TX: machine.PB24, RX: machine.PC24, BaudRate: 614400})
+
+	rtl := rtl8720dn.New(uart)
+	rtl.Debug(debug)
+
+	_, err := rtl.Rpc_tcpip_adapter_init()
+	if err != nil {
+		return nil, err
+	}
+
+	return rtl, nil
+}
+
+// Wait for user to open serial console
+func waitSerial() {
+	for !machine.Serial.DTR() {
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+type UARTx struct {
+	*machine.UART
+}
+
+func (u UARTx) Read(p []byte) (n int, err error) {
+	if u.Buffered() == 0 {
+		time.Sleep(1 * time.Millisecond)
+		return 0, nil
+	}
+	return u.UART.Read(p)
+}

examples/rtl8720dn/mqttsub/main.go

@@ -0,0 +1,154 @@
+// This is a sensor station that uses a RTL8720DN running on the device UART2.
+// It creates an MQTT connection that publishes a message every second
+// to an MQTT broker.
+//
+// In other words:
+// Your computer <--> USB-CDC <--> MCU <--> UART2 <--> RTL8720DN <--> Internet <--> MQTT broker.
+//
+// You must also install the Paho MQTT package to build this program:
+//
+// 		go get -u github.com/eclipse/paho.mqtt.golang
+//
+// You can check that mqttpub/mqttsub is running successfully with the following command.
+//
+// 		mosquitto_sub -h test.mosquitto.org -t tinygo/tx
+// 		mosquitto_pub -h test.mosquitto.org -t tinygo/rx -m "hello world"
+//
+package main
+
+import (
+	"fmt"
+	"math/rand"
+	"time"
+
+	"tinygo.org/x/drivers/net"
+	"tinygo.org/x/drivers/net/mqtt"
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+// You can override the setting with the init() in another source code.
+// func init() {
+//    ssid = "your-ssid"
+//    password = "your-password"
+//    debug = true
+//    server = "tinygo.org"
+// }
+
+var (
+	ssid     string
+	password string
+	server   string = "tcp://test.mosquitto.org:1883"
+	debug           = false
+)
+
+var buf [0x400]byte
+
+var lastRequestTime time.Time
+var conn net.Conn
+var adaptor *rtl8720dn.RTL8720DN
+
+func main() {
+	err := run()
+	for err != nil {
+		fmt.Printf("error: %s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}
+
+// change these to connect to a different UART or pins for the ESP8266/ESP32
+var (
+	cl      mqtt.Client
+	topicTx = "tinygo/tx"
+	topicRx = "tinygo/rx"
+)
+
+func subHandler(client mqtt.Client, msg mqtt.Message) {
+	fmt.Printf("[%s]  ", msg.Topic())
+	fmt.Printf("%s\r\n", msg.Payload())
+}
+
+func run() error {
+	rtl, err := setupRTL8720DN()
+	if err != nil {
+		return err
+	}
+	net.UseDriver(rtl)
+
+	err = rtl.ConnectToAP(ssid, password)
+	if err != nil {
+		return err
+	}
+
+	ip, subnet, gateway, err := rtl.GetIP()
+	if err != nil {
+		return err
+	}
+	fmt.Printf("IP Address : %s\r\n", ip)
+	fmt.Printf("Mask       : %s\r\n", subnet)
+	fmt.Printf("Gateway    : %s\r\n", gateway)
+
+	rand.Seed(time.Now().UnixNano())
+
+	opts := mqtt.NewClientOptions()
+	opts.AddBroker(server).SetClientID("tinygo-client-" + randomString(10))
+
+	println("Connecting to MQTT broker at", server)
+	cl = mqtt.NewClient(opts)
+	if token := cl.Connect(); token.Wait() && token.Error() != nil {
+		failMessage(token.Error().Error())
+	}
+
+	// subscribe
+	token := cl.Subscribe(topicRx, 0, subHandler)
+	token.Wait()
+	if token.Error() != nil {
+		failMessage(token.Error().Error())
+	}
+
+	go publishing()
+
+	select {}
+
+	// Right now this code is never reached. Need a way to trigger it...
+	println("Disconnecting MQTT...")
+	cl.Disconnect(100)
+
+	println("Done.")
+
+	return nil
+}
+
+func publishing() {
+	for i := 0; ; i++ {
+		println("Publishing MQTT message...")
+		data := []byte(fmt.Sprintf(`{"e":[{"n":"hello %d","v":101}]}`, i))
+		token := cl.Publish(topicTx, 0, false, data)
+		token.Wait()
+		if token.Error() != nil {
+			println(token.Error().Error())
+		}
+
+		time.Sleep(20 * 100 * time.Millisecond)
+	}
+}
+
+// Returns an int >= min, < max
+func randomInt(min, max int) int {
+	return min + rand.Intn(max-min)
+}
+
+// Generate a random string of A-Z chars with len = l
+func randomString(len int) string {
+	bytes := make([]byte, len)
+	for i := 0; i < len; i++ {
+		bytes[i] = byte(randomInt(65, 90))
+	}
+	return string(bytes)
+}
+
+func failMessage(msg string) {
+	for {
+		println(msg)
+		time.Sleep(1 * time.Second)
+	}
+}

examples/rtl8720dn/mqttsub/wioterminal.go

@@ -0,0 +1,74 @@
+//go:build wioterminal
+// +build wioterminal
+
+package main
+
+import (
+	"device/sam"
+	"machine"
+	"runtime/interrupt"
+	"time"
+
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+var (
+	uart UARTx
+)
+
+func handleInterrupt(interrupt.Interrupt) {
+	// should reset IRQ
+	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))
+	uart.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INT_INTFLAG_RXC)
+}
+
+func setupRTL8720DN() (*rtl8720dn.RTL8720DN, error) {
+	machine.RTL8720D_CHIP_PU.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	machine.RTL8720D_CHIP_PU.Low()
+	time.Sleep(100 * time.Millisecond)
+	machine.RTL8720D_CHIP_PU.High()
+	time.Sleep(1000 * time.Millisecond)
+	if debug {
+		waitSerial()
+	}
+
+	uart = UARTx{
+		UART: &machine.UART{
+			Buffer: machine.NewRingBuffer(),
+			Bus:    sam.SERCOM0_USART_INT,
+			SERCOM: 0,
+		},
+	}
+
+	uart.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, handleInterrupt)
+	uart.Configure(machine.UARTConfig{TX: machine.PB24, RX: machine.PC24, BaudRate: 614400})
+
+	rtl := rtl8720dn.New(uart)
+	rtl.Debug(debug)
+
+	_, err := rtl.Rpc_tcpip_adapter_init()
+	if err != nil {
+		return nil, err
+	}
+
+	return rtl, nil
+}
+
+// Wait for user to open serial console
+func waitSerial() {
+	for !machine.Serial.DTR() {
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+type UARTx struct {
+	*machine.UART
+}
+
+func (u UARTx) Read(p []byte) (n int, err error) {
+	if u.Buffered() == 0 {
+		time.Sleep(1 * time.Millisecond)
+		return 0, nil
+	}
+	return u.UART.Read(p)
+}

examples/rtl8720dn/ntpclient/main.go

@@ -0,0 +1,144 @@
+// This is an example of using the rtl8720dn driver to implement a NTP client.
+// It creates a UDP connection to request the current time and parse the
+// response from a NTP server.
+package main
+
+import (
+	"errors"
+	"fmt"
+	"runtime"
+	"time"
+
+	"tinygo.org/x/drivers/net"
+)
+
+// IP address of the server aka "hub". Replace with your own info.
+// You can override the setting with the init() in another source code.
+// func init() {
+//    ssid = "your-ssid"
+//    password = "your-password"
+//    ntpHost = "129.6.15.29"
+//    debug = true
+// }
+
+var (
+	ssid     string
+	password string
+	ntpHost  = "129.6.15.29"
+	debug    = false
+)
+
+const NTP_PACKET_SIZE = 48
+
+var b = make([]byte, NTP_PACKET_SIZE)
+
+func main() {
+	err := run()
+	for err != nil {
+		fmt.Printf("error: %s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}
+
+func run() error {
+	rtl, err := setupRTL8720DN()
+	if err != nil {
+		return err
+	}
+	net.UseDriver(rtl)
+
+	err = rtl.ConnectToAP(ssid, password)
+	if err != nil {
+		return err
+	}
+
+	ip, subnet, gateway, err := rtl.GetIP()
+	if err != nil {
+		return err
+	}
+	fmt.Printf("IP Address : %s\r\n", ip)
+	fmt.Printf("Mask       : %s\r\n", subnet)
+	fmt.Printf("Gateway    : %s\r\n", gateway)
+
+	// now make UDP connection
+	hip := net.ParseIP(ntpHost)
+	raddr := &net.UDPAddr{IP: hip, Port: 123}
+	laddr := &net.UDPAddr{Port: 2390}
+	conn, err := net.DialUDP("udp", laddr, raddr)
+	if err != nil {
+		return err
+	}
+
+	for {
+		// send data
+		println("Requesting NTP time...")
+		t, err := getCurrentTime(conn)
+		if err != nil {
+			message("Error getting current time: %v", err)
+		} else {
+			message("NTP time: %v", t)
+		}
+		runtime.AdjustTimeOffset(-1 * int64(time.Since(t)))
+		for i := 0; i < 10; i++ {
+			message("Current time: %v", time.Now())
+			time.Sleep(1 * time.Second)
+		}
+	}
+
+}
+
+func getCurrentTime(conn *net.UDPSerialConn) (time.Time, error) {
+	if err := sendNTPpacket(conn); err != nil {
+		return time.Time{}, err
+	}
+	clearBuffer()
+	for now := time.Now(); time.Since(now) < time.Second; {
+		time.Sleep(5 * time.Millisecond)
+		if n, err := conn.Read(b); err != nil {
+			return time.Time{}, fmt.Errorf("error reading UDP packet: %w", err)
+		} else if n == 0 {
+			continue // no packet received yet
+		} else if n != NTP_PACKET_SIZE {
+			if n != NTP_PACKET_SIZE {
+				return time.Time{}, fmt.Errorf("expected NTP packet size of %d: %d", NTP_PACKET_SIZE, n)
+			}
+		}
+		return parseNTPpacket(), nil
+	}
+	return time.Time{}, errors.New("no packet received after 1 second")
+}
+
+func sendNTPpacket(conn *net.UDPSerialConn) error {
+	clearBuffer()
+	b[0] = 0b11100011 // LI, Version, Mode
+	b[1] = 0          // Stratum, or type of clock
+	b[2] = 6          // Polling Interval
+	b[3] = 0xEC       // Peer Clock Precision
+	// 8 bytes of zero for Root Delay & Root Dispersion
+	b[12] = 49
+	b[13] = 0x4E
+	b[14] = 49
+	b[15] = 52
+	if _, err := conn.Write(b); err != nil {
+		return err
+	}
+	return nil
+}
+
+func parseNTPpacket() time.Time {
+	// the timestamp starts at byte 40 of the received packet and is four bytes,
+	// this is NTP time (seconds since Jan 1 1900):
+	t := uint32(b[40])<<24 | uint32(b[41])<<16 | uint32(b[42])<<8 | uint32(b[43])
+	const seventyYears = 2208988800
+	return time.Unix(int64(t-seventyYears), 0)
+}
+
+func clearBuffer() {
+	for i := range b {
+		b[i] = 0
+	}
+}
+
+func message(format string, args ...interface{}) {
+	println(fmt.Sprintf(format, args...), "\r")
+}

examples/rtl8720dn/ntpclient/wioterminal.go

@@ -0,0 +1,72 @@
+//go:build wioterminal
+// +build wioterminal
+
+package main
+
+import (
+	"device/sam"
+	"machine"
+	"runtime/interrupt"
+	"time"
+
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+var (
+	uart UARTx
+)
+
+func handleInterrupt(interrupt.Interrupt) {
+	// should reset IRQ
+	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))
+	uart.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INT_INTFLAG_RXC)
+}
+
+func setupRTL8720DN() (*rtl8720dn.RTL8720DN, error) {
+	machine.RTL8720D_CHIP_PU.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	machine.RTL8720D_CHIP_PU.Low()
+	time.Sleep(100 * time.Millisecond)
+	machine.RTL8720D_CHIP_PU.High()
+	time.Sleep(1000 * time.Millisecond)
+	waitSerial()
+
+	uart = UARTx{
+		UART: &machine.UART{
+			Buffer: machine.NewRingBuffer(),
+			Bus:    sam.SERCOM0_USART_INT,
+			SERCOM: 0,
+		},
+	}
+
+	uart.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, handleInterrupt)
+	uart.Configure(machine.UARTConfig{TX: machine.PB24, RX: machine.PC24, BaudRate: 614400})
+
+	rtl := rtl8720dn.New(uart)
+	rtl.Debug(debug)
+
+	_, err := rtl.Rpc_tcpip_adapter_init()
+	if err != nil {
+		return nil, err
+	}
+
+	return rtl, nil
+}
+
+// Wait for user to open serial console
+func waitSerial() {
+	for !machine.Serial.DTR() {
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+type UARTx struct {
+	*machine.UART
+}
+
+func (u UARTx) Read(p []byte) (n int, err error) {
+	if u.Buffered() == 0 {
+		time.Sleep(1 * time.Millisecond)
+		return 0, nil
+	}
+	return u.UART.Read(p)
+}

examples/rtl8720dn/tcpclient/main.go

@@ -0,0 +1,121 @@
+// This example opens a TCP connection using a device with RTL8720DN firmware
+// and sends some data, for the purpose of testing speed and connectivity.
+//
+// You can open a server to accept connections from this program using:
+//
+// nc -w 5 -lk 8080
+//
+package main
+
+import (
+	"bytes"
+	"fmt"
+	"time"
+
+	"tinygo.org/x/drivers/net"
+)
+
+// You can override the setting with the init() in another source code.
+// func init() {
+//    ssid = "sghome-gw"
+//    password = "3af25537b4524"
+//    serverIP = "192.168.1.119"
+//    debug = true
+// }
+
+var (
+	ssid     string
+	password string
+	serverIP = ""
+	debug    = false
+)
+
+var buf = &bytes.Buffer{}
+
+func main() {
+	err := run()
+	for err != nil {
+		fmt.Printf("error: %s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}
+
+func run() error {
+	rtl, err := setupRTL8720DN()
+	if err != nil {
+		return err
+	}
+	net.UseDriver(rtl)
+
+	err = rtl.ConnectToAP(ssid, password)
+	if err != nil {
+		return err
+	}
+
+	ip, subnet, gateway, err := rtl.GetIP()
+	if err != nil {
+		return err
+	}
+	fmt.Printf("IP Address : %s\r\n", ip)
+	fmt.Printf("Mask       : %s\r\n", subnet)
+	fmt.Printf("Gateway    : %s\r\n", gateway)
+
+	for {
+		sendBatch()
+		time.Sleep(500 * time.Millisecond)
+	}
+	println("Done.")
+
+	return nil
+}
+
+func sendBatch() {
+
+	// make TCP connection
+	ip := net.ParseIP(serverIP)
+	raddr := &net.TCPAddr{IP: ip, Port: 8080}
+	laddr := &net.TCPAddr{Port: 8080}
+
+	message("---------------\r\nDialing TCP connection")
+	conn, err := net.DialTCP("tcp", laddr, raddr)
+	for ; err != nil; conn, err = net.DialTCP("tcp", laddr, raddr) {
+		message(err.Error())
+		time.Sleep(5 * time.Second)
+	}
+
+	n := 0
+	w := 0
+	start := time.Now()
+
+	// send data
+	message("Sending data")
+
+	for i := 0; i < 1000; i++ {
+		buf.Reset()
+		fmt.Fprint(buf,
+			"\r---------------------------- i == ", i, " ----------------------------"+
+				"\r---------------------------- i == ", i, " ----------------------------")
+		if w, err = conn.Write(buf.Bytes()); err != nil {
+			println("error:", err.Error(), "\r")
+			continue
+		}
+		n += w
+	}
+
+	buf.Reset()
+	ms := time.Now().Sub(start).Milliseconds()
+	fmt.Fprint(buf, "\nWrote ", n, " bytes in ", ms, " ms\r\n")
+	message(buf.String())
+
+	if _, err := conn.Write(buf.Bytes()); err != nil {
+		println("error:", err.Error(), "\r")
+	}
+
+	// Right now this code is never reached. Need a way to trigger it...
+	println("Disconnecting TCP...")
+	conn.Close()
+}
+
+func message(msg string) {
+	println(msg, "\r")
+}

examples/rtl8720dn/tcpclient/wioterminal.go

@@ -0,0 +1,72 @@
+//go:build wioterminal
+// +build wioterminal
+
+package main
+
+import (
+	"device/sam"
+	"machine"
+	"runtime/interrupt"
+	"time"
+
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+var (
+	uart UARTx
+)
+
+func handleInterrupt(interrupt.Interrupt) {
+	// should reset IRQ
+	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))
+	uart.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INT_INTFLAG_RXC)
+}
+
+func setupRTL8720DN() (*rtl8720dn.RTL8720DN, error) {
+	machine.RTL8720D_CHIP_PU.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	machine.RTL8720D_CHIP_PU.Low()
+	time.Sleep(100 * time.Millisecond)
+	machine.RTL8720D_CHIP_PU.High()
+	time.Sleep(1000 * time.Millisecond)
+	waitSerial()
+
+	uart = UARTx{
+		UART: &machine.UART{
+			Buffer: machine.NewRingBuffer(),
+			Bus:    sam.SERCOM0_USART_INT,
+			SERCOM: 0,
+		},
+	}
+
+	uart.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, handleInterrupt)
+	uart.Configure(machine.UARTConfig{TX: machine.PB24, RX: machine.PC24, BaudRate: 614400})
+
+	rtl := rtl8720dn.New(uart)
+	rtl.Debug(debug)
+
+	_, err := rtl.Rpc_tcpip_adapter_init()
+	if err != nil {
+		return nil, err
+	}
+
+	return rtl, nil
+}
+
+// Wait for user to open serial console
+func waitSerial() {
+	for !machine.Serial.DTR() {
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+type UARTx struct {
+	*machine.UART
+}
+
+func (u UARTx) Read(p []byte) (n int, err error) {
+	if u.Buffered() == 0 {
+		time.Sleep(1 * time.Millisecond)
+		return 0, nil
+	}
+	return u.UART.Read(p)
+}

examples/rtl8720dn/tlsclient/main.go

@@ -1,12 +1,13 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
 	"strings"
 	"time"
 
 	"tinygo.org/x/drivers/net"
-	"tinygo.org/x/drivers/net/tls"
+	"tinygo.org/x/drivers/net/http"
 	"tinygo.org/x/drivers/rtl8720dn"
 )
 
@@ -15,14 +16,14 @@ import (
 //    ssid = "your-ssid"
 //    password = "your-password"
 //    debug = true
-//    server = "tinygo.org"
+//    url = "https://www.example.com"
 //    test_root_ca = "..."
 // }
 
 var (
 	ssid     string
 	password string
-	server   string = "www.example.com"
+	url      string = "https://www.example.com"
 	debug           = false
 )
 
@@ -52,7 +53,7 @@ CAUw7C29C79Fv1C5qfPrmAESrciIxpg0X40KPMbp1ZWVbd4=
 -----END CERTIFICATE-----
 `
 
-var buf [0x400]byte
+var buf [0x1000]byte
 
 var lastRequestTime time.Time
 var conn net.Conn
@@ -73,6 +74,7 @@ func run() error {
 	}
 	rtl.SetRootCA(&test_root_ca)
 	net.UseDriver(rtl)
+	http.SetBuf(buf[:])
 
 	err = rtl.ConnectToAP(ssid, password)
 	if err != nil {
@@ -87,55 +89,49 @@ func run() error {
 	fmt.Printf("Mask       : %s\r\n", subnet)
 	fmt.Printf("Gateway    : %s\r\n", gateway)
 
+	// You can send and receive cookies in the following way
+	// 	import "tinygo.org/x/drivers/net/http/cookiejar"
+	// 	jar, err := cookiejar.New(nil)
+	// 	if err != nil {
+	// 		return err
+	// 	}
+	// 	client := &http.Client{Jar: jar}
+	// 	http.DefaultClient = client
+
 	cnt := 0
 	for {
-		readConnection()
-		if time.Now().Sub(lastRequestTime).Milliseconds() >= 10000 {
-			makeHTTPSRequest()
-			cnt++
-			fmt.Printf("-------- %d --------\r\n", cnt)
+		// Various examples are as follows
+		//
+		// -- Get
+		// 	resp, err := http.Get(url)
+		//
+		// -- Post
+		// 	body := `cnt=12`
+		// 	resp, err = http.Post(url, "application/x-www-form-urlencoded", strings.NewReader(body))
+		//
+		// -- Post with JSON
+		// 	body := `{"msg": "hello"}`
+		// 	resp, err := http.Post(url, "application/json", strings.NewReader(body))
+
+		resp, err := http.Get(url)
+		if err != nil {
+			return err
 		}
-	}
-}
 
-func readConnection() {
-	if conn != nil {
-		for n, err := conn.Read(buf[:]); n > 0; n, err = conn.Read(buf[:]) {
-			if err != nil {
-				println("Read error: " + err.Error())
-			} else {
-				print(string(buf[0:n]))
-			}
+		fmt.Printf("%s %s\r\n", resp.Proto, resp.Status)
+		for k, v := range resp.Header {
+			fmt.Printf("%s: %s\r\n", k, strings.Join(v, " "))
 		}
+		fmt.Printf("\r\n")
+
+		scanner := bufio.NewScanner(resp.Body)
+		for scanner.Scan() {
+			fmt.Printf("%s\r\n", scanner.Text())
+		}
+		resp.Body.Close()
+
+		cnt++
+		fmt.Printf("-------- %d --------\r\n", cnt)
+		time.Sleep(10 * time.Second)
 	}
 }
-
-func makeHTTPSRequest() {
-
-	var err error
-	if conn != nil {
-		conn.Close()
-	}
-
-	message("\r\n---------------\r\nDialing TCP connection")
-	conn, err = tls.Dial("tcp", server, nil)
-	for ; err != nil; conn, err = tls.Dial("tcp", server, nil) {
-		message("Connection failed: " + err.Error())
-		time.Sleep(5 * time.Second)
-	}
-	println("Connected!\r")
-
-	print("Sending HTTPS request...")
-	fmt.Fprintln(conn, "GET / HTTP/1.1")
-	fmt.Fprintln(conn, "Host:", strings.Split(server, ":")[0])
-	fmt.Fprintln(conn, "User-Agent: TinyGo")
-	fmt.Fprintln(conn, "Connection: close")
-	fmt.Fprintln(conn)
-	println("Sent!\r\n\r")
-
-	lastRequestTime = time.Now()
-}
-
-func message(msg string) {
-	println(msg, "\r")
-}

examples/rtl8720dn/tlsclient/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/rtl8720dn/udpstation/main.go

@@ -0,0 +1,89 @@
+package main
+
+import (
+	"fmt"
+	"strconv"
+	"time"
+
+	"tinygo.org/x/drivers/net"
+	"tinygo.org/x/drivers/net/http"
+)
+
+// IP address of the server aka "hub". Replace with your own info.
+// You can override the setting with the init() in another source code.
+// func init() {
+//    ssid = "your-ssid"
+//    password = "your-password"
+//    hubIP = "192.168.1.118"
+//    debug = true
+// }
+
+var (
+	ssid     string
+	password string
+	hubIP    = ""
+	debug    = false
+)
+
+var buf [0x400]byte
+
+func main() {
+	err := run()
+	for err != nil {
+		fmt.Printf("error: %s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}
+
+func run() error {
+	rtl, err := setupRTL8720DN()
+	if err != nil {
+		return err
+	}
+	net.UseDriver(rtl)
+	http.SetBuf(buf[:])
+
+	err = rtl.ConnectToAP(ssid, password)
+	if err != nil {
+		return err
+	}
+
+	ip, subnet, gateway, err := rtl.GetIP()
+	if err != nil {
+		return err
+	}
+	fmt.Printf("IP Address : %s\r\n", ip)
+	fmt.Printf("Mask       : %s\r\n", subnet)
+	fmt.Printf("Gateway    : %s\r\n", gateway)
+
+	// now make UDP connection
+	hip := net.ParseIP(hubIP)
+	raddr := &net.UDPAddr{IP: hip, Port: 2222}
+	laddr := &net.UDPAddr{Port: 2222}
+
+	println("Dialing UDP connection...")
+	conn, err := net.DialUDP("udp", laddr, raddr)
+	if err != nil {
+		return err
+	}
+
+	for {
+		// send data
+		println("Sending data...")
+		for i := 0; i < 25; i++ {
+			conn.Write([]byte("hello " + strconv.Itoa(i) + "\r\n"))
+		}
+		time.Sleep(1000 * time.Millisecond)
+	}
+
+	// Right now this code is never reached. Need a way to trigger it...
+	println("Disconnecting UDP...")
+	conn.Close()
+	println("Done.")
+
+	return nil
+}
+
+func message(msg string) {
+	println(msg, "\r")
+}

examples/rtl8720dn/udpstation/wioterminal.go

@@ -0,0 +1,72 @@
+//go:build wioterminal
+// +build wioterminal
+
+package main
+
+import (
+	"device/sam"
+	"machine"
+	"runtime/interrupt"
+	"time"
+
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+var (
+	uart UARTx
+)
+
+func handleInterrupt(interrupt.Interrupt) {
+	// should reset IRQ
+	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))
+	uart.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INT_INTFLAG_RXC)
+}
+
+func setupRTL8720DN() (*rtl8720dn.RTL8720DN, error) {
+	machine.RTL8720D_CHIP_PU.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	machine.RTL8720D_CHIP_PU.Low()
+	time.Sleep(100 * time.Millisecond)
+	machine.RTL8720D_CHIP_PU.High()
+	time.Sleep(1000 * time.Millisecond)
+	waitSerial()
+
+	uart = UARTx{
+		UART: &machine.UART{
+			Buffer: machine.NewRingBuffer(),
+			Bus:    sam.SERCOM0_USART_INT,
+			SERCOM: 0,
+		},
+	}
+
+	uart.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, handleInterrupt)
+	uart.Configure(machine.UARTConfig{TX: machine.PB24, RX: machine.PC24, BaudRate: 614400})
+
+	rtl := rtl8720dn.New(uart)
+	rtl.Debug(debug)
+
+	_, err := rtl.Rpc_tcpip_adapter_init()
+	if err != nil {
+		return nil, err
+	}
+
+	return rtl, nil
+}
+
+// Wait for user to open serial console
+func waitSerial() {
+	for !machine.Serial.DTR() {
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+type UARTx struct {
+	*machine.UART
+}
+
+func (u UARTx) Read(p []byte) (n int, err error) {
+	if u.Buffered() == 0 {
+		time.Sleep(1 * time.Millisecond)
+		return 0, nil
+	}
+	return u.UART.Read(p)
+}

examples/rtl8720dn/webclient-tinyterm/main.go

@@ -1,29 +1,32 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
 	"image/color"
+	"strings"
 	"time"
 
 	"tinygo.org/x/drivers/net"
-	"tinygo.org/x/drivers/rtl8720dn"
+	"tinygo.org/x/drivers/net/http"
 	"tinygo.org/x/tinyfont/proggy"
 	"tinygo.org/x/tinyterm"
 )
 
 // You can override the setting with the init() in another source code.
+// If debug is enabled, a serial connection is required.
 // func init() {
 //    ssid = "your-ssid"
 //    password = "your-password"
-//    debug = true
+//    debug = false // true
 //    server = "tinygo.org"
 // }
 
 var (
 	ssid     string
 	password string
-	server   string = "tinygo.org"
-	debug           = false
+	url      = "http://tinygo.org/"
+	debug    = false
 )
 
 var (
@@ -40,10 +43,6 @@ var (
 
 var buf [0x400]byte
 
-var lastRequestTime time.Time
-var conn net.Conn
-var adaptor *rtl8720dn.RTL8720DN
-
 func main() {
 	display.FillScreen(black)
 	backlight.High()
@@ -63,11 +62,16 @@ func main() {
 
 func run() error {
 	fmt.Fprintf(terminal, "setupRTL8720DN()\r\n")
+	if debug {
+		fmt.Fprintf(terminal, "Running in debug mode.\r\n")
+		fmt.Fprintf(terminal, "A serial connection is required to continue execution.\r\n")
+	}
 	rtl, err := setupRTL8720DN()
 	if err != nil {
 		return err
 	}
 	net.UseDriver(rtl)
+	http.SetBuf(buf[:])
 
 	fmt.Fprintf(terminal, "ConnectToAP()\r\n")
 	err = rtl.ConnectToAP(ssid, password)
@@ -84,60 +88,49 @@ func run() error {
 	fmt.Fprintf(terminal, "Mask       : %s\r\n", subnet)
 	fmt.Fprintf(terminal, "Gateway    : %s\r\n", gateway)
 
+	// You can send and receive cookies in the following way
+	// 	import "tinygo.org/x/drivers/net/http/cookiejar"
+	// 	jar, err := cookiejar.New(nil)
+	// 	if err != nil {
+	// 		return err
+	// 	}
+	// 	client := &http.Client{Jar: jar}
+	// 	http.DefaultClient = client
+
 	cnt := 0
 	for {
-		readConnection()
-		if time.Now().Sub(lastRequestTime).Milliseconds() >= 10000 {
-			makeHTTPRequest()
-			cnt++
-			fmt.Fprintf(terminal, "-------- %d --------\r\n", cnt)
+		// Various examples are as follows
+		//
+		// -- Get
+		// 	resp, err := http.Get(url)
+		//
+		// -- Post
+		// 	body := `cnt=12`
+		// 	resp, err = http.Post(url, "application/x-www-form-urlencoded", strings.NewReader(body))
+		//
+		// -- Post with JSON
+		// 	body := `{"msg": "hello"}`
+		// 	resp, err := http.Post(url, "application/json", strings.NewReader(body))
+
+		resp, err := http.Get(url)
+		if err != nil {
+			return err
 		}
-	}
-}
 
-func readConnection() {
-	if conn != nil {
-		for n, err := conn.Read(buf[:]); n > 0; n, err = conn.Read(buf[:]) {
-			if err != nil {
-				fmt.Fprintf(terminal, "Read error: "+err.Error()+"\r\n")
-			} else {
-				fmt.Fprintf(terminal, string(buf[0:n]))
-			}
+		fmt.Fprintf(terminal, "%s %s\r\n", resp.Proto, resp.Status)
+		for k, v := range resp.Header {
+			fmt.Fprintf(terminal, "%s: %s\r\n", k, strings.Join(v, " "))
 		}
+		fmt.Printf("\r\n")
+
+		scanner := bufio.NewScanner(resp.Body)
+		for scanner.Scan() {
+			fmt.Fprintf(terminal, "%s\r\n", scanner.Text())
+		}
+		resp.Body.Close()
+
+		cnt++
+		fmt.Fprintf(terminal, "-------- %d --------\r\n", cnt)
+		time.Sleep(10 * time.Second)
 	}
 }
-
-func makeHTTPRequest() {
-
-	var err error
-	if conn != nil {
-		conn.Close()
-	}
-
-	// make TCP connection
-	ip := net.ParseIP(server)
-	raddr := &net.TCPAddr{IP: ip, Port: 80}
-	laddr := &net.TCPAddr{Port: 8080}
-
-	message("\r\n---------------\r\nDialing TCP connection")
-	conn, err = net.DialTCP("tcp", laddr, raddr)
-	for ; err != nil; conn, err = net.DialTCP("tcp", laddr, raddr) {
-		message("Connection failed: " + err.Error())
-		time.Sleep(5 * time.Second)
-	}
-	fmt.Fprintf(terminal, "Connected!\r\n")
-
-	fmt.Fprintf(terminal, "Sending HTTP request...")
-	fmt.Fprintln(conn, "GET / HTTP/1.1")
-	fmt.Fprintln(conn, "Host:", server)
-	fmt.Fprintln(conn, "User-Agent: TinyGo")
-	fmt.Fprintln(conn, "Connection: close")
-	fmt.Fprintln(conn)
-	fmt.Fprintf(terminal, "Sent!\r\n\r\n")
-
-	lastRequestTime = time.Now()
-}
-
-func message(msg string) {
-	fmt.Fprintf(terminal, "%s\r\n", msg)
-}

examples/rtl8720dn/webclient-tinyterm/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/rtl8720dn/webclient/main.go

@@ -1,34 +1,32 @@
 package main
 
 import (
+	"bufio"
 	"fmt"
+	"strings"
 	"time"
 
 	"tinygo.org/x/drivers/net"
-	"tinygo.org/x/drivers/rtl8720dn"
+	"tinygo.org/x/drivers/net/http"
 )
 
 // You can override the setting with the init() in another source code.
 // func init() {
 //    ssid = "your-ssid"
 //    password = "your-password"
+//    url = "http://tinygo.org/"
 //    debug = true
-//    server = "tinygo.org"
 // }
 
 var (
 	ssid     string
 	password string
-	server   string = "tinygo.org"
-	debug           = false
+	url      = "http://tinygo.org/"
+	debug    = false
 )
 
 var buf [0x400]byte
 
-var lastRequestTime time.Time
-var conn net.Conn
-var adaptor *rtl8720dn.RTL8720DN
-
 func main() {
 	err := run()
 	for err != nil {
@@ -43,6 +41,7 @@ func run() error {
 		return err
 	}
 	net.UseDriver(rtl)
+	http.SetBuf(buf[:])
 
 	err = rtl.ConnectToAP(ssid, password)
 	if err != nil {
@@ -57,60 +56,49 @@ func run() error {
 	fmt.Printf("Mask       : %s\r\n", subnet)
 	fmt.Printf("Gateway    : %s\r\n", gateway)
 
+	// You can send and receive cookies in the following way
+	// 	import "tinygo.org/x/drivers/net/http/cookiejar"
+	// 	jar, err := cookiejar.New(nil)
+	// 	if err != nil {
+	// 		return err
+	// 	}
+	// 	client := &http.Client{Jar: jar}
+	// 	http.DefaultClient = client
+
 	cnt := 0
 	for {
-		readConnection()
-		if time.Now().Sub(lastRequestTime).Milliseconds() >= 10000 {
-			makeHTTPRequest()
-			cnt++
-			fmt.Printf("-------- %d --------\r\n", cnt)
+		// Various examples are as follows
+		//
+		// -- Get
+		// 	resp, err := http.Get(url)
+		//
+		// -- Post
+		// 	body := `cnt=12`
+		// 	resp, err = http.Post(url, "application/x-www-form-urlencoded", strings.NewReader(body))
+		//
+		// -- Post with JSON
+		// 	body := `{"msg": "hello"}`
+		// 	resp, err := http.Post(url, "application/json", strings.NewReader(body))
+
+		resp, err := http.Get(url)
+		if err != nil {
+			return err
 		}
-	}
-}
 
-func readConnection() {
-	if conn != nil {
-		for n, err := conn.Read(buf[:]); n > 0; n, err = conn.Read(buf[:]) {
-			if err != nil {
-				println("Read error: " + err.Error())
-			} else {
-				print(string(buf[0:n]))
-			}
+		fmt.Printf("%s %s\r\n", resp.Proto, resp.Status)
+		for k, v := range resp.Header {
+			fmt.Printf("%s: %s\r\n", k, strings.Join(v, " "))
 		}
+		fmt.Printf("\r\n")
+
+		scanner := bufio.NewScanner(resp.Body)
+		for scanner.Scan() {
+			fmt.Printf("%s\r\n", scanner.Text())
+		}
+		resp.Body.Close()
+
+		cnt++
+		fmt.Printf("-------- %d --------\r\n", cnt)
+		time.Sleep(10 * time.Second)
 	}
 }
-
-func makeHTTPRequest() {
-
-	var err error
-	if conn != nil {
-		conn.Close()
-	}
-
-	// make TCP connection
-	ip := net.ParseIP(server)
-	raddr := &net.TCPAddr{IP: ip, Port: 80}
-	laddr := &net.TCPAddr{Port: 8080}
-
-	message("\r\n---------------\r\nDialing TCP connection")
-	conn, err = net.DialTCP("tcp", laddr, raddr)
-	for ; err != nil; conn, err = net.DialTCP("tcp", laddr, raddr) {
-		message("Connection failed: " + err.Error())
-		time.Sleep(5 * time.Second)
-	}
-	println("Connected!\r")
-
-	print("Sending HTTP request...")
-	fmt.Fprintln(conn, "GET / HTTP/1.1")
-	fmt.Fprintln(conn, "Host:", server)
-	fmt.Fprintln(conn, "User-Agent: TinyGo")
-	fmt.Fprintln(conn, "Connection: close")
-	fmt.Fprintln(conn)
-	println("Sent!\r\n\r")
-
-	lastRequestTime = time.Now()
-}
-
-func message(msg string) {
-	println(msg, "\r")
-}

examples/rtl8720dn/webclient/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/rtl8720dn/webserver/main.go

