Add httputil package

Signed-off-by: Itxaka <itxaka@kairos.io>

README.md

@@ -34,6 +34,11 @@ src/net
 │   │   └── server.go		*
 │   ├── httptest
 │   │   └── trace.go		*
+│   ├── httputil
+│   │   └── dump.go
+│   │   └── httputil.go
+│   │   └── persist.go
+│   │   └── reverseproxy.go
 │   ├── client.go		*
 │   ├── clone.go
 │   ├── cookie.go

http/httputil/dump.go

@@ -0,0 +1,339 @@
+// TINYGO: The following is copied from Go 1.21.5 official implementation.
+
+// 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 httputil
+
+import (
+	"bufio"
+	"bytes"
+	"errors"
+	"fmt"
+	"io"
+	"net"
+	"net/http"
+	"net/url"
+	"strings"
+	"time"
+)
+
+// drainBody reads all of b to memory and then returns two equivalent
+// ReadClosers yielding the same bytes.
+//
+// It returns an error if the initial slurp of all bytes fails. It does not attempt
+// to make the returned ReadClosers have identical error-matching behavior.
+func drainBody(b io.ReadCloser) (r1, r2 io.ReadCloser, err error) {
+	if b == nil || b == http.NoBody {
+		// No copying needed. Preserve the magic sentinel meaning of NoBody.
+		return http.NoBody, http.NoBody, nil
+	}
+	var buf bytes.Buffer
+	if _, err = buf.ReadFrom(b); err != nil {
+		return nil, b, err
+	}
+	if err = b.Close(); err != nil {
+		return nil, b, err
+	}
+	return io.NopCloser(&buf), io.NopCloser(bytes.NewReader(buf.Bytes())), nil
+}
+
+// dumpConn is a net.Conn which writes to Writer and reads from Reader
+type dumpConn struct {
+	io.Writer
+	io.Reader
+}
+
+func (c *dumpConn) Close() error                       { return nil }
+func (c *dumpConn) LocalAddr() net.Addr                { return nil }
+func (c *dumpConn) RemoteAddr() net.Addr               { return nil }
+func (c *dumpConn) SetDeadline(t time.Time) error      { return nil }
+func (c *dumpConn) SetReadDeadline(t time.Time) error  { return nil }
+func (c *dumpConn) SetWriteDeadline(t time.Time) error { return nil }
+
+type neverEnding byte
+
+func (b neverEnding) Read(p []byte) (n int, err error) {
+	for i := range p {
+		p[i] = byte(b)
+	}
+	return len(p), nil
+}
+
+// outgoingLength is a copy of the unexported
+// (*http.Request).outgoingLength method.
+func outgoingLength(req *http.Request) int64 {
+	if req.Body == nil || req.Body == http.NoBody {
+		return 0
+	}
+	if req.ContentLength != 0 {
+		return req.ContentLength
+	}
+	return -1
+}
+
+// DumpRequestOut is like DumpRequest but for outgoing client requests. It
+// includes any headers that the standard http.Transport adds, such as
+// User-Agent.
+func DumpRequestOut(req *http.Request, body bool) ([]byte, error) {
+	save := req.Body
+	dummyBody := false
+	if !body {
+		contentLength := outgoingLength(req)
+		if contentLength != 0 {
+			req.Body = io.NopCloser(io.LimitReader(neverEnding('x'), contentLength))
+			dummyBody = true
+		}
+	} else {
+		var err error
+		save, req.Body, err = drainBody(req.Body)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	// Since we're using the actual Transport code to write the request,
+	// switch to http so the Transport doesn't try to do an SSL
+	// negotiation with our dumpConn and its bytes.Buffer & pipe.
+	// The wire format for https and http are the same, anyway.
+	reqSend := req
+	if req.URL.Scheme == "https" {
+		reqSend = new(http.Request)
+		*reqSend = *req
+		reqSend.URL = new(url.URL)
+		*reqSend.URL = *req.URL
+		reqSend.URL.Scheme = "http"
+	}
+
+	// Use the actual Transport code to record what we would send
+	// on the wire, but not using TCP.  Use a Transport with a
+	// custom dialer that returns a fake net.Conn that waits
+	// for the full input (and recording it), and then responds
+	// with a dummy response.
+	var buf bytes.Buffer // records the output
+	pr, pw := io.Pipe()
+	defer pr.Close()
+	defer pw.Close()
+	dr := &delegateReader{c: make(chan io.Reader)}
+
+	t := &http.Transport{
+		Dial: func(net, addr string) (net.Conn, error) {
+			return &dumpConn{io.MultiWriter(&buf, pw), dr}, nil
+		},
+	}
+	defer t.CloseIdleConnections()
+
+	// We need this channel to ensure that the reader
+	// goroutine exits if t.RoundTrip returns an error.
+	// See golang.org/issue/32571.
+	quitReadCh := make(chan struct{})
+	// Wait for the request before replying with a dummy response:
+	go func() {
+		req, err := http.ReadRequest(bufio.NewReader(pr))
+		if err == nil {
+			// Ensure all the body is read; otherwise
+			// we'll get a partial dump.
+			io.Copy(io.Discard, req.Body)
+			req.Body.Close()
+		}
+		select {
+		case dr.c <- strings.NewReader("HTTP/1.1 204 No Content\r\nConnection: close\r\n\r\n"):
+		case <-quitReadCh:
+			// Ensure delegateReader.Read doesn't block forever if we get an error.
