implement sophisticated TAP interface to be able to debug stack on linux

2026-08-14 11:53:43 +00:00 · 2025-02-20 18:51:31 -03:00
parent f86bb6f01a
commit c9d1c4f239
3 changed files with 176 additions and 21 deletions
@@ -1,13 +1,19 @@
 package main

 import (
+	"bytes"
+	"encoding/json"
 	"errors"
 	"fmt"
 	"io"
 	"log"
 	"log/slog"
 	"net"
+	"net/http"
 	"net/netip"
+	"net/url"
+	"os"
+	"time"

 	"github.com/soypat/lneto/arp"
 	"github.com/soypat/lneto/ethernet"
@@ -23,6 +29,7 @@ const (
 	iface     = "192.168.10.1/24"
 	stackIP   = "192.168.10.2"
 	stackPort = 80
+	iss       = 100
 )

 var stackHWAddr = [6]byte{0xc0, 0xff, 0xee, 0x00, 0xde, 0xad}
@@ -40,21 +47,27 @@ func main() {
 		log.Fatal(err)
 	}

-	tap, err := internal.NewTap("tap0", iface)
-	if err != nil {
-		log.Fatal(err)
-	}
-	const port, iss = 80, 300
-	err = handler.OpenListen(port, iss)
-	if err != nil {
-		log.Fatal(err)
-	}
+	logger := slog.New(slog.NewTextHandler(os.Stdout, &slog.HandlerOptions{
+		Level: slog.LevelDebug,
+	}))
+	handler.SetLoggers(logger, logger)

+	err = handler.OpenListen(addrPort.Port(), iss)
+	if err != nil {
+		log.Fatal(err)
+	}
+	tap := NewHTTPTap("http://127.0.0.1:7070")
+	// tap, err := internal.NewTap("tap0", iface)
+	if err != nil {
+		log.Fatal(err)
+	}
 	defer tap.Close()
+	fmt.Println("hosting server at ", addrPort.String())
 	var buf [mtu]byte
 	for {
 		n, err := tap.Read(buf[:])
 		if err != nil {
+			slogger.error("tap-err", slog.String("err", err.Error()))
 			log.Fatal(err)
 		} else if n > 0 {
 			err = lStack.RecvEth(buf[:n])
@@ -63,6 +76,8 @@ func main() {
 			} else {
 				slogger.info("recv", slog.Int("plen", n))
 			}
+		} else if n == 0 {
+			time.Sleep(250 * time.Millisecond)
 		}
 		n, err = lStack.HandleEth(buf[:])
 		if err != nil {
@@ -519,3 +534,56 @@ func addHandler(handlers []handler, h Handler, remoteAddr []byte, lport uint16)
 	hh.lport = lport
 	return handlers
 }
+
+func NewHTTPTap(baseURL string) *HTTPTap {
+	var h HTTPTap
+	h.sendurl = baseURL + "/send"
+	h.recvurl = baseURL + "/recv"
+	_, err := url.Parse(h.sendurl)
+	if err != nil {
+		panic(err)
+	}
+	var data [2048]byte
+	var n int = -1
+	for n != 0 {
+		n, _ = h.Read(data[:]) // Empty remote data.
+	}
+	return &h
+}
+
+type HTTPTap struct {
+	c       http.Client
+	recvurl string
+	sendurl string
+}
+
+func (h *HTTPTap) Read(b []byte) (int, error) {
+	resp, err := h.c.Get(h.recvurl)
+	if err != nil {
+		return 0, err
+	} else if resp.StatusCode != 200 {
+		return 0, errors.New(resp.Status + " for " + h.recvurl)
+	}
+	var data []byte
+	err = json.NewDecoder(resp.Body).Decode(&data)
+	if err != nil {
+		return 0, err
+	} else if len(b) < len(data) {
+		return 0, fmt.Errorf("got too large packet %d for buffer %d", len(data), len(b))
+	}
+	copy(b, data)
+	return len(data), nil
+}
+
+func (h *HTTPTap) Write(b []byte) (int, error) {
+	data, _ := json.Marshal(b)
+	resp, err := h.c.Post(h.sendurl, "application/json", bytes.NewReader(data))
+	if err != nil {
+		return 0, err
+	} else if resp.StatusCode != 200 {
+		return 0, errors.New(resp.Status + " for " + h.sendurl)
+	}
+	return len(b), nil
+}
+
+func (h *HTTPTap) Close() error { return nil }
@@ -1,11 +1,13 @@
 package main

 import (
+	"encoding/json"
+	"errors"
 	"fmt"
 	"log"
+	"log/slog"
+	"net/http"
 	"net/netip"
-	"os"
-	"time"