@@ -0,0 +1,192 @@
+package main
+
+import (
+	"fmt"
+	"machine"
+	"strconv"
+	"time"
+
+	"tinygo.org/x/drivers/net/http"
+)
+
+// You can override the setting with the init() in another source code.
+// func init() {
+//    ssid = "your-ssid"
+//    password = "your-password"
+//    debug = true
+// }
+
+var (
+	ssid     string
+	password string
+	debug    = false
+)
+
+var led = machine.LED
+var backlight = machine.LCD_BACKLIGHT
+
+func main() {
+	led.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	backlight.Configure(machine.PinConfig{Mode: machine.PinOutput})
+
+	err := run()
+	for err != nil {
+		fmt.Printf("error: %s\r\n", err.Error())
+		time.Sleep(5 * time.Second)
+	}
+}
+
+func run() error {
+	rtl, err := setupRTL8720DN()
+	if err != nil {
+		return err
+	}
+	http.UseDriver(rtl)
+
+	err = rtl.ConnectToAP(ssid, password)
+	if err != nil {
+		return err
+	}
+
+	ip, subnet, gateway, err := rtl.GetIP()
+	if err != nil {
+		return err
+	}
+	fmt.Printf("IP Address : %s\r\n", ip)
+	fmt.Printf("Mask       : %s\r\n", subnet)
+	fmt.Printf("Gateway    : %s\r\n", gateway)
+
+	http.HandleFunc("/", root)
+	http.HandleFunc("/hello", hello)
+	http.HandleFunc("/cnt", cnt)
+	http.HandleFunc("/6", sixlines)
+	http.HandleFunc("/off", LED_OFF)
+	http.HandleFunc("/on", LED_ON)
+	if err := http.ListenAndServe(":80", nil); err != nil {
+		message(err.Error())
+	}
+	return nil
+}
+
+func root(w http.ResponseWriter, r *http.Request) {
+	access := 1
+
+	cookie, err := r.Cookie("access")
+	if err != nil {
+		if err == http.ErrNoCookie {
+			cookie = &http.Cookie{
+				Name:  "access",
+				Value: "1",
+			}
+		} else {
+			http.Error(w, fmt.Sprintf("%s", err.Error()), http.StatusBadRequest)
+			return
+		}
+	} else {
+		v, err := strconv.ParseInt(cookie.Value, 10, 0)
+		if err != nil {
+			http.Error(w, fmt.Sprintf("invalid cookie.Value : %s", cookie.Value), http.StatusBadRequest)
+			return
+		}
+		cookie.Value = fmt.Sprintf("%d", v+1)
+		access = int(v) + 1
+	}
+	http.SetCookie(w, cookie)
+	w.WriteHeader(http.StatusOK)
+
+	fmt.Fprintf(w, `
+<html>
+<head>
+    <title>TinyGo HTTP Server</title>
+    <script language="javascript" type="text/javascript">
+        var counter = 0
+        function ledOn() { fetch("/on").then(response => response.text()).then(text => { led.innerHTML = "<p>on</p>"; }); }
+        function ledOff() { fetch("/off").then(response => response.text()).then(text => { led.innerHTML = "<p>off</p>"; }); }
+        function fetchCnt() { fetch("/cnt").then(response => response.json()).then(json => { counter = json.cnt; cnt.innerHTML = counter; }); }
+        function incrCnt() { counter = counter + 1; fetch("/cnt?cnt=" + counter, { method: 'POST' }).then(response => response.json()).then(json => { counter = json.cnt; cnt.innerHTML = counter; }); }
+        function setCnt() { fetch("/cnt", {
+            method: "POST",
+            body: "cnt=" + document.getElementsByName("cnt")[0].value,
+            headers: { 'Content-Type': 'application/x-www-form-urlencoded' },
+        }).then(response => response.json()).then(json => { counter = json.cnt; cnt.innerHTML = counter; }); return false; }
+        function onLoad() { fetchCnt(); }
+    </script>
+</head>
+<body onLoad="onLoad()">
+    <h5>TinyGo HTTP Server</h5>
+
+    <p>
+        access: %d
+    </p>
+
+    <a href="/hello">/hello</a><br>
+    <a href="/6">/6</a><br>
+
+    <p>
+        LED<br>
+        <a href="javascript:ledOn();">/on</a><br>
+        <a href="javascript:ledOff();">/off</a><br>
+    </p>
+
+
+    <p>
+        <a href="/cnt">/cnt</a><br>
+        cnt: <span id="cnt"></span><br>
+        <a href="javascript:incrCnt()">incrCnt()</a><br>
+        <form id="form1" style="display: inline" onSubmit="return setCnt()">
+        <input type="text" name="cnt">
+        <input type="button" value="set cnt", onClick="setCnt()">
+        </form>
+    </p>
+</body>
+</html>
+    `, access)
+}
+
+func sixlines(w http.ResponseWriter, r *http.Request) {
+	// https://fukuno.jig.jp/3267
+	fmt.Fprint(w, `<body onload='onkeydown=e=>K=parseInt(e.key[5]||6,28)/3-8;Z=X=[B=A=12];Y=_=>`+
+		`{for(C=[q=c=i=4];f=i--*K;c-=!Z[h+(K+6?p+K:C[i]=p*A-(p/9|0)*145)])p=B[i];for(c?0:K+6?h+=K:B=C;`+
+		`i=K=q--;f+=Z[A+p])X[p=h+B[q]]=1;h+=A;if(f|B)for(Z=X,X=[l=228],B=[[-7,-20,6,h=17,-9,3,3][t=++t%7]-4,0,1,t-6?-A:2];l--;)`+
+		`for(l%A?l-=l%A*!Z[l]:(P++,c=l+=A);--c>A;)Z[c]=Z[c-A];for(S="";i<240;S+=X[i]|(X[i]=Z[i]|=++i%A<2|i>228)?i%A?"■":"■<br>":"　");`+
+		`D.innerHTML=S+P;setTimeout(Y,i-P)};Y(h=K=t=P=0)'id=D>`)
+}
+
+func LED_ON(w http.ResponseWriter, r *http.Request) {
+	led.High()
+	backlight.High()
+	w.Header().Set(`Content-Type`, `text/plain; charset=UTF-8`)
+	fmt.Fprintf(w, "led.High()")
+}
+
+func LED_OFF(w http.ResponseWriter, r *http.Request) {
+	led.Low()
+	backlight.Low()
+	w.Header().Set(`Content-Type`, `text/plain; charset=UTF-8`)
+	fmt.Fprintf(w, "led.Low()")
+}
+
+func hello(w http.ResponseWriter, r *http.Request) {
+	w.Header().Set(`Content-Type`, `text/plain; charset=UTF-8`)
+	fmt.Fprintf(w, "hello")
+}
+
+var counter int
+
+func cnt(w http.ResponseWriter, r *http.Request) {
+	r.ParseForm()
+	if r.Method == "POST" {
+		c := r.Form.Get("cnt")
+		if c != "" {
+			i64, _ := strconv.ParseInt(c, 0, 0)
+			counter = int(i64)
+		}
+	}
+
+	w.Header().Set(`Content-Type`, `application/json`)
+	fmt.Fprintf(w, `{"cnt": %d}`, counter)
+}
+
+func message(msg string) {
+	println(msg, "\r")
+}

examples/rtl8720dn/webserver/wioterminal.go

@@ -0,0 +1,74 @@
+//go:build wioterminal
+// +build wioterminal
+
+package main
+
+import (
+	"device/sam"
+	"machine"
+	"runtime/interrupt"
+	"time"
+
+	"tinygo.org/x/drivers/rtl8720dn"
+)
+
+var (
+	uart UARTx
+)
+
+func handleInterrupt(interrupt.Interrupt) {
+	// should reset IRQ
+	uart.Receive(byte((uart.Bus.DATA.Get() & 0xFF)))
+	uart.Bus.INTFLAG.SetBits(sam.SERCOM_USART_INT_INTFLAG_RXC)
+}
+
+func setupRTL8720DN() (*rtl8720dn.RTL8720DN, error) {
+	machine.RTL8720D_CHIP_PU.Configure(machine.PinConfig{Mode: machine.PinOutput})
+	machine.RTL8720D_CHIP_PU.Low()
+	time.Sleep(100 * time.Millisecond)
+	machine.RTL8720D_CHIP_PU.High()
+	time.Sleep(1000 * time.Millisecond)
+	if debug {
+		waitSerial()
+	}
+
+	uart = UARTx{
+		UART: &machine.UART{
+			Buffer: machine.NewRingBuffer(),
+			Bus:    sam.SERCOM0_USART_INT,
+			SERCOM: 0,
+		},
+	}
+
+	uart.Interrupt = interrupt.New(sam.IRQ_SERCOM0_2, handleInterrupt)
+	uart.Configure(machine.UARTConfig{TX: machine.PB24, RX: machine.PC24, BaudRate: 614400})
+
+	rtl := rtl8720dn.New(uart)
+	rtl.Debug(debug)
+
+	_, err := rtl.Rpc_tcpip_adapter_init()
+	if err != nil {
+		return nil, err
+	}
+
+	return rtl, nil
+}
+
+// Wait for user to open serial console
+func waitSerial() {
+	for !machine.Serial.DTR() {
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+type UARTx struct {
+	*machine.UART
+}
+
+func (u UARTx) Read(p []byte) (n int, err error) {
+	if u.Buffered() == 0 {
+		time.Sleep(1 * time.Millisecond)
+		return 0, nil
+	}
+	return u.UART.Read(p)
+}

examples/sdcard/console/feather-m4.go

@@ -1,3 +1,4 @@
+//go:build feather_m4 || feather_m4_can || feather_nrf52840
 // +build feather_m4 feather_m4_can feather_nrf52840
 
 package main

examples/sdcard/console/grandcentral-m4.go

@@ -1,4 +1,5 @@
-// +build grandcentral-m4
+//go:build grandcentral_m4
+// +build grandcentral_m4
 
 package main
 

examples/sdcard/console/m0.go

@@ -1,3 +1,4 @@
+//go:build atsamd21 && !p1am_100
 // +build atsamd21,!p1am_100
 
 package main

examples/sdcard/console/p1am-100.go

@@ -1,3 +1,4 @@
+//go:build p1am_100
 // +build p1am_100
 
 package main

examples/sdcard/console/pygamer.go

@@ -1,3 +1,4 @@
+//go:build pygamer
 // +build pygamer
 
 package main

examples/sdcard/console/pyportal.go

@@ -1,3 +1,4 @@
+//go:build pyportal
 // +build pyportal
 
 package main

examples/sdcard/console/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/sdcard/tinyfs/console/console.go

@@ -1,3 +1,4 @@
+//go:build tinygo
 // +build tinygo
 
 package console

examples/sdcard/tinyfs/feather-m4.go

@@ -1,3 +1,4 @@
+//go:build feather_m4 || feather_m4_can || feather_nrf52840
 // +build feather_m4 feather_m4_can feather_nrf52840
 
 package main

examples/sdcard/tinyfs/grandcentral-m4.go

@@ -1,4 +1,5 @@
-// +build grandcentral-m4
+//go:build grandcentral_m4
+// +build grandcentral_m4
 
 package main
 

examples/sdcard/tinyfs/m0.go

@@ -1,3 +1,4 @@
+//go:build atsamd21 && !p1am_100
 // +build atsamd21,!p1am_100
 
 package main

examples/sdcard/tinyfs/p1am-100.go

@@ -1,3 +1,4 @@
+//go:build p1am_100
 // +build p1am_100
 
 package main

examples/sdcard/tinyfs/pygamer.go

@@ -1,3 +1,4 @@
+//go:build pygamer
 // +build pygamer
 
 package main

examples/sdcard/tinyfs/pyportal.go

@@ -1,3 +1,4 @@
+//go:build pyportal
 // +build pyportal
 
 package main

examples/sdcard/tinyfs/wioterminal.go

@@ -1,3 +1,4 @@
+//go:build wioterminal
 // +build wioterminal
 
 package main

examples/wifinina/http-get/main.go

@@ -0,0 +1,161 @@
+// This example opens a TCP connection using a device with WiFiNINA firmware
+// and sends a HTTP request to retrieve a webpage, based on the following
+// Arduino example:
+//
+// https://github.com/arduino-libraries/WiFiNINA/blob/master/examples/WiFiWebClientRepeating/
+//
+// This example will not work with samd21 or other systems with less than 32KB
+// of RAM.  Use the following if you want to run wifinina on samd21, etc.
+//
+// examples/wifinina/webclient
+// examples/wifinina/tlsclient
+//
+package main
+
+import (
+	"bufio"
+	"fmt"
+	"machine"
+	"strings"
+	"time"
+
+	"tinygo.org/x/drivers/net"
+	"tinygo.org/x/drivers/net/http"
+	"tinygo.org/x/drivers/wifinina"
+)
+
+// access point info
+const ssid = ""
+const pass = ""
+
+// IP address of the server aka "hub". Replace with your own info.
+// Can specify a URL starting with http or https
+const url = "http://tinygo.org/"
+
+// these are the default pins for the Arduino Nano33 IoT.
+// change these to connect to a different UART or pins for the ESP8266/ESP32
+var (
+
+	// these are the default pins for the Arduino Nano33 IoT.
+	spi = machine.NINA_SPI
+
+	// this is the ESP chip that has the WIFININA firmware flashed on it
+	adaptor *wifinina.Device
+)
+
+var buf [0x400]byte
+
+var lastRequestTime time.Time
+var conn net.Conn
+
+func setup() {
+	// Configure SPI for 8Mhz, Mode 0, MSB First
+	spi.Configure(machine.SPIConfig{
+		Frequency: 8 * 1e6,
+		SDO:       machine.NINA_SDO,
+		SDI:       machine.NINA_SDI,
+		SCK:       machine.NINA_SCK,
+	})
+
+	adaptor = wifinina.New(spi,
+		machine.NINA_CS,
+		machine.NINA_ACK,
+		machine.NINA_GPIO0,
+		machine.NINA_RESETN)
+	adaptor.Configure()
+}
+
+func main() {
+
+	setup()
+	http.SetBuf(buf[:])
+
+	waitSerial()
+
+	connectToAP()
+
+	// You can send and receive cookies in the following way
+	// 	import "tinygo.org/x/drivers/net/http/cookiejar"
+	// 	jar, err := cookiejar.New(nil)
+	// 	if err != nil {
+	// 		return err
+	// 	}
+	// 	client := &http.Client{Jar: jar}
+	// 	http.DefaultClient = client
+
+	cnt := 0
+	for {
+		// Various examples are as follows
+		//
+		// -- Get
+		// 	resp, err := http.Get(url)
+		//
+		// -- Post
+		// 	body := `cnt=12`
+		// 	resp, err = http.Post(url, "application/x-www-form-urlencoded", strings.NewReader(body))
+		//
+		// -- Post with JSON
+		// 	body := `{"msg": "hello"}`
+		// 	resp, err := http.Post(url, "application/json", strings.NewReader(body))
+
+		resp, err := http.Get(url)
+		if err != nil {
+			fmt.Printf("%s\r\n", err.Error())
+			continue
+		}
+
+		fmt.Printf("%s %s\r\n", resp.Proto, resp.Status)
+		for k, v := range resp.Header {
+			fmt.Printf("%s: %s\r\n", k, strings.Join(v, " "))
+		}
+		fmt.Printf("\r\n")
+
+		scanner := bufio.NewScanner(resp.Body)
+		for scanner.Scan() {
+			fmt.Printf("%s\r\n", scanner.Text())
+		}
+		resp.Body.Close()
+
+		cnt++
+		fmt.Printf("-------- %d --------\r\n", cnt)
+		time.Sleep(10 * time.Second)
+	}
+
+}
+
+// Wait for user to open serial console
+func waitSerial() {
+	for !machine.Serial.DTR() {
+		time.Sleep(100 * time.Millisecond)
+	}
+}
+
+// connect to access point
+func connectToAP() {
+	if len(ssid) == 0 || len(pass) == 0 {
+		for {
+			println("Connection failed: Either ssid or password not set")
+			time.Sleep(10 * time.Second)
+		}
+	}
+	time.Sleep(2 * time.Second)
+	message("Connecting to " + ssid)
+	adaptor.SetPassphrase(ssid, pass)
+	for st, _ := adaptor.GetConnectionStatus(); st != wifinina.StatusConnected; {
+		message("Connection status: " + st.String())
+		time.Sleep(1 * time.Second)
+		st, _ = adaptor.GetConnectionStatus()
+	}
+	message("Connected.")
+	time.Sleep(2 * time.Second)
+	ip, _, _, err := adaptor.GetIP()
+	for ; err != nil; ip, _, _, err = adaptor.GetIP() {
+		message(err.Error())
+		time.Sleep(1 * time.Second)
+	}
+	message(ip.String())
+}
+
+func message(msg string) {
+	println(msg, "\r")
+}

examples/ws2812/arduino.go

@@ -1,3 +1,4 @@
+//go:build arduino
 // +build arduino
 
 package main

examples/ws2812/digispark.go

@@ -1,3 +1,4 @@
+//go:build digispark
 // +build digispark
 
 package main

examples/ws2812/others.go

@@ -1,3 +1,4 @@
+//go:build !digispark && !arduino && !qtpy
 // +build !digispark,!arduino,!qtpy
 
 package main

examples/ws2812/qtpy.go

@@ -1,3 +1,4 @@
+//go:build qtpy
 // +build qtpy
 
 package main

flash/transport_qspi_samd.go

@@ -1,3 +1,4 @@
+//go:build atsamd51
 // +build atsamd51
 
 package flash

go.mod

@@ -5,6 +5,7 @@ go 1.15
 require (
 	github.com/eclipse/paho.mqtt.golang v1.2.0
 	github.com/frankban/quicktest v1.10.2
+	golang.org/x/net v0.0.0-20210614182718-04defd469f4e // indirect
 	tinygo.org/x/tinyfont v0.2.1
 	tinygo.org/x/tinyfs v0.1.0
 	tinygo.org/x/tinyterm v0.1.0

go.sum

@@ -11,6 +11,14 @@ github.com/kr/pty v1.1.1/go.mod h1:pFQYn66WHrOpPYNljwOMqo10TkYh1fy3cYio2l3bCsQ=
 github.com/kr/text v0.1.0 h1:45sCR5RtlFHMR4UwH9sdQ5TC8v0qDQCHnXt+kaKSTVE=
 github.com/kr/text v0.1.0/go.mod h1:4Jbv+DJW3UT/LiOwJeYQe1efqtUx/iVham/4vfdArNI=
 github.com/valyala/fastjson v1.6.3/go.mod h1:CLCAqky6SMuOcxStkYQvblddUtoRxhYMGLrsQns1aXY=
+golang.org/x/net v0.0.0-20210614182718-04defd469f4e h1:XpT3nA5TvE525Ne3hInMh6+GETgn27Zfm9dxsThnX2Q=
+golang.org/x/net v0.0.0-20210614182718-04defd469f4e/go.mod h1:9nx3DQGgdP8bBQD5qxJ1jj9UTztislL4KSBs9R2vV5Y=
+golang.org/x/sys v0.0.0-20201119102817-f84b799fce68/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/sys v0.0.0-20210423082822-04245dca01da/go.mod h1:h1NjWce9XRLGQEsW7wpKNCjG9DtNlClVuFLEZdDNbEs=
+golang.org/x/term v0.0.0-20201126162022-7de9c90e9dd1/go.mod h1:bj7SfCRtBDWHUb9snDiAeCFNEtKQo2Wmx5Cou7ajbmo=
+golang.org/x/text v0.3.6 h1:aRYxNxv6iGQlyVaZmk6ZgYEDa+Jg18DxebPSrd6bg1M=
+golang.org/x/text v0.3.6/go.mod h1:5Zoc/QRtKVWzQhOtBMvqHzDpF6irO9z98xDceosuGiQ=
+golang.org/x/tools v0.0.0-20180917221912-90fa682c2a6e/go.mod h1:n7NCudcB/nEzxVGmLbDWY5pfWTLqBcC2KZ6jyYvM4mQ=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543 h1:E7g+9GITq07hpfrRu66IVDexMakfv52eLZ2CXBWiKr4=
 golang.org/x/xerrors v0.0.0-20191204190536-9bdfabe68543/go.mod h1:I/5z698sn9Ka8TeJc9MKroUUfqBBauWjQqLJ2OPfmY0=
 tinygo.org/x/drivers v0.14.0/go.mod h1:uT2svMq3EpBZpKkGO+NQHjxjGf1f42ra4OnMMwQL2aI=

ili9341/parallel_atsamd51.go

@@ -1,3 +1,4 @@
+//go:build atsamd51
 // +build atsamd51
 
 package ili9341

ili9341/spi.go

@@ -1,18 +1,21 @@
+//go:build !atsamd51 && !atsamd21
 // +build !atsamd51,!atsamd21
 
 package ili9341
 
 import (
 	"machine"
+
+	"tinygo.org/x/drivers"
 )
 
 var buf [64]byte
 
 type spiDriver struct {
-	bus machine.SPI
+	bus drivers.SPI
 }
 
-func NewSPI(bus machine.SPI, dc, cs, rst machine.Pin) *Device {
+func NewSPI(bus drivers.SPI, dc, cs, rst machine.Pin) *Device {
 	return &Device{
 		dc:  dc,
 		cs:  cs,

ili9341/spi_atsamd21.go

@@ -1,3 +1,4 @@
+//go:build atsamd21
 // +build atsamd21
 
 package ili9341

ili9341/spi_atsamd51.go

@@ -1,3 +1,4 @@
+//go:build atsamd51
 // +build atsamd51
 
 package ili9341

image/README.md

@@ -0,0 +1,60 @@
+# tinygo.org/x/drivers/image
+
+This is an image package that uses less RAM to run on a microcontroller.
+Unlike Go's original image package, `image.Decode()` does not return `image.Image`.
+
+Instead, a callback can be set to process the data corresponding to the image.
+
+## How to use
+
+First, use `SetCallback()` to set the callback.
+Then call `png.Decode()` or `jpeg.Decode()`.
+The callback will be called as many times as necessary to load the image.
+
+`SetCallback()` needs to be given a Buffer to handle the callback and the actual function to be called.
+The `data []uint16` in the callback is in RGB565 format.
+
+The `io.Reader` to pass to `Decode()` specifies the binary data of the image.
+
+```go
+func drawPng(display *ili9341.Device) error {
+	p := strings.NewReader(pngImage)
+	png.SetCallback(buffer[:], func(data []uint16, x, y, w, h, width, height int16) {
+		err := display.DrawRGBBitmap(x, y, data[:w*h], w, h)
+		if err != nil {
+			errorMessage(fmt.Errorf("error drawPng: %s", err))
+		}
+	})
+
+	return png.Decode(p)
+}
+```
+
+```go
+func drawJpeg(display *ili9341.Device) error {
+	p := strings.NewReader(jpegImage)
+	jpeg.SetCallback(buffer[:], func(data []uint16, x, y, w, h, width, height int16) {
+		err := display.DrawRGBBitmap(x, y, data[:w*h], w, h)
+		if err != nil {
+			errorMessage(fmt.Errorf("error drawJpeg: %s", err))
+		}
+	})
+
+	return jpeg.Decode(p)
+}
+```
+
+## How to create an image
+
+The following program will output an image binary like the one in [images.go](./examples/ili9341/slideshow/images.go).  
+
+```
+go run ./cmd/convert2bin ./path/to/png_or_jpg.png
+```
+
+## Examples
+
+An example can be found below.
+Processing jpegs requires a minimum of 32KB of RAM.
+
+* [./examples/ili9341/slideshow](./examples/ili9341/slideshow)

image/internal/compress/flate/deflate.go

@@ -0,0 +1,748 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"fmt"
+	"io"
+	"math"
+)
+
+const (
+	NoCompression      = 0
+	BestSpeed          = 1
+	BestCompression    = 9
+	DefaultCompression = -1
+
+	// HuffmanOnly disables Lempel-Ziv match searching and only performs Huffman
+	// entropy encoding. This mode is useful in compressing data that has
+	// already been compressed with an LZ style algorithm (e.g. Snappy or LZ4)
+	// that lacks an entropy encoder. Compression gains are achieved when
+	// certain bytes in the input stream occur more frequently than others.
+	//
+	// Note that HuffmanOnly produces a compressed output that is
+	// RFC 1951 compliant. That is, any valid DEFLATE decompressor will
+	// continue to be able to decompress this output.
+	HuffmanOnly = -2
+)
+
+const (
+	logWindowSize = 15
+	windowSize    = 1 << logWindowSize
+	windowMask    = windowSize - 1
+
+	// The LZ77 step produces a sequence of literal tokens and <length, offset>
+	// pair tokens. The offset is also known as distance. The underlying wire
+	// format limits the range of lengths and offsets. For example, there are
+	// 256 legitimate lengths: those in the range [3, 258]. This package's
+	// compressor uses a higher minimum match length, enabling optimizations
+	// such as finding matches via 32-bit loads and compares.
+	baseMatchLength = 3       // The smallest match length per the RFC section 3.2.5
+	minMatchLength  = 4       // The smallest match length that the compressor actually emits
+	maxMatchLength  = 258     // The largest match length
+	baseMatchOffset = 1       // The smallest match offset
+	maxMatchOffset  = 1 << 15 // The largest match offset
+
+	// The maximum number of tokens we put into a single flate block, just to
+	// stop things from getting too large.
+	maxFlateBlockTokens = 1 << 14
+	maxStoreBlockSize   = 65535
+	hashBits            = 17 // After 17 performance degrades
+	hashSize            = 1 << hashBits
+	hashMask            = (1 << hashBits) - 1
+	maxHashOffset       = 1 << 24
+
+	skipNever = math.MaxInt32
+)
+
+type compressionLevel struct {
+	level, good, lazy, nice, chain, fastSkipHashing int
+}
+
+var levels = []compressionLevel{
+	{0, 0, 0, 0, 0, 0}, // NoCompression.
+	{1, 0, 0, 0, 0, 0}, // BestSpeed uses a custom algorithm; see deflatefast.go.
+	// For levels 2-3 we don't bother trying with lazy matches.
+	{2, 4, 0, 16, 8, 5},
+	{3, 4, 0, 32, 32, 6},
+	// Levels 4-9 use increasingly more lazy matching
+	// and increasingly stringent conditions for "good enough".
+	{4, 4, 4, 16, 16, skipNever},
+	{5, 8, 16, 32, 32, skipNever},
+	{6, 8, 16, 128, 128, skipNever},
+	{7, 8, 32, 128, 256, skipNever},
+	{8, 32, 128, 258, 1024, skipNever},
+	{9, 32, 258, 258, 4096, skipNever},
+}
+
+type compressor struct {
+	compressionLevel
+
+	w          *huffmanBitWriter
+	bulkHasher func([]byte, []uint32)
+
+	// compression algorithm
+	fill      func(*compressor, []byte) int // copy data to window
+	step      func(*compressor)             // process window
+	sync      bool                          // requesting flush
+	bestSpeed *deflateFast                  // Encoder for BestSpeed
+
+	// Input hash chains
+	// hashHead[hashValue] contains the largest inputIndex with the specified hash value
+	// If hashHead[hashValue] is within the current window, then
+	// hashPrev[hashHead[hashValue] & windowMask] contains the previous index
+	// with the same hash value.
+	chainHead  int
+	hashHead   [hashSize]uint32
+	hashPrev   [windowSize]uint32
+	hashOffset int
+
+	// input window: unprocessed data is window[index:windowEnd]
+	index         int
+	window        []byte
+	windowEnd     int
+	blockStart    int  // window index where current tokens start
+	byteAvailable bool // if true, still need to process window[index-1].
+
+	// queued output tokens
+	tokens []token
+
+	// deflate state
+	length         int
+	offset         int
+	hash           uint32
+	maxInsertIndex int
+	err            error
+
+	// hashMatch must be able to contain hashes for the maximum match length.
+	hashMatch [maxMatchLength - 1]uint32
+}
+
+func (d *compressor) fillDeflate(b []byte) int {
+	if d.index >= 2*windowSize-(minMatchLength+maxMatchLength) {
+		// shift the window by windowSize
+		copy(d.window, d.window[windowSize:2*windowSize])
+		d.index -= windowSize
+		d.windowEnd -= windowSize
+		if d.blockStart >= windowSize {
+			d.blockStart -= windowSize
+		} else {
+			d.blockStart = math.MaxInt32
+		}
+		d.hashOffset += windowSize
+		if d.hashOffset > maxHashOffset {
+			delta := d.hashOffset - 1
+			d.hashOffset -= delta
+			d.chainHead -= delta
+
+			// Iterate over slices instead of arrays to avoid copying
+			// the entire table onto the stack (Issue #18625).
+			for i, v := range d.hashPrev[:] {
+				if int(v) > delta {
+					d.hashPrev[i] = uint32(int(v) - delta)
+				} else {
+					d.hashPrev[i] = 0
+				}
+			}
+			for i, v := range d.hashHead[:] {
+				if int(v) > delta {
+					d.hashHead[i] = uint32(int(v) - delta)
+				} else {
+					d.hashHead[i] = 0
+				}
+			}
+		}
+	}
+	n := copy(d.window[d.windowEnd:], b)
+	d.windowEnd += n
+	return n
+}
+
+func (d *compressor) writeBlock(tokens []token, index int) error {
+	if index > 0 {
+		var window []byte
+		if d.blockStart <= index {
+			window = d.window[d.blockStart:index]
+		}
+		d.blockStart = index
+		d.w.writeBlock(tokens, false, window)
+		return d.w.err
+	}
+	return nil
+}
+
+// fillWindow will fill the current window with the supplied
+// dictionary and calculate all hashes.
+// This is much faster than doing a full encode.
+// Should only be used after a reset.
+func (d *compressor) fillWindow(b []byte) {
+	// Do not fill window if we are in store-only mode.
+	if d.compressionLevel.level < 2 {
+		return
+	}
+	if d.index != 0 || d.windowEnd != 0 {
+		panic("internal error: fillWindow called with stale data")
+	}
+
+	// If we are given too much, cut it.
+	if len(b) > windowSize {
+		b = b[len(b)-windowSize:]
+	}
+	// Add all to window.
+	n := copy(d.window, b)
+
+	// Calculate 256 hashes at the time (more L1 cache hits)
+	loops := (n + 256 - minMatchLength) / 256
+	for j := 0; j < loops; j++ {
+		index := j * 256
+		end := index + 256 + minMatchLength - 1
+		if end > n {
+			end = n
+		}
+		toCheck := d.window[index:end]
+		dstSize := len(toCheck) - minMatchLength + 1
+
+		if dstSize <= 0 {
+			continue
+		}
+
+		dst := d.hashMatch[:dstSize]
+		d.bulkHasher(toCheck, dst)
+		var newH uint32
+		for i, val := range dst {
+			di := i + index
+			newH = val
+			hh := &d.hashHead[newH&hashMask]
+			// Get previous value with the same hash.
+			// Our chain should point to the previous value.
+			d.hashPrev[di&windowMask] = *hh
+			// Set the head of the hash chain to us.
+			*hh = uint32(di + d.hashOffset)
+		}
+		d.hash = newH
+	}
+	// Update window information.
+	d.windowEnd = n
+	d.index = n
+}
+
+// Try to find a match starting at index whose length is greater than prevSize.
+// We only look at chainCount possibilities before giving up.
+func (d *compressor) findMatch(pos int, prevHead int, prevLength int, lookahead int) (length, offset int, ok bool) {
+	minMatchLook := maxMatchLength
+	if lookahead < minMatchLook {
+		minMatchLook = lookahead
+	}
+
+	win := d.window[0 : pos+minMatchLook]
+
+	// We quit when we get a match that's at least nice long
+	nice := len(win) - pos
+	if d.nice < nice {
+		nice = d.nice
+	}
+
+	// If we've got a match that's good enough, only look in 1/4 the chain.
+	tries := d.chain
+	length = prevLength
+	if length >= d.good {
+		tries >>= 2
+	}
+
+	wEnd := win[pos+length]
+	wPos := win[pos:]
+	minIndex := pos - windowSize
+
+	for i := prevHead; tries > 0; tries-- {
+		if wEnd == win[i+length] {
+			n := matchLen(win[i:], wPos, minMatchLook)
+
+			if n > length && (n > minMatchLength || pos-i <= 4096) {
+				length = n
+				offset = pos - i
+				ok = true
+				if n >= nice {
+					// The match is good enough that we don't try to find a better one.
+					break
+				}
+				wEnd = win[pos+n]
+			}
+		}
+		if i == minIndex {
+			// hashPrev[i & windowMask] has already been overwritten, so stop now.
+			break
+		}
+		i = int(d.hashPrev[i&windowMask]) - d.hashOffset
+		if i < minIndex || i < 0 {
+			break
+		}
+	}
+	return
+}
+
+func (d *compressor) writeStoredBlock(buf []byte) error {
+	if d.w.writeStoredHeader(len(buf), false); d.w.err != nil {
+		return d.w.err
+	}
+	d.w.writeBytes(buf)
+	return d.w.err
+}
+
+const hashmul = 0x1e35a7bd
+
+// hash4 returns a hash representation of the first 4 bytes
+// of the supplied slice.
+// The caller must ensure that len(b) >= 4.
+func hash4(b []byte) uint32 {
+	return ((uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24) * hashmul) >> (32 - hashBits)
+}
+
+// bulkHash4 will compute hashes using the same
+// algorithm as hash4
+func bulkHash4(b []byte, dst []uint32) {
+	if len(b) < minMatchLength {
+		return
+	}
+	hb := uint32(b[3]) | uint32(b[2])<<8 | uint32(b[1])<<16 | uint32(b[0])<<24
+	dst[0] = (hb * hashmul) >> (32 - hashBits)
+	end := len(b) - minMatchLength + 1
+	for i := 1; i < end; i++ {
+		hb = (hb << 8) | uint32(b[i+3])
+		dst[i] = (hb * hashmul) >> (32 - hashBits)
+	}
+}
+
+// matchLen returns the number of matching bytes in a and b
+// up to length 'max'. Both slices must be at least 'max'
+// bytes in size.
+func matchLen(a, b []byte, max int) int {
+	a = a[:max]
+	b = b[:len(a)]
+	for i, av := range a {
+		if b[i] != av {
+			return i
+		}
+	}
+	return max
+}
+
+// encSpeed will compress and store the currently added data,
+// if enough has been accumulated or we at the end of the stream.
+// Any error that occurred will be in d.err
+func (d *compressor) encSpeed() {
+	// We only compress if we have maxStoreBlockSize.
+	if d.windowEnd < maxStoreBlockSize {
+		if !d.sync {
+			return
+		}
+
+		// Handle small sizes.
+		if d.windowEnd < 128 {
+			switch {
+			case d.windowEnd == 0:
+				return
+			case d.windowEnd <= 16:
+				d.err = d.writeStoredBlock(d.window[:d.windowEnd])
+			default:
+				d.w.writeBlockHuff(false, d.window[:d.windowEnd])
+				d.err = d.w.err
+			}
+			d.windowEnd = 0
+			d.bestSpeed.reset()
+			return
+		}
+
+	}
+	// Encode the block.
+	d.tokens = d.bestSpeed.encode(d.tokens[:0], d.window[:d.windowEnd])
+
+	// If we removed less than 1/16th, Huffman compress the block.
+	if len(d.tokens) > d.windowEnd-(d.windowEnd>>4) {
+		d.w.writeBlockHuff(false, d.window[:d.windowEnd])
+	} else {
+		d.w.writeBlockDynamic(d.tokens, false, d.window[:d.windowEnd])
+	}
+	d.err = d.w.err
+	d.windowEnd = 0
+}
+
+func (d *compressor) initDeflate() {
+	d.window = make([]byte, 2*windowSize)
+	d.hashOffset = 1
+	d.tokens = make([]token, 0, maxFlateBlockTokens+1)
+	d.length = minMatchLength - 1
+	d.offset = 0
+	d.byteAvailable = false
+	d.index = 0
+	d.hash = 0
+	d.chainHead = -1
+	d.bulkHasher = bulkHash4
+}
+
+func (d *compressor) deflate() {
+	if d.windowEnd-d.index < minMatchLength+maxMatchLength && !d.sync {
+		return
+	}
+
+	d.maxInsertIndex = d.windowEnd - (minMatchLength - 1)
+	if d.index < d.maxInsertIndex {
+		d.hash = hash4(d.window[d.index : d.index+minMatchLength])
+	}
+
+Loop:
+	for {
+		if d.index > d.windowEnd {
+			panic("index > windowEnd")
+		}
+		lookahead := d.windowEnd - d.index
+		if lookahead < minMatchLength+maxMatchLength {
+			if !d.sync {
+				break Loop
+			}
+			if d.index > d.windowEnd {
+				panic("index > windowEnd")
+			}
+			if lookahead == 0 {
+				// Flush current output block if any.
+				if d.byteAvailable {
+					// There is still one pending token that needs to be flushed
+					d.tokens = append(d.tokens, literalToken(uint32(d.window[d.index-1])))
+					d.byteAvailable = false
+				}
+				if len(d.tokens) > 0 {
+					if d.err = d.writeBlock(d.tokens, d.index); d.err != nil {
+						return
+					}
+					d.tokens = d.tokens[:0]
+				}
+				break Loop
+			}
+		}
+		if d.index < d.maxInsertIndex {
+			// Update the hash
+			d.hash = hash4(d.window[d.index : d.index+minMatchLength])
+			hh := &d.hashHead[d.hash&hashMask]
+			d.chainHead = int(*hh)
+			d.hashPrev[d.index&windowMask] = uint32(d.chainHead)
+			*hh = uint32(d.index + d.hashOffset)
+		}
+		prevLength := d.length
+		prevOffset := d.offset
+		d.length = minMatchLength - 1
+		d.offset = 0
+		minIndex := d.index - windowSize
+		if minIndex < 0 {
+			minIndex = 0
+		}
+
+		if d.chainHead-d.hashOffset >= minIndex &&
+			(d.fastSkipHashing != skipNever && lookahead > minMatchLength-1 ||
+				d.fastSkipHashing == skipNever && lookahead > prevLength && prevLength < d.lazy) {
+			if newLength, newOffset, ok := d.findMatch(d.index, d.chainHead-d.hashOffset, minMatchLength-1, lookahead); ok {
+				d.length = newLength
+				d.offset = newOffset
+			}
+		}
+		if d.fastSkipHashing != skipNever && d.length >= minMatchLength ||
+			d.fastSkipHashing == skipNever && prevLength >= minMatchLength && d.length <= prevLength {
+			// There was a match at the previous step, and the current match is
+			// not better. Output the previous match.
+			if d.fastSkipHashing != skipNever {
+				d.tokens = append(d.tokens, matchToken(uint32(d.length-baseMatchLength), uint32(d.offset-baseMatchOffset)))
+			} else {
+				d.tokens = append(d.tokens, matchToken(uint32(prevLength-baseMatchLength), uint32(prevOffset-baseMatchOffset)))
+			}
+			// Insert in the hash table all strings up to the end of the match.
+			// index and index-1 are already inserted. If there is not enough
+			// lookahead, the last two strings are not inserted into the hash
+			// table.
+			if d.length <= d.fastSkipHashing {
+				var newIndex int
+				if d.fastSkipHashing != skipNever {
+					newIndex = d.index + d.length
+				} else {
+					newIndex = d.index + prevLength - 1
+				}
+				index := d.index
+				for index++; index < newIndex; index++ {
+					if index < d.maxInsertIndex {
+						d.hash = hash4(d.window[index : index+minMatchLength])
+						// Get previous value with the same hash.
+						// Our chain should point to the previous value.
+						hh := &d.hashHead[d.hash&hashMask]
+						d.hashPrev[index&windowMask] = *hh
+						// Set the head of the hash chain to us.
+						*hh = uint32(index + d.hashOffset)
+					}
+				}
+				d.index = index
+
+				if d.fastSkipHashing == skipNever {
+					d.byteAvailable = false
+					d.length = minMatchLength - 1
+				}
+			} else {
+				// For matches this long, we don't bother inserting each individual
+				// item into the table.
+				d.index += d.length
+				if d.index < d.maxInsertIndex {
+					d.hash = hash4(d.window[d.index : d.index+minMatchLength])
+				}
+			}
+			if len(d.tokens) == maxFlateBlockTokens {
+				// The block includes the current character
+				if d.err = d.writeBlock(d.tokens, d.index); d.err != nil {
+					return
+				}
+				d.tokens = d.tokens[:0]
+			}
+		} else {
+			if d.fastSkipHashing != skipNever || d.byteAvailable {
+				i := d.index - 1
+				if d.fastSkipHashing != skipNever {
+					i = d.index
+				}
+				d.tokens = append(d.tokens, literalToken(uint32(d.window[i])))
+				if len(d.tokens) == maxFlateBlockTokens {
+					if d.err = d.writeBlock(d.tokens, i+1); d.err != nil {
+						return
+					}
+					d.tokens = d.tokens[:0]
+				}
+			}
+			d.index++
+			if d.fastSkipHashing == skipNever {
+				d.byteAvailable = true
+			}
+		}
+	}
+}
+
+func (d *compressor) fillStore(b []byte) int {
+	n := copy(d.window[d.windowEnd:], b)
+	d.windowEnd += n
+	return n
+}
+
+func (d *compressor) store() {
+	if d.windowEnd > 0 && (d.windowEnd == maxStoreBlockSize || d.sync) {
+		d.err = d.writeStoredBlock(d.window[:d.windowEnd])
+		d.windowEnd = 0
+	}
+}
+
+// storeHuff compresses and stores the currently added data
+// when the d.window is full or we are at the end of the stream.
+// Any error that occurred will be in d.err
+func (d *compressor) storeHuff() {
+	if d.windowEnd < len(d.window) && !d.sync || d.windowEnd == 0 {
+		return
+	}
+	d.w.writeBlockHuff(false, d.window[:d.windowEnd])
+	d.err = d.w.err
+	d.windowEnd = 0
+}
+
+func (d *compressor) write(b []byte) (n int, err error) {
+	if d.err != nil {
+		return 0, d.err
+	}
+	n = len(b)
+	for len(b) > 0 {
+		d.step(d)
+		b = b[d.fill(d, b):]
+		if d.err != nil {
+			return 0, d.err
+		}
+	}
+	return n, nil
+}
+
+func (d *compressor) syncFlush() error {
+	if d.err != nil {
+		return d.err
+	}
+	d.sync = true
+	d.step(d)
+	if d.err == nil {
+		d.w.writeStoredHeader(0, false)
+		d.w.flush()
+		d.err = d.w.err
+	}
+	d.sync = false
+	return d.err
+}
+
+func (d *compressor) init(w io.Writer, level int) (err error) {
+	d.w = newHuffmanBitWriter(w)
+
+	switch {
+	case level == NoCompression:
+		d.window = make([]byte, maxStoreBlockSize)
+		d.fill = (*compressor).fillStore
+		d.step = (*compressor).store
+	case level == HuffmanOnly:
+		d.window = make([]byte, maxStoreBlockSize)
+		d.fill = (*compressor).fillStore
+		d.step = (*compressor).storeHuff
+	case level == BestSpeed:
+		d.compressionLevel = levels[level]
+		d.window = make([]byte, maxStoreBlockSize)
+		d.fill = (*compressor).fillStore
+		d.step = (*compressor).encSpeed
+		d.bestSpeed = newDeflateFast()
+		d.tokens = make([]token, maxStoreBlockSize)
+	case level == DefaultCompression:
+		level = 6
+		fallthrough
+	case 2 <= level && level <= 9:
+		d.compressionLevel = levels[level]
+		d.initDeflate()
+		d.fill = (*compressor).fillDeflate
+		d.step = (*compressor).deflate
+	default:
+		return fmt.Errorf("flate: invalid compression level %d: want value in range [-2, 9]", level)
+	}
+	return nil
+}
+
+func (d *compressor) reset(w io.Writer) {
+	d.w.reset(w)
+	d.sync = false
+	d.err = nil
+	switch d.compressionLevel.level {
+	case NoCompression:
+		d.windowEnd = 0
+	case BestSpeed:
+		d.windowEnd = 0
+		d.tokens = d.tokens[:0]
+		d.bestSpeed.reset()
+	default:
+		d.chainHead = -1
+		for i := range d.hashHead {
+			d.hashHead[i] = 0
+		}
+		for i := range d.hashPrev {
+			d.hashPrev[i] = 0
+		}
+		d.hashOffset = 1
+		d.index, d.windowEnd = 0, 0
+		d.blockStart, d.byteAvailable = 0, false
+		d.tokens = d.tokens[:0]
+		d.length = minMatchLength - 1
+		d.offset = 0
+		d.hash = 0
+		d.maxInsertIndex = 0
+	}
+}
+
+func (d *compressor) close() error {
+	if d.err != nil {
+		return d.err
+	}
+	d.sync = true
+	d.step(d)
+	if d.err != nil {
+		return d.err
+	}
+	if d.w.writeStoredHeader(0, true); d.w.err != nil {
+		return d.w.err
+	}
+	d.w.flush()
+	return d.w.err
+}
+
+// NewWriter returns a new Writer compressing data at the given level.
+// Following zlib, levels range from 1 (BestSpeed) to 9 (BestCompression);
+// higher levels typically run slower but compress more. Level 0
+// (NoCompression) does not attempt any compression; it only adds the
+// necessary DEFLATE framing.
+// Level -1 (DefaultCompression) uses the default compression level.
+// Level -2 (HuffmanOnly) will use Huffman compression only, giving
+// a very fast compression for all types of input, but sacrificing considerable
+// compression efficiency.
+//
+// If level is in the range [-2, 9] then the error returned will be nil.
+// Otherwise the error returned will be non-nil.
+func NewWriter(w io.Writer, level int) (*Writer, error) {
+	var dw Writer
+	if err := dw.d.init(w, level); err != nil {
+		return nil, err
+	}
+	return &dw, nil
+}
+
+// NewWriterDict is like NewWriter but initializes the new
+// Writer with a preset dictionary. The returned Writer behaves
+// as if the dictionary had been written to it without producing
+// any compressed output. The compressed data written to w
+// can only be decompressed by a Reader initialized with the
+// same dictionary.
+func NewWriterDict(w io.Writer, level int, dict []byte) (*Writer, error) {
+	dw := &dictWriter{w}
+	zw, err := NewWriter(dw, level)
+	if err != nil {
+		return nil, err
+	}
+	zw.d.fillWindow(dict)
+	zw.dict = append(zw.dict, dict...) // duplicate dictionary for Reset method.
+	return zw, err
+}
+
+type dictWriter struct {
+	w io.Writer
+}
+
+func (w *dictWriter) Write(b []byte) (n int, err error) {
+	return w.w.Write(b)
+}
+
+// A Writer takes data written to it and writes the compressed
+// form of that data to an underlying writer (see NewWriter).
+type Writer struct {
+	d    compressor
+	dict []byte
+}
+
+// Write writes data to w, which will eventually write the
+// compressed form of data to its underlying writer.
+func (w *Writer) Write(data []byte) (n int, err error) {
+	return w.d.write(data)
+}
+
+// Flush flushes any pending data to the underlying writer.
+// It is useful mainly in compressed network protocols, to ensure that
+// a remote reader has enough data to reconstruct a packet.
+// Flush does not return until the data has been written.
+// Calling Flush when there is no pending data still causes the Writer
+// to emit a sync marker of at least 4 bytes.
+// If the underlying writer returns an error, Flush returns that error.
+//
+// In the terminology of the zlib library, Flush is equivalent to Z_SYNC_FLUSH.
+func (w *Writer) Flush() error {
+	// For more about flushing:
+	// https://www.bolet.org/~pornin/deflate-flush.html
+	return w.d.syncFlush()
+}
+
+// Close flushes and closes the writer.
+func (w *Writer) Close() error {
+	return w.d.close()
+}
+
+// Reset discards the writer's state and makes it equivalent to
+// the result of NewWriter or NewWriterDict called with dst
+// and w's level and dictionary.
+func (w *Writer) Reset(dst io.Writer) {
+	if dw, ok := w.d.w.writer.(*dictWriter); ok {
+		// w was created with NewWriterDict
+		dw.w = dst
+		w.d.reset(dw)
+		w.d.fillWindow(w.dict)
+	} else {
+		// w was created with NewWriter
+		w.d.reset(dst)
+	}
+}