+			close(dr.c)
+		}
+	}()
+
+	_, err := t.RoundTrip(reqSend)
+
+	req.Body = save
+	if err != nil {
+		pw.Close()
+		dr.err = err
+		close(quitReadCh)
+		return nil, err
+	}
+	dump := buf.Bytes()
+
+	// If we used a dummy body above, remove it now.
+	// TODO: if the req.ContentLength is large, we allocate memory
+	// unnecessarily just to slice it off here. But this is just
+	// a debug function, so this is acceptable for now. We could
+	// discard the body earlier if this matters.
+	if dummyBody {
+		if i := bytes.Index(dump, []byte("\r\n\r\n")); i >= 0 {
+			dump = dump[:i+4]
+		}
+	}
+	return dump, nil
+}
+
+// delegateReader is a reader that delegates to another reader,
+// once it arrives on a channel.
+type delegateReader struct {
+	c   chan io.Reader
+	err error     // only used if r is nil and c is closed.
+	r   io.Reader // nil until received from c
+}
+
+func (r *delegateReader) Read(p []byte) (int, error) {
+	if r.r == nil {
+		var ok bool
+		if r.r, ok = <-r.c; !ok {
+			return 0, r.err
+		}
+	}
+	return r.r.Read(p)
+}
+
+// Return value if nonempty, def otherwise.
+func valueOrDefault(value, def string) string {
+	if value != "" {
+		return value
+	}
+	return def
+}
+
+var reqWriteExcludeHeaderDump = map[string]bool{
+	"Host":              true, // not in Header map anyway
+	"Transfer-Encoding": true,
+	"Trailer":           true,
+}
+
+// DumpRequest returns the given request in its HTTP/1.x wire
+// representation. It should only be used by servers to debug client
+// requests. The returned representation is an approximation only;
+// some details of the initial request are lost while parsing it into
+// an http.Request. In particular, the order and case of header field
+// names are lost. The order of values in multi-valued headers is kept
+// intact. HTTP/2 requests are dumped in HTTP/1.x form, not in their
+// original binary representations.
+//
+// If body is true, DumpRequest also returns the body. To do so, it
+// consumes req.Body and then replaces it with a new io.ReadCloser
+// that yields the same bytes. If DumpRequest returns an error,
+// the state of req is undefined.
+//
+// The documentation for http.Request.Write details which fields
+// of req are included in the dump.
+func DumpRequest(req *http.Request, body bool) ([]byte, error) {
+	var err error
+	save := req.Body
+	if !body || req.Body == nil {
+		req.Body = nil
+	} else {
+		save, req.Body, err = drainBody(req.Body)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	var b bytes.Buffer
+
+	// By default, print out the unmodified req.RequestURI, which
+	// is always set for incoming server requests. But because we
+	// previously used req.URL.RequestURI and the docs weren't
+	// always so clear about when to use DumpRequest vs
+	// DumpRequestOut, fall back to the old way if the caller
+	// provides a non-server Request.
+	reqURI := req.RequestURI
+	if reqURI == "" {
+		reqURI = req.URL.RequestURI()
+	}
+
+	fmt.Fprintf(&b, "%s %s HTTP/%d.%d\r\n", valueOrDefault(req.Method, "GET"),
+		reqURI, req.ProtoMajor, req.ProtoMinor)
+
+	absRequestURI := strings.HasPrefix(req.RequestURI, "http://") || strings.HasPrefix(req.RequestURI, "https://")
+	if !absRequestURI {
+		host := req.Host
+		if host == "" && req.URL != nil {
+			host = req.URL.Host
+		}
+		if host != "" {
+			fmt.Fprintf(&b, "Host: %s\r\n", host)
+		}
+	}
+
+	chunked := len(req.TransferEncoding) > 0 && req.TransferEncoding[0] == "chunked"
+	if len(req.TransferEncoding) > 0 {
+		fmt.Fprintf(&b, "Transfer-Encoding: %s\r\n", strings.Join(req.TransferEncoding, ","))
+	}
+
+	err = req.Header.WriteSubset(&b, reqWriteExcludeHeaderDump)
+	if err != nil {
+		return nil, err
+	}
+
+	io.WriteString(&b, "\r\n")
+
+	if req.Body != nil {
+		var dest io.Writer = &b
+		if chunked {
+			dest = NewChunkedWriter(dest)
+		}
+		_, err = io.Copy(dest, req.Body)
+		if chunked {
+			dest.(io.Closer).Close()
+			io.WriteString(&b, "\r\n")
+		}
+	}
+
+	req.Body = save
+	if err != nil {
+		return nil, err
+	}
+	return b.Bytes(), nil
+}
+
+// errNoBody is a sentinel error value used by failureToReadBody so we
+// can detect that the lack of body was intentional.
+var errNoBody = errors.New("sentinel error value")
+
+// failureToReadBody is an io.ReadCloser that just returns errNoBody on
+// Read. It's swapped in when we don't actually want to consume
+// the body, but need a non-nil one, and want to distinguish the
+// error from reading the dummy body.
+type failureToReadBody struct{}
+
+func (failureToReadBody) Read([]byte) (int, error) { return 0, errNoBody }
+func (failureToReadBody) Close() error             { return nil }
+
+// emptyBody is an instance of empty reader.
+var emptyBody = io.NopCloser(strings.NewReader(""))
+
+// DumpResponse is like DumpRequest but dumps a response.
+func DumpResponse(resp *http.Response, body bool) ([]byte, error) {
+	var b bytes.Buffer
+	var err error
+	save := resp.Body
+	savecl := resp.ContentLength
+
+	if !body {
+		// For content length of zero. Make sure the body is an empty
+		// reader, instead of returning error through failureToReadBody{}.