 	"github.com/soypat/lneto/internal"
 )
@@ -20,23 +22,103 @@ func main() {
 }

 func run() error {
-	ip := netip.MustParsePrefix("192.168.10.1/24")
-	tap, err := internal.NewTap("tap0", ip)
+	var (
+		flagNet   = "192.168.10.1/24"
+		flagiface = "tap0"
+		flagMTU   = 1500
+	)
+	slogger := slog.Default()
+	ip, err := netip.ParsePrefix(flagNet)
+	if err != nil {
+		return err
+	}
+	tap, err := internal.NewTap(flagiface, ip)
 	if err != nil {
 		return err
 	}
 	defer tap.Close()
-	var buf [2048]byte
-	pkt := 0
+	s := stack{
+		out: make(chan []byte, 256),
+		in:  make(chan []byte, 2048),
+	}
+	sv := http.NewServeMux()
+	sv.HandleFunc("/send", func(w http.ResponseWriter, r *http.Request) {
+		var data []byte
+		err := json.NewDecoder(r.Body).Decode(&data)
+		if err != nil {
+			http.Error(w, err.Error(), http.StatusBadRequest)
+		} else {
+			select {
+			case s.out <- data:
+				slog.Info("http-send", slog.Int("plen", len(data)))
+			default:
+				http.Error(w, "outgoing packet queue full", http.StatusInternalServerError)
+			}
+		}
+	})
+	sv.HandleFunc("/recv", func(w http.ResponseWriter, r *http.Request) {
+		select {
+		case data := <-s.in:
+			json.NewEncoder(w).Encode(data)
+			slog.Info("http-recv", slog.Int("plen", len(data)))
+		default:
+			json.NewEncoder(w).Encode("") // send empty string.
+		}
+	})
+	fmt.Println("listening on http://127.0.0.1:7070/recv  and  http://127.0.0.1:7070/send")
+	go http.ListenAndServe(":7070", sv)
+
+	buf := make([]byte, flagMTU)
 	for {
 		n, err := tap.Read(buf[:])
 		if err != nil {
-			return err
-		} else if n == 0 {
-			time.Sleep(250 * time.Millisecond)
-			continue
+			log.Fatal(err)
+		} else if n > 0 {
+			err = s.recv(buf[:n])
+			if err != nil {
+				slogger.Error("recv", slog.String("err", err.Error()), slog.Int("plen", n))
+			} else {
+				slogger.Info("recv", slog.Int("plen", n))
+			}
+		}
+		n, err = s.handle(buf[:])
+		if err != nil {
+			slogger.Error("handle", slog.String("err", err.Error()))
+		} else if n > 0 {
+			_, err = tap.Write(buf[:n])
+			if err != nil {
+				log.Fatal(err)
+			} else {
+				slogger.Info("write", slog.Int("plen", n))
+			}
 		}
-		pkt++
-		fmt.Fprintf(os.Stdout, "rx%d (%d): %q\n\n", pkt, n, buf[:n])
 	}
 }
+
+type stack struct {
+	out chan []byte
+	in  chan []byte
+}
+
+func (s *stack) recv(b []byte) (err error) {
+	bcopy := append([]byte{}, b...)
+RETRY:
+	select {
+	case s.in <- bcopy:
+	default:
+		err = errors.New("receive queue packet full, dropping packet")
+		<-s.in
+		goto RETRY
+	}
+	return err
+}
+
+func (s *stack) handle(b []byte) (n int, _ error) {
+	select {
+	case incoming := <-s.out:
+		n = copy(b, incoming)
+	default:
+		// pass if no data available.
+	}
+	return n, nil
+}
@@ -33,6 +33,11 @@ type Handler struct {
 	closing bool
 }

+func (h *Handler) SetLoggers(handler, scb *slog.Logger) {
+	h.logger.log = handler
+	h.scb.logger.log = scb
+}
+
 func (h *Handler) State() State { return h.scb.State() }

 func (h *Handler) SetBuffers(txbuf, rxbuf []byte, packets int) error {