image/internal/compress/flate/deflate_test.go

@@ -0,0 +1,984 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"errors"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"math/rand"
+	"os"
+	"reflect"
+	"runtime/debug"
+	"sync"
+	"testing"
+)
+
+type deflateTest struct {
+	in    []byte
+	level int
+	out   []byte
+}
+
+type deflateInflateTest struct {
+	in []byte
+}
+
+type reverseBitsTest struct {
+	in       uint16
+	bitCount uint8
+	out      uint16
+}
+
+var deflateTests = []*deflateTest{
+	{[]byte{}, 0, []byte{1, 0, 0, 255, 255}},
+	{[]byte{0x11}, -1, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11}, DefaultCompression, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11}, 4, []byte{18, 4, 4, 0, 0, 255, 255}},
+
+	{[]byte{0x11}, 0, []byte{0, 1, 0, 254, 255, 17, 1, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x12}, 0, []byte{0, 2, 0, 253, 255, 17, 18, 1, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}, 0,
+		[]byte{0, 8, 0, 247, 255, 17, 17, 17, 17, 17, 17, 17, 17, 1, 0, 0, 255, 255},
+	},
+	{[]byte{}, 2, []byte{1, 0, 0, 255, 255}},
+	{[]byte{0x11}, 2, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x12}, 2, []byte{18, 20, 2, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}, 2, []byte{18, 132, 2, 64, 0, 0, 0, 255, 255}},
+	{[]byte{}, 9, []byte{1, 0, 0, 255, 255}},
+	{[]byte{0x11}, 9, []byte{18, 4, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x12}, 9, []byte{18, 20, 2, 4, 0, 0, 255, 255}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}, 9, []byte{18, 132, 2, 64, 0, 0, 0, 255, 255}},
+}
+
+var deflateInflateTests = []*deflateInflateTest{
+	{[]byte{}},
+	{[]byte{0x11}},
+	{[]byte{0x11, 0x12}},
+	{[]byte{0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11, 0x11}},
+	{[]byte{0x11, 0x10, 0x13, 0x41, 0x21, 0x21, 0x41, 0x13, 0x87, 0x78, 0x13}},
+	{largeDataChunk()},
+}
+
+var reverseBitsTests = []*reverseBitsTest{
+	{1, 1, 1},
+	{1, 2, 2},
+	{1, 3, 4},
+	{1, 4, 8},
+	{1, 5, 16},
+	{17, 5, 17},
+	{257, 9, 257},
+	{29, 5, 23},
+}
+
+func largeDataChunk() []byte {
+	result := make([]byte, 100000)
+	for i := range result {
+		result[i] = byte(i * i & 0xFF)
+	}
+	return result
+}
+
+func TestBulkHash4(t *testing.T) {
+	for _, x := range deflateTests {
+		y := x.out
+		if len(y) < minMatchLength {
+			continue
+		}
+		y = append(y, y...)
+		for j := 4; j < len(y); j++ {
+			y := y[:j]
+			dst := make([]uint32, len(y)-minMatchLength+1)
+			for i := range dst {
+				dst[i] = uint32(i + 100)
+			}
+			bulkHash4(y, dst)
+			for i, got := range dst {
+				want := hash4(y[i:])
+				if got != want && got == uint32(i)+100 {
+					t.Errorf("Len:%d Index:%d, want 0x%08x but not modified", len(y), i, want)
+				} else if got != want {
+					t.Errorf("Len:%d Index:%d, got 0x%08x want:0x%08x", len(y), i, got, want)
+				}
+			}
+		}
+	}
+}
+
+func TestDeflate(t *testing.T) {
+	for _, h := range deflateTests {
+		var buf bytes.Buffer
+		w, err := NewWriter(&buf, h.level)
+		if err != nil {
+			t.Errorf("NewWriter: %v", err)
+			continue
+		}
+		w.Write(h.in)
+		w.Close()
+		if !bytes.Equal(buf.Bytes(), h.out) {
+			t.Errorf("Deflate(%d, %x) = \n%#v, want \n%#v", h.level, h.in, buf.Bytes(), h.out)
+		}
+	}
+}
+
+// A sparseReader returns a stream consisting of 0s followed by 1<<16 1s.
+// This tests missing hash references in a very large input.
+type sparseReader struct {
+	l   int64
+	cur int64
+}
+
+func (r *sparseReader) Read(b []byte) (n int, err error) {
+	if r.cur >= r.l {
+		return 0, io.EOF
+	}
+	n = len(b)
+	cur := r.cur + int64(n)
+	if cur > r.l {
+		n -= int(cur - r.l)
+		cur = r.l
+	}
+	for i := range b[0:n] {
+		if r.cur+int64(i) >= r.l-1<<16 {
+			b[i] = 1
+		} else {
+			b[i] = 0
+		}
+	}
+	r.cur = cur
+	return
+}
+
+func TestVeryLongSparseChunk(t *testing.T) {
+	if testing.Short() {
+		t.Skip("skipping sparse chunk during short test")
+	}
+	w, err := NewWriter(io.Discard, 1)
+	if err != nil {
+		t.Errorf("NewWriter: %v", err)
+		return
+	}
+	if _, err = io.Copy(w, &sparseReader{l: 23e8}); err != nil {
+		t.Errorf("Compress failed: %v", err)
+		return
+	}
+}
+
+type syncBuffer struct {
+	buf    bytes.Buffer
+	mu     sync.RWMutex
+	closed bool
+	ready  chan bool
+}
+
+func newSyncBuffer() *syncBuffer {
+	return &syncBuffer{ready: make(chan bool, 1)}
+}
+
+func (b *syncBuffer) Read(p []byte) (n int, err error) {
+	for {
+		b.mu.RLock()
+		n, err = b.buf.Read(p)
+		b.mu.RUnlock()
+		if n > 0 || b.closed {
+			return
+		}
+		<-b.ready
+	}
+}
+
+func (b *syncBuffer) signal() {
+	select {
+	case b.ready <- true:
+	default:
+	}
+}
+
+func (b *syncBuffer) Write(p []byte) (n int, err error) {
+	n, err = b.buf.Write(p)
+	b.signal()
+	return
+}
+
+func (b *syncBuffer) WriteMode() {
+	b.mu.Lock()
+}
+
+func (b *syncBuffer) ReadMode() {
+	b.mu.Unlock()
+	b.signal()
+}
+
+func (b *syncBuffer) Close() error {
+	b.closed = true
+	b.signal()
+	return nil
+}
+
+func testSync(t *testing.T, level int, input []byte, name string) {
+	if len(input) == 0 {
+		return
+	}
+
+	t.Logf("--testSync %d, %d, %s", level, len(input), name)
+	buf := newSyncBuffer()
+	buf1 := new(bytes.Buffer)
+	buf.WriteMode()
+	w, err := NewWriter(io.MultiWriter(buf, buf1), level)
+	if err != nil {
+		t.Errorf("NewWriter: %v", err)
+		return
+	}
+	r := NewReader(buf)
+
+	// Write half the input and read back.
+	for i := 0; i < 2; i++ {
+		var lo, hi int
+		if i == 0 {
+			lo, hi = 0, (len(input)+1)/2
+		} else {
+			lo, hi = (len(input)+1)/2, len(input)
+		}
+		t.Logf("#%d: write %d-%d", i, lo, hi)
+		if _, err := w.Write(input[lo:hi]); err != nil {
+			t.Errorf("testSync: write: %v", err)
+			return
+		}
+		if i == 0 {
+			if err := w.Flush(); err != nil {
+				t.Errorf("testSync: flush: %v", err)
+				return
+			}
+		} else {
+			if err := w.Close(); err != nil {
+				t.Errorf("testSync: close: %v", err)
+			}
+		}
+		buf.ReadMode()
+		out := make([]byte, hi-lo+1)
+		m, err := io.ReadAtLeast(r, out, hi-lo)
+		t.Logf("#%d: read %d", i, m)
+		if m != hi-lo || err != nil {
+			t.Errorf("testSync/%d (%d, %d, %s): read %d: %d, %v (%d left)", i, level, len(input), name, hi-lo, m, err, buf.buf.Len())
+			return
+		}
+		if !bytes.Equal(input[lo:hi], out[:hi-lo]) {
+			t.Errorf("testSync/%d: read wrong bytes: %x vs %x", i, input[lo:hi], out[:hi-lo])
+			return
+		}
+		// This test originally checked that after reading
+		// the first half of the input, there was nothing left
+		// in the read buffer (buf.buf.Len() != 0) but that is
+		// not necessarily the case: the write Flush may emit
+		// some extra framing bits that are not necessary
+		// to process to obtain the first half of the uncompressed
+		// data. The test ran correctly most of the time, because
+		// the background goroutine had usually read even
+		// those extra bits by now, but it's not a useful thing to
+		// check.
+		buf.WriteMode()
+	}
+	buf.ReadMode()
+	out := make([]byte, 10)
+	if n, err := r.Read(out); n > 0 || err != io.EOF {
+		t.Errorf("testSync (%d, %d, %s): final Read: %d, %v (hex: %x)", level, len(input), name, n, err, out[0:n])
+	}
+	if buf.buf.Len() != 0 {
+		t.Errorf("testSync (%d, %d, %s): extra data at end", level, len(input), name)
+	}
+	r.Close()
+
+	// stream should work for ordinary reader too
+	r = NewReader(buf1)
+	out, err = io.ReadAll(r)
+	if err != nil {
+		t.Errorf("testSync: read: %s", err)
+		return
+	}
+	r.Close()
+	if !bytes.Equal(input, out) {
+		t.Errorf("testSync: decompress(compress(data)) != data: level=%d input=%s", level, name)
+	}
+}
+
+func testToFromWithLevelAndLimit(t *testing.T, level int, input []byte, name string, limit int) {
+	var buffer bytes.Buffer
+	w, err := NewWriter(&buffer, level)
+	if err != nil {
+		t.Errorf("NewWriter: %v", err)
+		return
+	}
+	w.Write(input)
+	w.Close()
+	if limit > 0 && buffer.Len() > limit {
+		t.Errorf("level: %d, len(compress(data)) = %d > limit = %d", level, buffer.Len(), limit)
+		return
+	}
+	if limit > 0 {
+		t.Logf("level: %d, size:%.2f%%, %d b\n", level, float64(buffer.Len()*100)/float64(limit), buffer.Len())
+	}
+	r := NewReader(&buffer)
+	out, err := io.ReadAll(r)
+	if err != nil {
+		t.Errorf("read: %s", err)
+		return
+	}
+	r.Close()
+	if !bytes.Equal(input, out) {
+		t.Errorf("decompress(compress(data)) != data: level=%d input=%s", level, name)
+		return
+	}
+	testSync(t, level, input, name)
+}
+
+func testToFromWithLimit(t *testing.T, input []byte, name string, limit [11]int) {
+	for i := 0; i < 10; i++ {
+		testToFromWithLevelAndLimit(t, i, input, name, limit[i])
+	}
+	// Test HuffmanCompression
+	testToFromWithLevelAndLimit(t, -2, input, name, limit[10])
+}
+
+func TestDeflateInflate(t *testing.T) {
+	t.Parallel()
+	for i, h := range deflateInflateTests {
+		if testing.Short() && len(h.in) > 10000 {
+			continue
+		}
+		testToFromWithLimit(t, h.in, fmt.Sprintf("#%d", i), [11]int{})
+	}
+}
+
+func TestReverseBits(t *testing.T) {
+	for _, h := range reverseBitsTests {
+		if v := reverseBits(h.in, h.bitCount); v != h.out {
+			t.Errorf("reverseBits(%v,%v) = %v, want %v",
+				h.in, h.bitCount, v, h.out)
+		}
+	}
+}
+
+type deflateInflateStringTest struct {
+	filename string
+	label    string
+	limit    [11]int
+}
+
+var deflateInflateStringTests = []deflateInflateStringTest{
+	{
+		"../testdata/e.txt",
+		"2.718281828...",
+		[...]int{100018, 50650, 50960, 51150, 50930, 50790, 50790, 50790, 50790, 50790, 43683},
+	},
+	{
+		"../../testdata/Isaac.Newton-Opticks.txt",
+		"Isaac.Newton-Opticks",
+		[...]int{567248, 218338, 198211, 193152, 181100, 175427, 175427, 173597, 173422, 173422, 325240},
+	},
+}
+
+func TestDeflateInflateString(t *testing.T) {
+	t.Parallel()
+	if testing.Short() && testenv.Builder() == "" {
+		t.Skip("skipping in short mode")
+	}
+	for _, test := range deflateInflateStringTests {
+		gold, err := os.ReadFile(test.filename)
+		if err != nil {
+			t.Error(err)
+		}
+		testToFromWithLimit(t, gold, test.label, test.limit)
+		if testing.Short() {
+			break
+		}
+	}
+}
+
+func TestReaderDict(t *testing.T) {
+	const (
+		dict = "hello world"
+		text = "hello again world"
+	)
+	var b bytes.Buffer
+	w, err := NewWriter(&b, 5)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+	w.Write([]byte(dict))
+	w.Flush()
+	b.Reset()
+	w.Write([]byte(text))
+	w.Close()
+
+	r := NewReaderDict(&b, []byte(dict))
+	data, err := io.ReadAll(r)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if string(data) != "hello again world" {
+		t.Fatalf("read returned %q want %q", string(data), text)
+	}
+}
+
+func TestWriterDict(t *testing.T) {
+	const (
+		dict = "hello world"
+		text = "hello again world"
+	)
+	var b bytes.Buffer
+	w, err := NewWriter(&b, 5)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+	w.Write([]byte(dict))
+	w.Flush()
+	b.Reset()
+	w.Write([]byte(text))
+	w.Close()
+
+	var b1 bytes.Buffer
+	w, _ = NewWriterDict(&b1, 5, []byte(dict))
+	w.Write([]byte(text))
+	w.Close()
+
+	if !bytes.Equal(b1.Bytes(), b.Bytes()) {
+		t.Fatalf("writer wrote %q want %q", b1.Bytes(), b.Bytes())
+	}
+}
+
+// See https://golang.org/issue/2508
+func TestRegression2508(t *testing.T) {
+	if testing.Short() {
+		t.Logf("test disabled with -short")
+		return
+	}
+	w, err := NewWriter(io.Discard, 1)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+	buf := make([]byte, 1024)
+	for i := 0; i < 131072; i++ {
+		if _, err := w.Write(buf); err != nil {
+			t.Fatalf("writer failed: %v", err)
+		}
+	}
+	w.Close()
+}
+
+func TestWriterReset(t *testing.T) {
+	t.Parallel()
+	for level := 0; level <= 9; level++ {
+		if testing.Short() && level > 1 {
+			break
+		}
+		w, err := NewWriter(io.Discard, level)
+		if err != nil {
+			t.Fatalf("NewWriter: %v", err)
+		}
+		buf := []byte("hello world")
+		n := 1024
+		if testing.Short() {
+			n = 10
+		}
+		for i := 0; i < n; i++ {
+			w.Write(buf)
+		}
+		w.Reset(io.Discard)
+
+		wref, err := NewWriter(io.Discard, level)
+		if err != nil {
+			t.Fatalf("NewWriter: %v", err)
+		}
+
+		// DeepEqual doesn't compare functions.
+		w.d.fill, wref.d.fill = nil, nil
+		w.d.step, wref.d.step = nil, nil
+		w.d.bulkHasher, wref.d.bulkHasher = nil, nil
+		w.d.bestSpeed, wref.d.bestSpeed = nil, nil
+		// hashMatch is always overwritten when used.
+		copy(w.d.hashMatch[:], wref.d.hashMatch[:])
+		if len(w.d.tokens) != 0 {
+			t.Errorf("level %d Writer not reset after Reset. %d tokens were present", level, len(w.d.tokens))
+		}
+		// As long as the length is 0, we don't care about the content.
+		w.d.tokens = wref.d.tokens
+
+		// We don't care if there are values in the window, as long as it is at d.index is 0
+		w.d.window = wref.d.window
+		if !reflect.DeepEqual(w, wref) {
+			t.Errorf("level %d Writer not reset after Reset", level)
+		}
+	}
+
+	levels := []int{0, 1, 2, 5, 9}
+	for _, level := range levels {
+		t.Run(fmt.Sprint(level), func(t *testing.T) {
+			testResetOutput(t, level, nil)
+		})
+	}
+
+	t.Run("dict", func(t *testing.T) {
+		for _, level := range levels {
+			t.Run(fmt.Sprint(level), func(t *testing.T) {
+				testResetOutput(t, level, nil)
+			})
+		}
+	})
+}
+
+func testResetOutput(t *testing.T, level int, dict []byte) {
+	writeData := func(w *Writer) {
+		msg := []byte("now is the time for all good gophers")
+		w.Write(msg)
+		w.Flush()
+
+		hello := []byte("hello world")
+		for i := 0; i < 1024; i++ {
+			w.Write(hello)
+		}
+
+		fill := bytes.Repeat([]byte("x"), 65000)
+		w.Write(fill)
+	}
+
+	buf := new(bytes.Buffer)
+	var w *Writer
+	var err error
+	if dict == nil {
+		w, err = NewWriter(buf, level)
+	} else {
+		w, err = NewWriterDict(buf, level, dict)
+	}
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+
+	writeData(w)
+	w.Close()
+	out1 := buf.Bytes()
+
+	buf2 := new(bytes.Buffer)
+	w.Reset(buf2)
+	writeData(w)
+	w.Close()
+	out2 := buf2.Bytes()
+
+	if len(out1) != len(out2) {
+		t.Errorf("got %d, expected %d bytes", len(out2), len(out1))
+		return
+	}
+	if !bytes.Equal(out1, out2) {
+		mm := 0
+		for i, b := range out1[:len(out2)] {
+			if b != out2[i] {
+				t.Errorf("mismatch index %d: %#02x, expected %#02x", i, out2[i], b)
+			}
+			mm++
+			if mm == 10 {
+				t.Fatal("Stopping")
+			}
+		}
+	}
+	t.Logf("got %d bytes", len(out1))
+}
+
+// TestBestSpeed tests that round-tripping through deflate and then inflate
+// recovers the original input. The Write sizes are near the thresholds in the
+// compressor.encSpeed method (0, 16, 128), as well as near maxStoreBlockSize
+// (65535).
+func TestBestSpeed(t *testing.T) {
+	t.Parallel()
+	abc := make([]byte, 128)
+	for i := range abc {
+		abc[i] = byte(i)
+	}
+	abcabc := bytes.Repeat(abc, 131072/len(abc))
+	var want []byte
+
+	testCases := [][]int{
+		{65536, 0},
+		{65536, 1},
+		{65536, 1, 256},
+		{65536, 1, 65536},
+		{65536, 14},
+		{65536, 15},
+		{65536, 16},
+		{65536, 16, 256},
+		{65536, 16, 65536},
+		{65536, 127},
+		{65536, 128},
+		{65536, 128, 256},
+		{65536, 128, 65536},
+		{65536, 129},
+		{65536, 65536, 256},
+		{65536, 65536, 65536},
+	}
+
+	for i, tc := range testCases {
+		if i >= 3 && testing.Short() {
+			break
+		}
+		for _, firstN := range []int{1, 65534, 65535, 65536, 65537, 131072} {
+			tc[0] = firstN
+		outer:
+			for _, flush := range []bool{false, true} {
+				buf := new(bytes.Buffer)
+				want = want[:0]
+
+				w, err := NewWriter(buf, BestSpeed)
+				if err != nil {
+					t.Errorf("i=%d, firstN=%d, flush=%t: NewWriter: %v", i, firstN, flush, err)
+					continue
+				}
+				for _, n := range tc {
+					want = append(want, abcabc[:n]...)
+					if _, err := w.Write(abcabc[:n]); err != nil {
+						t.Errorf("i=%d, firstN=%d, flush=%t: Write: %v", i, firstN, flush, err)
+						continue outer
+					}
+					if !flush {
+						continue
+					}
+					if err := w.Flush(); err != nil {
+						t.Errorf("i=%d, firstN=%d, flush=%t: Flush: %v", i, firstN, flush, err)
+						continue outer
+					}
+				}
+				if err := w.Close(); err != nil {
+					t.Errorf("i=%d, firstN=%d, flush=%t: Close: %v", i, firstN, flush, err)
+					continue
+				}
+
+				r := NewReader(buf)
+				got, err := io.ReadAll(r)
+				if err != nil {
+					t.Errorf("i=%d, firstN=%d, flush=%t: ReadAll: %v", i, firstN, flush, err)
+					continue
+				}
+				r.Close()
+
+				if !bytes.Equal(got, want) {
+					t.Errorf("i=%d, firstN=%d, flush=%t: corruption during deflate-then-inflate", i, firstN, flush)
+					continue
+				}
+			}
+		}
+	}
+}
+
+var errIO = errors.New("IO error")
+
+// failWriter fails with errIO exactly at the nth call to Write.
+type failWriter struct{ n int }
+
+func (w *failWriter) Write(b []byte) (int, error) {
+	w.n--
+	if w.n == -1 {
+		return 0, errIO
+	}
+	return len(b), nil
+}
+
+func TestWriterPersistentError(t *testing.T) {
+	t.Parallel()
+	d, err := os.ReadFile("../../testdata/Isaac.Newton-Opticks.txt")
+	if err != nil {
+		t.Fatalf("ReadFile: %v", err)
+	}
+	d = d[:10000] // Keep this test short
+
+	zw, err := NewWriter(nil, DefaultCompression)
+	if err != nil {
+		t.Fatalf("NewWriter: %v", err)
+	}
+
+	// Sweep over the threshold at which an error is returned.
+	// The variable i makes it such that the ith call to failWriter.Write will
+	// return errIO. Since failWriter errors are not persistent, we must ensure
+	// that flate.Writer errors are persistent.
+	for i := 0; i < 1000; i++ {
+		fw := &failWriter{i}
+		zw.Reset(fw)
+
+		_, werr := zw.Write(d)
+		cerr := zw.Close()
+		if werr != errIO && werr != nil {
+			t.Errorf("test %d, mismatching Write error: got %v, want %v", i, werr, errIO)
+		}
+		if cerr != errIO && fw.n < 0 {
+			t.Errorf("test %d, mismatching Close error: got %v, want %v", i, cerr, errIO)
+		}
+		if fw.n >= 0 {
+			// At this point, the failure threshold was sufficiently high enough
+			// that we wrote the whole stream without any errors.
+			return
+		}
+	}
+}
+
+func TestBestSpeedMatch(t *testing.T) {
+	t.Parallel()
+	cases := []struct {
+		previous, current []byte
+		t, s, want        int32
+	}{{
+		previous: []byte{0, 0, 0, 1, 2},
+		current:  []byte{3, 4, 5, 0, 1, 2, 3, 4, 5},
+		t:        -3,
+		s:        3,
+		want:     6,
+	}, {
+		previous: []byte{0, 0, 0, 1, 2},
+		current:  []byte{2, 4, 5, 0, 1, 2, 3, 4, 5},
+		t:        -3,
+		s:        3,
+		want:     3,
+	}, {
+		previous: []byte{0, 0, 0, 1, 1},
+		current:  []byte{3, 4, 5, 0, 1, 2, 3, 4, 5},
+		t:        -3,
+		s:        3,
+		want:     2,
+	}, {
+		previous: []byte{0, 0, 0, 1, 2},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -1,
+		s:        0,
+		want:     4,
+	}, {
+		previous: []byte{0, 0, 0, 1, 2, 3, 4, 5, 2, 2},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -7,
+		s:        4,
+		want:     5,
+	}, {
+		previous: []byte{9, 9, 9, 9, 9},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -1,
+		s:        0,
+		want:     0,
+	}, {
+		previous: []byte{9, 9, 9, 9, 9},
+		current:  []byte{9, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        0,
+		s:        1,
+		want:     0,
+	}, {
+		previous: []byte{},
+		current:  []byte{9, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -5,
+		s:        1,
+		want:     0,
+	}, {
+		previous: []byte{},
+		current:  []byte{9, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        -1,
+		s:        1,
+		want:     0,
+	}, {
+		previous: []byte{},
+		current:  []byte{2, 2, 2, 2, 1, 2, 3, 4, 5},
+		t:        0,
+		s:        1,
+		want:     3,
+	}, {
+		previous: []byte{3, 4, 5},
+		current:  []byte{3, 4, 5},
+		t:        -3,
+		s:        0,
+		want:     3,
+	}, {
+		previous: make([]byte, 1000),
+		current:  make([]byte, 1000),
+		t:        -1000,
+		s:        0,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, 200),
+		current:  make([]byte, 500),
+		t:        -200,
+		s:        0,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, 200),
+		current:  make([]byte, 500),
+		t:        0,
+		s:        1,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, maxMatchLength-4),
+		current:  make([]byte, 500),
+		t:        -(maxMatchLength - 4),
+		s:        0,
+		want:     maxMatchLength - 4,
+	}, {
+		previous: make([]byte, 200),
+		current:  make([]byte, 500),
+		t:        -200,
+		s:        400,
+		want:     100,
+	}, {
+		previous: make([]byte, 10),
+		current:  make([]byte, 500),
+		t:        200,
+		s:        400,
+		want:     100,
+	}}
+	for i, c := range cases {
+		e := deflateFast{prev: c.previous}
+		got := e.matchLen(c.s, c.t, c.current)
+		if got != c.want {
+			t.Errorf("Test %d: match length, want %d, got %d", i, c.want, got)
+		}
+	}
+}
+
+func TestBestSpeedMaxMatchOffset(t *testing.T) {
+	t.Parallel()
+	const abc, xyz = "abcdefgh", "stuvwxyz"
+	for _, matchBefore := range []bool{false, true} {
+		for _, extra := range []int{0, inputMargin - 1, inputMargin, inputMargin + 1, 2 * inputMargin} {
+			for offsetAdj := -5; offsetAdj <= +5; offsetAdj++ {
+				report := func(desc string, err error) {
+					t.Errorf("matchBefore=%t, extra=%d, offsetAdj=%d: %s%v",
+						matchBefore, extra, offsetAdj, desc, err)
+				}
+
+				offset := maxMatchOffset + offsetAdj
+
+				// Make src to be a []byte of the form
+				//	"%s%s%s%s%s" % (abc, zeros0, xyzMaybe, abc, zeros1)
+				// where:
+				//	zeros0 is approximately maxMatchOffset zeros.
+				//	xyzMaybe is either xyz or the empty string.
+				//	zeros1 is between 0 and 30 zeros.
+				// The difference between the two abc's will be offset, which
+				// is maxMatchOffset plus or minus a small adjustment.
+				src := make([]byte, offset+len(abc)+extra)
+				copy(src, abc)
+				if !matchBefore {
+					copy(src[offset-len(xyz):], xyz)
+				}
+				copy(src[offset:], abc)
+
+				buf := new(bytes.Buffer)
+				w, err := NewWriter(buf, BestSpeed)
+				if err != nil {
+					report("NewWriter: ", err)
+					continue
+				}
+				if _, err := w.Write(src); err != nil {
+					report("Write: ", err)
+					continue
+				}
+				if err := w.Close(); err != nil {
+					report("Writer.Close: ", err)
+					continue
+				}
+
+				r := NewReader(buf)
+				dst, err := io.ReadAll(r)
+				r.Close()
+				if err != nil {
+					report("ReadAll: ", err)
+					continue
+				}
+
+				if !bytes.Equal(dst, src) {
+					report("", fmt.Errorf("bytes differ after round-tripping"))
+					continue
+				}
+			}
+		}
+	}
+}
+
+func TestBestSpeedShiftOffsets(t *testing.T) {
+	// Test if shiftoffsets properly preserves matches and resets out-of-range matches
+	// seen in https://github.com/golang/go/issues/4142
+	enc := newDeflateFast()
+
+	// testData may not generate internal matches.
+	testData := make([]byte, 32)
+	rng := rand.New(rand.NewSource(0))
+	for i := range testData {
+		testData[i] = byte(rng.Uint32())
+	}
+
+	// Encode the testdata with clean state.
+	// Second part should pick up matches from the first block.
+	wantFirstTokens := len(enc.encode(nil, testData))
+	wantSecondTokens := len(enc.encode(nil, testData))
+
+	if wantFirstTokens <= wantSecondTokens {
+		t.Fatalf("test needs matches between inputs to be generated")
+	}
+	// Forward the current indicator to before wraparound.
+	enc.cur = bufferReset - int32(len(testData))
+
+	// Part 1 before wrap, should match clean state.
+	got := len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+
+	// Verify we are about to wrap.
+	if enc.cur != bufferReset {
+		t.Errorf("got %d, want e.cur to be at bufferReset (%d)", enc.cur, bufferReset)
+	}
+
+	// Part 2 should match clean state as well even if wrapped.
+	got = len(enc.encode(nil, testData))
+	if wantSecondTokens != got {
+		t.Errorf("got %d, want %d token", got, wantSecondTokens)
+	}
+
+	// Verify that we wrapped.
+	if enc.cur >= bufferReset {
+		t.Errorf("want e.cur to be < bufferReset (%d), got %d", bufferReset, enc.cur)
+	}
+
+	// Forward the current buffer, leaving the matches at the bottom.
+	enc.cur = bufferReset
+	enc.shiftOffsets()
+
+	// Ensure that no matches were picked up.
+	got = len(enc.encode(nil, testData))
+	if wantFirstTokens != got {
+		t.Errorf("got %d, want %d tokens", got, wantFirstTokens)
+	}
+}
+
+func TestMaxStackSize(t *testing.T) {
+	// This test must not run in parallel with other tests as debug.SetMaxStack
+	// affects all goroutines.
+	n := debug.SetMaxStack(1 << 16)
+	defer debug.SetMaxStack(n)
+
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	b := make([]byte, 1<<20)
+	for level := HuffmanOnly; level <= BestCompression; level++ {
+		// Run in separate goroutine to increase probability of stack regrowth.
+		wg.Add(1)
+		go func(level int) {
+			defer wg.Done()
+			zw, err := NewWriter(io.Discard, level)
+			if err != nil {
+				t.Errorf("level %d, NewWriter() = %v, want nil", level, err)
+			}
+			if n, err := zw.Write(b); n != len(b) || err != nil {
+				t.Errorf("level %d, Write() = (%d, %v), want (%d, nil)", level, n, err, len(b))
+			}
+			if err := zw.Close(); err != nil {
+				t.Errorf("level %d, Close() = %v, want nil", level, err)
+			}
+			zw.Reset(io.Discard)
+		}(level)
+	}
+}