+		if resp.ContentLength == 0 {
+			resp.Body = emptyBody
+		} else {
+			resp.Body = failureToReadBody{}
+		}
+	} else if resp.Body == nil {
+		resp.Body = emptyBody
+	} else {
+		save, resp.Body, err = drainBody(resp.Body)
+		if err != nil {
+			return nil, err
+		}
+	}
+	err = resp.Write(&b)
+	if err == errNoBody {
+		err = nil
+	}
+	resp.Body = save
+	resp.ContentLength = savecl
+	if err != nil {
+		return nil, err
+	}
+	return b.Bytes(), nil
+}

http/httputil/httputil.go

@@ -0,0 +1,43 @@
+// TINYGO: The following is copied from Go 1.21.5 official implementation.
+
+// 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 httputil provides HTTP utility functions, complementing the
+// more common ones in the net/http package.
+package httputil
+
+import (
+	"io"
+	"net/http/internal"
+)
+
+// NewChunkedReader returns a new chunkedReader that translates the data read from r
+// out of HTTP "chunked" format before returning it.
+// The chunkedReader returns io.EOF when the final 0-length chunk is read.
+//
+// NewChunkedReader is not needed by normal applications. The http package
+// automatically decodes chunking when reading response bodies.
+func NewChunkedReader(r io.Reader) io.Reader {
+	return internal.NewChunkedReader(r)
+}
+
+// NewChunkedWriter returns a new chunkedWriter that translates writes into HTTP
+// "chunked" format before writing them to w. Closing the returned chunkedWriter
+// sends the final 0-length chunk that marks the end of the stream but does
+// not send the final CRLF that appears after trailers; trailers and the last
+// CRLF must be written separately.
+//
+// NewChunkedWriter is not needed by normal applications. The http
+// package adds chunking automatically if handlers don't set a
+// Content-Length header. Using NewChunkedWriter inside a handler
+// would result in double chunking or chunking with a Content-Length
+// length, both of which are wrong.
+func NewChunkedWriter(w io.Writer) io.WriteCloser {
+	return internal.NewChunkedWriter(w)
+}
+
+// ErrLineTooLong is returned when reading malformed chunked data
+// with lines that are too long.
+var ErrLineTooLong = internal.ErrLineTooLong

http/httputil/persist.go

@@ -0,0 +1,433 @@
+// TINYGO: The following is copied from Go 1.21.5 official implementation.
+
+// 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 httputil
+
+import (
+	"bufio"
+	"errors"
+	"io"
+	"net"
+	"net/http"
+	"net/textproto"
+	"sync"
+)
+
+var (
+	// Deprecated: No longer used.
+	ErrPersistEOF = &http.ProtocolError{ErrorString: "persistent connection closed"}
+
+	// Deprecated: No longer used.
+	ErrClosed = &http.ProtocolError{ErrorString: "connection closed by user"}
+
+	// Deprecated: No longer used.
+	ErrPipeline = &http.ProtocolError{ErrorString: "pipeline error"}
+)
+
+// This is an API usage error - the local side is closed.
+// ErrPersistEOF (above) reports that the remote side is closed.
+var errClosed = errors.New("i/o operation on closed connection")
+
+// ServerConn is an artifact of Go's early HTTP implementation.
+// It is low-level, old, and unused by Go's current HTTP stack.
+// We should have deleted it before Go 1.
+//
+// Deprecated: Use the Server in package net/http instead.
+type ServerConn struct {
+	mu              sync.Mutex // read-write protects the following fields
+	c               net.Conn
+	r               *bufio.Reader
+	re, we          error // read/write errors
+	lastbody        io.ReadCloser
+	nread, nwritten int
+	pipereq         map[*http.Request]uint
+
+	pipe textproto.Pipeline
+}
+
+// NewServerConn is an artifact of Go's early HTTP implementation.
+// It is low-level, old, and unused by Go's current HTTP stack.
+// We should have deleted it before Go 1.
+//
+// Deprecated: Use the Server in package net/http instead.
+func NewServerConn(c net.Conn, r *bufio.Reader) *ServerConn {
+	if r == nil {
+		r = bufio.NewReader(c)
+	}
+	return &ServerConn{c: c, r: r, pipereq: make(map[*http.Request]uint)}
+}
+
+// Hijack detaches the ServerConn and returns the underlying connection as well
+// as the read-side bufio which may have some left over data. Hijack may be
+// called before Read has signaled the end of the keep-alive logic. The user
+// should not call Hijack while Read or Write is in progress.
+func (sc *ServerConn) Hijack() (net.Conn, *bufio.Reader) {
+	sc.mu.Lock()
+	defer sc.mu.Unlock()
+	c := sc.c
+	r := sc.r
+	sc.c = nil
+	sc.r = nil
+	return c, r
+}
+
+// Close calls Hijack and then also closes the underlying connection.
+func (sc *ServerConn) Close() error {
+	c, _ := sc.Hijack()
+	if c != nil {
+		return c.Close()
+	}
+	return nil
+}
+
+// Read returns the next request on the wire. An ErrPersistEOF is returned if
+// it is gracefully determined that there are no more requests (e.g. after the
+// first request on an HTTP/1.0 connection, or after a Connection:close on a
+// HTTP/1.1 connection).