image/internal/compress/flate/deflatefast.go

@@ -0,0 +1,309 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import "math"
+
+// This encoding algorithm, which prioritizes speed over output size, is
+// based on Snappy's LZ77-style encoder: github.com/golang/snappy
+
+const (
+	tableBits  = 14             // Bits used in the table.
+	tableSize  = 1 << tableBits // Size of the table.
+	tableMask  = tableSize - 1  // Mask for table indices. Redundant, but can eliminate bounds checks.
+	tableShift = 32 - tableBits // Right-shift to get the tableBits most significant bits of a uint32.
+
+	// Reset the buffer offset when reaching this.
+	// Offsets are stored between blocks as int32 values.
+	// Since the offset we are checking against is at the beginning
+	// of the buffer, we need to subtract the current and input
+	// buffer to not risk overflowing the int32.
+	bufferReset = math.MaxInt32 - maxStoreBlockSize*2
+)
+
+func load32(b []byte, i int32) uint32 {
+	b = b[i : i+4 : len(b)] // Help the compiler eliminate bounds checks on the next line.
+	return uint32(b[0]) | uint32(b[1])<<8 | uint32(b[2])<<16 | uint32(b[3])<<24
+}
+
+func load64(b []byte, i int32) uint64 {
+	b = b[i : i+8 : len(b)] // Help the compiler eliminate bounds checks on the next line.
+	return uint64(b[0]) | uint64(b[1])<<8 | uint64(b[2])<<16 | uint64(b[3])<<24 |
+		uint64(b[4])<<32 | uint64(b[5])<<40 | uint64(b[6])<<48 | uint64(b[7])<<56
+}
+
+func hash(u uint32) uint32 {
+	return (u * 0x1e35a7bd) >> tableShift
+}
+
+// These constants are defined by the Snappy implementation so that its
+// assembly implementation can fast-path some 16-bytes-at-a-time copies. They
+// aren't necessary in the pure Go implementation, as we don't use those same
+// optimizations, but using the same thresholds doesn't really hurt.
+const (
+	inputMargin            = 16 - 1
+	minNonLiteralBlockSize = 1 + 1 + inputMargin
+)
+
+type tableEntry struct {
+	val    uint32 // Value at destination
+	offset int32
+}
+
+// deflateFast maintains the table for matches,
+// and the previous byte block for cross block matching.
+type deflateFast struct {
+	table [tableSize]tableEntry
+	prev  []byte // Previous block, zero length if unknown.
+	cur   int32  // Current match offset.
+}
+
+func newDeflateFast() *deflateFast {
+	return &deflateFast{cur: maxStoreBlockSize, prev: make([]byte, 0, maxStoreBlockSize)}
+}
+
+// encode encodes a block given in src and appends tokens
+// to dst and returns the result.
+func (e *deflateFast) encode(dst []token, src []byte) []token {
+	// Ensure that e.cur doesn't wrap.
+	if e.cur >= bufferReset {
+		e.shiftOffsets()
+	}
+
+	// This check isn't in the Snappy implementation, but there, the caller
+	// instead of the callee handles this case.
+	if len(src) < minNonLiteralBlockSize {
+		e.cur += maxStoreBlockSize
+		e.prev = e.prev[:0]
+		return emitLiteral(dst, src)
+	}
+
+	// sLimit is when to stop looking for offset/length copies. The inputMargin
+	// lets us use a fast path for emitLiteral in the main loop, while we are
+	// looking for copies.
+	sLimit := int32(len(src) - inputMargin)
+
+	// nextEmit is where in src the next emitLiteral should start from.
+	nextEmit := int32(0)
+	s := int32(0)
+	cv := load32(src, s)
+	nextHash := hash(cv)
+
+	for {
+		// Copied from the C++ snappy implementation:
+		//
+		// Heuristic match skipping: If 32 bytes are scanned with no matches
+		// found, start looking only at every other byte. If 32 more bytes are
+		// scanned (or skipped), look at every third byte, etc.. When a match
+		// is found, immediately go back to looking at every byte. This is a
+		// small loss (~5% performance, ~0.1% density) for compressible data
+		// due to more bookkeeping, but for non-compressible data (such as
+		// JPEG) it's a huge win since the compressor quickly "realizes" the
+		// data is incompressible and doesn't bother looking for matches
+		// everywhere.
+		//
+		// The "skip" variable keeps track of how many bytes there are since
+		// the last match; dividing it by 32 (ie. right-shifting by five) gives
+		// the number of bytes to move ahead for each iteration.
+		skip := int32(32)
+
+		nextS := s
+		var candidate tableEntry
+		for {
+			s = nextS
+			bytesBetweenHashLookups := skip >> 5
+			nextS = s + bytesBetweenHashLookups
+			skip += bytesBetweenHashLookups
+			if nextS > sLimit {
+				goto emitRemainder
+			}
+			candidate = e.table[nextHash&tableMask]
+			now := load32(src, nextS)
+			e.table[nextHash&tableMask] = tableEntry{offset: s + e.cur, val: cv}
+			nextHash = hash(now)
+
+			offset := s - (candidate.offset - e.cur)
+			if offset > maxMatchOffset || cv != candidate.val {
+				// Out of range or not matched.
+				cv = now
+				continue
+			}
+			break
+		}
+
+		// A 4-byte match has been found. We'll later see if more than 4 bytes
+		// match. But, prior to the match, src[nextEmit:s] are unmatched. Emit
+		// them as literal bytes.
+		dst = emitLiteral(dst, src[nextEmit:s])
+
+		// Call emitCopy, and then see if another emitCopy could be our next
+		// move. Repeat until we find no match for the input immediately after
+		// what was consumed by the last emitCopy call.
+		//
+		// If we exit this loop normally then we need to call emitLiteral next,
+		// though we don't yet know how big the literal will be. We handle that
+		// by proceeding to the next iteration of the main loop. We also can
+		// exit this loop via goto if we get close to exhausting the input.
+		for {
+			// Invariant: we have a 4-byte match at s, and no need to emit any
+			// literal bytes prior to s.
+
+			// Extend the 4-byte match as long as possible.
+			//
+			s += 4
+			t := candidate.offset - e.cur + 4
+			l := e.matchLen(s, t, src)
+
+			// matchToken is flate's equivalent of Snappy's emitCopy. (length,offset)
+			dst = append(dst, matchToken(uint32(l+4-baseMatchLength), uint32(s-t-baseMatchOffset)))
+			s += l
+			nextEmit = s
+			if s >= sLimit {
+				goto emitRemainder
+			}
+
+			// We could immediately start working at s now, but to improve
+			// compression we first update the hash table at s-1 and at s. If
+			// another emitCopy is not our next move, also calculate nextHash
+			// at s+1. At least on GOARCH=amd64, these three hash calculations
+			// are faster as one load64 call (with some shifts) instead of
+			// three load32 calls.
+			x := load64(src, s-1)
+			prevHash := hash(uint32(x))
+			e.table[prevHash&tableMask] = tableEntry{offset: e.cur + s - 1, val: uint32(x)}
+			x >>= 8
+			currHash := hash(uint32(x))
+			candidate = e.table[currHash&tableMask]
+			e.table[currHash&tableMask] = tableEntry{offset: e.cur + s, val: uint32(x)}
+
+			offset := s - (candidate.offset - e.cur)
+			if offset > maxMatchOffset || uint32(x) != candidate.val {
+				cv = uint32(x >> 8)
+				nextHash = hash(cv)
+				s++
+				break
+			}
+		}
+	}
+
+emitRemainder:
+	if int(nextEmit) < len(src) {
+		dst = emitLiteral(dst, src[nextEmit:])
+	}
+	e.cur += int32(len(src))
+	e.prev = e.prev[:len(src)]
+	copy(e.prev, src)
+	return dst
+}
+
+func emitLiteral(dst []token, lit []byte) []token {
+	for _, v := range lit {
+		dst = append(dst, literalToken(uint32(v)))
+	}
+	return dst
+}
+
+// matchLen returns the match length between src[s:] and src[t:].
+// t can be negative to indicate the match is starting in e.prev.
+// We assume that src[s-4:s] and src[t-4:t] already match.
+func (e *deflateFast) matchLen(s, t int32, src []byte) int32 {
+	s1 := int(s) + maxMatchLength - 4
+	if s1 > len(src) {
+		s1 = len(src)
+	}
+
+	// If we are inside the current block
+	if t >= 0 {
+		b := src[t:]
+		a := src[s:s1]
+		b = b[:len(a)]
+		// Extend the match to be as long as possible.
+		for i := range a {
+			if a[i] != b[i] {
+				return int32(i)
+			}
+		}
+		return int32(len(a))
+	}
+
+	// We found a match in the previous block.
+	tp := int32(len(e.prev)) + t
+	if tp < 0 {
+		return 0
+	}
+
+	// Extend the match to be as long as possible.
+	a := src[s:s1]
+	b := e.prev[tp:]
+	if len(b) > len(a) {
+		b = b[:len(a)]
+	}
+	a = a[:len(b)]
+	for i := range b {
+		if a[i] != b[i] {
+			return int32(i)
+		}
+	}
+
+	// If we reached our limit, we matched everything we are
+	// allowed to in the previous block and we return.
+	n := int32(len(b))
+	if int(s+n) == s1 {
+		return n
+	}
+
+	// Continue looking for more matches in the current block.
+	a = src[s+n : s1]
+	b = src[:len(a)]
+	for i := range a {
+		if a[i] != b[i] {
+			return int32(i) + n
+		}
+	}
+	return int32(len(a)) + n
+}
+
+// Reset resets the encoding history.
+// This ensures that no matches are made to the previous block.
+func (e *deflateFast) reset() {
+	e.prev = e.prev[:0]
+	// Bump the offset, so all matches will fail distance check.
+	// Nothing should be >= e.cur in the table.
+	e.cur += maxMatchOffset
+
+	// Protect against e.cur wraparound.
+	if e.cur >= bufferReset {
+		e.shiftOffsets()
+	}
+}
+
+// shiftOffsets will shift down all match offset.
+// This is only called in rare situations to prevent integer overflow.
+//
+// See https://golang.org/issue/18636 and https://github.com/golang/go/issues/34121.
+func (e *deflateFast) shiftOffsets() {
+	if len(e.prev) == 0 {
+		// We have no history; just clear the table.
+		for i := range e.table[:] {
+			e.table[i] = tableEntry{}
+		}
+		e.cur = maxMatchOffset + 1
+		return
+	}
+
+	// Shift down everything in the table that isn't already too far away.
+	for i := range e.table[:] {
+		v := e.table[i].offset - e.cur + maxMatchOffset + 1
+		if v < 0 {
+			// We want to reset e.cur to maxMatchOffset + 1, so we need to shift
+			// all table entries down by (e.cur - (maxMatchOffset + 1)).
+			// Because we ignore matches > maxMatchOffset, we can cap
+			// any negative offsets at 0.
+			v = 0
+		}
+		e.table[i].offset = v
+	}
+	e.cur = maxMatchOffset + 1
+}

image/internal/compress/flate/dict_decoder.go

@@ -0,0 +1,186 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+// dictDecoder implements the LZ77 sliding dictionary as used in decompression.
+// LZ77 decompresses data through sequences of two forms of commands:
+//
+//	* Literal insertions: Runs of one or more symbols are inserted into the data
+//	stream as is. This is accomplished through the writeByte method for a
+//	single symbol, or combinations of writeSlice/writeMark for multiple symbols.
+//	Any valid stream must start with a literal insertion if no preset dictionary
+//	is used.
+//
+//	* Backward copies: Runs of one or more symbols are copied from previously
+//	emitted data. Backward copies come as the tuple (dist, length) where dist
+//	determines how far back in the stream to copy from and length determines how
+//	many bytes to copy. Note that it is valid for the length to be greater than
+//	the distance. Since LZ77 uses forward copies, that situation is used to
+//	perform a form of run-length encoding on repeated runs of symbols.
+//	The writeCopy and tryWriteCopy are used to implement this command.
+//
+// For performance reasons, this implementation performs little to no sanity
+// checks about the arguments. As such, the invariants documented for each
+// method call must be respected.
+type dictDecoder struct {
+	hist []byte // Sliding window history
+
+	// Invariant: 0 <= rdPos <= wrPos <= len(hist)
+	wrPos int  // Current output position in buffer
+	rdPos int  // Have emitted hist[:rdPos] already
+	full  bool // Has a full window length been written yet?
+}
+
+// To minimize the memory usage in TinyGo, it is defined as a fixed array
+// instead of a make().
+var ddHistBuf [1 << 15]byte
+
+// init initializes dictDecoder to have a sliding window dictionary of the given
+// size. If a preset dict is provided, it will initialize the dictionary with
+// the contents of dict.
+func (dd *dictDecoder) init(size int, dict []byte) {
+	*dd = dictDecoder{hist: dd.hist}
+
+	if cap(dd.hist) < size {
+		dd.hist = ddHistBuf[:size]
+	}
+	dd.hist = dd.hist[:size]
+
+	if len(dict) > len(dd.hist) {
+		dict = dict[len(dict)-len(dd.hist):]
+	}
+	dd.wrPos = copy(dd.hist, dict)
+	if dd.wrPos == len(dd.hist) {
+		dd.wrPos = 0
+		dd.full = true
+	}
+	dd.rdPos = dd.wrPos
+}
+
+// histSize reports the total amount of historical data in the dictionary.
+func (dd *dictDecoder) histSize() int {
+	if dd.full {
+		return len(dd.hist)
+	}
+	return dd.wrPos
+}
+
+// availRead reports the number of bytes that can be flushed by readFlush.
+func (dd *dictDecoder) availRead() int {
+	return dd.wrPos - dd.rdPos
+}
+
+// availWrite reports the available amount of output buffer space.
+func (dd *dictDecoder) availWrite() int {
+	return len(dd.hist) - dd.wrPos
+}
+
+// writeSlice returns a slice of the available buffer to write data to.
+//
+// This invariant will be kept: len(s) <= availWrite()
+func (dd *dictDecoder) writeSlice() []byte {
+	return dd.hist[dd.wrPos:]
+}
+
+// writeMark advances the writer pointer by cnt.
+//
+// This invariant must be kept: 0 <= cnt <= availWrite()
+func (dd *dictDecoder) writeMark(cnt int) {
+	dd.wrPos += cnt
+}
+
+// writeByte writes a single byte to the dictionary.
+//
+// This invariant must be kept: 0 < availWrite()
+func (dd *dictDecoder) writeByte(c byte) {
+	dd.hist[dd.wrPos] = c
+	dd.wrPos++
+}
+
+// writeCopy copies a string at a given (dist, length) to the output.
+// This returns the number of bytes copied and may be less than the requested
+// length if the available space in the output buffer is too small.
+//
+// This invariant must be kept: 0 < dist <= histSize()
+func (dd *dictDecoder) writeCopy(dist, length int) int {
+	dstBase := dd.wrPos
+	dstPos := dstBase
+	srcPos := dstPos - dist
+	endPos := dstPos + length
+	if endPos > len(dd.hist) {
+		endPos = len(dd.hist)
+	}
+
+	// Copy non-overlapping section after destination position.
+	//
+	// This section is non-overlapping in that the copy length for this section
+	// is always less than or equal to the backwards distance. This can occur
+	// if a distance refers to data that wraps-around in the buffer.
+	// Thus, a backwards copy is performed here; that is, the exact bytes in
+	// the source prior to the copy is placed in the destination.
+	if srcPos < 0 {
+		srcPos += len(dd.hist)
+		dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:])
+		srcPos = 0
+	}
+
+	// Copy possibly overlapping section before destination position.
+	//
+	// This section can overlap if the copy length for this section is larger
+	// than the backwards distance. This is allowed by LZ77 so that repeated
+	// strings can be succinctly represented using (dist, length) pairs.
+	// Thus, a forwards copy is performed here; that is, the bytes copied is
+	// possibly dependent on the resulting bytes in the destination as the copy
+	// progresses along. This is functionally equivalent to the following:
+	//
+	//	for i := 0; i < endPos-dstPos; i++ {
+	//		dd.hist[dstPos+i] = dd.hist[srcPos+i]
+	//	}
+	//	dstPos = endPos
+	//
+	for dstPos < endPos {
+		dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos])
+	}
+
+	dd.wrPos = dstPos
+	return dstPos - dstBase
+}
+
+// tryWriteCopy tries to copy a string at a given (distance, length) to the
+// output. This specialized version is optimized for short distances.
+//
+// This method is designed to be inlined for performance reasons.
+//
+// This invariant must be kept: 0 < dist <= histSize()
+func (dd *dictDecoder) tryWriteCopy(dist, length int) int {
+	dstPos := dd.wrPos
+	endPos := dstPos + length
+	if dstPos < dist || endPos > len(dd.hist) {
+		return 0
+	}
+	dstBase := dstPos
+	srcPos := dstPos - dist
+
+	// Copy possibly overlapping section before destination position.
+	for dstPos < endPos {
+		dstPos += copy(dd.hist[dstPos:endPos], dd.hist[srcPos:dstPos])
+	}
+
+	dd.wrPos = dstPos
+	return dstPos - dstBase
+}
+
+// readFlush returns a slice of the historical buffer that is ready to be
+// emitted to the user. The data returned by readFlush must be fully consumed
+// before calling any other dictDecoder methods.
+func (dd *dictDecoder) readFlush() []byte {
+	toRead := dd.hist[dd.rdPos:dd.wrPos]
+	dd.rdPos = dd.wrPos
+	if dd.wrPos == len(dd.hist) {
+		dd.wrPos, dd.rdPos = 0, 0
+		dd.full = true
+	}
+	return toRead
+}

image/internal/compress/flate/dict_decoder_test.go

@@ -0,0 +1,139 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"strings"
+	"testing"
+)
+
+func TestDictDecoder(t *testing.T) {
+	const (
+		abc  = "ABC\n"
+		fox  = "The quick brown fox jumped over the lazy dog!\n"
+		poem = "The Road Not Taken\nRobert Frost\n" +
+			"\n" +
+			"Two roads diverged in a yellow wood,\n" +
+			"And sorry I could not travel both\n" +
+			"And be one traveler, long I stood\n" +
+			"And looked down one as far as I could\n" +
+			"To where it bent in the undergrowth;\n" +
+			"\n" +
+			"Then took the other, as just as fair,\n" +
+			"And having perhaps the better claim,\n" +
+			"Because it was grassy and wanted wear;\n" +
+			"Though as for that the passing there\n" +
+			"Had worn them really about the same,\n" +
+			"\n" +
+			"And both that morning equally lay\n" +
+			"In leaves no step had trodden black.\n" +
+			"Oh, I kept the first for another day!\n" +
+			"Yet knowing how way leads on to way,\n" +
+			"I doubted if I should ever come back.\n" +
+			"\n" +
+			"I shall be telling this with a sigh\n" +
+			"Somewhere ages and ages hence:\n" +
+			"Two roads diverged in a wood, and I-\n" +
+			"I took the one less traveled by,\n" +
+			"And that has made all the difference.\n"
+	)
+
+	var poemRefs = []struct {
+		dist   int // Backward distance (0 if this is an insertion)
+		length int // Length of copy or insertion
+	}{
+		{0, 38}, {33, 3}, {0, 48}, {79, 3}, {0, 11}, {34, 5}, {0, 6}, {23, 7},
+		{0, 8}, {50, 3}, {0, 2}, {69, 3}, {34, 5}, {0, 4}, {97, 3}, {0, 4},
+		{43, 5}, {0, 6}, {7, 4}, {88, 7}, {0, 12}, {80, 3}, {0, 2}, {141, 4},
+		{0, 1}, {196, 3}, {0, 3}, {157, 3}, {0, 6}, {181, 3}, {0, 2}, {23, 3},
+		{77, 3}, {28, 5}, {128, 3}, {110, 4}, {70, 3}, {0, 4}, {85, 6}, {0, 2},
+		{182, 6}, {0, 4}, {133, 3}, {0, 7}, {47, 5}, {0, 20}, {112, 5}, {0, 1},
+		{58, 3}, {0, 8}, {59, 3}, {0, 4}, {173, 3}, {0, 5}, {114, 3}, {0, 4},
+		{92, 5}, {0, 2}, {71, 3}, {0, 2}, {76, 5}, {0, 1}, {46, 3}, {96, 4},
+		{130, 4}, {0, 3}, {360, 3}, {0, 3}, {178, 5}, {0, 7}, {75, 3}, {0, 3},
+		{45, 6}, {0, 6}, {299, 6}, {180, 3}, {70, 6}, {0, 1}, {48, 3}, {66, 4},
+		{0, 3}, {47, 5}, {0, 9}, {325, 3}, {0, 1}, {359, 3}, {318, 3}, {0, 2},
+		{199, 3}, {0, 1}, {344, 3}, {0, 3}, {248, 3}, {0, 10}, {310, 3}, {0, 3},
+		{93, 6}, {0, 3}, {252, 3}, {157, 4}, {0, 2}, {273, 5}, {0, 14}, {99, 4},
+		{0, 1}, {464, 4}, {0, 2}, {92, 4}, {495, 3}, {0, 1}, {322, 4}, {16, 4},
+		{0, 3}, {402, 3}, {0, 2}, {237, 4}, {0, 2}, {432, 4}, {0, 1}, {483, 5},
+		{0, 2}, {294, 4}, {0, 2}, {306, 3}, {113, 5}, {0, 1}, {26, 4}, {164, 3},
+		{488, 4}, {0, 1}, {542, 3}, {248, 6}, {0, 5}, {205, 3}, {0, 8}, {48, 3},
+		{449, 6}, {0, 2}, {192, 3}, {328, 4}, {9, 5}, {433, 3}, {0, 3}, {622, 25},
+		{615, 5}, {46, 5}, {0, 2}, {104, 3}, {475, 10}, {549, 3}, {0, 4}, {597, 8},
+		{314, 3}, {0, 1}, {473, 6}, {317, 5}, {0, 1}, {400, 3}, {0, 3}, {109, 3},
+		{151, 3}, {48, 4}, {0, 4}, {125, 3}, {108, 3}, {0, 2},
+	}
+
+	var got, want bytes.Buffer
+	var dd dictDecoder
+	dd.init(1<<11, nil)
+
+	var writeCopy = func(dist, length int) {
+		for length > 0 {
+			cnt := dd.tryWriteCopy(dist, length)
+			if cnt == 0 {
+				cnt = dd.writeCopy(dist, length)
+			}
+
+			length -= cnt
+			if dd.availWrite() == 0 {
+				got.Write(dd.readFlush())
+			}
+		}
+	}
+	var writeString = func(str string) {
+		for len(str) > 0 {
+			cnt := copy(dd.writeSlice(), str)
+			str = str[cnt:]
+			dd.writeMark(cnt)
+			if dd.availWrite() == 0 {
+				got.Write(dd.readFlush())
+			}
+		}
+	}
+
+	writeString(".")
+	want.WriteByte('.')
+
+	str := poem
+	for _, ref := range poemRefs {
+		if ref.dist == 0 {
+			writeString(str[:ref.length])
+		} else {
+			writeCopy(ref.dist, ref.length)
+		}
+		str = str[ref.length:]
+	}
+	want.WriteString(poem)
+
+	writeCopy(dd.histSize(), 33)
+	want.Write(want.Bytes()[:33])
+
+	writeString(abc)
+	writeCopy(len(abc), 59*len(abc))
+	want.WriteString(strings.Repeat(abc, 60))
+
+	writeString(fox)
+	writeCopy(len(fox), 9*len(fox))
+	want.WriteString(strings.Repeat(fox, 10))
+
+	writeString(".")
+	writeCopy(1, 9)
+	want.WriteString(strings.Repeat(".", 10))
+
+	writeString(strings.ToUpper(poem))
+	writeCopy(len(poem), 7*len(poem))
+	want.WriteString(strings.Repeat(strings.ToUpper(poem), 8))
+
+	writeCopy(dd.histSize(), 10)
+	want.Write(want.Bytes()[want.Len()-dd.histSize():][:10])
+
+	got.Write(dd.readFlush())
+	if got.String() != want.String() {
+		t.Errorf("final string mismatch:\ngot  %q\nwant %q", got.String(), want.String())
+	}
+}

image/internal/compress/flate/example_test.go

@@ -0,0 +1,243 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate_test
+
+import (
+	"bytes"
+	"compress/flate"
+	"fmt"
+	"io"
+	"log"
+	"os"
+	"strings"
+	"sync"
+)
+
+// In performance critical applications, Reset can be used to discard the
+// current compressor or decompressor state and reinitialize them quickly
+// by taking advantage of previously allocated memory.
+func Example_reset() {
+	proverbs := []string{
+		"Don't communicate by sharing memory, share memory by communicating.\n",
+		"Concurrency is not parallelism.\n",
+		"The bigger the interface, the weaker the abstraction.\n",
+		"Documentation is for users.\n",
+	}
+
+	var r strings.Reader
+	var b bytes.Buffer
+	buf := make([]byte, 32<<10)
+
+	zw, err := flate.NewWriter(nil, flate.DefaultCompression)
+	if err != nil {
+		log.Fatal(err)
+	}
+	zr := flate.NewReader(nil)
+
+	for _, s := range proverbs {
+		r.Reset(s)
+		b.Reset()
+
+		// Reset the compressor and encode from some input stream.
+		zw.Reset(&b)
+		if _, err := io.CopyBuffer(zw, &r, buf); err != nil {
+			log.Fatal(err)
+		}
+		if err := zw.Close(); err != nil {
+			log.Fatal(err)
+		}
+
+		// Reset the decompressor and decode to some output stream.
+		if err := zr.(flate.Resetter).Reset(&b, nil); err != nil {
+			log.Fatal(err)
+		}
+		if _, err := io.CopyBuffer(os.Stdout, zr, buf); err != nil {
+			log.Fatal(err)
+		}
+		if err := zr.Close(); err != nil {
+			log.Fatal(err)
+		}
+	}
+
+	// Output:
+	// Don't communicate by sharing memory, share memory by communicating.
+	// Concurrency is not parallelism.
+	// The bigger the interface, the weaker the abstraction.
+	// Documentation is for users.
+}
+
+// A preset dictionary can be used to improve the compression ratio.
+// The downside to using a dictionary is that the compressor and decompressor
+// must agree in advance what dictionary to use.
+func Example_dictionary() {
+	// The dictionary is a string of bytes. When compressing some input data,
+	// the compressor will attempt to substitute substrings with matches found
+	// in the dictionary. As such, the dictionary should only contain substrings
+	// that are expected to be found in the actual data stream.
+	const dict = `<?xml version="1.0"?>` + `<book>` + `<data>` + `<meta name="` + `" content="`
+
+	// The data to compress should (but is not required to) contain frequent
+	// substrings that match those in the dictionary.
+	const data = `<?xml version="1.0"?>
+<book>
+	<meta name="title" content="The Go Programming Language"/>
+	<meta name="authors" content="Alan Donovan and Brian Kernighan"/>
+	<meta name="published" content="2015-10-26"/>
+	<meta name="isbn" content="978-0134190440"/>
+	<data>...</data>
+</book>
+`
+
+	var b bytes.Buffer
+
+	// Compress the data using the specially crafted dictionary.
+	zw, err := flate.NewWriterDict(&b, flate.DefaultCompression, []byte(dict))
+	if err != nil {
+		log.Fatal(err)
+	}
+	if _, err := io.Copy(zw, strings.NewReader(data)); err != nil {
+		log.Fatal(err)
+	}
+	if err := zw.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	// The decompressor must use the same dictionary as the compressor.
+	// Otherwise, the input may appear as corrupted.
+	fmt.Println("Decompressed output using the dictionary:")
+	zr := flate.NewReaderDict(bytes.NewReader(b.Bytes()), []byte(dict))
+	if _, err := io.Copy(os.Stdout, zr); err != nil {
+		log.Fatal(err)
+	}
+	if err := zr.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	fmt.Println()
+
+	// Substitute all of the bytes in the dictionary with a '#' to visually
+	// demonstrate the approximate effectiveness of using a preset dictionary.
+	fmt.Println("Substrings matched by the dictionary are marked with #:")
+	hashDict := []byte(dict)
+	for i := range hashDict {
+		hashDict[i] = '#'
+	}
+	zr = flate.NewReaderDict(&b, hashDict)
+	if _, err := io.Copy(os.Stdout, zr); err != nil {
+		log.Fatal(err)
+	}
+	if err := zr.Close(); err != nil {
+		log.Fatal(err)
+	}
+
+	// Output:
+	// Decompressed output using the dictionary:
+	// <?xml version="1.0"?>
+	// <book>
+	// 	<meta name="title" content="The Go Programming Language"/>
+	// 	<meta name="authors" content="Alan Donovan and Brian Kernighan"/>
+	// 	<meta name="published" content="2015-10-26"/>
+	// 	<meta name="isbn" content="978-0134190440"/>
+	// 	<data>...</data>
+	// </book>
+	//
+	// Substrings matched by the dictionary are marked with #:
+	// #####################
+	// ######
+	// 	############title###########The Go Programming Language"/#
+	// 	############authors###########Alan Donovan and Brian Kernighan"/#
+	// 	############published###########2015-10-26"/#
+	// 	############isbn###########978-0134190440"/#
+	// 	######...</#####
+	// </#####
+}
+
+// DEFLATE is suitable for transmitting compressed data across the network.
+func Example_synchronization() {
+	var wg sync.WaitGroup
+	defer wg.Wait()
+
+	// Use io.Pipe to simulate a network connection.
+	// A real network application should take care to properly close the
+	// underlying connection.
+	rp, wp := io.Pipe()
+
+	// Start a goroutine to act as the transmitter.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+
+		zw, err := flate.NewWriter(wp, flate.BestSpeed)
+		if err != nil {
+			log.Fatal(err)
+		}
+
+		b := make([]byte, 256)
+		for _, m := range strings.Fields("A long time ago in a galaxy far, far away...") {
+			// We use a simple framing format where the first byte is the
+			// message length, followed the message itself.
+			b[0] = uint8(copy(b[1:], m))
+
+			if _, err := zw.Write(b[:1+len(m)]); err != nil {
+				log.Fatal(err)
+			}
+
+			// Flush ensures that the receiver can read all data sent so far.
+			if err := zw.Flush(); err != nil {
+				log.Fatal(err)
+			}
+		}
+
+		if err := zw.Close(); err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	// Start a goroutine to act as the receiver.
+	wg.Add(1)
+	go func() {
+		defer wg.Done()
+
+		zr := flate.NewReader(rp)
+
+		b := make([]byte, 256)
+		for {
+			// Read the message length.
+			// This is guaranteed to return for every corresponding
+			// Flush and Close on the transmitter side.
+			if _, err := io.ReadFull(zr, b[:1]); err != nil {
+				if err == io.EOF {
+					break // The transmitter closed the stream
+				}
+				log.Fatal(err)
+			}
+
+			// Read the message content.
+			n := int(b[0])
+			if _, err := io.ReadFull(zr, b[:n]); err != nil {
+				log.Fatal(err)
+			}
+
+			fmt.Printf("Received %d bytes: %s\n", n, b[:n])
+		}
+		fmt.Println()
+
+		if err := zr.Close(); err != nil {
+			log.Fatal(err)
+		}
+	}()
+
+	// Output:
+	// Received 1 bytes: A
+	// Received 4 bytes: long
+	// Received 4 bytes: time
+	// Received 3 bytes: ago
+	// Received 2 bytes: in
+	// Received 1 bytes: a
+	// Received 6 bytes: galaxy
+	// Received 4 bytes: far,
+	// Received 3 bytes: far
+	// Received 7 bytes: away...
+}