+func (sc *ServerConn) Read() (*http.Request, error) {
+	var req *http.Request
+	var err error
+
+	// Ensure ordered execution of Reads and Writes
+	id := sc.pipe.Next()
+	sc.pipe.StartRequest(id)
+	defer func() {
+		sc.pipe.EndRequest(id)
+		if req == nil {
+			sc.pipe.StartResponse(id)
+			sc.pipe.EndResponse(id)
+		} else {
+			// Remember the pipeline id of this request
+			sc.mu.Lock()
+			sc.pipereq[req] = id
+			sc.mu.Unlock()
+		}
+	}()
+
+	sc.mu.Lock()
+	if sc.we != nil { // no point receiving if write-side broken or closed
+		defer sc.mu.Unlock()
+		return nil, sc.we
+	}
+	if sc.re != nil {
+		defer sc.mu.Unlock()
+		return nil, sc.re
+	}
+	if sc.r == nil { // connection closed by user in the meantime
+		defer sc.mu.Unlock()
+		return nil, errClosed
+	}
+	r := sc.r
+	lastbody := sc.lastbody
+	sc.lastbody = nil
+	sc.mu.Unlock()
+
+	// Make sure body is fully consumed, even if user does not call body.Close
+	if lastbody != nil {
+		// body.Close is assumed to be idempotent and multiple calls to
+		// it should return the error that its first invocation
+		// returned.
+		err = lastbody.Close()
+		if err != nil {
+			sc.mu.Lock()
+			defer sc.mu.Unlock()
+			sc.re = err
+			return nil, err
+		}
+	}
+
+	req, err = http.ReadRequest(r)
+	sc.mu.Lock()
+	defer sc.mu.Unlock()
+	if err != nil {
+		if err == io.ErrUnexpectedEOF {
+			// A close from the opposing client is treated as a
+			// graceful close, even if there was some unparse-able
+			// data before the close.
+			sc.re = ErrPersistEOF
+			return nil, sc.re
+		} else {
+			sc.re = err
+			return req, err
+		}
+	}
+	sc.lastbody = req.Body
+	sc.nread++
+	if req.Close {
+		sc.re = ErrPersistEOF
+		return req, sc.re
+	}
+	return req, err
+}
+
+// Pending returns the number of unanswered requests
+// that have been received on the connection.
+func (sc *ServerConn) Pending() int {
+	sc.mu.Lock()
+	defer sc.mu.Unlock()
+	return sc.nread - sc.nwritten
+}
+
+// Write writes resp in response to req. To close the connection gracefully, set the
+// Response.Close field to true. Write should be considered operational until
+// it returns an error, regardless of any errors returned on the Read side.
+func (sc *ServerConn) Write(req *http.Request, resp *http.Response) error {
+
+	// Retrieve the pipeline ID of this request/response pair
+	sc.mu.Lock()
+	id, ok := sc.pipereq[req]
+	delete(sc.pipereq, req)
+	if !ok {
+		sc.mu.Unlock()
+		return ErrPipeline
+	}
+	sc.mu.Unlock()
+
+	// Ensure pipeline order
+	sc.pipe.StartResponse(id)
+	defer sc.pipe.EndResponse(id)
+
+	sc.mu.Lock()
+	if sc.we != nil {
+		defer sc.mu.Unlock()
+		return sc.we
+	}
+	if sc.c == nil { // connection closed by user in the meantime
+		defer sc.mu.Unlock()
+		return ErrClosed
+	}
+	c := sc.c
+	if sc.nread <= sc.nwritten {
+		defer sc.mu.Unlock()
+		return errors.New("persist server pipe count")
+	}
+	if resp.Close {
+		// After signaling a keep-alive close, any pipelined unread
+		// requests will be lost. It is up to the user to drain them
+		// before signaling.
+		sc.re = ErrPersistEOF
+	}
+	sc.mu.Unlock()
+
+	err := resp.Write(c)
+	sc.mu.Lock()
+	defer sc.mu.Unlock()
+	if err != nil {
+		sc.we = err
+		return err
+	}
+	sc.nwritten++
+
+	return nil
+}
+
+// ClientConn is an artifact of Go's early HTTP implementation.
+// It is low-level, old, and unused by Go's current HTTP stack.
+// We should have deleted it before Go 1.
+//
+// Deprecated: Use Client or Transport in package net/http instead.
+type ClientConn struct {
+	mu              sync.Mutex // read-write protects the following fields
+	c               net.Conn
+	r               *bufio.Reader
+	re, we          error // read/write errors
+	lastbody        io.ReadCloser
+	nread, nwritten int
+	pipereq         map[*http.Request]uint
+
+	pipe     textproto.Pipeline
+	writeReq func(*http.Request, io.Writer) error
+}
+
+// NewClientConn is an artifact of Go's early HTTP implementation.
+// It is low-level, old, and unused by Go's current HTTP stack.
+// We should have deleted it before Go 1.
+//
+// Deprecated: Use the Client or Transport in package net/http instead.
+func NewClientConn(c net.Conn, r *bufio.Reader) *ClientConn {
+	if r == nil {
+		r = bufio.NewReader(c)
+	}
+	return &ClientConn{
+		c:        c,
+		r:        r,
+		pipereq:  make(map[*http.Request]uint),
+		writeReq: (*http.Request).Write,
+	}
+}
+
+// NewProxyClientConn is an artifact of Go's early HTTP implementation.
+// It is low-level, old, and unused by Go's current HTTP stack.
+// We should have deleted it before Go 1.
+//
+// Deprecated: Use the Client or Transport in package net/http instead.
+func NewProxyClientConn(c net.Conn, r *bufio.Reader) *ClientConn {
+	cc := NewClientConn(c, r)
+	cc.writeReq = (*http.Request).WriteProxy
+	return cc
+}
+
+// Hijack detaches the ClientConn and returns the underlying connection as well
+// as the read-side bufio which may have some left over data. Hijack may be
+// called before the user or Read have signaled the end of the keep-alive
+// logic. The user should not call Hijack while Read or Write is in progress.