image/internal/compress/flate/flate_test.go

@@ -0,0 +1,352 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// This test tests some internals of the flate package.
+// The tests in package compress/gzip serve as the
+// end-to-end test of the decompressor.
+
+package flate
+
+import (
+	"bytes"
+	"encoding/hex"
+	"io"
+	"strings"
+	"testing"
+)
+
+// The following test should not panic.
+func TestIssue5915(t *testing.T) {
+	bits := []int{4, 0, 0, 6, 4, 3, 2, 3, 3, 4, 4, 5, 0, 0, 0, 0, 5, 5, 6,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
+		0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 7, 8, 6, 0, 11, 0, 8, 0, 6, 6, 10, 8}
+	var h huffmanDecoder
+	if h.init(bits) {
+		t.Fatalf("Given sequence of bits is bad, and should not succeed.")
+	}
+}
+
+// The following test should not panic.
+func TestIssue5962(t *testing.T) {
+	bits := []int{4, 0, 0, 6, 4, 3, 2, 3, 3, 4, 4, 5, 0, 0, 0, 0,
+		5, 5, 6, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 11}
+	var h huffmanDecoder
+	if h.init(bits) {
+		t.Fatalf("Given sequence of bits is bad, and should not succeed.")
+	}
+}
+
+// The following test should not panic.
+func TestIssue6255(t *testing.T) {
+	bits1 := []int{1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 11}
+	bits2 := []int{11, 13}
+	var h huffmanDecoder
+	if !h.init(bits1) {
+		t.Fatalf("Given sequence of bits is good and should succeed.")
+	}
+	if h.init(bits2) {
+		t.Fatalf("Given sequence of bits is bad and should not succeed.")
+	}
+}
+
+func TestInvalidEncoding(t *testing.T) {
+	// Initialize Huffman decoder to recognize "0".
+	var h huffmanDecoder
+	if !h.init([]int{1}) {
+		t.Fatal("Failed to initialize Huffman decoder")
+	}
+
+	// Initialize decompressor with invalid Huffman coding.
+	var f decompressor
+	f.r = bytes.NewReader([]byte{0xff})
+
+	_, err := f.huffSym(&h)
+	if err == nil {
+		t.Fatal("Should have rejected invalid bit sequence")
+	}
+}
+
+func TestInvalidBits(t *testing.T) {
+	oversubscribed := []int{1, 2, 3, 4, 4, 5}
+	incomplete := []int{1, 2, 4, 4}
+	var h huffmanDecoder
+	if h.init(oversubscribed) {
+		t.Fatal("Should reject oversubscribed bit-length set")
+	}
+	if h.init(incomplete) {
+		t.Fatal("Should reject incomplete bit-length set")
+	}
+}
+
+func TestStreams(t *testing.T) {
+	// To verify any of these hexstrings as valid or invalid flate streams
+	// according to the C zlib library, you can use the Python wrapper library:
+	// >>> hex_string = "010100feff11"
+	// >>> import zlib
+	// >>> zlib.decompress(hex_string.decode("hex"), -15) # Negative means raw DEFLATE
+	// '\x11'
+
+	testCases := []struct {
+		desc   string // Description of the stream
+		stream string // Hexstring of the input DEFLATE stream
+		want   string // Expected result. Use "fail" to expect failure
+	}{{
+		"degenerate HCLenTree",
+		"05e0010000000000100000000000000000000000000000000000000000000000" +
+			"00000000000000000004",
+		"fail",
+	}, {
+		"complete HCLenTree, empty HLitTree, empty HDistTree",
+		"05e0010400000000000000000000000000000000000000000000000000000000" +
+			"00000000000000000010",
+		"fail",
+	}, {
+		"empty HCLenTree",
+		"05e0010000000000000000000000000000000000000000000000000000000000" +
+			"00000000000000000010",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree, use missing HDist symbol",
+		"000100feff000de0010400000000100000000000000000000000000000000000" +
+			"0000000000000000000000000000002c",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use missing HDist symbol",
+		"000100feff000de0010000000000000000000000000000000000000000000000" +
+			"00000000000000000610000000004070",
+		"fail",
+	}, {
+		"complete HCLenTree, empty HLitTree, empty HDistTree",
+		"05e0010400000000100400000000000000000000000000000000000000000000" +
+			"0000000000000000000000000008",
+		"fail",
+	}, {
+		"complete HCLenTree, empty HLitTree, degenerate HDistTree",
+		"05e0010400000000100400000000000000000000000000000000000000000000" +
+			"0000000000000000000800000008",
+		"fail",
+	}, {
+		"complete HCLenTree, degenerate HLitTree, degenerate HDistTree, use missing HLit symbol",
+		"05e0010400000000100000000000000000000000000000000000000000000000" +
+			"0000000000000000001c",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, too large HDistTree",
+		"edff870500000000200400000000000000000000000000000000000000000000" +
+			"000000000000000000080000000000000004",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree, excessive repeater code",
+		"edfd870500000000200400000000000000000000000000000000000000000000" +
+			"000000000000000000e8b100",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree of normal length 30",
+		"05fd01240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07000000fe01",
+		"",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree of excessive length 31",
+		"05fe01240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07000000fc03",
+		"fail",
+	}, {
+		"complete HCLenTree, over-subscribed HLitTree, empty HDistTree",
+		"05e001240000000000fcffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07f00f",
+		"fail",
+	}, {
+		"complete HCLenTree, under-subscribed HLitTree, empty HDistTree",
+		"05e001240000000000fcffffffffffffffffffffffffffffffffffffffffffff" +
+			"fffffffffcffffffff07f00f",
+		"fail",
+	}, {
+		"complete HCLenTree, complete HLitTree with single code, empty HDistTree",
+		"05e001240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07f00f",
+		"01",
+	}, {
+		"complete HCLenTree, complete HLitTree with multiple codes, empty HDistTree",
+		"05e301240000000000f8ffffffffffffffffffffffffffffffffffffffffffff" +
+			"ffffffffffffffffff07807f",
+		"01",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use valid HDist symbol",
+		"000100feff000de0010400000000100000000000000000000000000000000000" +
+			"0000000000000000000000000000003c",
+		"00000000",
+	}, {
+		"complete HCLenTree, degenerate HLitTree, degenerate HDistTree",
+		"05e0010400000000100000000000000000000000000000000000000000000000" +
+			"0000000000000000000c",
+		"",
+	}, {
+		"complete HCLenTree, degenerate HLitTree, empty HDistTree",
+		"05e0010400000000100000000000000000000000000000000000000000000000" +
+			"00000000000000000004",
+		"",
+	}, {
+		"complete HCLenTree, complete HLitTree, empty HDistTree, spanning repeater code",
+		"edfd870500000000200400000000000000000000000000000000000000000000" +
+			"000000000000000000e8b000",
+		"",
+	}, {
+		"complete HCLenTree with length codes, complete HLitTree, empty HDistTree",
+		"ede0010400000000100000000000000000000000000000000000000000000000" +
+			"0000000000000000000400004000",
+		"",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use valid HLit symbol 284 with count 31",
+		"000100feff00ede0010400000000100000000000000000000000000000000000" +
+			"000000000000000000000000000000040000407f00",
+		"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"0000000000000000000000000000000000000000000000000000000000000000" +
+			"000000",
+	}, {
+		"complete HCLenTree, complete HLitTree, degenerate HDistTree, use valid HLit and HDist symbols",
+		"0cc2010d00000082b0ac4aff0eb07d27060000ffff",
+		"616263616263",
+	}, {
+		"fixed block, use reserved symbol 287",
+		"33180700",
+		"fail",
+	}, {
+		"raw block",
+		"010100feff11",
+		"11",
+	}, {
+		"issue 10426 - over-subscribed HCLenTree causes a hang",
+		"344c4a4e494d4b070000ff2e2eff2e2e2e2e2eff",
+		"fail",
+	}, {
+		"issue 11030 - empty HDistTree unexpectedly leads to error",
+		"05c0070600000080400fff37a0ca",
+		"",
+	}, {
+		"issue 11033 - empty HDistTree unexpectedly leads to error",
+		"050fb109c020cca5d017dcbca044881ee1034ec149c8980bbc413c2ab35be9dc" +
+			"b1473449922449922411202306ee97b0383a521b4ffdcf3217f9f7d3adb701",
+		"3130303634342068652e706870005d05355f7ed957ff084a90925d19e3ebc6d0" +
+			"c6d7",
+	}}
+
+	for i, tc := range testCases {
+		data, err := hex.DecodeString(tc.stream)
+		if err != nil {
+			t.Fatal(err)
+		}
+		data, err = io.ReadAll(NewReader(bytes.NewReader(data)))
+		if tc.want == "fail" {
+			if err == nil {
+				t.Errorf("#%d (%s): got nil error, want non-nil", i, tc.desc)
+			}
+		} else {
+			if err != nil {
+				t.Errorf("#%d (%s): %v", i, tc.desc, err)
+				continue
+			}
+			if got := hex.EncodeToString(data); got != tc.want {
+				t.Errorf("#%d (%s):\ngot  %q\nwant %q", i, tc.desc, got, tc.want)
+			}
+
+		}
+	}
+}
+
+func TestTruncatedStreams(t *testing.T) {
+	const data = "\x00\f\x00\xf3\xffhello, world\x01\x00\x00\xff\xff"
+
+	for i := 0; i < len(data)-1; i++ {
+		r := NewReader(strings.NewReader(data[:i]))
+		_, err := io.Copy(io.Discard, r)
+		if err != io.ErrUnexpectedEOF {
+			t.Errorf("io.Copy(%d) on truncated stream: got %v, want %v", i, err, io.ErrUnexpectedEOF)
+		}
+	}
+}
+
+// Verify that flate.Reader.Read returns (n, io.EOF) instead
+// of (n, nil) + (0, io.EOF) when possible.
+//
+// This helps net/http.Transport reuse HTTP/1 connections more
+// aggressively.
+//
+// See https://github.com/google/go-github/pull/317 for background.
+func TestReaderEarlyEOF(t *testing.T) {
+	t.Parallel()
+	testSizes := []int{
+		1, 2, 3, 4, 5, 6, 7, 8,
+		100, 1000, 10000, 100000,
+		128, 1024, 16384, 131072,
+
+		// Testing multiples of windowSize triggers the case
+		// where Read will fail to return an early io.EOF.
+		windowSize * 1, windowSize * 2, windowSize * 3,
+	}
+
+	var maxSize int
+	for _, n := range testSizes {
+		if maxSize < n {
+			maxSize = n
+		}
+	}
+
+	readBuf := make([]byte, 40)
+	data := make([]byte, maxSize)
+	for i := range data {
+		data[i] = byte(i)
+	}
+
+	for _, sz := range testSizes {
+		if testing.Short() && sz > windowSize {
+			continue
+		}
+		for _, flush := range []bool{true, false} {
+			earlyEOF := true // Do we expect early io.EOF?
+
+			var buf bytes.Buffer
+			w, _ := NewWriter(&buf, 5)
+			w.Write(data[:sz])
+			if flush {
+				// If a Flush occurs after all the actual data, the flushing
+				// semantics dictate that we will observe a (0, io.EOF) since
+				// Read must return data before it knows that the stream ended.
+				w.Flush()
+				earlyEOF = false
+			}
+			w.Close()
+
+			r := NewReader(&buf)
+			for {
+				n, err := r.Read(readBuf)
+				if err == io.EOF {
+					// If the availWrite == windowSize, then that means that the
+					// previous Read returned because the write buffer was full
+					// and it just so happened that the stream had no more data.
+					// This situation is rare, but unavoidable.
+					if r.(*decompressor).dict.availWrite() == windowSize {
+						earlyEOF = false
+					}
+
+					if n == 0 && earlyEOF {
+						t.Errorf("On size:%d flush:%v, Read() = (0, io.EOF), want (n, io.EOF)", sz, flush)
+					}
+					if n != 0 && !earlyEOF {
+						t.Errorf("On size:%d flush:%v, Read() = (%d, io.EOF), want (0, io.EOF)", sz, flush, n)
+					}
+					break
+				}
+				if err != nil {
+					t.Fatal(err)
+				}
+			}
+		}
+	}
+}

image/internal/compress/flate/huffman_bit_writer.go

@@ -0,0 +1,704 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"io"
+)
+
+const (
+	// The largest offset code.
+	offsetCodeCount = 30
+
+	// The special code used to mark the end of a block.
+	endBlockMarker = 256
+
+	// The first length code.
+	lengthCodesStart = 257
+
+	// The number of codegen codes.
+	codegenCodeCount = 19
+	badCode          = 255
+
+	// bufferFlushSize indicates the buffer size
+	// after which bytes are flushed to the writer.
+	// Should preferably be a multiple of 6, since
+	// we accumulate 6 bytes between writes to the buffer.
+	bufferFlushSize = 240
+
+	// bufferSize is the actual output byte buffer size.
+	// It must have additional headroom for a flush
+	// which can contain up to 8 bytes.
+	bufferSize = bufferFlushSize + 8
+)
+
+// The number of extra bits needed by length code X - LENGTH_CODES_START.
+var lengthExtraBits = []int8{
+	/* 257 */ 0, 0, 0,
+	/* 260 */ 0, 0, 0, 0, 0, 1, 1, 1, 1, 2,
+	/* 270 */ 2, 2, 2, 3, 3, 3, 3, 4, 4, 4,
+	/* 280 */ 4, 5, 5, 5, 5, 0,
+}
+
+// The length indicated by length code X - LENGTH_CODES_START.
+var lengthBase = []uint32{
+	0, 1, 2, 3, 4, 5, 6, 7, 8, 10,
+	12, 14, 16, 20, 24, 28, 32, 40, 48, 56,
+	64, 80, 96, 112, 128, 160, 192, 224, 255,
+}
+
+// offset code word extra bits.
+var offsetExtraBits = []int8{
+	0, 0, 0, 0, 1, 1, 2, 2, 3, 3,
+	4, 4, 5, 5, 6, 6, 7, 7, 8, 8,
+	9, 9, 10, 10, 11, 11, 12, 12, 13, 13,
+}
+
+var offsetBase = []uint32{
+	0x000000, 0x000001, 0x000002, 0x000003, 0x000004,
+	0x000006, 0x000008, 0x00000c, 0x000010, 0x000018,
+	0x000020, 0x000030, 0x000040, 0x000060, 0x000080,
+	0x0000c0, 0x000100, 0x000180, 0x000200, 0x000300,
+	0x000400, 0x000600, 0x000800, 0x000c00, 0x001000,
+	0x001800, 0x002000, 0x003000, 0x004000, 0x006000,
+}
+
+// The odd order in which the codegen code sizes are written.
+var codegenOrder = []uint32{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
+
+type huffmanBitWriter struct {
+	// writer is the underlying writer.
+	// Do not use it directly; use the write method, which ensures
+	// that Write errors are sticky.
+	writer io.Writer
+
+	// Data waiting to be written is bytes[0:nbytes]
+	// and then the low nbits of bits.  Data is always written
+	// sequentially into the bytes array.
+	bits            uint64
+	nbits           uint
+	bytes           [bufferSize]byte
+	codegenFreq     [codegenCodeCount]int32
+	nbytes          int
+	literalFreq     []int32
+	offsetFreq      []int32
+	codegen         []uint8
+	literalEncoding *huffmanEncoder
+	offsetEncoding  *huffmanEncoder
+	codegenEncoding *huffmanEncoder
+	err             error
+}
+
+func newHuffmanBitWriter(w io.Writer) *huffmanBitWriter {
+	return &huffmanBitWriter{
+		writer:          w,
+		literalFreq:     make([]int32, maxNumLit),
+		offsetFreq:      make([]int32, offsetCodeCount),
+		codegen:         make([]uint8, maxNumLit+offsetCodeCount+1),
+		literalEncoding: newHuffmanEncoder(maxNumLit),
+		codegenEncoding: newHuffmanEncoder(codegenCodeCount),
+		offsetEncoding:  newHuffmanEncoder(offsetCodeCount),
+	}
+}
+
+func (w *huffmanBitWriter) reset(writer io.Writer) {
+	w.writer = writer
+	w.bits, w.nbits, w.nbytes, w.err = 0, 0, 0, nil
+}
+
+func (w *huffmanBitWriter) flush() {
+	if w.err != nil {
+		w.nbits = 0
+		return
+	}
+	n := w.nbytes
+	for w.nbits != 0 {
+		w.bytes[n] = byte(w.bits)
+		w.bits >>= 8
+		if w.nbits > 8 { // Avoid underflow
+			w.nbits -= 8
+		} else {
+			w.nbits = 0
+		}
+		n++
+	}
+	w.bits = 0
+	w.write(w.bytes[:n])
+	w.nbytes = 0
+}
+
+func (w *huffmanBitWriter) write(b []byte) {
+	if w.err != nil {
+		return
+	}
+	_, w.err = w.writer.Write(b)
+}
+
+func (w *huffmanBitWriter) writeBits(b int32, nb uint) {
+	if w.err != nil {
+		return
+	}
+	w.bits |= uint64(b) << w.nbits
+	w.nbits += nb
+	if w.nbits >= 48 {
+		bits := w.bits
+		w.bits >>= 48
+		w.nbits -= 48
+		n := w.nbytes
+		bytes := w.bytes[n : n+6]
+		bytes[0] = byte(bits)
+		bytes[1] = byte(bits >> 8)
+		bytes[2] = byte(bits >> 16)
+		bytes[3] = byte(bits >> 24)
+		bytes[4] = byte(bits >> 32)
+		bytes[5] = byte(bits >> 40)
+		n += 6
+		if n >= bufferFlushSize {
+			w.write(w.bytes[:n])
+			n = 0
+		}
+		w.nbytes = n
+	}
+}
+
+func (w *huffmanBitWriter) writeBytes(bytes []byte) {
+	if w.err != nil {
+		return
+	}
+	n := w.nbytes
+	if w.nbits&7 != 0 {
+		w.err = InternalError("writeBytes with unfinished bits")
+		return
+	}
+	for w.nbits != 0 {
+		w.bytes[n] = byte(w.bits)
+		w.bits >>= 8
+		w.nbits -= 8
+		n++
+	}
+	if n != 0 {
+		w.write(w.bytes[:n])
+	}
+	w.nbytes = 0
+	w.write(bytes)
+}
+
+// RFC 1951 3.2.7 specifies a special run-length encoding for specifying
+// the literal and offset lengths arrays (which are concatenated into a single
+// array).  This method generates that run-length encoding.
+//
+// The result is written into the codegen array, and the frequencies
+// of each code is written into the codegenFreq array.
+// Codes 0-15 are single byte codes. Codes 16-18 are followed by additional
+// information. Code badCode is an end marker
+//
+//  numLiterals      The number of literals in literalEncoding
+//  numOffsets       The number of offsets in offsetEncoding
+//  litenc, offenc   The literal and offset encoder to use
+func (w *huffmanBitWriter) generateCodegen(numLiterals int, numOffsets int, litEnc, offEnc *huffmanEncoder) {
+	for i := range w.codegenFreq {
+		w.codegenFreq[i] = 0
+	}
+	// Note that we are using codegen both as a temporary variable for holding
+	// a copy of the frequencies, and as the place where we put the result.
+	// This is fine because the output is always shorter than the input used
+	// so far.
+	codegen := w.codegen // cache
+	// Copy the concatenated code sizes to codegen. Put a marker at the end.
+	cgnl := codegen[:numLiterals]
+	for i := range cgnl {
+		cgnl[i] = uint8(litEnc.codes[i].len)
+	}
+
+	cgnl = codegen[numLiterals : numLiterals+numOffsets]
+	for i := range cgnl {
+		cgnl[i] = uint8(offEnc.codes[i].len)
+	}
+	codegen[numLiterals+numOffsets] = badCode
+
+	size := codegen[0]
+	count := 1
+	outIndex := 0
+	for inIndex := 1; size != badCode; inIndex++ {
+		// INVARIANT: We have seen "count" copies of size that have not yet
+		// had output generated for them.
+		nextSize := codegen[inIndex]
+		if nextSize == size {
+			count++
+			continue
+		}
+		// We need to generate codegen indicating "count" of size.
+		if size != 0 {
+			codegen[outIndex] = size
+			outIndex++
+			w.codegenFreq[size]++
+			count--
+			for count >= 3 {
+				n := 6
+				if n > count {
+					n = count
+				}
+				codegen[outIndex] = 16
+				outIndex++
+				codegen[outIndex] = uint8(n - 3)
+				outIndex++
+				w.codegenFreq[16]++
+				count -= n
+			}
+		} else {
+			for count >= 11 {
+				n := 138
+				if n > count {
+					n = count
+				}
+				codegen[outIndex] = 18
+				outIndex++
+				codegen[outIndex] = uint8(n - 11)
+				outIndex++
+				w.codegenFreq[18]++
+				count -= n
+			}
+			if count >= 3 {
+				// count >= 3 && count <= 10
+				codegen[outIndex] = 17
+				outIndex++
+				codegen[outIndex] = uint8(count - 3)
+				outIndex++
+				w.codegenFreq[17]++
+				count = 0
+			}
+		}
+		count--
+		for ; count >= 0; count-- {
+			codegen[outIndex] = size
+			outIndex++
+			w.codegenFreq[size]++
+		}
+		// Set up invariant for next time through the loop.
+		size = nextSize
+		count = 1
+	}
+	// Marker indicating the end of the codegen.
+	codegen[outIndex] = badCode
+}
+
+// dynamicSize returns the size of dynamically encoded data in bits.
+func (w *huffmanBitWriter) dynamicSize(litEnc, offEnc *huffmanEncoder, extraBits int) (size, numCodegens int) {
+	numCodegens = len(w.codegenFreq)
+	for numCodegens > 4 && w.codegenFreq[codegenOrder[numCodegens-1]] == 0 {
+		numCodegens--
+	}
+	header := 3 + 5 + 5 + 4 + (3 * numCodegens) +
+		w.codegenEncoding.bitLength(w.codegenFreq[:]) +
+		int(w.codegenFreq[16])*2 +
+		int(w.codegenFreq[17])*3 +
+		int(w.codegenFreq[18])*7
+	size = header +
+		litEnc.bitLength(w.literalFreq) +
+		offEnc.bitLength(w.offsetFreq) +
+		extraBits
+
+	return size, numCodegens
+}
+
+// fixedSize returns the size of dynamically encoded data in bits.
+func (w *huffmanBitWriter) fixedSize(extraBits int) int {
+	return 3 +
+		fixedLiteralEncoding.bitLength(w.literalFreq) +
+		fixedOffsetEncoding.bitLength(w.offsetFreq) +
+		extraBits
+}
+
+// storedSize calculates the stored size, including header.
+// The function returns the size in bits and whether the block
+// fits inside a single block.
+func (w *huffmanBitWriter) storedSize(in []byte) (int, bool) {
+	if in == nil {
+		return 0, false
+	}
+	if len(in) <= maxStoreBlockSize {
+		return (len(in) + 5) * 8, true
+	}
+	return 0, false
+}
+
+func (w *huffmanBitWriter) writeCode(c hcode) {
+	if w.err != nil {
+		return
+	}
+	w.bits |= uint64(c.code) << w.nbits
+	w.nbits += uint(c.len)
+	if w.nbits >= 48 {
+		bits := w.bits
+		w.bits >>= 48
+		w.nbits -= 48
+		n := w.nbytes
+		bytes := w.bytes[n : n+6]
+		bytes[0] = byte(bits)
+		bytes[1] = byte(bits >> 8)
+		bytes[2] = byte(bits >> 16)
+		bytes[3] = byte(bits >> 24)
+		bytes[4] = byte(bits >> 32)
+		bytes[5] = byte(bits >> 40)
+		n += 6
+		if n >= bufferFlushSize {
+			w.write(w.bytes[:n])
+			n = 0
+		}
+		w.nbytes = n
+	}
+}
+
+// Write the header of a dynamic Huffman block to the output stream.
+//
+//  numLiterals  The number of literals specified in codegen
+//  numOffsets   The number of offsets specified in codegen
+//  numCodegens  The number of codegens used in codegen
+func (w *huffmanBitWriter) writeDynamicHeader(numLiterals int, numOffsets int, numCodegens int, isEof bool) {
+	if w.err != nil {
+		return
+	}
+	var firstBits int32 = 4
+	if isEof {
+		firstBits = 5
+	}
+	w.writeBits(firstBits, 3)
+	w.writeBits(int32(numLiterals-257), 5)
+	w.writeBits(int32(numOffsets-1), 5)
+	w.writeBits(int32(numCodegens-4), 4)
+
+	for i := 0; i < numCodegens; i++ {
+		value := uint(w.codegenEncoding.codes[codegenOrder[i]].len)
+		w.writeBits(int32(value), 3)
+	}
+
+	i := 0
+	for {
+		var codeWord int = int(w.codegen[i])
+		i++
+		if codeWord == badCode {
+			break
+		}
+		w.writeCode(w.codegenEncoding.codes[uint32(codeWord)])
+
+		switch codeWord {
+		case 16:
+			w.writeBits(int32(w.codegen[i]), 2)
+			i++
+			break
+		case 17:
+			w.writeBits(int32(w.codegen[i]), 3)
+			i++
+			break
+		case 18:
+			w.writeBits(int32(w.codegen[i]), 7)
+			i++
+			break
+		}
+	}
+}
+
+func (w *huffmanBitWriter) writeStoredHeader(length int, isEof bool) {
+	if w.err != nil {
+		return
+	}
+	var flag int32
+	if isEof {
+		flag = 1
+	}
+	w.writeBits(flag, 3)
+	w.flush()
+	w.writeBits(int32(length), 16)
+	w.writeBits(int32(^uint16(length)), 16)
+}
+
+func (w *huffmanBitWriter) writeFixedHeader(isEof bool) {
+	if w.err != nil {
+		return
+	}
+	// Indicate that we are a fixed Huffman block
+	var value int32 = 2
+	if isEof {
+		value = 3
+	}
+	w.writeBits(value, 3)
+}
+
+// writeBlock will write a block of tokens with the smallest encoding.
+// The original input can be supplied, and if the huffman encoded data
+// is larger than the original bytes, the data will be written as a
+// stored block.
+// If the input is nil, the tokens will always be Huffman encoded.
+func (w *huffmanBitWriter) writeBlock(tokens []token, eof bool, input []byte) {
+	if w.err != nil {
+		return
+	}
+
+	tokens = append(tokens, endBlockMarker)
+	numLiterals, numOffsets := w.indexTokens(tokens)
+
+	var extraBits int
+	storedSize, storable := w.storedSize(input)
+	if storable {
+		// We only bother calculating the costs of the extra bits required by
+		// the length of offset fields (which will be the same for both fixed
+		// and dynamic encoding), if we need to compare those two encodings
+		// against stored encoding.
+		for lengthCode := lengthCodesStart + 8; lengthCode < numLiterals; lengthCode++ {
+			// First eight length codes have extra size = 0.
+			extraBits += int(w.literalFreq[lengthCode]) * int(lengthExtraBits[lengthCode-lengthCodesStart])
+		}
+		for offsetCode := 4; offsetCode < numOffsets; offsetCode++ {
+			// First four offset codes have extra size = 0.
+			extraBits += int(w.offsetFreq[offsetCode]) * int(offsetExtraBits[offsetCode])
+		}
+	}
+
+	// Figure out smallest code.
+	// Fixed Huffman baseline.
+	var literalEncoding = fixedLiteralEncoding
+	var offsetEncoding = fixedOffsetEncoding
+	var size = w.fixedSize(extraBits)
+
+	// Dynamic Huffman?
+	var numCodegens int
+
+	// Generate codegen and codegenFrequencies, which indicates how to encode
+	// the literalEncoding and the offsetEncoding.
+	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
+	w.codegenEncoding.generate(w.codegenFreq[:], 7)
+	dynamicSize, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, extraBits)
+
+	if dynamicSize < size {
+		size = dynamicSize
+		literalEncoding = w.literalEncoding
+		offsetEncoding = w.offsetEncoding
+	}
+
+	// Stored bytes?
+	if storable && storedSize < size {
+		w.writeStoredHeader(len(input), eof)
+		w.writeBytes(input)
+		return
+	}
+
+	// Huffman.
+	if literalEncoding == fixedLiteralEncoding {
+		w.writeFixedHeader(eof)
+	} else {
+		w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+	}
+
+	// Write the tokens.
+	w.writeTokens(tokens, literalEncoding.codes, offsetEncoding.codes)
+}
+
+// writeBlockDynamic encodes a block using a dynamic Huffman table.
+// This should be used if the symbols used have a disproportionate
+// histogram distribution.
+// If input is supplied and the compression savings are below 1/16th of the
+// input size the block is stored.
+func (w *huffmanBitWriter) writeBlockDynamic(tokens []token, eof bool, input []byte) {
+	if w.err != nil {
+		return
+	}
+
+	tokens = append(tokens, endBlockMarker)
+	numLiterals, numOffsets := w.indexTokens(tokens)
+
+	// Generate codegen and codegenFrequencies, which indicates how to encode
+	// the literalEncoding and the offsetEncoding.
+	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, w.offsetEncoding)
+	w.codegenEncoding.generate(w.codegenFreq[:], 7)
+	size, numCodegens := w.dynamicSize(w.literalEncoding, w.offsetEncoding, 0)
+
+	// Store bytes, if we don't get a reasonable improvement.
+	if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
+		w.writeStoredHeader(len(input), eof)
+		w.writeBytes(input)
+		return
+	}
+
+	// Write Huffman table.
+	w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+
+	// Write the tokens.
+	w.writeTokens(tokens, w.literalEncoding.codes, w.offsetEncoding.codes)
+}
+
+// indexTokens indexes a slice of tokens, and updates
+// literalFreq and offsetFreq, and generates literalEncoding
+// and offsetEncoding.
+// The number of literal and offset tokens is returned.
+func (w *huffmanBitWriter) indexTokens(tokens []token) (numLiterals, numOffsets int) {
+	for i := range w.literalFreq {
+		w.literalFreq[i] = 0
+	}
+	for i := range w.offsetFreq {
+		w.offsetFreq[i] = 0
+	}
+
+	for _, t := range tokens {
+		if t < matchType {
+			w.literalFreq[t.literal()]++
+			continue
+		}
+		length := t.length()
+		offset := t.offset()
+		w.literalFreq[lengthCodesStart+lengthCode(length)]++
+		w.offsetFreq[offsetCode(offset)]++
+	}
+
+	// get the number of literals
+	numLiterals = len(w.literalFreq)
+	for w.literalFreq[numLiterals-1] == 0 {
+		numLiterals--
+	}
+	// get the number of offsets
+	numOffsets = len(w.offsetFreq)
+	for numOffsets > 0 && w.offsetFreq[numOffsets-1] == 0 {
+		numOffsets--
+	}
+	if numOffsets == 0 {
+		// We haven't found a single match. If we want to go with the dynamic encoding,
+		// we should count at least one offset to be sure that the offset huffman tree could be encoded.
+		w.offsetFreq[0] = 1
+		numOffsets = 1
+	}
+	w.literalEncoding.generate(w.literalFreq, 15)
+	w.offsetEncoding.generate(w.offsetFreq, 15)
+	return
+}
+
+// writeTokens writes a slice of tokens to the output.
+// codes for literal and offset encoding must be supplied.
+func (w *huffmanBitWriter) writeTokens(tokens []token, leCodes, oeCodes []hcode) {
+	if w.err != nil {
+		return
+	}
+	for _, t := range tokens {
+		if t < matchType {
+			w.writeCode(leCodes[t.literal()])
+			continue
+		}
+		// Write the length
+		length := t.length()
+		lengthCode := lengthCode(length)
+		w.writeCode(leCodes[lengthCode+lengthCodesStart])
+		extraLengthBits := uint(lengthExtraBits[lengthCode])
+		if extraLengthBits > 0 {
+			extraLength := int32(length - lengthBase[lengthCode])
+			w.writeBits(extraLength, extraLengthBits)
+		}
+		// Write the offset
+		offset := t.offset()
+		offsetCode := offsetCode(offset)
+		w.writeCode(oeCodes[offsetCode])
+		extraOffsetBits := uint(offsetExtraBits[offsetCode])
+		if extraOffsetBits > 0 {
+			extraOffset := int32(offset - offsetBase[offsetCode])
+			w.writeBits(extraOffset, extraOffsetBits)
+		}
+	}
+}
+
+// huffOffset is a static offset encoder used for huffman only encoding.
+// It can be reused since we will not be encoding offset values.
+var huffOffset *huffmanEncoder
+
+func init() {
+	offsetFreq := make([]int32, offsetCodeCount)
+	offsetFreq[0] = 1
+	huffOffset = newHuffmanEncoder(offsetCodeCount)
+	huffOffset.generate(offsetFreq, 15)
+}
+
+// writeBlockHuff encodes a block of bytes as either
+// Huffman encoded literals or uncompressed bytes if the
+// results only gains very little from compression.
+func (w *huffmanBitWriter) writeBlockHuff(eof bool, input []byte) {
+	if w.err != nil {
+		return
+	}
+
+	// Clear histogram
+	for i := range w.literalFreq {
+		w.literalFreq[i] = 0
+	}
+
+	// Add everything as literals
+	histogram(input, w.literalFreq)
+
+	w.literalFreq[endBlockMarker] = 1
+
+	const numLiterals = endBlockMarker + 1
+	w.offsetFreq[0] = 1
+	const numOffsets = 1
+
+	w.literalEncoding.generate(w.literalFreq, 15)
+
+	// Figure out smallest code.
+	// Always use dynamic Huffman or Store
+	var numCodegens int
+
+	// Generate codegen and codegenFrequencies, which indicates how to encode
+	// the literalEncoding and the offsetEncoding.
+	w.generateCodegen(numLiterals, numOffsets, w.literalEncoding, huffOffset)
+	w.codegenEncoding.generate(w.codegenFreq[:], 7)
+	size, numCodegens := w.dynamicSize(w.literalEncoding, huffOffset, 0)
+
+	// Store bytes, if we don't get a reasonable improvement.
+	if ssize, storable := w.storedSize(input); storable && ssize < (size+size>>4) {
+		w.writeStoredHeader(len(input), eof)
+		w.writeBytes(input)
+		return
+	}
+
+	// Huffman.
+	w.writeDynamicHeader(numLiterals, numOffsets, numCodegens, eof)
+	encoding := w.literalEncoding.codes[:257]
+	n := w.nbytes
+	for _, t := range input {
+		// Bitwriting inlined, ~30% speedup
+		c := encoding[t]
+		w.bits |= uint64(c.code) << w.nbits
+		w.nbits += uint(c.len)
+		if w.nbits < 48 {
+			continue
+		}
+		// Store 6 bytes
+		bits := w.bits
+		w.bits >>= 48
+		w.nbits -= 48
+		bytes := w.bytes[n : n+6]
+		bytes[0] = byte(bits)
+		bytes[1] = byte(bits >> 8)
+		bytes[2] = byte(bits >> 16)
+		bytes[3] = byte(bits >> 24)
+		bytes[4] = byte(bits >> 32)
+		bytes[5] = byte(bits >> 40)
+		n += 6
+		if n < bufferFlushSize {
+			continue
+		}
+		w.write(w.bytes[:n])
+		if w.err != nil {
+			return // Return early in the event of write failures
+		}
+		n = 0
+	}
+	w.nbytes = n
+	w.writeCode(encoding[endBlockMarker])
+}
+
+// histogram accumulates a histogram of b in h.
+//
+// len(h) must be >= 256, and h's elements must be all zeroes.
+func histogram(b []byte, h []int32) {
+	h = h[:256]
+	for _, t := range b {
+		h[t]++
+	}
+}