+func (cc *ClientConn) Hijack() (c net.Conn, r *bufio.Reader) {
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
+	c = cc.c
+	r = cc.r
+	cc.c = nil
+	cc.r = nil
+	return
+}
+
+// Close calls Hijack and then also closes the underlying connection.
+func (cc *ClientConn) Close() error {
+	c, _ := cc.Hijack()
+	if c != nil {
+		return c.Close()
+	}
+	return nil
+}
+
+// Write writes a request. An ErrPersistEOF error is returned if the connection
+// has been closed in an HTTP keep-alive sense. If req.Close equals true, the
+// keep-alive connection is logically closed after this request and the opposing
+// server is informed. An ErrUnexpectedEOF indicates the remote closed the
+// underlying TCP connection, which is usually considered as graceful close.
+func (cc *ClientConn) Write(req *http.Request) error {
+	var err error
+
+	// Ensure ordered execution of Writes
+	id := cc.pipe.Next()
+	cc.pipe.StartRequest(id)
+	defer func() {
+		cc.pipe.EndRequest(id)
+		if err != nil {
+			cc.pipe.StartResponse(id)
+			cc.pipe.EndResponse(id)
+		} else {
+			// Remember the pipeline id of this request
+			cc.mu.Lock()
+			cc.pipereq[req] = id
+			cc.mu.Unlock()
+		}
+	}()
+
+	cc.mu.Lock()
+	if cc.re != nil { // no point sending if read-side closed or broken
+		defer cc.mu.Unlock()
+		return cc.re
+	}
+	if cc.we != nil {
+		defer cc.mu.Unlock()
+		return cc.we
+	}
+	if cc.c == nil { // connection closed by user in the meantime
+		defer cc.mu.Unlock()
+		return errClosed
+	}
+	c := cc.c
+	if req.Close {
+		// We write the EOF to the write-side error, because there
+		// still might be some pipelined reads
+		cc.we = ErrPersistEOF
+	}
+	cc.mu.Unlock()
+
+	err = cc.writeReq(req, c)
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
+	if err != nil {
+		cc.we = err
+		return err
+	}
+	cc.nwritten++
+
+	return nil
+}
+
+// Pending returns the number of unanswered requests
+// that have been sent on the connection.
+func (cc *ClientConn) Pending() int {
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
+	return cc.nwritten - cc.nread
+}
+
+// Read reads the next response from the wire. A valid response might be
+// returned together with an ErrPersistEOF, which means that the remote
+// requested that this be the last request serviced. Read can be called
+// concurrently with Write, but not with another Read.
+func (cc *ClientConn) Read(req *http.Request) (resp *http.Response, err error) {
+	// Retrieve the pipeline ID of this request/response pair
+	cc.mu.Lock()
+	id, ok := cc.pipereq[req]
+	delete(cc.pipereq, req)
+	if !ok {
+		cc.mu.Unlock()
+		return nil, ErrPipeline
+	}
+	cc.mu.Unlock()
+
+	// Ensure pipeline order
+	cc.pipe.StartResponse(id)
+	defer cc.pipe.EndResponse(id)
+
+	cc.mu.Lock()
+	if cc.re != nil {
+		defer cc.mu.Unlock()
+		return nil, cc.re
+	}
+	if cc.r == nil { // connection closed by user in the meantime
+		defer cc.mu.Unlock()
+		return nil, errClosed
+	}
+	r := cc.r
+	lastbody := cc.lastbody
+	cc.lastbody = nil
+	cc.mu.Unlock()
+
+	// Make sure body is fully consumed, even if user does not call body.Close
+	if lastbody != nil {
+		// body.Close is assumed to be idempotent and multiple calls to
+		// it should return the error that its first invocation
+		// returned.
+		err = lastbody.Close()
+		if err != nil {
+			cc.mu.Lock()
+			defer cc.mu.Unlock()
+			cc.re = err
+			return nil, err
+		}
+	}
+
+	resp, err = http.ReadResponse(r, req)
+	cc.mu.Lock()
+	defer cc.mu.Unlock()
+	if err != nil {
+		cc.re = err
+		return resp, err
+	}
+	cc.lastbody = resp.Body
+
+	cc.nread++
+
+	if resp.Close {
+		cc.re = ErrPersistEOF // don't send any more requests
+		return resp, cc.re
+	}
+	return resp, err
+}
+
+// Do is convenience method that writes a request and reads a response.
+func (cc *ClientConn) Do(req *http.Request) (*http.Response, error) {
+	err := cc.Write(req)
+	if err != nil {
+		return nil, err
+	}
+	return cc.Read(req)
+}

http/httputil/reverseproxy.go

@@ -0,0 +1,836 @@
+// TINYGO: The following is copied from Go 1.21.5 official implementation.
+
+// 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.
+
+// HTTP reverse proxy handler
+
+package httputil
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"mime"
+	"net"
+	"net/http"
+	"net/http/httptrace"
+	"net/http/internal/ascii"
+	"net/textproto"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+
+	"golang.org/x/net/http/httpguts"
+)
+
+// A ProxyRequest contains a request to be rewritten by a ReverseProxy.
+type ProxyRequest struct {
+	// In is the request received by the proxy.
+	// The Rewrite function must not modify In.
+	In *http.Request
+
+	// Out is the request which will be sent by the proxy.
+	// The Rewrite function may modify or replace this request.
+	// Hop-by-hop headers are removed from this request
+	// before Rewrite is called.
+	Out *http.Request
+}
+
+// SetURL routes the outbound request to the scheme, host, and base path
+// provided in target. If the target's path is "/base" and the incoming
+// request was for "/dir", the target request will be for "/base/dir".
+//
+// SetURL rewrites the outbound Host header to match the target's host.
+// To preserve the inbound request's Host header (the default behavior
+// of NewSingleHostReverseProxy):
+//
+//	rewriteFunc := func(r *httputil.ProxyRequest) {
+//		r.SetURL(url)
+//		r.Out.Host = r.In.Host
+//	}
+func (r *ProxyRequest) SetURL(target *url.URL) {
+	rewriteRequestURL(r.Out, target)
+	r.Out.Host = ""
+}
+
+// SetXForwarded sets the X-Forwarded-For, X-Forwarded-Host, and
+// X-Forwarded-Proto headers of the outbound request.
+//
+//   - The X-Forwarded-For header is set to the client IP address.
+//   - The X-Forwarded-Host header is set to the host name requested
+//     by the client.
+//   - The X-Forwarded-Proto header is set to "http" or "https", depending
+//     on whether the inbound request was made on a TLS-enabled connection.
+//
+// If the outbound request contains an existing X-Forwarded-For header,
+// SetXForwarded appends the client IP address to it. To append to the
+// inbound request's X-Forwarded-For header (the default behavior of
+// ReverseProxy when using a Director function), copy the header
+// from the inbound request before calling SetXForwarded:
+//
+//	rewriteFunc := func(r *httputil.ProxyRequest) {
+//		r.Out.Header["X-Forwarded-For"] = r.In.Header["X-Forwarded-For"]
+//		r.SetXForwarded()
+//	}
+func (r *ProxyRequest) SetXForwarded() {
+	clientIP, _, err := net.SplitHostPort(r.In.RemoteAddr)
+	if err == nil {
+		prior := r.Out.Header["X-Forwarded-For"]
+		if len(prior) > 0 {
+			clientIP = strings.Join(prior, ", ") + ", " + clientIP
+		}
+		r.Out.Header.Set("X-Forwarded-For", clientIP)
+	} else {
+		r.Out.Header.Del("X-Forwarded-For")
+	}
+	r.Out.Header.Set("X-Forwarded-Host", r.In.Host)
+	if r.In.TLS == nil {
+		r.Out.Header.Set("X-Forwarded-Proto", "http")
+	} else {
+		r.Out.Header.Set("X-Forwarded-Proto", "https")
+	}
+}
+
+// ReverseProxy is an HTTP Handler that takes an incoming request and
+// sends it to another server, proxying the response back to the
+// client.
+//
+// 1xx responses are forwarded to the client if the underlying
+// transport supports ClientTrace.Got1xxResponse.
+type ReverseProxy struct {
+	// Rewrite must be a function which modifies
+	// the request into a new request to be sent
+	// using Transport. Its response is then copied
+	// back to the original client unmodified.
+	// Rewrite must not access the provided ProxyRequest
+	// or its contents after returning.
+	//
+	// The Forwarded, X-Forwarded, X-Forwarded-Host,
+	// and X-Forwarded-Proto headers are removed from the
+	// outbound request before Rewrite is called. See also
+	// the ProxyRequest.SetXForwarded method.
+	//
+	// Unparsable query parameters are removed from the
+	// outbound request before Rewrite is called.
+	// The Rewrite function may copy the inbound URL's
+	// RawQuery to the outbound URL to preserve the original
+	// parameter string. Note that this can lead to security
+	// issues if the proxy's interpretation of query parameters
+	// does not match that of the downstream server.
+	//
+	// At most one of Rewrite or Director may be set.
+	Rewrite func(*ProxyRequest)
+
+	// Director is a function which modifies
+	// the request into a new request to be sent
+	// using Transport. Its response is then copied
+	// back to the original client unmodified.
+	// Director must not access the provided Request
+	// after returning.
+	//
+	// By default, the X-Forwarded-For header is set to the
+	// value of the client IP address. If an X-Forwarded-For
+	// header already exists, the client IP is appended to the
+	// existing values. As a special case, if the header
+	// exists in the Request.Header map but has a nil value
+	// (such as when set by the Director func), the X-Forwarded-For
+	// header is not modified.
+	//
+	// To prevent IP spoofing, be sure to delete any pre-existing
+	// X-Forwarded-For header coming from the client or
+	// an untrusted proxy.
+	//
+	// Hop-by-hop headers are removed from the request after
+	// Director returns, which can remove headers added by
+	// Director. Use a Rewrite function instead to ensure
+	// modifications to the request are preserved.
+	//
+	// Unparsable query parameters are removed from the outbound
+	// request if Request.Form is set after Director returns.
+	//
+	// At most one of Rewrite or Director may be set.
+	Director func(*http.Request)
+
+	// The transport used to perform proxy requests.
+	// If nil, http.DefaultTransport is used.
+	Transport http.RoundTripper
+
+	// FlushInterval specifies the flush interval
+	// to flush to the client while copying the
+	// response body.
+	// If zero, no periodic flushing is done.
+	// A negative value means to flush immediately
+	// after each write to the client.
+	// The FlushInterval is ignored when ReverseProxy
+	// recognizes a response as a streaming response, or
+	// if its ContentLength is -1; for such responses, writes
+	// are flushed to the client immediately.
+	FlushInterval time.Duration
+
+	// ErrorLog specifies an optional logger for errors
+	// that occur when attempting to proxy the request.