image/internal/compress/flate/huffman_code.go

@@ -0,0 +1,349 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"math"
+	"math/bits"
+	"sort"
+)
+
+// hcode is a huffman code with a bit code and bit length.
+type hcode struct {
+	code, len uint16
+}
+
+type huffmanEncoder struct {
+	codes     []hcode
+	freqcache []literalNode
+	bitCount  [17]int32
+	lns       byLiteral // stored to avoid repeated allocation in generate
+	lfs       byFreq    // stored to avoid repeated allocation in generate
+}
+
+type literalNode struct {
+	literal uint16
+	freq    int32
+}
+
+// A levelInfo describes the state of the constructed tree for a given depth.
+type levelInfo struct {
+	// Our level.  for better printing
+	level int32
+
+	// The frequency of the last node at this level
+	lastFreq int32
+
+	// The frequency of the next character to add to this level
+	nextCharFreq int32
+
+	// The frequency of the next pair (from level below) to add to this level.
+	// Only valid if the "needed" value of the next lower level is 0.
+	nextPairFreq int32
+
+	// The number of chains remaining to generate for this level before moving
+	// up to the next level
+	needed int32
+}
+
+// set sets the code and length of an hcode.
+func (h *hcode) set(code uint16, length uint16) {
+	h.len = length
+	h.code = code
+}
+
+func maxNode() literalNode { return literalNode{math.MaxUint16, math.MaxInt32} }
+
+func newHuffmanEncoder(size int) *huffmanEncoder {
+	return &huffmanEncoder{codes: make([]hcode, size)}
+}
+
+// Generates a HuffmanCode corresponding to the fixed literal table
+func generateFixedLiteralEncoding() *huffmanEncoder {
+	h := newHuffmanEncoder(maxNumLit)
+	codes := h.codes
+	var ch uint16
+	for ch = 0; ch < maxNumLit; ch++ {
+		var bits uint16
+		var size uint16
+		switch {
+		case ch < 144:
+			// size 8, 000110000  .. 10111111
+			bits = ch + 48
+			size = 8
+			break
+		case ch < 256:
+			// size 9, 110010000 .. 111111111
+			bits = ch + 400 - 144
+			size = 9
+			break
+		case ch < 280:
+			// size 7, 0000000 .. 0010111
+			bits = ch - 256
+			size = 7
+			break
+		default:
+			// size 8, 11000000 .. 11000111
+			bits = ch + 192 - 280
+			size = 8
+		}
+		codes[ch] = hcode{code: reverseBits(bits, byte(size)), len: size}
+	}
+	return h
+}
+
+func generateFixedOffsetEncoding() *huffmanEncoder {
+	h := newHuffmanEncoder(30)
+	codes := h.codes
+	for ch := range codes {
+		codes[ch] = hcode{code: reverseBits(uint16(ch), 5), len: 5}
+	}
+	return h
+}
+
+var fixedLiteralEncoding *huffmanEncoder = generateFixedLiteralEncoding()
+var fixedOffsetEncoding *huffmanEncoder = generateFixedOffsetEncoding()
+
+func (h *huffmanEncoder) bitLength(freq []int32) int {
+	var total int
+	for i, f := range freq {
+		if f != 0 {
+			total += int(f) * int(h.codes[i].len)
+		}
+	}
+	return total
+}
+
+const maxBitsLimit = 16
+
+// Return the number of literals assigned to each bit size in the Huffman encoding
+//
+// This method is only called when list.length >= 3
+// The cases of 0, 1, and 2 literals are handled by special case code.
+//
+// list  An array of the literals with non-zero frequencies
+//             and their associated frequencies. The array is in order of increasing
+//             frequency, and has as its last element a special element with frequency
+//             MaxInt32
+// maxBits     The maximum number of bits that should be used to encode any literal.
+//             Must be less than 16.
+// return      An integer array in which array[i] indicates the number of literals
+//             that should be encoded in i bits.
+func (h *huffmanEncoder) bitCounts(list []literalNode, maxBits int32) []int32 {
+	if maxBits >= maxBitsLimit {
+		panic("flate: maxBits too large")
+	}
+	n := int32(len(list))
+	list = list[0 : n+1]
+	list[n] = maxNode()
+
+	// The tree can't have greater depth than n - 1, no matter what. This
+	// saves a little bit of work in some small cases
+	if maxBits > n-1 {
+		maxBits = n - 1
+	}
+
+	// Create information about each of the levels.
+	// A bogus "Level 0" whose sole purpose is so that
+	// level1.prev.needed==0.  This makes level1.nextPairFreq
+	// be a legitimate value that never gets chosen.
+	var levels [maxBitsLimit]levelInfo
+	// leafCounts[i] counts the number of literals at the left
+	// of ancestors of the rightmost node at level i.
+	// leafCounts[i][j] is the number of literals at the left
+	// of the level j ancestor.
+	var leafCounts [maxBitsLimit][maxBitsLimit]int32
+
+	for level := int32(1); level <= maxBits; level++ {
+		// For every level, the first two items are the first two characters.
+		// We initialize the levels as if we had already figured this out.
+		levels[level] = levelInfo{
+			level:        level,
+			lastFreq:     list[1].freq,
+			nextCharFreq: list[2].freq,
+			nextPairFreq: list[0].freq + list[1].freq,
+		}
+		leafCounts[level][level] = 2
+		if level == 1 {
+			levels[level].nextPairFreq = math.MaxInt32
+		}
+	}
+
+	// We need a total of 2*n - 2 items at top level and have already generated 2.
+	levels[maxBits].needed = 2*n - 4
+
+	level := maxBits
+	for {
+		l := &levels[level]
+		if l.nextPairFreq == math.MaxInt32 && l.nextCharFreq == math.MaxInt32 {
+			// We've run out of both leafs and pairs.
+			// End all calculations for this level.
+			// To make sure we never come back to this level or any lower level,
+			// set nextPairFreq impossibly large.
+			l.needed = 0
+			levels[level+1].nextPairFreq = math.MaxInt32
+			level++
+			continue
+		}
+
+		prevFreq := l.lastFreq
+		if l.nextCharFreq < l.nextPairFreq {
+			// The next item on this row is a leaf node.
+			n := leafCounts[level][level] + 1
+			l.lastFreq = l.nextCharFreq
+			// Lower leafCounts are the same of the previous node.
+			leafCounts[level][level] = n
+			l.nextCharFreq = list[n].freq
+		} else {
+			// The next item on this row is a pair from the previous row.
+			// nextPairFreq isn't valid until we generate two
+			// more values in the level below
+			l.lastFreq = l.nextPairFreq
+			// Take leaf counts from the lower level, except counts[level] remains the same.
+			copy(leafCounts[level][:level], leafCounts[level-1][:level])
+			levels[l.level-1].needed = 2
+		}
+
+		if l.needed--; l.needed == 0 {
+			// We've done everything we need to do for this level.
+			// Continue calculating one level up. Fill in nextPairFreq
+			// of that level with the sum of the two nodes we've just calculated on
+			// this level.
+			if l.level == maxBits {
+				// All done!
+				break
+			}
+			levels[l.level+1].nextPairFreq = prevFreq + l.lastFreq
+			level++
+		} else {
+			// If we stole from below, move down temporarily to replenish it.
+			for levels[level-1].needed > 0 {
+				level--
+			}
+		}
+	}
+
+	// Somethings is wrong if at the end, the top level is null or hasn't used
+	// all of the leaves.
+	if leafCounts[maxBits][maxBits] != n {
+		panic("leafCounts[maxBits][maxBits] != n")
+	}
+
+	bitCount := h.bitCount[:maxBits+1]
+	bits := 1
+	counts := &leafCounts[maxBits]
+	for level := maxBits; level > 0; level-- {
+		// chain.leafCount gives the number of literals requiring at least "bits"
+		// bits to encode.
+		bitCount[bits] = counts[level] - counts[level-1]
+		bits++
+	}
+	return bitCount
+}
+
+// Look at the leaves and assign them a bit count and an encoding as specified
+// in RFC 1951 3.2.2
+func (h *huffmanEncoder) assignEncodingAndSize(bitCount []int32, list []literalNode) {
+	code := uint16(0)
+	for n, bits := range bitCount {
+		code <<= 1
+		if n == 0 || bits == 0 {
+			continue
+		}
+		// The literals list[len(list)-bits] .. list[len(list)-bits]
+		// are encoded using "bits" bits, and get the values
+		// code, code + 1, ....  The code values are
+		// assigned in literal order (not frequency order).
+		chunk := list[len(list)-int(bits):]
+
+		h.lns.sort(chunk)
+		for _, node := range chunk {
+			h.codes[node.literal] = hcode{code: reverseBits(code, uint8(n)), len: uint16(n)}
+			code++
+		}
+		list = list[0 : len(list)-int(bits)]
+	}
+}
+
+// Update this Huffman Code object to be the minimum code for the specified frequency count.
+//
+// freq  An array of frequencies, in which frequency[i] gives the frequency of literal i.
+// maxBits  The maximum number of bits to use for any literal.
+func (h *huffmanEncoder) generate(freq []int32, maxBits int32) {
+	if h.freqcache == nil {
+		// Allocate a reusable buffer with the longest possible frequency table.
+		// Possible lengths are codegenCodeCount, offsetCodeCount and maxNumLit.
+		// The largest of these is maxNumLit, so we allocate for that case.
+		h.freqcache = make([]literalNode, maxNumLit+1)
+	}
+	list := h.freqcache[:len(freq)+1]
+	// Number of non-zero literals
+	count := 0
+	// Set list to be the set of all non-zero literals and their frequencies
+	for i, f := range freq {
+		if f != 0 {
+			list[count] = literalNode{uint16(i), f}
+			count++
+		} else {
+			list[count] = literalNode{}
+			h.codes[i].len = 0
+		}
+	}
+	list[len(freq)] = literalNode{}
+
+	list = list[:count]
+	if count <= 2 {
+		// Handle the small cases here, because they are awkward for the general case code. With
+		// two or fewer literals, everything has bit length 1.
+		for i, node := range list {
+			// "list" is in order of increasing literal value.
+			h.codes[node.literal].set(uint16(i), 1)
+		}
+		return
+	}
+	h.lfs.sort(list)
+
+	// Get the number of literals for each bit count
+	bitCount := h.bitCounts(list, maxBits)
+	// And do the assignment
+	h.assignEncodingAndSize(bitCount, list)
+}
+
+type byLiteral []literalNode
+
+func (s *byLiteral) sort(a []literalNode) {
+	*s = byLiteral(a)
+	sort.Sort(s)
+}
+
+func (s byLiteral) Len() int { return len(s) }
+
+func (s byLiteral) Less(i, j int) bool {
+	return s[i].literal < s[j].literal
+}
+
+func (s byLiteral) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+type byFreq []literalNode
+
+func (s *byFreq) sort(a []literalNode) {
+	*s = byFreq(a)
+	sort.Sort(s)
+}
+
+func (s byFreq) Len() int { return len(s) }
+
+func (s byFreq) Less(i, j int) bool {
+	if s[i].freq == s[j].freq {
+		return s[i].literal < s[j].literal
+	}
+	return s[i].freq < s[j].freq
+}
+
+func (s byFreq) Swap(i, j int) { s[i], s[j] = s[j], s[i] }
+
+func reverseBits(number uint16, bitLength byte) uint16 {
+	return bits.Reverse16(number << (16 - bitLength))
+}

image/internal/compress/flate/inflate.go

@@ -0,0 +1,825 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package flate implements the DEFLATE compressed data format, described in
+// RFC 1951.  The gzip and zlib packages implement access to DEFLATE-based file
+// formats.
+package flate
+
+import (
+	"bufio"
+	"io"
+	"math/bits"
+	"strconv"
+	"sync"
+)
+
+const (
+	maxCodeLen = 16 // max length of Huffman code
+	// The next three numbers come from the RFC section 3.2.7, with the
+	// additional proviso in section 3.2.5 which implies that distance codes
+	// 30 and 31 should never occur in compressed data.
+	maxNumLit  = 286
+	maxNumDist = 30
+	numCodes   = 19 // number of codes in Huffman meta-code
+)
+
+// Initialize the fixedHuffmanDecoder only once upon first use.
+var fixedOnce sync.Once
+var fixedHuffmanDecoder huffmanDecoder
+
+// A CorruptInputError reports the presence of corrupt input at a given offset.
+type CorruptInputError int64
+
+func (e CorruptInputError) Error() string {
+	return "flate: corrupt input before offset " + strconv.FormatInt(int64(e), 10)
+}
+
+// An InternalError reports an error in the flate code itself.
+type InternalError string
+
+func (e InternalError) Error() string { return "flate: internal error: " + string(e) }
+
+// A ReadError reports an error encountered while reading input.
+//
+// Deprecated: No longer returned.
+type ReadError struct {
+	Offset int64 // byte offset where error occurred
+	Err    error // error returned by underlying Read
+}
+
+func (e *ReadError) Error() string {
+	return "flate: read error at offset " + strconv.FormatInt(e.Offset, 10) + ": " + e.Err.Error()
+}
+
+// A WriteError reports an error encountered while writing output.
+//
+// Deprecated: No longer returned.
+type WriteError struct {
+	Offset int64 // byte offset where error occurred
+	Err    error // error returned by underlying Write
+}
+
+func (e *WriteError) Error() string {
+	return "flate: write error at offset " + strconv.FormatInt(e.Offset, 10) + ": " + e.Err.Error()
+}
+
+// Resetter resets a ReadCloser returned by NewReader or NewReaderDict
+// to switch to a new underlying Reader. This permits reusing a ReadCloser
+// instead of allocating a new one.
+type Resetter interface {
+	// Reset discards any buffered data and resets the Resetter as if it was
+	// newly initialized with the given reader.
+	Reset(r io.Reader, dict []byte) error
+}
+
+// The data structure for decoding Huffman tables is based on that of
+// zlib. There is a lookup table of a fixed bit width (huffmanChunkBits),
+// For codes smaller than the table width, there are multiple entries
+// (each combination of trailing bits has the same value). For codes
+// larger than the table width, the table contains a link to an overflow
+// table. The width of each entry in the link table is the maximum code
+// size minus the chunk width.
+//
+// Note that you can do a lookup in the table even without all bits
+// filled. Since the extra bits are zero, and the DEFLATE Huffman codes
+// have the property that shorter codes come before longer ones, the
+// bit length estimate in the result is a lower bound on the actual
+// number of bits.
+//
+// See the following:
+//	https://github.com/madler/zlib/raw/master/doc/algorithm.txt
+
+// chunk & 15 is number of bits
+// chunk >> 4 is value, including table link
+
+const (
+	huffmanChunkBits  = 9
+	huffmanNumChunks  = 1 << huffmanChunkBits
+	huffmanCountMask  = 15
+	huffmanValueShift = 4
+)
+
+type huffmanDecoder struct {
+	min      int                      // the minimum code length
+	chunks   [huffmanNumChunks]uint32 // chunks as described above
+	links    [][]uint32               // overflow links
+	linkMask uint32                   // mask the width of the link table
+}
+
+// Initialize Huffman decoding tables from array of code lengths.
+// Following this function, h is guaranteed to be initialized into a complete
+// tree (i.e., neither over-subscribed nor under-subscribed). The exception is a
+// degenerate case where the tree has only a single symbol with length 1. Empty
+// trees are permitted.
+func (h *huffmanDecoder) init(lengths []int) bool {
+	// Sanity enables additional runtime tests during Huffman
+	// table construction. It's intended to be used during
+	// development to supplement the currently ad-hoc unit tests.
+	const sanity = false
+
+	if h.min != 0 {
+		*h = huffmanDecoder{}
+	}
+
+	// Count number of codes of each length,
+	// compute min and max length.
+	var count [maxCodeLen]int
+	var min, max int
+	for _, n := range lengths {
+		if n == 0 {
+			continue
+		}
+		if min == 0 || n < min {
+			min = n
+		}
+		if n > max {
+			max = n
+		}
+		count[n]++
+	}
+
+	// Empty tree. The decompressor.huffSym function will fail later if the tree
+	// is used. Technically, an empty tree is only valid for the HDIST tree and
+	// not the HCLEN and HLIT tree. However, a stream with an empty HCLEN tree
+	// is guaranteed to fail since it will attempt to use the tree to decode the
+	// codes for the HLIT and HDIST trees. Similarly, an empty HLIT tree is
+	// guaranteed to fail later since the compressed data section must be
+	// composed of at least one symbol (the end-of-block marker).
+	if max == 0 {
+		return true
+	}
+
+	code := 0
+	var nextcode [maxCodeLen]int
+	for i := min; i <= max; i++ {
+		code <<= 1
+		nextcode[i] = code
+		code += count[i]
+	}
+
+	// Check that the coding is complete (i.e., that we've
+	// assigned all 2-to-the-max possible bit sequences).
+	// Exception: To be compatible with zlib, we also need to
+	// accept degenerate single-code codings. See also
+	// TestDegenerateHuffmanCoding.
+	if code != 1<<uint(max) && !(code == 1 && max == 1) {
+		return false
+	}
+
+	h.min = min
+	if max > huffmanChunkBits {
+		numLinks := 1 << (uint(max) - huffmanChunkBits)
+		h.linkMask = uint32(numLinks - 1)
+
+		// create link tables
+		link := nextcode[huffmanChunkBits+1] >> 1
+		h.links = make([][]uint32, huffmanNumChunks-link)
+		for j := uint(link); j < huffmanNumChunks; j++ {
+			reverse := int(bits.Reverse16(uint16(j)))
+			reverse >>= uint(16 - huffmanChunkBits)
+			off := j - uint(link)
+			if sanity && h.chunks[reverse] != 0 {
+				panic("impossible: overwriting existing chunk")
+			}
+			h.chunks[reverse] = uint32(off<<huffmanValueShift | (huffmanChunkBits + 1))
+			h.links[off] = make([]uint32, numLinks)
+		}
+	}
+
+	for i, n := range lengths {
+		if n == 0 {
+			continue
+		}
+		code := nextcode[n]
+		nextcode[n]++
+		chunk := uint32(i<<huffmanValueShift | n)
+		reverse := int(bits.Reverse16(uint16(code)))
+		reverse >>= uint(16 - n)
+		if n <= huffmanChunkBits {
+			for off := reverse; off < len(h.chunks); off += 1 << uint(n) {
+				// We should never need to overwrite
+				// an existing chunk. Also, 0 is
+				// never a valid chunk, because the
+				// lower 4 "count" bits should be
+				// between 1 and 15.
+				if sanity && h.chunks[off] != 0 {
+					panic("impossible: overwriting existing chunk")
+				}
+				h.chunks[off] = chunk
+			}
+		} else {
+			j := reverse & (huffmanNumChunks - 1)
+			if sanity && h.chunks[j]&huffmanCountMask != huffmanChunkBits+1 {
+				// Longer codes should have been
+				// associated with a link table above.
+				panic("impossible: not an indirect chunk")
+			}
+			value := h.chunks[j] >> huffmanValueShift
+			linktab := h.links[value]
+			reverse >>= huffmanChunkBits
+			for off := reverse; off < len(linktab); off += 1 << uint(n-huffmanChunkBits) {
+				if sanity && linktab[off] != 0 {
+					panic("impossible: overwriting existing chunk")
+				}
+				linktab[off] = chunk
+			}
+		}
+	}
+
+	if sanity {
+		// Above we've sanity checked that we never overwrote
+		// an existing entry. Here we additionally check that
+		// we filled the tables completely.
+		for i, chunk := range h.chunks {
+			if chunk == 0 {
+				// As an exception, in the degenerate
+				// single-code case, we allow odd
+				// chunks to be missing.
+				if code == 1 && i%2 == 1 {
+					continue
+				}
+				panic("impossible: missing chunk")
+			}
+		}
+		for _, linktab := range h.links {
+			for _, chunk := range linktab {
+				if chunk == 0 {
+					panic("impossible: missing chunk")
+				}
+			}
+		}
+	}
+
+	return true
+}
+
+// The actual read interface needed by NewReader.
+// If the passed in io.Reader does not also have ReadByte,
+// the NewReader will introduce its own buffering.
+type Reader interface {
+	io.Reader
+	io.ByteReader
+}
+
+// Decompress state.
+type decompressor struct {
+	// Input source.
+	r       Reader
+	roffset int64
+
+	// Input bits, in top of b.
+	b  uint32
+	nb uint
+
+	// Huffman decoders for literal/length, distance.
+	h1, h2 huffmanDecoder
+
+	// Length arrays used to define Huffman codes.
+	bits     *[maxNumLit + maxNumDist]int
+	codebits *[numCodes]int
+
+	// Output history, buffer.
+	dict dictDecoder
+
+	// Temporary buffer (avoids repeated allocation).
+	buf [4]byte
+
+	// Next step in the decompression,
+	// and decompression state.
+	step      func(*decompressor)
+	stepState int
+	final     bool
+	err       error
+	toRead    []byte
+	hl, hd    *huffmanDecoder
+	copyLen   int
+	copyDist  int
+}
+
+func (f *decompressor) nextBlock() {
+	for f.nb < 1+2 {
+		if f.err = f.moreBits(); f.err != nil {
+			return
+		}
+	}
+	f.final = f.b&1 == 1
+	f.b >>= 1
+	typ := f.b & 3
+	f.b >>= 2
+	f.nb -= 1 + 2
+	switch typ {
+	case 0:
+		f.dataBlock()
+	case 1:
+		// compressed, fixed Huffman tables
+		f.hl = &fixedHuffmanDecoder
+		f.hd = nil
+		f.huffmanBlock()
+	case 2:
+		// compressed, dynamic Huffman tables
+		if f.err = f.readHuffman(); f.err != nil {
+			break
+		}
+		f.hl = &f.h1
+		f.hd = &f.h2
+		f.huffmanBlock()
+	default:
+		// 3 is reserved.
+		f.err = CorruptInputError(f.roffset)
+	}
+}
+
+func (f *decompressor) Read(b []byte) (int, error) {
+	for {
+		if len(f.toRead) > 0 {
+			n := copy(b, f.toRead)
+			f.toRead = f.toRead[n:]
+			if len(f.toRead) == 0 {
+				return n, f.err
+			}
+			return n, nil
+		}
+		if f.err != nil {
+			return 0, f.err
+		}
+		f.step(f)
+		if f.err != nil && len(f.toRead) == 0 {
+			f.toRead = f.dict.readFlush() // Flush what's left in case of error
+		}
+	}
+}
+
+func (f *decompressor) Close() error {
+	if f.err == io.EOF {
+		return nil
+	}
+	return f.err
+}
+
+// RFC 1951 section 3.2.7.
+// Compression with dynamic Huffman codes
+
+var codeOrder = [...]int{16, 17, 18, 0, 8, 7, 9, 6, 10, 5, 11, 4, 12, 3, 13, 2, 14, 1, 15}
+
+func (f *decompressor) readHuffman() error {
+	// HLIT[5], HDIST[5], HCLEN[4].
+	for f.nb < 5+5+4 {
+		if err := f.moreBits(); err != nil {
+			return err
+		}
+	}
+	nlit := int(f.b&0x1F) + 257
+	if nlit > maxNumLit {
+		return CorruptInputError(f.roffset)
+	}
+	f.b >>= 5
+	ndist := int(f.b&0x1F) + 1
+	if ndist > maxNumDist {
+		return CorruptInputError(f.roffset)
+	}
+	f.b >>= 5
+	nclen := int(f.b&0xF) + 4
+	// numCodes is 19, so nclen is always valid.
+	f.b >>= 4
+	f.nb -= 5 + 5 + 4
+
+	// (HCLEN+4)*3 bits: code lengths in the magic codeOrder order.
+	for i := 0; i < nclen; i++ {
+		for f.nb < 3 {
+			if err := f.moreBits(); err != nil {
+				return err
+			}
+		}
+		f.codebits[codeOrder[i]] = int(f.b & 0x7)
+		f.b >>= 3
+		f.nb -= 3
+	}
+	for i := nclen; i < len(codeOrder); i++ {
+		f.codebits[codeOrder[i]] = 0
+	}
+	if !f.h1.init(f.codebits[0:]) {
+		return CorruptInputError(f.roffset)
+	}
+
+	// HLIT + 257 code lengths, HDIST + 1 code lengths,
+	// using the code length Huffman code.
+	for i, n := 0, nlit+ndist; i < n; {
+		x, err := f.huffSym(&f.h1)
+		if err != nil {
+			return err
+		}
+		if x < 16 {
+			// Actual length.
+			f.bits[i] = x
+			i++
+			continue
+		}
+		// Repeat previous length or zero.
+		var rep int
+		var nb uint
+		var b int
+		switch x {
+		default:
+			return InternalError("unexpected length code")
+		case 16:
+			rep = 3
+			nb = 2
+			if i == 0 {
+				return CorruptInputError(f.roffset)
+			}
+			b = f.bits[i-1]
+		case 17:
+			rep = 3
+			nb = 3
+			b = 0
+		case 18:
+			rep = 11
+			nb = 7
+			b = 0
+		}
+		for f.nb < nb {
+			if err := f.moreBits(); err != nil {
+				return err
+			}
+		}
+		rep += int(f.b & uint32(1<<nb-1))
+		f.b >>= nb
+		f.nb -= nb
+		if i+rep > n {
+			return CorruptInputError(f.roffset)
+		}
+		for j := 0; j < rep; j++ {
+			f.bits[i] = b
+			i++
+		}
+	}
+
+	if !f.h1.init(f.bits[0:nlit]) || !f.h2.init(f.bits[nlit:nlit+ndist]) {
+		return CorruptInputError(f.roffset)
+	}
+
+	// As an optimization, we can initialize the min bits to read at a time
+	// for the HLIT tree to the length of the EOB marker since we know that
+	// every block must terminate with one. This preserves the property that
+	// we never read any extra bytes after the end of the DEFLATE stream.
+	if f.h1.min < f.bits[endBlockMarker] {
+		f.h1.min = f.bits[endBlockMarker]
+	}
+
+	return nil
+}
+
+// Decode a single Huffman block from f.
+// hl and hd are the Huffman states for the lit/length values
+// and the distance values, respectively. If hd == nil, using the
+// fixed distance encoding associated with fixed Huffman blocks.
+func (f *decompressor) huffmanBlock() {
+	const (
+		stateInit = iota // Zero value must be stateInit
+		stateDict
+	)
+
+	switch f.stepState {
+	case stateInit:
+		goto readLiteral
+	case stateDict:
+		goto copyHistory
+	}
+
+readLiteral:
+	// Read literal and/or (length, distance) according to RFC section 3.2.3.
+	{
+		v, err := f.huffSym(f.hl)
+		if err != nil {
+			f.err = err
+			return
+		}
+		var n uint // number of bits extra
+		var length int
+		switch {
+		case v < 256:
+			f.dict.writeByte(byte(v))
+			if f.dict.availWrite() == 0 {
+				f.toRead = f.dict.readFlush()
+				f.step = (*decompressor).huffmanBlock
+				f.stepState = stateInit
+				return
+			}
+			goto readLiteral
+		case v == 256:
+			f.finishBlock()
+			return
+		// otherwise, reference to older data
+		case v < 265:
+			length = v - (257 - 3)
+			n = 0
+		case v < 269:
+			length = v*2 - (265*2 - 11)
+			n = 1
+		case v < 273:
+			length = v*4 - (269*4 - 19)
+			n = 2
+		case v < 277:
+			length = v*8 - (273*8 - 35)
+			n = 3
+		case v < 281:
+			length = v*16 - (277*16 - 67)
+			n = 4
+		case v < 285:
+			length = v*32 - (281*32 - 131)
+			n = 5
+		case v < maxNumLit:
+			length = 258
+			n = 0
+		default:
+			f.err = CorruptInputError(f.roffset)
+			return
+		}
+		if n > 0 {
+			for f.nb < n {
+				if err = f.moreBits(); err != nil {
+					f.err = err
+					return
+				}
+			}
+			length += int(f.b & uint32(1<<n-1))
+			f.b >>= n
+			f.nb -= n
+		}
+
+		var dist int
+		if f.hd == nil {
+			for f.nb < 5 {
+				if err = f.moreBits(); err != nil {
+					f.err = err
+					return
+				}
+			}
+			dist = int(bits.Reverse8(uint8(f.b & 0x1F << 3)))
+			f.b >>= 5
+			f.nb -= 5
+		} else {
+			if dist, err = f.huffSym(f.hd); err != nil {
+				f.err = err
+				return
+			}
+		}
+
+		switch {
+		case dist < 4:
+			dist++
+		case dist < maxNumDist:
+			nb := uint(dist-2) >> 1
+			// have 1 bit in bottom of dist, need nb more.
+			extra := (dist & 1) << nb
+			for f.nb < nb {
+				if err = f.moreBits(); err != nil {
+					f.err = err
+					return
+				}
+			}
+			extra |= int(f.b & uint32(1<<nb-1))
+			f.b >>= nb
+			f.nb -= nb
+			dist = 1<<(nb+1) + 1 + extra
+		default:
+			f.err = CorruptInputError(f.roffset)
+			return
+		}
+
+		// No check on length; encoding can be prescient.
+		if dist > f.dict.histSize() {
+			f.err = CorruptInputError(f.roffset)
+			return
+		}
+
+		f.copyLen, f.copyDist = length, dist
+		goto copyHistory
+	}
+
+copyHistory:
+	// Perform a backwards copy according to RFC section 3.2.3.
+	{
+		cnt := f.dict.tryWriteCopy(f.copyDist, f.copyLen)
+		if cnt == 0 {
+			cnt = f.dict.writeCopy(f.copyDist, f.copyLen)
+		}
+		f.copyLen -= cnt
+
+		if f.dict.availWrite() == 0 || f.copyLen > 0 {
+			f.toRead = f.dict.readFlush()
+			f.step = (*decompressor).huffmanBlock // We need to continue this work
+			f.stepState = stateDict
+			return
+		}
+		goto readLiteral
+	}
+}
+
+// Copy a single uncompressed data block from input to output.
+func (f *decompressor) dataBlock() {
+	// Uncompressed.
+	// Discard current half-byte.
+	f.nb = 0
+	f.b = 0
+
+	// Length then ones-complement of length.
+	nr, err := io.ReadFull(f.r, f.buf[0:4])
+	f.roffset += int64(nr)
+	if err != nil {
+		f.err = noEOF(err)
+		return
+	}
+	n := int(f.buf[0]) | int(f.buf[1])<<8
+	nn := int(f.buf[2]) | int(f.buf[3])<<8
+	if uint16(nn) != uint16(^n) {
+		f.err = CorruptInputError(f.roffset)
+		return
+	}
+
+	if n == 0 {
+		f.toRead = f.dict.readFlush()
+		f.finishBlock()
+		return
+	}
+
+	f.copyLen = n
+	f.copyData()
+}
+
+// copyData copies f.copyLen bytes from the underlying reader into f.hist.
+// It pauses for reads when f.hist is full.
+func (f *decompressor) copyData() {
+	buf := f.dict.writeSlice()
+	if len(buf) > f.copyLen {
+		buf = buf[:f.copyLen]
+	}
+
+	cnt, err := io.ReadFull(f.r, buf)
+	f.roffset += int64(cnt)
+	f.copyLen -= cnt
+	f.dict.writeMark(cnt)
+	if err != nil {
+		f.err = noEOF(err)
+		return
+	}
+
+	if f.dict.availWrite() == 0 || f.copyLen > 0 {
+		f.toRead = f.dict.readFlush()
+		f.step = (*decompressor).copyData
+		return
+	}
+	f.finishBlock()
+}
+
+func (f *decompressor) finishBlock() {
+	if f.final {
+		if f.dict.availRead() > 0 {
+			f.toRead = f.dict.readFlush()
+		}
+		f.err = io.EOF
+	}
+	f.step = (*decompressor).nextBlock
+}
+
+// noEOF returns err, unless err == io.EOF, in which case it returns io.ErrUnexpectedEOF.
+func noEOF(e error) error {
+	if e == io.EOF {
+		return io.ErrUnexpectedEOF
+	}
+	return e
+}
+
+func (f *decompressor) moreBits() error {
+	c, err := f.r.ReadByte()
+	if err != nil {
+		return noEOF(err)
+	}
+	f.roffset++
+	f.b |= uint32(c) << f.nb
+	f.nb += 8
+	return nil
+}
+
+// Read the next Huffman-encoded symbol from f according to h.
+func (f *decompressor) huffSym(h *huffmanDecoder) (int, error) {
+	// Since a huffmanDecoder can be empty or be composed of a degenerate tree
+	// with single element, huffSym must error on these two edge cases. In both
+	// cases, the chunks slice will be 0 for the invalid sequence, leading it
+	// satisfy the n == 0 check below.
+	n := uint(h.min)
+	// Optimization. Compiler isn't smart enough to keep f.b,f.nb in registers,
+	// but is smart enough to keep local variables in registers, so use nb and b,
+	// inline call to moreBits and reassign b,nb back to f on return.
+	nb, b := f.nb, f.b
+	for {
+		for nb < n {
+			c, err := f.r.ReadByte()
+			if err != nil {
+				f.b = b
+				f.nb = nb
+				return 0, noEOF(err)
+			}
+			f.roffset++
+			b |= uint32(c) << (nb & 31)
+			nb += 8
+		}
+		chunk := h.chunks[b&(huffmanNumChunks-1)]
+		n = uint(chunk & huffmanCountMask)
+		if n > huffmanChunkBits {
+			chunk = h.links[chunk>>huffmanValueShift][(b>>huffmanChunkBits)&h.linkMask]
+			n = uint(chunk & huffmanCountMask)
+		}
+		if n <= nb {
+			if n == 0 {
+				f.b = b
+				f.nb = nb
+				f.err = CorruptInputError(f.roffset)
+				return 0, f.err
+			}
+			f.b = b >> (n & 31)
+			f.nb = nb - n
+			return int(chunk >> huffmanValueShift), nil
+		}
+	}
+}
+
+func makeReader(r io.Reader) Reader {
+	if rr, ok := r.(Reader); ok {
+		return rr
+	}
+	return bufio.NewReader(r)
+}
+
+func fixedHuffmanDecoderInit() {
+	fixedOnce.Do(func() {
+		// These come from the RFC section 3.2.6.
+		var bits [288]int
+		for i := 0; i < 144; i++ {
+			bits[i] = 8
+		}
+		for i := 144; i < 256; i++ {
+			bits[i] = 9
+		}
+		for i := 256; i < 280; i++ {
+			bits[i] = 7
+		}
+		for i := 280; i < 288; i++ {
+			bits[i] = 8
+		}
+		fixedHuffmanDecoder.init(bits[:])
+	})
+}
+
+func (f *decompressor) Reset(r io.Reader, dict []byte) error {
+	*f = decompressor{
+		r:        makeReader(r),
+		bits:     f.bits,
+		codebits: f.codebits,
+		dict:     f.dict,
+		step:     (*decompressor).nextBlock,
+	}
+	f.dict.init(maxMatchOffset, dict)
+	return nil
+}
+
+// NewReader returns a new ReadCloser that can be used
+// to read the uncompressed version of r.
+// If r does not also implement io.ByteReader,
+// the decompressor may read more data than necessary from r.
+// It is the caller's responsibility to call Close on the ReadCloser
+// when finished reading.
+//
+// The ReadCloser returned by NewReader also implements Resetter.
+func NewReader(r io.Reader) io.ReadCloser {
+	fixedHuffmanDecoderInit()
+
+	var f decompressor
+	f.r = makeReader(r)
+	f.bits = new([maxNumLit + maxNumDist]int)
+	f.codebits = new([numCodes]int)
+	f.step = (*decompressor).nextBlock
+	f.dict.init(maxMatchOffset, nil)
+	return &f
+}
+
+// NewReaderDict is like NewReader but initializes the reader
+// with a preset dictionary. The returned Reader behaves as if
+// the uncompressed data stream started with the given dictionary,
+// which has already been read. NewReaderDict is typically used
+// to read data compressed by NewWriterDict.
+//
+// The ReadCloser returned by NewReader also implements Resetter.
+func NewReaderDict(r io.Reader, dict []byte) io.ReadCloser {
+	fixedHuffmanDecoderInit()
+
+	var f decompressor
+	f.r = makeReader(r)
+	f.bits = new([maxNumLit + maxNumDist]int)
+	f.codebits = new([numCodes]int)
+	f.step = (*decompressor).nextBlock
+	f.dict.init(maxMatchOffset, dict)
+	return &f
+}

image/internal/compress/flate/inflate_test.go

@@ -0,0 +1,97 @@
+// Copyright 2014 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"io"
+	"strings"
+	"testing"
+)
+
+func TestReset(t *testing.T) {
+	ss := []string{
+		"lorem ipsum izzle fo rizzle",
+		"the quick brown fox jumped over",
+	}
+
+	deflated := make([]bytes.Buffer, 2)
+	for i, s := range ss {
+		w, _ := NewWriter(&deflated[i], 1)
+		w.Write([]byte(s))
+		w.Close()
+	}
+
+	inflated := make([]bytes.Buffer, 2)
+
+	f := NewReader(&deflated[0])
+	io.Copy(&inflated[0], f)
+	f.(Resetter).Reset(&deflated[1], nil)
+	io.Copy(&inflated[1], f)
+	f.Close()
+
+	for i, s := range ss {
+		if s != inflated[i].String() {
+			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, inflated[i], s)
+		}
+	}
+}
+
+func TestReaderTruncated(t *testing.T) {
+	vectors := []struct{ input, output string }{
+		{"\x00", ""},
+		{"\x00\f", ""},
+		{"\x00\f\x00", ""},
+		{"\x00\f\x00\xf3\xff", ""},
+		{"\x00\f\x00\xf3\xffhello", "hello"},
+		{"\x00\f\x00\xf3\xffhello, world", "hello, world"},
+		{"\x02", ""},
+		{"\xf2H\xcd", "He"},
+		{"\xf2H͙0a\u0084\t", "Hel\x90\x90\x90\x90\x90"},
+		{"\xf2H͙0a\u0084\t\x00", "Hel\x90\x90\x90\x90\x90"},
+	}
+
+	for i, v := range vectors {
+		r := strings.NewReader(v.input)
+		zr := NewReader(r)
+		b, err := io.ReadAll(zr)
+		if err != io.ErrUnexpectedEOF {
+			t.Errorf("test %d, error mismatch: got %v, want io.ErrUnexpectedEOF", i, err)
+		}
+		if string(b) != v.output {
+			t.Errorf("test %d, output mismatch: got %q, want %q", i, b, v.output)
+		}
+	}
+}
+
+func TestResetDict(t *testing.T) {
+	dict := []byte("the lorem fox")
+	ss := []string{
+		"lorem ipsum izzle fo rizzle",
+		"the quick brown fox jumped over",
+	}
+
+	deflated := make([]bytes.Buffer, len(ss))
+	for i, s := range ss {
+		w, _ := NewWriterDict(&deflated[i], DefaultCompression, dict)
+		w.Write([]byte(s))
+		w.Close()
+	}
+
+	inflated := make([]bytes.Buffer, len(ss))
+
+	f := NewReader(nil)
+	for i := range inflated {
+		f.(Resetter).Reset(&deflated[i], dict)
+		io.Copy(&inflated[i], f)
+	}
+	f.Close()
+
+	for i, s := range ss {
+		if s != inflated[i].String() {
+			t.Errorf("inflated[%d]:\ngot  %q\nwant %q", i, inflated[i], s)
+		}
+	}
+}