+	// If nil, logging is done via the log package's standard logger.
+	ErrorLog *log.Logger
+
+	// BufferPool optionally specifies a buffer pool to
+	// get byte slices for use by io.CopyBuffer when
+	// copying HTTP response bodies.
+	BufferPool BufferPool
+
+	// ModifyResponse is an optional function that modifies the
+	// Response from the backend. It is called if the backend
+	// returns a response at all, with any HTTP status code.
+	// If the backend is unreachable, the optional ErrorHandler is
+	// called without any call to ModifyResponse.
+	//
+	// If ModifyResponse returns an error, ErrorHandler is called
+	// with its error value. If ErrorHandler is nil, its default
+	// implementation is used.
+	ModifyResponse func(*http.Response) error
+
+	// ErrorHandler is an optional function that handles errors
+	// reaching the backend or errors from ModifyResponse.
+	//
+	// If nil, the default is to log the provided error and return
+	// a 502 Status Bad Gateway response.
+	ErrorHandler func(http.ResponseWriter, *http.Request, error)
+}
+
+// A BufferPool is an interface for getting and returning temporary
+// byte slices for use by io.CopyBuffer.
+type BufferPool interface {
+	Get() []byte
+	Put([]byte)
+}
+
+func singleJoiningSlash(a, b string) string {
+	aslash := strings.HasSuffix(a, "/")
+	bslash := strings.HasPrefix(b, "/")
+	switch {
+	case aslash && bslash:
+		return a + b[1:]
+	case !aslash && !bslash:
+		return a + "/" + b
+	}
+	return a + b
+}
+
+func joinURLPath(a, b *url.URL) (path, rawpath string) {
+	if a.RawPath == "" && b.RawPath == "" {
+		return singleJoiningSlash(a.Path, b.Path), ""
+	}
+	// Same as singleJoiningSlash, but uses EscapedPath to determine
+	// whether a slash should be added
+	apath := a.EscapedPath()
+	bpath := b.EscapedPath()
+
+	aslash := strings.HasSuffix(apath, "/")
+	bslash := strings.HasPrefix(bpath, "/")
+
+	switch {
+	case aslash && bslash:
+		return a.Path + b.Path[1:], apath + bpath[1:]
+	case !aslash && !bslash:
+		return a.Path + "/" + b.Path, apath + "/" + bpath
+	}
+	return a.Path + b.Path, apath + bpath
+}
+
+// NewSingleHostReverseProxy returns a new ReverseProxy that routes
+// URLs to the scheme, host, and base path provided in target. If the
+// target's path is "/base" and the incoming request was for "/dir",
+// the target request will be for /base/dir.
+//
+// NewSingleHostReverseProxy does not rewrite the Host header.
+//
+// To customize the ReverseProxy behavior beyond what
+// NewSingleHostReverseProxy provides, use ReverseProxy directly
+// with a Rewrite function. The ProxyRequest SetURL method
+// may be used to route the outbound request. (Note that SetURL,
+// unlike NewSingleHostReverseProxy, rewrites the Host header
+// of the outbound request by default.)
+//
+//	proxy := &ReverseProxy{
+//		Rewrite: func(r *ProxyRequest) {
+//			r.SetURL(target)
+//			r.Out.Host = r.In.Host // if desired
+//		},
+//	}
+func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {
+	director := func(req *http.Request) {
+		rewriteRequestURL(req, target)
+	}
+	return &ReverseProxy{Director: director}
+}
+
+func rewriteRequestURL(req *http.Request, target *url.URL) {
+	targetQuery := target.RawQuery
+	req.URL.Scheme = target.Scheme
+	req.URL.Host = target.Host
+	req.URL.Path, req.URL.RawPath = joinURLPath(target, req.URL)
+	if targetQuery == "" || req.URL.RawQuery == "" {
+		req.URL.RawQuery = targetQuery + req.URL.RawQuery
+	} else {
+		req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
+	}
+}
+
+func copyHeader(dst, src http.Header) {
+	for k, vv := range src {
+		for _, v := range vv {
+			dst.Add(k, v)
+		}
+	}
+}
+
+// Hop-by-hop headers. These are removed when sent to the backend.
+// As of RFC 7230, hop-by-hop headers are required to appear in the
+// Connection header field. These are the headers defined by the
+// obsoleted RFC 2616 (section 13.5.1) and are used for backward
+// compatibility.
+var hopHeaders = []string{
+	"Connection",
+	"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
+	"Keep-Alive",
+	"Proxy-Authenticate",
+	"Proxy-Authorization",
+	"Te",      // canonicalized version of "TE"
+	"Trailer", // not Trailers per URL above; https://www.rfc-editor.org/errata_search.php?eid=4522
+	"Transfer-Encoding",
+	"Upgrade",
+}
+
+func (p *ReverseProxy) defaultErrorHandler(rw http.ResponseWriter, req *http.Request, err error) {
+	p.logf("http: proxy error: %v", err)
+	rw.WriteHeader(http.StatusBadGateway)
+}
+
+func (p *ReverseProxy) getErrorHandler() func(http.ResponseWriter, *http.Request, error) {
+	if p.ErrorHandler != nil {
+		return p.ErrorHandler
+	}
+	return p.defaultErrorHandler
+}
+
+// modifyResponse conditionally runs the optional ModifyResponse hook
+// and reports whether the request should proceed.