image/internal/compress/flate/reader_test.go

@@ -0,0 +1,98 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"runtime"
+	"strings"
+	"testing"
+)
+
+func TestNlitOutOfRange(t *testing.T) {
+	// Trying to decode this bogus flate data, which has a Huffman table
+	// with nlit=288, should not panic.
+	io.Copy(io.Discard, NewReader(strings.NewReader(
+		"\xfc\xfe\x36\xe7\x5e\x1c\xef\xb3\x55\x58\x77\xb6\x56\xb5\x43\xf4"+
+			"\x6f\xf2\xd2\xe6\x3d\x99\xa0\x85\x8c\x48\xeb\xf8\xda\x83\x04\x2a"+
+			"\x75\xc4\xf8\x0f\x12\x11\xb9\xb4\x4b\x09\xa0\xbe\x8b\x91\x4c")))
+}
+
+var suites = []struct{ name, file string }{
+	// Digits is the digits of the irrational number e. Its decimal representation
+	// does not repeat, but there are only 10 possible digits, so it should be
+	// reasonably compressible.
+	{"Digits", "../testdata/e.txt"},
+	// Newton is Isaac Newtons's educational text on Opticks.
+	{"Newton", "../../testdata/Isaac.Newton-Opticks.txt"},
+}
+
+func BenchmarkDecode(b *testing.B) {
+	doBench(b, func(b *testing.B, buf0 []byte, level, n int) {
+		b.ReportAllocs()
+		b.StopTimer()
+		b.SetBytes(int64(n))
+
+		compressed := new(bytes.Buffer)
+		w, err := NewWriter(compressed, level)
+		if err != nil {
+			b.Fatal(err)
+		}
+		for i := 0; i < n; i += len(buf0) {
+			if len(buf0) > n-i {
+				buf0 = buf0[:n-i]
+			}
+			io.Copy(w, bytes.NewReader(buf0))
+		}
+		w.Close()
+		buf1 := compressed.Bytes()
+		buf0, compressed, w = nil, nil, nil
+		runtime.GC()
+		b.StartTimer()
+		for i := 0; i < b.N; i++ {
+			io.Copy(io.Discard, NewReader(bytes.NewReader(buf1)))
+		}
+	})
+}
+
+var levelTests = []struct {
+	name  string
+	level int
+}{
+	{"Huffman", HuffmanOnly},
+	{"Speed", BestSpeed},
+	{"Default", DefaultCompression},
+	{"Compression", BestCompression},
+}
+
+var sizes = []struct {
+	name string
+	n    int
+}{
+	{"1e4", 1e4},
+	{"1e5", 1e5},
+	{"1e6", 1e6},
+}
+
+func doBench(b *testing.B, f func(b *testing.B, buf []byte, level, n int)) {
+	for _, suite := range suites {
+		buf, err := os.ReadFile(suite.file)
+		if err != nil {
+			b.Fatal(err)
+		}
+		if len(buf) == 0 {
+			b.Fatalf("test file %q has no data", suite.file)
+		}
+		for _, l := range levelTests {
+			for _, s := range sizes {
+				b.Run(suite.name+"/"+l.name+"/"+s.name, func(b *testing.B) {
+					f(b, buf, l.level, s.n)
+				})
+			}
+		}
+	}
+}

image/internal/compress/flate/token.go

@@ -0,0 +1,97 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+const (
+	// 2 bits:   type   0 = literal  1=EOF  2=Match   3=Unused
+	// 8 bits:   xlength = length - MIN_MATCH_LENGTH
+	// 22 bits   xoffset = offset - MIN_OFFSET_SIZE, or literal
+	lengthShift = 22
+	offsetMask  = 1<<lengthShift - 1
+	typeMask    = 3 << 30
+	literalType = 0 << 30
+	matchType   = 1 << 30
+)
+
+// The length code for length X (MIN_MATCH_LENGTH <= X <= MAX_MATCH_LENGTH)
+// is lengthCodes[length - MIN_MATCH_LENGTH]
+var lengthCodes = [...]uint32{
+	0, 1, 2, 3, 4, 5, 6, 7, 8, 8,
+	9, 9, 10, 10, 11, 11, 12, 12, 12, 12,
+	13, 13, 13, 13, 14, 14, 14, 14, 15, 15,
+	15, 15, 16, 16, 16, 16, 16, 16, 16, 16,
+	17, 17, 17, 17, 17, 17, 17, 17, 18, 18,
+	18, 18, 18, 18, 18, 18, 19, 19, 19, 19,
+	19, 19, 19, 19, 20, 20, 20, 20, 20, 20,
+	20, 20, 20, 20, 20, 20, 20, 20, 20, 20,
+	21, 21, 21, 21, 21, 21, 21, 21, 21, 21,
+	21, 21, 21, 21, 21, 21, 22, 22, 22, 22,
+	22, 22, 22, 22, 22, 22, 22, 22, 22, 22,
+	22, 22, 23, 23, 23, 23, 23, 23, 23, 23,
+	23, 23, 23, 23, 23, 23, 23, 23, 24, 24,
+	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
+	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
+	24, 24, 24, 24, 24, 24, 24, 24, 24, 24,
+	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
+	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
+	25, 25, 25, 25, 25, 25, 25, 25, 25, 25,
+	25, 25, 26, 26, 26, 26, 26, 26, 26, 26,
+	26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
+	26, 26, 26, 26, 26, 26, 26, 26, 26, 26,
+	26, 26, 26, 26, 27, 27, 27, 27, 27, 27,
+	27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
+	27, 27, 27, 27, 27, 27, 27, 27, 27, 27,
+	27, 27, 27, 27, 27, 28,
+}
+
+var offsetCodes = [...]uint32{
+	0, 1, 2, 3, 4, 4, 5, 5, 6, 6, 6, 6, 7, 7, 7, 7,
+	8, 8, 8, 8, 8, 8, 8, 8, 9, 9, 9, 9, 9, 9, 9, 9,
+	10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10, 10,
+	11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11, 11,
+	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
+	12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12, 12,
+	13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
+	13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13, 13,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14, 14,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+	15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15, 15,
+}
+
+type token uint32
+
+// Convert a literal into a literal token.
+func literalToken(literal uint32) token { return token(literalType + literal) }
+
+// Convert a < xlength, xoffset > pair into a match token.
+func matchToken(xlength uint32, xoffset uint32) token {
+	return token(matchType + xlength<<lengthShift + xoffset)
+}
+
+// Returns the literal of a literal token
+func (t token) literal() uint32 { return uint32(t - literalType) }
+
+// Returns the extra offset of a match token
+func (t token) offset() uint32 { return uint32(t) & offsetMask }
+
+func (t token) length() uint32 { return uint32((t - matchType) >> lengthShift) }
+
+func lengthCode(len uint32) uint32 { return lengthCodes[len] }
+
+// Returns the offset code corresponding to a specific offset
+func offsetCode(off uint32) uint32 {
+	if off < uint32(len(offsetCodes)) {
+		return offsetCodes[off]
+	}
+	if off>>7 < uint32(len(offsetCodes)) {
+		return offsetCodes[off>>7] + 14
+	}
+	return offsetCodes[off>>14] + 28
+}

image/internal/compress/flate/writer_test.go

@@ -0,0 +1,237 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package flate
+
+import (
+	"bytes"
+	"fmt"
+	"io"
+	"math/rand"
+	"runtime"
+	"testing"
+)
+
+func BenchmarkEncode(b *testing.B) {
+	doBench(b, func(b *testing.B, buf0 []byte, level, n int) {
+		b.StopTimer()
+		b.SetBytes(int64(n))
+
+		buf1 := make([]byte, n)
+		for i := 0; i < n; i += len(buf0) {
+			if len(buf0) > n-i {
+				buf0 = buf0[:n-i]
+			}
+			copy(buf1[i:], buf0)
+		}
+		buf0 = nil
+		w, err := NewWriter(io.Discard, level)
+		if err != nil {
+			b.Fatal(err)
+		}
+		runtime.GC()
+		b.StartTimer()
+		for i := 0; i < b.N; i++ {
+			w.Reset(io.Discard)
+			w.Write(buf1)
+			w.Close()
+		}
+	})
+}
+
+// errorWriter is a writer that fails after N writes.
+type errorWriter struct {
+	N int
+}
+
+func (e *errorWriter) Write(b []byte) (int, error) {
+	if e.N <= 0 {
+		return 0, io.ErrClosedPipe
+	}
+	e.N--
+	return len(b), nil
+}
+
+// Test if errors from the underlying writer is passed upwards.
+func TestWriteError(t *testing.T) {
+	t.Parallel()
+	buf := new(bytes.Buffer)
+	n := 65536
+	if !testing.Short() {
+		n *= 4
+	}
+	for i := 0; i < n; i++ {
+		fmt.Fprintf(buf, "asdasfasf%d%dfghfgujyut%dyutyu\n", i, i, i)
+	}
+	in := buf.Bytes()
+	// We create our own buffer to control number of writes.
+	copyBuffer := make([]byte, 128)
+	for l := 0; l < 10; l++ {
+		for fail := 1; fail <= 256; fail *= 2 {
+			// Fail after 'fail' writes
+			ew := &errorWriter{N: fail}
+			w, err := NewWriter(ew, l)
+			if err != nil {
+				t.Fatalf("NewWriter: level %d: %v", l, err)
+			}
+			n, err := io.CopyBuffer(w, struct{ io.Reader }{bytes.NewBuffer(in)}, copyBuffer)
+			if err == nil {
+				t.Fatalf("Level %d: Expected an error, writer was %#v", l, ew)
+			}
+			n2, err := w.Write([]byte{1, 2, 2, 3, 4, 5})
+			if n2 != 0 {
+				t.Fatal("Level", l, "Expected 0 length write, got", n)
+			}
+			if err == nil {
+				t.Fatal("Level", l, "Expected an error")
+			}
+			err = w.Flush()
+			if err == nil {
+				t.Fatal("Level", l, "Expected an error on flush")
+			}
+			err = w.Close()
+			if err == nil {
+				t.Fatal("Level", l, "Expected an error on close")
+			}
+
+			w.Reset(io.Discard)
+			n2, err = w.Write([]byte{1, 2, 3, 4, 5, 6})
+			if err != nil {
+				t.Fatal("Level", l, "Got unexpected error after reset:", err)
+			}
+			if n2 == 0 {
+				t.Fatal("Level", l, "Got 0 length write, expected > 0")
+			}
+			if testing.Short() {
+				return
+			}
+		}
+	}
+}
+
+// Test if two runs produce identical results
+// even when writing different sizes to the Writer.
+func TestDeterministic(t *testing.T) {
+	t.Parallel()
+	for i := 0; i <= 9; i++ {
+		t.Run(fmt.Sprint("L", i), func(t *testing.T) { testDeterministic(i, t) })
+	}
+	t.Run("LM2", func(t *testing.T) { testDeterministic(-2, t) })
+}
+
+func testDeterministic(i int, t *testing.T) {
+	t.Parallel()
+	// Test so much we cross a good number of block boundaries.
+	var length = maxStoreBlockSize*30 + 500
+	if testing.Short() {
+		length /= 10
+	}
+
+	// Create a random, but compressible stream.
+	rng := rand.New(rand.NewSource(1))
+	t1 := make([]byte, length)
+	for i := range t1 {
+		t1[i] = byte(rng.Int63() & 7)
+	}
+
+	// Do our first encode.
+	var b1 bytes.Buffer
+	br := bytes.NewBuffer(t1)
+	w, err := NewWriter(&b1, i)
+	if err != nil {
+		t.Fatal(err)
+	}
+	// Use a very small prime sized buffer.
+	cbuf := make([]byte, 787)
+	_, err = io.CopyBuffer(w, struct{ io.Reader }{br}, cbuf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	w.Close()
+
+	// We choose a different buffer size,
+	// bigger than a maximum block, and also a prime.
+	var b2 bytes.Buffer
+	cbuf = make([]byte, 81761)
+	br2 := bytes.NewBuffer(t1)
+	w2, err := NewWriter(&b2, i)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, err = io.CopyBuffer(w2, struct{ io.Reader }{br2}, cbuf)
+	if err != nil {
+		t.Fatal(err)
+	}
+	w2.Close()
+
+	b1b := b1.Bytes()
+	b2b := b2.Bytes()
+
+	if !bytes.Equal(b1b, b2b) {
+		t.Errorf("level %d did not produce deterministic result, result mismatch, len(a) = %d, len(b) = %d", i, len(b1b), len(b2b))
+	}
+}
+
+// TestDeflateFast_Reset will test that encoding is consistent
+// across a warparound of the table offset.
+// See https://github.com/golang/go/issues/34121
+func TestDeflateFast_Reset(t *testing.T) {
+	buf := new(bytes.Buffer)
+	n := 65536
+
+	for i := 0; i < n; i++ {
+		fmt.Fprintf(buf, "asdfasdfasdfasdf%d%dfghfgujyut%dyutyu\n", i, i, i)
+	}
+	// This is specific to level 1.
+	const level = 1
+	in := buf.Bytes()
+	offset := 1
+	if testing.Short() {
+		offset = 256
+	}
+
+	// We do an encode with a clean buffer to compare.
+	var want bytes.Buffer
+	w, err := NewWriter(&want, level)
+	if err != nil {
+		t.Fatalf("NewWriter: level %d: %v", level, err)
+	}
+
+	// Output written 3 times.
+	w.Write(in)
+	w.Write(in)
+	w.Write(in)
+	w.Close()
+
+	for ; offset <= 256; offset *= 2 {
+		w, err := NewWriter(io.Discard, level)
+		if err != nil {
+			t.Fatalf("NewWriter: level %d: %v", level, err)
+		}
+
+		// Reset until we are right before the wraparound.
+		// Each reset adds maxMatchOffset to the offset.
+		for i := 0; i < (bufferReset-len(in)-offset-maxMatchOffset)/maxMatchOffset; i++ {
+			// skip ahead to where we are close to wrap around...
+			w.d.reset(nil)
+		}
+		var got bytes.Buffer
+		w.Reset(&got)
+
+		// Write 3 times, close.
+		for i := 0; i < 3; i++ {
+			_, err = w.Write(in)
+			if err != nil {
+				t.Fatal(err)
+			}
+		}
+		err = w.Close()
+		if err != nil {
+			t.Fatal(err)
+		}
+		if !bytes.Equal(got.Bytes(), want.Bytes()) {
+			t.Fatalf("output did not match at wraparound, len(want)  = %d, len(got) = %d", want.Len(), got.Len())
+		}
+	}
+}

image/internal/compress/zlib/example_test.go

@@ -0,0 +1,37 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package zlib_test
+
+import (
+	"bytes"
+	"compress/zlib"
+	"fmt"
+	"io"
+	"os"
+)
+
+func ExampleNewWriter() {
+	var b bytes.Buffer
+
+	w := zlib.NewWriter(&b)
+	w.Write([]byte("hello, world\n"))
+	w.Close()
+	fmt.Println(b.Bytes())
+	// Output: [120 156 202 72 205 201 201 215 81 40 207 47 202 73 225 2 4 0 0 255 255 33 231 4 147]
+}
+
+func ExampleNewReader() {
+	buff := []byte{120, 156, 202, 72, 205, 201, 201, 215, 81, 40, 207,
+		47, 202, 73, 225, 2, 4, 0, 0, 255, 255, 33, 231, 4, 147}
+	b := bytes.NewReader(buff)
+
+	r, err := zlib.NewReader(b)
+	if err != nil {
+		panic(err)
+	}
+	io.Copy(os.Stdout, r)
+	// Output: hello, world
+	r.Close()
+}

image/internal/compress/zlib/reader.go

@@ -0,0 +1,178 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+/*
+Package zlib implements reading and writing of zlib format compressed data,
+as specified in RFC 1950.
+
+The implementation provides filters that uncompress during reading
+and compress during writing.  For example, to write compressed data
+to a buffer:
+
+	var b bytes.Buffer
+	w := zlib.NewWriter(&b)
+	w.Write([]byte("hello, world\n"))
+	w.Close()
+
+and to read that data back:
+
+	r, err := zlib.NewReader(&b)
+	io.Copy(os.Stdout, r)
+	r.Close()
+*/
+package zlib
+
+import (
+	"bufio"
+	"errors"
+	"hash"
+	"hash/adler32"
+	"io"
+
+	"tinygo.org/x/drivers/image/internal/compress/flate"
+)
+
+const zlibDeflate = 8
+
+var (
+	// ErrChecksum is returned when reading ZLIB data that has an invalid checksum.
+	ErrChecksum = errors.New("zlib: invalid checksum")
+	// ErrDictionary is returned when reading ZLIB data that has an invalid dictionary.
+	ErrDictionary = errors.New("zlib: invalid dictionary")
+	// ErrHeader is returned when reading ZLIB data that has an invalid header.
+	ErrHeader = errors.New("zlib: invalid header")
+)
+
+type reader struct {
+	r            flate.Reader
+	decompressor io.ReadCloser
+	digest       hash.Hash32
+	err          error
+	scratch      [4]byte
+}
+
+// Resetter resets a ReadCloser returned by NewReader or NewReaderDict
+// to switch to a new underlying Reader. This permits reusing a ReadCloser
+// instead of allocating a new one.
+type Resetter interface {
+	// Reset discards any buffered data and resets the Resetter as if it was
+	// newly initialized with the given reader.
+	Reset(r io.Reader, dict []byte) error
+}
+
+// NewReader creates a new ReadCloser.
+// Reads from the returned ReadCloser read and decompress data from r.
+// If r does not implement io.ByteReader, the decompressor may read more
+// data than necessary from r.
+// It is the caller's responsibility to call Close on the ReadCloser when done.
+//
+// The ReadCloser returned by NewReader also implements Resetter.
+func NewReader(r io.Reader) (io.ReadCloser, error) {
+	return NewReaderDict(r, nil)
+}
+
+// NewReaderDict is like NewReader but uses a preset dictionary.
+// NewReaderDict ignores the dictionary if the compressed data does not refer to it.
+// If the compressed data refers to a different dictionary, NewReaderDict returns ErrDictionary.
+//
+// The ReadCloser returned by NewReaderDict also implements Resetter.
+func NewReaderDict(r io.Reader, dict []byte) (io.ReadCloser, error) {
+	z := new(reader)
+	err := z.Reset(r, dict)
+	if err != nil {
+		return nil, err
+	}
+	return z, nil
+}
+
+func (z *reader) Read(p []byte) (int, error) {
+	if z.err != nil {
+		return 0, z.err
+	}
+
+	var n int
+	n, z.err = z.decompressor.Read(p)
+	z.digest.Write(p[0:n])
+	if z.err != io.EOF {
+		// In the normal case we return here.
+		return n, z.err
+	}
+
+	// Finished file; check checksum.
+	if _, err := io.ReadFull(z.r, z.scratch[0:4]); err != nil {
+		if err == io.EOF {
+			err = io.ErrUnexpectedEOF
+		}
+		z.err = err
+		return n, z.err
+	}
+	// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
+	checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3])
+	if checksum != z.digest.Sum32() {
+		z.err = ErrChecksum
+		return n, z.err
+	}
+	return n, io.EOF
+}
+
+// Calling Close does not close the wrapped io.Reader originally passed to NewReader.
+// In order for the ZLIB checksum to be verified, the reader must be
+// fully consumed until the io.EOF.
+func (z *reader) Close() error {
+	if z.err != nil && z.err != io.EOF {
+		return z.err
+	}
+	z.err = z.decompressor.Close()
+	return z.err
+}
+
+func (z *reader) Reset(r io.Reader, dict []byte) error {
+	*z = reader{decompressor: z.decompressor}
+	if fr, ok := r.(flate.Reader); ok {
+		z.r = fr
+	} else {
+		z.r = bufio.NewReader(r)
+	}
+
+	// Read the header (RFC 1950 section 2.2.).
+	_, z.err = io.ReadFull(z.r, z.scratch[0:2])
+	if z.err != nil {
+		if z.err == io.EOF {
+			z.err = io.ErrUnexpectedEOF
+		}
+		return z.err
+	}
+	h := uint(z.scratch[0])<<8 | uint(z.scratch[1])
+	if (z.scratch[0]&0x0f != zlibDeflate) || (h%31 != 0) {
+		z.err = ErrHeader
+		return z.err
+	}
+	haveDict := z.scratch[1]&0x20 != 0
+	if haveDict {
+		_, z.err = io.ReadFull(z.r, z.scratch[0:4])
+		if z.err != nil {
+			if z.err == io.EOF {
+				z.err = io.ErrUnexpectedEOF
+			}
+			return z.err
+		}
+		checksum := uint32(z.scratch[0])<<24 | uint32(z.scratch[1])<<16 | uint32(z.scratch[2])<<8 | uint32(z.scratch[3])
+		if checksum != adler32.Checksum(dict) {
+			z.err = ErrDictionary
+			return z.err
+		}
+	}
+
+	if z.decompressor == nil {
+		if haveDict {
+			z.decompressor = flate.NewReaderDict(z.r, dict)
+		} else {
+			z.decompressor = flate.NewReader(z.r)
+		}
+	} else {
+		z.decompressor.(flate.Resetter).Reset(z.r, dict)
+	}
+	z.digest = adler32.New()
+	return nil
+}

image/internal/compress/zlib/reader_test.go

@@ -0,0 +1,179 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package zlib
+
+import (
+	"bytes"
+	"io"
+	"testing"
+)
+
+type zlibTest struct {
+	desc       string
+	raw        string
+	compressed []byte
+	dict       []byte
+	err        error
+}
+
+// Compare-to-golden test data was generated by the ZLIB example program at
+// https://www.zlib.net/zpipe.c
+
+var zlibTests = []zlibTest{
+	{
+		"truncated empty",
+		"",
+		[]byte{},
+		nil,
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"truncated dict",
+		"",
+		[]byte{0x78, 0xbb},
+		[]byte{0x00},
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"truncated checksum",
+		"",
+		[]byte{0x78, 0xbb, 0x00, 0x01, 0x00, 0x01, 0xca, 0x48,
+			0xcd, 0xc9, 0xc9, 0xd7, 0x51, 0x28, 0xcf, 0x2f,
+			0xca, 0x49, 0x01, 0x04, 0x00, 0x00, 0xff, 0xff,
+		},
+		[]byte{0x00},
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"empty",
+		"",
+		[]byte{0x78, 0x9c, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01},
+		nil,
+		nil,
+	},
+	{
+		"goodbye",
+		"goodbye, world",
+		[]byte{
+			0x78, 0x9c, 0x4b, 0xcf, 0xcf, 0x4f, 0x49, 0xaa,
+			0x4c, 0xd5, 0x51, 0x28, 0xcf, 0x2f, 0xca, 0x49,
+			0x01, 0x00, 0x28, 0xa5, 0x05, 0x5e,
+		},
+		nil,
+		nil,
+	},
+	{
+		"bad header",
+		"",
+		[]byte{0x78, 0x9f, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01},
+		nil,
+		ErrHeader,
+	},
+	{
+		"bad checksum",
+		"",
+		[]byte{0x78, 0x9c, 0x03, 0x00, 0x00, 0x00, 0x00, 0xff},
+		nil,
+		ErrChecksum,
+	},
+	{
+		"not enough data",
+		"",
+		[]byte{0x78, 0x9c, 0x03, 0x00, 0x00, 0x00},
+		nil,
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"excess data is silently ignored",
+		"",
+		[]byte{
+			0x78, 0x9c, 0x03, 0x00, 0x00, 0x00, 0x00, 0x01,
+			0x78, 0x9c, 0xff,
+		},
+		nil,
+		nil,
+	},
+	{
+		"dictionary",
+		"Hello, World!\n",
+		[]byte{
+			0x78, 0xbb, 0x1c, 0x32, 0x04, 0x27, 0xf3, 0x00,
+			0xb1, 0x75, 0x20, 0x1c, 0x45, 0x2e, 0x00, 0x24,
+			0x12, 0x04, 0x74,
+		},
+		[]byte{
+			0x48, 0x65, 0x6c, 0x6c, 0x6f, 0x20, 0x57, 0x6f, 0x72, 0x6c, 0x64, 0x0a,
+		},
+		nil,
+	},
+	{
+		"wrong dictionary",
+		"",
+		[]byte{
+			0x78, 0xbb, 0x1c, 0x32, 0x04, 0x27, 0xf3, 0x00,
+			0xb1, 0x75, 0x20, 0x1c, 0x45, 0x2e, 0x00, 0x24,
+			0x12, 0x04, 0x74,
+		},
+		[]byte{
+			0x48, 0x65, 0x6c, 0x6c,
+		},
+		ErrDictionary,
+	},
+	{
+		"truncated zlib stream amid raw-block",
+		"hello",
+		[]byte{
+			0x78, 0x9c, 0x00, 0x0c, 0x00, 0xf3, 0xff, 0x68, 0x65, 0x6c, 0x6c, 0x6f,
+		},
+		nil,
+		io.ErrUnexpectedEOF,
+	},
+	{
+		"truncated zlib stream amid fixed-block",
+		"He",
+		[]byte{
+			0x78, 0x9c, 0xf2, 0x48, 0xcd,
+		},
+		nil,
+		io.ErrUnexpectedEOF,
+	},
+}
+
+func TestDecompressor(t *testing.T) {
+	b := new(bytes.Buffer)
+	for _, tt := range zlibTests {
+		in := bytes.NewReader(tt.compressed)
+		zr, err := NewReaderDict(in, tt.dict)
+		if err != nil {
+			if err != tt.err {
+				t.Errorf("%s: NewReader: %s", tt.desc, err)
+			}
+			continue
+		}
+		defer zr.Close()
+
+		// Read and verify correctness of data.
+		b.Reset()
+		n, err := io.Copy(b, zr)
+		if err != nil {
+			if err != tt.err {
+				t.Errorf("%s: io.Copy: %v want %v", tt.desc, err, tt.err)
+			}
+			continue
+		}
+		s := b.String()
+		if s != tt.raw {
+			t.Errorf("%s: got %d-byte %q want %d-byte %q", tt.desc, n, s, len(tt.raw), tt.raw)
+		}
+
+		// Check for sticky errors.
+		if n, err := zr.Read([]byte{0}); n != 0 || err != io.EOF {
+			t.Errorf("%s: Read() = (%d, %v), want (0, io.EOF)", tt.desc, n, err)
+		}
+		if err := zr.Close(); err != nil {
+			t.Errorf("%s: Close() = %v, want nil", tt.desc, err)
+		}
+	}
+}

image/internal/compress/zlib/writer.go

@@ -0,0 +1,193 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package zlib
+
+import (
+	"compress/flate"
+	"encoding/binary"
+	"fmt"
+	"hash"
+	"hash/adler32"
+	"io"
+)
+
+// These constants are copied from the flate package, so that code that imports
+// "compress/zlib" does not also have to import "compress/flate".
+const (
+	NoCompression      = flate.NoCompression
+	BestSpeed          = flate.BestSpeed
+	BestCompression    = flate.BestCompression
+	DefaultCompression = flate.DefaultCompression
+	HuffmanOnly        = flate.HuffmanOnly
+)
+
+// A Writer takes data written to it and writes the compressed
+// form of that data to an underlying writer (see NewWriter).
+type Writer struct {
+	w           io.Writer
+	level       int
+	dict        []byte
+	compressor  *flate.Writer
+	digest      hash.Hash32
+	err         error
+	scratch     [4]byte
+	wroteHeader bool
+}
+
+// NewWriter creates a new Writer.
+// Writes to the returned Writer are compressed and written to w.
+//
+// It is the caller's responsibility to call Close on the Writer when done.
+// Writes may be buffered and not flushed until Close.
+func NewWriter(w io.Writer) *Writer {
+	z, _ := NewWriterLevelDict(w, DefaultCompression, nil)
+	return z
+}
+
+// NewWriterLevel is like NewWriter but specifies the compression level instead
+// of assuming DefaultCompression.
+//
+// The compression level can be DefaultCompression, NoCompression, HuffmanOnly
+// or any integer value between BestSpeed and BestCompression inclusive.
+// The error returned will be nil if the level is valid.
+func NewWriterLevel(w io.Writer, level int) (*Writer, error) {
+	return NewWriterLevelDict(w, level, nil)
+}
+
+// NewWriterLevelDict is like NewWriterLevel but specifies a dictionary to
+// compress with.
+//
+// The dictionary may be nil. If not, its contents should not be modified until
+// the Writer is closed.
+func NewWriterLevelDict(w io.Writer, level int, dict []byte) (*Writer, error) {
+	if level < HuffmanOnly || level > BestCompression {
+		return nil, fmt.Errorf("zlib: invalid compression level: %d", level)
+	}
+	return &Writer{
+		w:     w,
+		level: level,
+		dict:  dict,
+	}, nil
+}
+
+// Reset clears the state of the Writer z such that it is equivalent to its
+// initial state from NewWriterLevel or NewWriterLevelDict, but instead writing
+// to w.
+func (z *Writer) Reset(w io.Writer) {
+	z.w = w
+	// z.level and z.dict left unchanged.
+	if z.compressor != nil {
+		z.compressor.Reset(w)
+	}
+	if z.digest != nil {
+		z.digest.Reset()
+	}
+	z.err = nil
+	z.scratch = [4]byte{}
+	z.wroteHeader = false
+}
+
+// writeHeader writes the ZLIB header.
+func (z *Writer) writeHeader() (err error) {
+	z.wroteHeader = true
+	// ZLIB has a two-byte header (as documented in RFC 1950).
+	// The first four bits is the CINFO (compression info), which is 7 for the default deflate window size.
+	// The next four bits is the CM (compression method), which is 8 for deflate.
+	z.scratch[0] = 0x78
+	// The next two bits is the FLEVEL (compression level). The four values are:
+	// 0=fastest, 1=fast, 2=default, 3=best.
+	// The next bit, FDICT, is set if a dictionary is given.
+	// The final five FCHECK bits form a mod-31 checksum.
+	switch z.level {
+	case -2, 0, 1:
+		z.scratch[1] = 0 << 6
+	case 2, 3, 4, 5:
+		z.scratch[1] = 1 << 6
+	case 6, -1:
+		z.scratch[1] = 2 << 6
+	case 7, 8, 9:
+		z.scratch[1] = 3 << 6
+	default:
+		panic("unreachable")
+	}
+	if z.dict != nil {
+		z.scratch[1] |= 1 << 5
+	}
+	z.scratch[1] += uint8(31 - (uint16(z.scratch[0])<<8+uint16(z.scratch[1]))%31)
+	if _, err = z.w.Write(z.scratch[0:2]); err != nil {
+		return err
+	}
+	if z.dict != nil {
+		// The next four bytes are the Adler-32 checksum of the dictionary.
+		binary.BigEndian.PutUint32(z.scratch[:], adler32.Checksum(z.dict))
+		if _, err = z.w.Write(z.scratch[0:4]); err != nil {
+			return err
+		}
+	}
+	if z.compressor == nil {
+		// Initialize deflater unless the Writer is being reused
+		// after a Reset call.
+		z.compressor, err = flate.NewWriterDict(z.w, z.level, z.dict)
+		if err != nil {
+			return err
+		}
+		z.digest = adler32.New()
+	}
+	return nil
+}
+
+// Write writes a compressed form of p to the underlying io.Writer. The
+// compressed bytes are not necessarily flushed until the Writer is closed or
+// explicitly flushed.
+func (z *Writer) Write(p []byte) (n int, err error) {
+	if !z.wroteHeader {
+		z.err = z.writeHeader()
+	}
+	if z.err != nil {
+		return 0, z.err
+	}
+	if len(p) == 0 {
+		return 0, nil
+	}
+	n, err = z.compressor.Write(p)
+	if err != nil {
+		z.err = err
+		return
+	}
+	z.digest.Write(p)
+	return
+}
+
+// Flush flushes the Writer to its underlying io.Writer.
+func (z *Writer) Flush() error {
+	if !z.wroteHeader {
+		z.err = z.writeHeader()
+	}
+	if z.err != nil {
+		return z.err
+	}
+	z.err = z.compressor.Flush()
+	return z.err
+}
+
+// Close closes the Writer, flushing any unwritten data to the underlying
+// io.Writer, but does not close the underlying io.Writer.
+func (z *Writer) Close() error {
+	if !z.wroteHeader {
+		z.err = z.writeHeader()
+	}
+	if z.err != nil {
+		return z.err
+	}
+	z.err = z.compressor.Close()
+	if z.err != nil {
+		return z.err
+	}
+	checksum := z.digest.Sum32()
+	// ZLIB (RFC 1950) is big-endian, unlike GZIP (RFC 1952).
+	binary.BigEndian.PutUint32(z.scratch[:], checksum)
+	_, z.err = z.w.Write(z.scratch[0:4])
+	return z.err
+}

image/internal/compress/zlib/writer_test.go

@@ -0,0 +1,224 @@
+// Copyright 2009 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package zlib
+
+import (
+	"bytes"
+	"fmt"
+	"internal/testenv"
+	"io"
+	"os"
+	"testing"
+)
+
+var filenames = []string{
+	"../testdata/gettysburg.txt",
+	"../testdata/e.txt",
+	"../testdata/pi.txt",
+}
+
+var data = []string{
+	"test a reasonable sized string that can be compressed",
+}
+
+// Tests that compressing and then decompressing the given file at the given compression level and dictionary
+// yields equivalent bytes to the original file.
+func testFileLevelDict(t *testing.T, fn string, level int, d string) {
+	// Read the file, as golden output.
+	golden, err := os.Open(fn)
+	if err != nil {
+		t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err)
+		return
+	}
+	defer golden.Close()
+	b0, err0 := io.ReadAll(golden)
+	if err0 != nil {
+		t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err0)
+		return
+	}
+	testLevelDict(t, fn, b0, level, d)
+}
+
+func testLevelDict(t *testing.T, fn string, b0 []byte, level int, d string) {
+	// Make dictionary, if given.
+	var dict []byte
+	if d != "" {
+		dict = []byte(d)
+	}
+
+	// Push data through a pipe that compresses at the write end, and decompresses at the read end.
+	piper, pipew := io.Pipe()
+	defer piper.Close()
+	go func() {
+		defer pipew.Close()
+		zlibw, err := NewWriterLevelDict(pipew, level, dict)
+		if err != nil {
+			t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err)
+			return
+		}
+		defer zlibw.Close()
+		_, err = zlibw.Write(b0)
+		if err != nil {
+			t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err)
+			return
+		}
+	}()
+	zlibr, err := NewReaderDict(piper, dict)
+	if err != nil {
+		t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err)
+		return
+	}
+	defer zlibr.Close()
+
+	// Compare the decompressed data.
+	b1, err1 := io.ReadAll(zlibr)
+	if err1 != nil {
+		t.Errorf("%s (level=%d, dict=%q): %v", fn, level, d, err1)
+		return
+	}
+	if len(b0) != len(b1) {
+		t.Errorf("%s (level=%d, dict=%q): length mismatch %d versus %d", fn, level, d, len(b0), len(b1))
+		return
+	}
+	for i := 0; i < len(b0); i++ {
+		if b0[i] != b1[i] {
+			t.Errorf("%s (level=%d, dict=%q): mismatch at %d, 0x%02x versus 0x%02x\n", fn, level, d, i, b0[i], b1[i])
+			return
+		}
+	}
+}
+
+func testFileLevelDictReset(t *testing.T, fn string, level int, dict []byte) {
+	var b0 []byte
+	var err error
+	if fn != "" {
+		b0, err = os.ReadFile(fn)
+		if err != nil {
+			t.Errorf("%s (level=%d): %v", fn, level, err)
+			return
+		}
+	}
+
+	// Compress once.
+	buf := new(bytes.Buffer)
+	var zlibw *Writer
+	if dict == nil {
+		zlibw, err = NewWriterLevel(buf, level)
+	} else {
+		zlibw, err = NewWriterLevelDict(buf, level, dict)
+	}
+	if err == nil {
+		_, err = zlibw.Write(b0)
+	}
+	if err == nil {
+		err = zlibw.Close()
+	}
+	if err != nil {
+		t.Errorf("%s (level=%d): %v", fn, level, err)
+		return
+	}
+	out := buf.String()
+
+	// Reset and compress again.
+	buf2 := new(bytes.Buffer)
+	zlibw.Reset(buf2)
+	_, err = zlibw.Write(b0)
+	if err == nil {
+		err = zlibw.Close()
+	}
+	if err != nil {
+		t.Errorf("%s (level=%d): %v", fn, level, err)
+		return
+	}
+	out2 := buf2.String()
+
+	if out2 != out {
+		t.Errorf("%s (level=%d): different output after reset (got %d bytes, expected %d",
+			fn, level, len(out2), len(out))
+	}
+}
+
+func TestWriter(t *testing.T) {
+	for i, s := range data {
+		b := []byte(s)
+		tag := fmt.Sprintf("#%d", i)
+		testLevelDict(t, tag, b, DefaultCompression, "")
+		testLevelDict(t, tag, b, NoCompression, "")
+		testLevelDict(t, tag, b, HuffmanOnly, "")
+		for level := BestSpeed; level <= BestCompression; level++ {
+			testLevelDict(t, tag, b, level, "")
+		}
+	}
+}
+
+func TestWriterBig(t *testing.T) {
+	for i, fn := range filenames {
+		testFileLevelDict(t, fn, DefaultCompression, "")
+		testFileLevelDict(t, fn, NoCompression, "")
+		testFileLevelDict(t, fn, HuffmanOnly, "")
+		for level := BestSpeed; level <= BestCompression; level++ {
+			testFileLevelDict(t, fn, level, "")
+			if level >= 1 && testing.Short() && testenv.Builder() == "" {
+				break
+			}
+		}
+		if i == 0 && testing.Short() && testenv.Builder() == "" {
+			break
+		}
+	}
+}
+
+func TestWriterDict(t *testing.T) {
+	const dictionary = "0123456789."
+	for i, fn := range filenames {
+		testFileLevelDict(t, fn, DefaultCompression, dictionary)
+		testFileLevelDict(t, fn, NoCompression, dictionary)
+		testFileLevelDict(t, fn, HuffmanOnly, dictionary)
+		for level := BestSpeed; level <= BestCompression; level++ {
+			testFileLevelDict(t, fn, level, dictionary)
+			if level >= 1 && testing.Short() && testenv.Builder() == "" {
+				break
+			}
+		}
+		if i == 0 && testing.Short() && testenv.Builder() == "" {
+			break
+		}
+	}
+}
+
+func TestWriterReset(t *testing.T) {
+	const dictionary = "0123456789."
+	for _, fn := range filenames {
+		testFileLevelDictReset(t, fn, NoCompression, nil)
+		testFileLevelDictReset(t, fn, DefaultCompression, nil)
+		testFileLevelDictReset(t, fn, HuffmanOnly, nil)
+		testFileLevelDictReset(t, fn, NoCompression, []byte(dictionary))
+		testFileLevelDictReset(t, fn, DefaultCompression, []byte(dictionary))
+		testFileLevelDictReset(t, fn, HuffmanOnly, []byte(dictionary))
+		if testing.Short() {
+			break
+		}
+		for level := BestSpeed; level <= BestCompression; level++ {
+			testFileLevelDictReset(t, fn, level, nil)
+		}
+	}
+}
+
+func TestWriterDictIsUsed(t *testing.T) {
+	var input = []byte("Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.")
+	var buf bytes.Buffer
+	compressor, err := NewWriterLevelDict(&buf, BestCompression, input)
+	if err != nil {
+		t.Errorf("error in NewWriterLevelDict: %s", err)
+		return
+	}
+	compressor.Write(input)
+	compressor.Close()
+	const expectedMaxSize = 25
+	output := buf.Bytes()
+	if len(output) > expectedMaxSize {
+		t.Errorf("result too large (got %d, want <= %d bytes). Is the dictionary being used?", len(output), expectedMaxSize)
+	}
+}

image/internal/imageutil/gen.go

@@ -0,0 +1,173 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build ignore
+// +build ignore
+
+package main
+
+import (
+	"bytes"
+	"flag"
+	"fmt"
+	"go/format"
+	"log"
+	"os"
+)
+
+var debug = flag.Bool("debug", false, "")
+
+func main() {
+	flag.Parse()
+
+	w := new(bytes.Buffer)
+	w.WriteString(pre)
+	for _, sratio := range subsampleRatios {
+		fmt.Fprintf(w, sratioCase, sratio, sratioLines[sratio])
+	}
+	w.WriteString(post)
+
+	if *debug {
+		os.Stdout.Write(w.Bytes())
+		return
+	}
+	out, err := format.Source(w.Bytes())
+	if err != nil {
+		log.Fatal(err)
+	}
+	if err := os.WriteFile("impl.go", out, 0660); err != nil {
+		log.Fatal(err)
+	}
+}
+
+const pre = `// Code generated by go run gen.go; DO NOT EDIT.
+
+package imageutil
+
+import (
+	"image"
+)
+
+// DrawYCbCr draws the YCbCr source image on the RGBA destination image with
+// r.Min in dst aligned with sp in src. It reports whether the draw was
+// successful. If it returns false, no dst pixels were changed.
+//
+// This function assumes that r is entirely within dst's bounds and the
+// translation of r from dst coordinate space to src coordinate space is
+// entirely within src's bounds.
+func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Point) (ok bool) {
+	// This function exists in the image/internal/imageutil package because it
+	// is needed by both the image/draw and image/jpeg packages, but it doesn't
+	// seem right for one of those two to depend on the other.
+	//
+	// Another option is to have this code be exported in the image package,
+	// but we'd need to make sure we're totally happy with the API (for the
+	// rest of Go 1 compatibility), and decide if we want to have a more
+	// general purpose DrawToRGBA method for other image types. One possibility
+	// is:
+	//
+	// func (src *YCbCr) CopyToRGBA(dst *RGBA, dr, sr Rectangle) (effectiveDr, effectiveSr Rectangle)
+	//
+	// in the spirit of the built-in copy function for 1-dimensional slices,
+	// that also allowed a CopyFromRGBA method if needed.
+
+	x0 := (r.Min.X - dst.Rect.Min.X) * 4
+	x1 := (r.Max.X - dst.Rect.Min.X) * 4
+	y0 := r.Min.Y - dst.Rect.Min.Y
+	y1 := r.Max.Y - dst.Rect.Min.Y
+	switch src.SubsampleRatio {
+`
+
+const post = `
+	default:
+		return false
+	}
+	return true
+}
+`
+
+const sratioCase = `
+	case image.YCbCrSubsampleRatio%s:
+		for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+			dpix := dst.Pix[y*dst.Stride:]
+			yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+			%s
+
+				// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
+				yy1 := int32(src.Y[yi]) * 0x10101
+				cb1 := int32(src.Cb[ci]) - 128
+				cr1 := int32(src.Cr[ci]) - 128
+
+				// The bit twiddling below is equivalent to
+				//
+				// r := (yy1 + 91881*cr1) >> 16
+				// if r < 0 {
+				//     r = 0
+				// } else if r > 0xff {
+				//     r = ^int32(0)
+				// }
+				//
+				// but uses fewer branches and is faster.
+				// Note that the uint8 type conversion in the return
+				// statement will convert ^int32(0) to 0xff.
+				// The code below to compute g and b uses a similar pattern.
+				r := yy1 + 91881*cr1
+				if uint32(r)&0xff000000 == 0 {
+					r >>= 16
+				} else {
+					r = ^(r >> 31)
+				}
+
+				g := yy1 - 22554*cb1 - 46802*cr1
+				if uint32(g)&0xff000000 == 0 {
+					g >>= 16
+				} else {
+					g = ^(g >> 31)
+				}
+
+				b := yy1 + 116130*cb1
+				if uint32(b)&0xff000000 == 0 {
+					b >>= 16
+				} else {
+					b = ^(b >> 31)
+				}
+
+
+				// use a temp slice to hint to the compiler that a single bounds check suffices
+				rgba := dpix[x : x+4 : len(dpix)]
+				rgba[0] = uint8(r)
+				rgba[1] = uint8(g)
+				rgba[2] = uint8(b)
+				rgba[3] = 255
+			}
+		}
+`
+
+var subsampleRatios = []string{
+	"444",
+	"422",
+	"420",
+	"440",
+}
+
+var sratioLines = map[string]string{
+	"444": `
+		ci := (sy-src.Rect.Min.Y)*src.CStride + (sp.X - src.Rect.Min.X)
+		for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
+	`,
+	"422": `
+		ciBase := (sy-src.Rect.Min.Y)*src.CStride - src.Rect.Min.X/2
+		for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 {
+			ci := ciBase + sx/2
+	`,
+	"420": `
+		ciBase := (sy/2-src.Rect.Min.Y/2)*src.CStride - src.Rect.Min.X/2
+		for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 {
+			ci := ciBase + sx/2
+	`,
+	"440": `
+		ci := (sy/2-src.Rect.Min.Y/2)*src.CStride + (sp.X - src.Rect.Min.X)
+		for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
+	`,
+}

image/internal/imageutil/imageutil.go

@@ -0,0 +1,8 @@
+// Copyright 2015 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:generate go run gen.go
+
+// Package imageutil contains code shared by image-related packages.
+package imageutil

image/internal/imageutil/impl.go

@@ -0,0 +1,268 @@
+// Code generated by go run gen.go; DO NOT EDIT.
+
+package imageutil
+
+import (
+	"image"
+)
+
+// DrawYCbCr draws the YCbCr source image on the RGBA destination image with
+// r.Min in dst aligned with sp in src. It reports whether the draw was
+// successful. If it returns false, no dst pixels were changed.
+//
+// This function assumes that r is entirely within dst's bounds and the
+// translation of r from dst coordinate space to src coordinate space is
+// entirely within src's bounds.
+func DrawYCbCr(dst *image.RGBA, r image.Rectangle, src *image.YCbCr, sp image.Point) (ok bool) {
+	// This function exists in the image/internal/imageutil package because it
+	// is needed by both the image/draw and image/jpeg packages, but it doesn't
+	// seem right for one of those two to depend on the other.
+	//
+	// Another option is to have this code be exported in the image package,
+	// but we'd need to make sure we're totally happy with the API (for the
+	// rest of Go 1 compatibility), and decide if we want to have a more
+	// general purpose DrawToRGBA method for other image types. One possibility
+	// is:
+	//
+	// func (src *YCbCr) CopyToRGBA(dst *RGBA, dr, sr Rectangle) (effectiveDr, effectiveSr Rectangle)
+	//
+	// in the spirit of the built-in copy function for 1-dimensional slices,
+	// that also allowed a CopyFromRGBA method if needed.
+
+	x0 := (r.Min.X - dst.Rect.Min.X) * 4
+	x1 := (r.Max.X - dst.Rect.Min.X) * 4
+	y0 := r.Min.Y - dst.Rect.Min.Y
+	y1 := r.Max.Y - dst.Rect.Min.Y
+	switch src.SubsampleRatio {
+
+	case image.YCbCrSubsampleRatio444:
+		for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+			dpix := dst.Pix[y*dst.Stride:]
+			yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+
+			ci := (sy-src.Rect.Min.Y)*src.CStride + (sp.X - src.Rect.Min.X)
+			for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
+
+				// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
+				yy1 := int32(src.Y[yi]) * 0x10101
+				cb1 := int32(src.Cb[ci]) - 128
+				cr1 := int32(src.Cr[ci]) - 128
+
+				// The bit twiddling below is equivalent to
+				//
+				// r := (yy1 + 91881*cr1) >> 16
+				// if r < 0 {
+				//     r = 0
+				// } else if r > 0xff {
+				//     r = ^int32(0)
+				// }
+				//
+				// but uses fewer branches and is faster.
+				// Note that the uint8 type conversion in the return
+				// statement will convert ^int32(0) to 0xff.
+				// The code below to compute g and b uses a similar pattern.
+				r := yy1 + 91881*cr1
+				if uint32(r)&0xff000000 == 0 {
+					r >>= 16
+				} else {
+					r = ^(r >> 31)
+				}
+
+				g := yy1 - 22554*cb1 - 46802*cr1
+				if uint32(g)&0xff000000 == 0 {
+					g >>= 16
+				} else {
+					g = ^(g >> 31)
+				}
+
+				b := yy1 + 116130*cb1
+				if uint32(b)&0xff000000 == 0 {
+					b >>= 16
+				} else {
+					b = ^(b >> 31)
+				}
+
+				// use a temp slice to hint to the compiler that a single bounds check suffices
+				rgba := dpix[x : x+4 : len(dpix)]
+				rgba[0] = uint8(r)
+				rgba[1] = uint8(g)
+				rgba[2] = uint8(b)
+				rgba[3] = 255
+			}
+		}
+
+	case image.YCbCrSubsampleRatio422:
+		for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+			dpix := dst.Pix[y*dst.Stride:]
+			yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+
+			ciBase := (sy-src.Rect.Min.Y)*src.CStride - src.Rect.Min.X/2
+			for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 {
+				ci := ciBase + sx/2
+
+				// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
+				yy1 := int32(src.Y[yi]) * 0x10101
+				cb1 := int32(src.Cb[ci]) - 128
+				cr1 := int32(src.Cr[ci]) - 128
+
+				// The bit twiddling below is equivalent to
+				//
+				// r := (yy1 + 91881*cr1) >> 16
+				// if r < 0 {
+				//     r = 0
+				// } else if r > 0xff {
+				//     r = ^int32(0)
+				// }
+				//
+				// but uses fewer branches and is faster.
+				// Note that the uint8 type conversion in the return
+				// statement will convert ^int32(0) to 0xff.
+				// The code below to compute g and b uses a similar pattern.
+				r := yy1 + 91881*cr1
+				if uint32(r)&0xff000000 == 0 {
+					r >>= 16
+				} else {
+					r = ^(r >> 31)
+				}
+
+				g := yy1 - 22554*cb1 - 46802*cr1
+				if uint32(g)&0xff000000 == 0 {
+					g >>= 16
+				} else {
+					g = ^(g >> 31)
+				}
+
+				b := yy1 + 116130*cb1
+				if uint32(b)&0xff000000 == 0 {
+					b >>= 16
+				} else {
+					b = ^(b >> 31)
+				}
+
+				// use a temp slice to hint to the compiler that a single bounds check suffices
+				rgba := dpix[x : x+4 : len(dpix)]
+				rgba[0] = uint8(r)
+				rgba[1] = uint8(g)
+				rgba[2] = uint8(b)
+				rgba[3] = 255
+			}
+		}
+
+	case image.YCbCrSubsampleRatio420:
+		for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+			dpix := dst.Pix[y*dst.Stride:]
+			yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+
+			ciBase := (sy/2-src.Rect.Min.Y/2)*src.CStride - src.Rect.Min.X/2
+			for x, sx := x0, sp.X; x != x1; x, sx, yi = x+4, sx+1, yi+1 {
+				ci := ciBase + sx/2
+
+				// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
+				yy1 := int32(src.Y[yi]) * 0x10101
+				cb1 := int32(src.Cb[ci]) - 128
+				cr1 := int32(src.Cr[ci]) - 128
+
+				// The bit twiddling below is equivalent to
+				//
+				// r := (yy1 + 91881*cr1) >> 16
+				// if r < 0 {
+				//     r = 0
+				// } else if r > 0xff {
+				//     r = ^int32(0)
+				// }
+				//
+				// but uses fewer branches and is faster.
+				// Note that the uint8 type conversion in the return
+				// statement will convert ^int32(0) to 0xff.
+				// The code below to compute g and b uses a similar pattern.
+				r := yy1 + 91881*cr1
+				if uint32(r)&0xff000000 == 0 {
+					r >>= 16
+				} else {
+					r = ^(r >> 31)
+				}
+
+				g := yy1 - 22554*cb1 - 46802*cr1
+				if uint32(g)&0xff000000 == 0 {
+					g >>= 16
+				} else {
+					g = ^(g >> 31)
+				}
+
+				b := yy1 + 116130*cb1
+				if uint32(b)&0xff000000 == 0 {
+					b >>= 16
+				} else {
+					b = ^(b >> 31)
+				}
+
+				// use a temp slice to hint to the compiler that a single bounds check suffices
+				rgba := dpix[x : x+4 : len(dpix)]
+				rgba[0] = uint8(r)
+				rgba[1] = uint8(g)
+				rgba[2] = uint8(b)
+				rgba[3] = 255
+			}
+		}
+
+	case image.YCbCrSubsampleRatio440:
+		for y, sy := y0, sp.Y; y != y1; y, sy = y+1, sy+1 {
+			dpix := dst.Pix[y*dst.Stride:]
+			yi := (sy-src.Rect.Min.Y)*src.YStride + (sp.X - src.Rect.Min.X)
+
+			ci := (sy/2-src.Rect.Min.Y/2)*src.CStride + (sp.X - src.Rect.Min.X)
+			for x := x0; x != x1; x, yi, ci = x+4, yi+1, ci+1 {
+
+				// This is an inline version of image/color/ycbcr.go's func YCbCrToRGB.
+				yy1 := int32(src.Y[yi]) * 0x10101
+				cb1 := int32(src.Cb[ci]) - 128
+				cr1 := int32(src.Cr[ci]) - 128
+
+				// The bit twiddling below is equivalent to
+				//
+				// r := (yy1 + 91881*cr1) >> 16
+				// if r < 0 {
+				//     r = 0
+				// } else if r > 0xff {
+				//     r = ^int32(0)
+				// }
+				//
+				// but uses fewer branches and is faster.
+				// Note that the uint8 type conversion in the return
+				// statement will convert ^int32(0) to 0xff.
+				// The code below to compute g and b uses a similar pattern.
+				r := yy1 + 91881*cr1
+				if uint32(r)&0xff000000 == 0 {
+					r >>= 16
+				} else {
+					r = ^(r >> 31)
+				}
+
+				g := yy1 - 22554*cb1 - 46802*cr1
+				if uint32(g)&0xff000000 == 0 {
+					g >>= 16
+				} else {
+					g = ^(g >> 31)
+				}
+
+				b := yy1 + 116130*cb1
+				if uint32(b)&0xff000000 == 0 {
+					b >>= 16
+				} else {
+					b = ^(b >> 31)
+				}
+
+				// use a temp slice to hint to the compiler that a single bounds check suffices
+				rgba := dpix[x : x+4 : len(dpix)]
+				rgba[0] = uint8(r)
+				rgba[1] = uint8(g)
+				rgba[2] = uint8(b)
+				rgba[3] = 255
+			}
+		}
+
+	default:
+		return false
+	}
+	return true
+}

image/jpeg/callback.go

@@ -0,0 +1,19 @@
+package jpeg
+
+var (
+	callback    Callback = func(data []uint16, x, y, w, h, width, height int16) {}
+	callbackBuf []uint16
+)
+
+// A portion of the image data consisting of data, x, y, w, and h is passed to
+// Callback. The size of the whole image is passed as width and height.
+// If the callback is not called, add the implementation to
+// image/png.readImagePass.
+type Callback func(data []uint16, x, y, w, h, width, height int16)
+
+// SetCallback registers the buffer and fn required for Callback. Callback can
+// be called multiple times by calling Decode().
+func SetCallback(buf []uint16, fn Callback) {
+	callbackBuf = buf
+	callback = fn
+}

image/jpeg/dct_test.go

@@ -0,0 +1,299 @@
+// Copyright 2012 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package jpeg
+
+import (
+	"bytes"
+	"fmt"
+	"math"
+	"math/rand"
+	"testing"
+)
+
+func benchmarkDCT(b *testing.B, f func(*block)) {
+	b.StopTimer()
+	blocks := make([]block, 0, b.N*len(testBlocks))
+	for i := 0; i < b.N; i++ {
+		blocks = append(blocks, testBlocks[:]...)
+	}
+	b.StartTimer()
+	for i := range blocks {
+		f(&blocks[i])
+	}
+}
+
+func BenchmarkFDCT(b *testing.B) {
+	benchmarkDCT(b, fdct)
+}
+
+func BenchmarkIDCT(b *testing.B) {
+	benchmarkDCT(b, idct)
+}
+
+func TestDCT(t *testing.T) {
+	blocks := make([]block, len(testBlocks))
+	copy(blocks, testBlocks[:])
+
+	// Append some randomly generated blocks of varying sparseness.
+	r := rand.New(rand.NewSource(123))
+	for i := 0; i < 100; i++ {
+		b := block{}
+		n := r.Int() % 64
+		for j := 0; j < n; j++ {
+			b[r.Int()%len(b)] = r.Int31() % 256
+		}
+		blocks = append(blocks, b)
+	}
+
+	// Check that the FDCT and IDCT functions are inverses, after a scale and
+	// level shift. Scaling reduces the rounding errors in the conversion from
+	// floats to ints.
+	for i, b := range blocks {
+		got, want := b, b
+		for j := range got {
+			got[j] = (got[j] - 128) * 8
+		}
+		slowFDCT(&got)
+		slowIDCT(&got)
+		for j := range got {
+			got[j] = got[j]/8 + 128
+		}
+		if differ(&got, &want) {
+			t.Errorf("i=%d: IDCT(FDCT)\nsrc\n%s\ngot\n%s\nwant\n%s\n", i, &b, &got, &want)
+		}
+	}
+
+	// Check that the optimized and slow FDCT implementations agree.
+	// The fdct function already does a scale and level shift.
+	for i, b := range blocks {
+		got, want := b, b
+		fdct(&got)
+		for j := range want {
+			want[j] = (want[j] - 128) * 8
+		}
+		slowFDCT(&want)
+		if differ(&got, &want) {
+			t.Errorf("i=%d: FDCT\nsrc\n%s\ngot\n%s\nwant\n%s\n", i, &b, &got, &want)
+		}
+	}
+
+	// Check that the optimized and slow IDCT implementations agree.
+	for i, b := range blocks {
+		got, want := b, b
+		idct(&got)
+		slowIDCT(&want)
+		if differ(&got, &want) {
+			t.Errorf("i=%d: IDCT\nsrc\n%s\ngot\n%s\nwant\n%s\n", i, &b, &got, &want)
+		}
+	}
+}
+
+// differ reports whether any pair-wise elements in b0 and b1 differ by 2 or
+// more. That tolerance is because there isn't a single definitive decoding of
+// a given JPEG image, even before the YCbCr to RGB conversion; implementations
+// can have different IDCT rounding errors.
+func differ(b0, b1 *block) bool {
+	for i := range b0 {
+		delta := b0[i] - b1[i]
+		if delta < -2 || +2 < delta {
+			return true
+		}
+	}
+	return false
+}
+
+// alpha returns 1 if i is 0 and returns √2 otherwise.
+func alpha(i int) float64 {
+	if i == 0 {
+		return 1
+	}
+	return math.Sqrt2
+}
+
+var cosines [32]float64 // cosines[k] = cos(π/2 * k/8)
+
+func init() {
+	for k := range cosines {
+		cosines[k] = math.Cos(math.Pi * float64(k) / 16)
+	}
+}
+
+// slowFDCT performs the 8*8 2-dimensional forward discrete cosine transform:
+//
+//	dst[u,v] = (1/8) * Σ_x Σ_y alpha(u) * alpha(v) * src[x,y] *
+//		cos((π/2) * (2*x + 1) * u / 8) *
+//		cos((π/2) * (2*y + 1) * v / 8)
+//
+// x and y are in pixel space, and u and v are in transform space.
+//
+// b acts as both dst and src.
+func slowFDCT(b *block) {
+	var dst [blockSize]float64
+	for v := 0; v < 8; v++ {
+		for u := 0; u < 8; u++ {
+			sum := 0.0
+			for y := 0; y < 8; y++ {
+				for x := 0; x < 8; x++ {
+					sum += alpha(u) * alpha(v) * float64(b[8*y+x]) *
+						cosines[((2*x+1)*u)%32] *
+						cosines[((2*y+1)*v)%32]
+				}
+			}
+			dst[8*v+u] = sum / 8
+		}
+	}
+	// Convert from float64 to int32.
+	for i := range dst {
+		b[i] = int32(dst[i] + 0.5)
+	}
+}
+
+// slowIDCT performs the 8*8 2-dimensional inverse discrete cosine transform:
+//
+//	dst[x,y] = (1/8) * Σ_u Σ_v alpha(u) * alpha(v) * src[u,v] *
+//		cos((π/2) * (2*x + 1) * u / 8) *
+//		cos((π/2) * (2*y + 1) * v / 8)
+//
+// x and y are in pixel space, and u and v are in transform space.
+//
+// b acts as both dst and src.
+func slowIDCT(b *block) {
+	var dst [blockSize]float64
+	for y := 0; y < 8; y++ {
+		for x := 0; x < 8; x++ {
+			sum := 0.0
+			for v := 0; v < 8; v++ {
+				for u := 0; u < 8; u++ {
+					sum += alpha(u) * alpha(v) * float64(b[8*v+u]) *
+						cosines[((2*x+1)*u)%32] *
+						cosines[((2*y+1)*v)%32]
+				}
+			}
+			dst[8*y+x] = sum / 8
+		}
+	}
+	// Convert from float64 to int32.
+	for i := range dst {
+		b[i] = int32(dst[i] + 0.5)
+	}
+}
+
+func (b *block) String() string {
+	s := bytes.NewBuffer(nil)
+	fmt.Fprintf(s, "{\n")
+	for y := 0; y < 8; y++ {
+		fmt.Fprintf(s, "\t")
+		for x := 0; x < 8; x++ {
+			fmt.Fprintf(s, "0x%04x, ", uint16(b[8*y+x]))
+		}
+		fmt.Fprintln(s)
+	}
+	fmt.Fprintf(s, "}")
+	return s.String()
+}
+
+// testBlocks are the first 10 pre-IDCT blocks from ../testdata/video-001.jpeg.
+var testBlocks = [10]block{
+	{
+		0x7f, 0xf6, 0x01, 0x07, 0xff, 0x00, 0x00, 0x00,
+		0xf5, 0x01, 0xfa, 0x01, 0xfe, 0x00, 0x01, 0x00,
+		0x05, 0x05, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x01, 0xff, 0xf8, 0x00, 0x01, 0xff, 0x00, 0x00,
+		0x00, 0x01, 0x00, 0x01, 0x00, 0xff, 0xff, 0x00,
+		0xff, 0x0c, 0x00, 0x00, 0x00, 0x00, 0xff, 0x01,
+		0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0x00, 0x01, 0xff, 0x01, 0x00, 0xfe,
+	},
+	{
+		0x29, 0x07, 0x00, 0xfc, 0x01, 0x01, 0x00, 0x00,
+		0x07, 0x00, 0x03, 0x00, 0x01, 0x00, 0xff, 0xff,
+		0xff, 0xfd, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x04, 0x00, 0xff, 0x01, 0x00, 0x00,
+		0x01, 0x00, 0x01, 0xff, 0x00, 0x00, 0x00, 0x00,
+		0x01, 0xfa, 0x01, 0x00, 0x01, 0x00, 0x01, 0xff,
+		0x00, 0x00, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0xff, 0x00, 0xff, 0x00, 0x02,
+	},
+	{
+		0xc5, 0xfa, 0x01, 0x00, 0x00, 0x01, 0x00, 0xff,
+		0x02, 0xff, 0x01, 0x00, 0x01, 0x00, 0xff, 0x00,
+		0xff, 0xff, 0x00, 0xff, 0x01, 0x00, 0x00, 0x00,
+		0xff, 0x00, 0x01, 0x00, 0x00, 0x00, 0xff, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
+		0x00, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+	},
+	{
+		0x86, 0x05, 0x00, 0x02, 0x00, 0x00, 0x01, 0x00,
+		0xf2, 0x06, 0x00, 0x00, 0x01, 0x02, 0x00, 0x00,
+		0xf6, 0xfa, 0xf9, 0x00, 0xff, 0x01, 0x00, 0x00,
+		0xf9, 0x00, 0x00, 0xff, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0xff, 0x00, 0xff, 0xff, 0xff, 0x00, 0x00,
+		0xff, 0x00, 0x00, 0x01, 0x00, 0xff, 0x01, 0x00,
+		0x00, 0x00, 0x00, 0xff, 0x00, 0x00, 0x00, 0x01,
+		0x00, 0x01, 0xff, 0x01, 0x00, 0xff, 0x00, 0x00,
+	},
+	{
+		0x24, 0xfe, 0x00, 0xff, 0x00, 0xff, 0xff, 0x00,
+		0x08, 0xfd, 0x00, 0x01, 0x01, 0x00, 0x01, 0x00,
+		0x06, 0x03, 0x03, 0xff, 0x00, 0x00, 0x00, 0x00,
+		0x04, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
+		0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x01,
+		0x01, 0x00, 0x01, 0xff, 0x00, 0x01, 0x00, 0x00,
+		0x01, 0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0xff, 0x01,
+	},
+	{
+		0xcd, 0xff, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01,
+		0x03, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0xff,
+		0x01, 0x01, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0x00, 0x00, 0x00, 0x01, 0x01, 0x00,
+		0x00, 0x00, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0xff, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0xff,
+	},
+	{
+		0x81, 0xfe, 0x05, 0xff, 0x01, 0xff, 0x01, 0x00,
+		0xef, 0xf9, 0x00, 0xf9, 0x00, 0xff, 0x00, 0xff,
+		0x05, 0xf9, 0x00, 0xf8, 0x01, 0xff, 0x01, 0xff,
+		0x00, 0xff, 0x07, 0x00, 0x01, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0x01, 0x01, 0x00, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0x00, 0x00, 0xff, 0xff, 0x00, 0x01,
+		0xff, 0x01, 0x01, 0x00, 0xff, 0x00, 0x00, 0x00,
+		0x01, 0x01, 0x00, 0xff, 0x00, 0x00, 0x00, 0xff,
+	},
+	{
+		0x28, 0x00, 0xfe, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x0b, 0x02, 0x01, 0x03, 0x00, 0xff, 0x00, 0x01,
+		0xfe, 0x02, 0x01, 0x03, 0xff, 0x00, 0x00, 0x00,
+		0x01, 0x00, 0xfd, 0x00, 0x01, 0x00, 0xff, 0x00,
+		0x01, 0xff, 0x00, 0xff, 0x01, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0xff, 0x01, 0x01, 0x00, 0xff,
+		0x01, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0xff, 0xff, 0x00, 0x00, 0x00, 0xff, 0x00, 0x01,
+	},
+	{
+		0xdf, 0xf9, 0xfe, 0x00, 0x03, 0x01, 0xff, 0xff,
+		0x04, 0x01, 0x00, 0x01, 0x00, 0x00, 0x00, 0x00,
+		0xff, 0x01, 0x01, 0x01, 0x00, 0x00, 0x00, 0x01,
+		0x00, 0x00, 0xfe, 0x01, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0xff, 0x01, 0x00, 0x00, 0x00, 0x01,
+		0xff, 0x00, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
+		0x00, 0xff, 0x00, 0xff, 0x01, 0x00, 0x00, 0x01,
+		0xff, 0xff, 0x00, 0x00, 0x00, 0x01, 0x00, 0x00,
+	},
+	{
+		0x88, 0xfd, 0x00, 0x00, 0xff, 0x00, 0x01, 0xff,
+		0xe1, 0x06, 0x06, 0x01, 0xff, 0x00, 0x01, 0x00,
+		0x08, 0x00, 0xfa, 0x00, 0xff, 0xff, 0xff, 0xff,
+		0x08, 0x01, 0x00, 0xff, 0x01, 0xff, 0x00, 0x00,
+		0xf5, 0xff, 0x00, 0x01, 0xff, 0x01, 0x01, 0x00,
+		0xff, 0xff, 0x01, 0xff, 0x01, 0x00, 0x01, 0x00,
+		0x00, 0x01, 0x01, 0xff, 0x00, 0xff, 0x00, 0x01,
+		0x02, 0x00, 0x00, 0xff, 0xff, 0x00, 0xff, 0x00,
+	},
+}

image/jpeg/fdct.go

@@ -0,0 +1,192 @@
+// Copyright 2011 The Go Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package jpeg
+
+// This file implements a Forward Discrete Cosine Transformation.
+
+/*
+It is based on the code in jfdctint.c from the Independent JPEG Group,
+found at http://www.ijg.org/files/jpegsrc.v8c.tar.gz.
+
+The "LEGAL ISSUES" section of the README in that archive says:
+
+In plain English:
+
+1. We don't promise that this software works.  (But if you find any bugs,
+   please let us know!)
+2. You can use this software for whatever you want.  You don't have to pay us.
+3. You may not pretend that you wrote this software.  If you use it in a
+   program, you must acknowledge somewhere in your documentation that
+   you've used the IJG code.
+
+In legalese:
+
+The authors make NO WARRANTY or representation, either express or implied,
+with respect to this software, its quality, accuracy, merchantability, or
+fitness for a particular purpose.  This software is provided "AS IS", and you,
+its user, assume the entire risk as to its quality and accuracy.
+
+This software is copyright (C) 1991-2011, Thomas G. Lane, Guido Vollbeding.
+All Rights Reserved except as specified below.
+
+Permission is hereby granted to use, copy, modify, and distribute this
+software (or portions thereof) for any purpose, without fee, subject to these
+conditions:
+(1) If any part of the source code for this software is distributed, then this
+README file must be included, with this copyright and no-warranty notice
+unaltered; and any additions, deletions, or changes to the original files
+must be clearly indicated in accompanying documentation.
+(2) If only executable code is distributed, then the accompanying
+documentation must state that "this software is based in part on the work of
+the Independent JPEG Group".
+(3) Permission for use of this software is granted only if the user accepts
+full responsibility for any undesirable consequences; the authors accept
+NO LIABILITY for damages of any kind.
+
+These conditions apply to any software derived from or based on the IJG code,
+not just to the unmodified library.  If you use our work, you ought to
+acknowledge us.
+
+Permission is NOT granted for the use of any IJG author's name or company name
+in advertising or publicity relating to this software or products derived from
+it.  This software may be referred to only as "the Independent JPEG Group's
+software".
+
+We specifically permit and encourage the use of this software as the basis of
+commercial products, provided that all warranty or liability claims are
+assumed by the product vendor.
+*/
+
+// Trigonometric constants in 13-bit fixed point format.
+const (
+	fix_0_298631336 = 2446
+	fix_0_390180644 = 3196
+	fix_0_541196100 = 4433
+	fix_0_765366865 = 6270
+	fix_0_899976223 = 7373
+	fix_1_175875602 = 9633
+	fix_1_501321110 = 12299
+	fix_1_847759065 = 15137
+	fix_1_961570560 = 16069
+	fix_2_053119869 = 16819
+	fix_2_562915447 = 20995
+	fix_3_072711026 = 25172
+)
+
+const (
+	constBits     = 13
+	pass1Bits     = 2
+	centerJSample = 128
+)
+
+// fdct performs a forward DCT on an 8x8 block of coefficients, including a
+// level shift.
+func fdct(b *block) {
+	// Pass 1: process rows.
+	for y := 0; y < 8; y++ {
+		y8 := y * 8
+		s := b[y8 : y8+8 : y8+8] // Small cap improves performance, see https://golang.org/issue/27857
+		x0 := s[0]
+		x1 := s[1]
+		x2 := s[2]
+		x3 := s[3]
+		x4 := s[4]
+		x5 := s[5]
+		x6 := s[6]
+		x7 := s[7]
+
+		tmp0 := x0 + x7
+		tmp1 := x1 + x6
+		tmp2 := x2 + x5
+		tmp3 := x3 + x4
+
+		tmp10 := tmp0 + tmp3
+		tmp12 := tmp0 - tmp3
+		tmp11 := tmp1 + tmp2
+		tmp13 := tmp1 - tmp2
+
+		tmp0 = x0 - x7
+		tmp1 = x1 - x6
+		tmp2 = x2 - x5
+		tmp3 = x3 - x4
+
+		s[0] = (tmp10 + tmp11 - 8*centerJSample) << pass1Bits
+		s[4] = (tmp10 - tmp11) << pass1Bits
+		z1 := (tmp12 + tmp13) * fix_0_541196100
+		z1 += 1 << (constBits - pass1Bits - 1)
+		s[2] = (z1 + tmp12*fix_0_765366865) >> (constBits - pass1Bits)
+		s[6] = (z1 - tmp13*fix_1_847759065) >> (constBits - pass1Bits)
+
+		tmp10 = tmp0 + tmp3
+		tmp11 = tmp1 + tmp2
+		tmp12 = tmp0 + tmp2
+		tmp13 = tmp1 + tmp3
+		z1 = (tmp12 + tmp13) * fix_1_175875602
+		z1 += 1 << (constBits - pass1Bits - 1)
+		tmp0 *= fix_1_501321110
+		tmp1 *= fix_3_072711026
+		tmp2 *= fix_2_053119869
+		tmp3 *= fix_0_298631336
+		tmp10 *= -fix_0_899976223
+		tmp11 *= -fix_2_562915447
+		tmp12 *= -fix_0_390180644
+		tmp13 *= -fix_1_961570560
+
+		tmp12 += z1
+		tmp13 += z1
+		s[1] = (tmp0 + tmp10 + tmp12) >> (constBits - pass1Bits)
+		s[3] = (tmp1 + tmp11 + tmp13) >> (constBits - pass1Bits)
+		s[5] = (tmp2 + tmp11 + tmp12) >> (constBits - pass1Bits)
+		s[7] = (tmp3 + tmp10 + tmp13) >> (constBits - pass1Bits)
+	}
+	// Pass 2: process columns.
+	// We remove pass1Bits scaling, but leave results scaled up by an overall factor of 8.
+	for x := 0; x < 8; x++ {
+		tmp0 := b[0*8+x] + b[7*8+x]
+		tmp1 := b[1*8+x] + b[6*8+x]
+		tmp2 := b[2*8+x] + b[5*8+x]
+		tmp3 := b[3*8+x] + b[4*8+x]
+
+		tmp10 := tmp0 + tmp3 + 1<<(pass1Bits-1)
+		tmp12 := tmp0 - tmp3
+		tmp11 := tmp1 + tmp2
+		tmp13 := tmp1 - tmp2
+
+		tmp0 = b[0*8+x] - b[7*8+x]
+		tmp1 = b[1*8+x] - b[6*8+x]
+		tmp2 = b[2*8+x] - b[5*8+x]
+		tmp3 = b[3*8+x] - b[4*8+x]
+
+		b[0*8+x] = (tmp10 + tmp11) >> pass1Bits
+		b[4*8+x] = (tmp10 - tmp11) >> pass1Bits
+
+		z1 := (tmp12 + tmp13) * fix_0_541196100
+		z1 += 1 << (constBits + pass1Bits - 1)
+		b[2*8+x] = (z1 + tmp12*fix_0_765366865) >> (constBits + pass1Bits)
+		b[6*8+x] = (z1 - tmp13*fix_1_847759065) >> (constBits + pass1Bits)
+
+		tmp10 = tmp0 + tmp3
+		tmp11 = tmp1 + tmp2
+		tmp12 = tmp0 + tmp2
+		tmp13 = tmp1 + tmp3
+		z1 = (tmp12 + tmp13) * fix_1_175875602
+		z1 += 1 << (constBits + pass1Bits - 1)
+		tmp0 *= fix_1_501321110
+		tmp1 *= fix_3_072711026
+		tmp2 *= fix_2_053119869
+		tmp3 *= fix_0_298631336
+		tmp10 *= -fix_0_899976223
+		tmp11 *= -fix_2_562915447
+		tmp12 *= -fix_0_390180644
+		tmp13 *= -fix_1_961570560
+
+		tmp12 += z1
+		tmp13 += z1
+		b[1*8+x] = (tmp0 + tmp10 + tmp12) >> (constBits + pass1Bits)
+		b[3*8+x] = (tmp1 + tmp11 + tmp13) >> (constBits + pass1Bits)
+		b[5*8+x] = (tmp2 + tmp11 + tmp12) >> (constBits + pass1Bits)
+		b[7*8+x] = (tmp3 + tmp10 + tmp13) >> (constBits + pass1Bits)
+	}
+}