+func (p *ReverseProxy) modifyResponse(rw http.ResponseWriter, res *http.Response, req *http.Request) bool {
+	if p.ModifyResponse == nil {
+		return true
+	}
+	if err := p.ModifyResponse(res); err != nil {
+		res.Body.Close()
+		p.getErrorHandler()(rw, req, err)
+		return false
+	}
+	return true
+}
+
+func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
+	transport := p.Transport
+	if transport == nil {
+		transport = http.DefaultTransport
+	}
+
+	ctx := req.Context()
+	if ctx.Done() != nil {
+		// CloseNotifier predates context.Context, and has been
+		// entirely superseded by it. If the request contains
+		// a Context that carries a cancellation signal, don't
+		// bother spinning up a goroutine to watch the CloseNotify
+		// channel (if any).
+		//
+		// If the request Context has a nil Done channel (which
+		// means it is either context.Background, or a custom
+		// Context implementation with no cancellation signal),
+		// then consult the CloseNotifier if available.
+	} else if cn, ok := rw.(http.CloseNotifier); ok {
+		var cancel context.CancelFunc
+		ctx, cancel = context.WithCancel(ctx)
+		defer cancel()
+		notifyChan := cn.CloseNotify()
+		go func() {
+			select {
+			case <-notifyChan:
+				cancel()
+			case <-ctx.Done():
+			}
+		}()
+	}
+
+	outreq := req.Clone(ctx)
+	if req.ContentLength == 0 {
+		outreq.Body = nil // Issue 16036: nil Body for http.Transport retries
+	}
+	if outreq.Body != nil {
+		// Reading from the request body after returning from a handler is not
+		// allowed, and the RoundTrip goroutine that reads the Body can outlive
+		// this handler. This can lead to a crash if the handler panics (see
+		// Issue 46866). Although calling Close doesn't guarantee there isn't
+		// any Read in flight after the handle returns, in practice it's safe to
+		// read after closing it.
+		defer outreq.Body.Close()
+	}
+	if outreq.Header == nil {
+		outreq.Header = make(http.Header) // Issue 33142: historical behavior was to always allocate
+	}
+
+	if (p.Director != nil) == (p.Rewrite != nil) {
+		p.getErrorHandler()(rw, req, errors.New("ReverseProxy must have exactly one of Director or Rewrite set"))
+		return
+	}
+
+	if p.Director != nil {
+		p.Director(outreq)
+		if outreq.Form != nil {
+			outreq.URL.RawQuery = cleanQueryParams(outreq.URL.RawQuery)
+		}
+	}
+	outreq.Close = false
+
+	reqUpType := upgradeType(outreq.Header)
+	if !ascii.IsPrint(reqUpType) {
+		p.getErrorHandler()(rw, req, fmt.Errorf("client tried to switch to invalid protocol %q", reqUpType))
+		return
+	}
+	removeHopByHopHeaders(outreq.Header)
+
+	// Issue 21096: tell backend applications that care about trailer support
+	// that we support trailers. (We do, but we don't go out of our way to
+	// advertise that unless the incoming client request thought it was worth
+	// mentioning.) Note that we look at req.Header, not outreq.Header, since
+	// the latter has passed through removeHopByHopHeaders.
+	if httpguts.HeaderValuesContainsToken(req.Header["Te"], "trailers") {
+		outreq.Header.Set("Te", "trailers")
+	}
+
+	// After stripping all the hop-by-hop connection headers above, add back any
+	// necessary for protocol upgrades, such as for websockets.
+	if reqUpType != "" {
+		outreq.Header.Set("Connection", "Upgrade")
+		outreq.Header.Set("Upgrade", reqUpType)
+	}
+
+	if p.Rewrite != nil {
+		// Strip client-provided forwarding headers.
+		// The Rewrite func may use SetXForwarded to set new values
+		// for these or copy the previous values from the inbound request.
+		outreq.Header.Del("Forwarded")
+		outreq.Header.Del("X-Forwarded-For")
+		outreq.Header.Del("X-Forwarded-Host")
+		outreq.Header.Del("X-Forwarded-Proto")
+
+		// Remove unparsable query parameters from the outbound request.
+		outreq.URL.RawQuery = cleanQueryParams(outreq.URL.RawQuery)
+
+		pr := &ProxyRequest{
+			In:  req,
+			Out: outreq,
+		}
+		p.Rewrite(pr)
+		outreq = pr.Out
+	} else {
+		if clientIP, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
+			// If we aren't the first proxy retain prior
+			// X-Forwarded-For information as a comma+space
+			// separated list and fold multiple headers into one.
+			prior, ok := outreq.Header["X-Forwarded-For"]
+			omit := ok && prior == nil // Issue 38079: nil now means don't populate the header
+			if len(prior) > 0 {
+				clientIP = strings.Join(prior, ", ") + ", " + clientIP
+			}
+			if !omit {
+				outreq.Header.Set("X-Forwarded-For", clientIP)
+			}
+		}
+	}
+
+	if _, ok := outreq.Header["User-Agent"]; !ok {
+		// If the outbound request doesn't have a User-Agent header set,
+		// don't send the default Go HTTP client User-Agent.
+		outreq.Header.Set("User-Agent", "")
+	}
+
+	trace := &httptrace.ClientTrace{
+		Got1xxResponse: func(code int, header textproto.MIMEHeader) error {
+			h := rw.Header()
+			copyHeader(h, http.Header(header))
+			rw.WriteHeader(code)
+
+			// Clear headers, it's not automatically done by ResponseWriter.WriteHeader() for 1xx responses
+			for k := range h {
+				delete(h, k)
+			}
+
+			return nil
+		},
+	}
+	outreq = outreq.WithContext(httptrace.WithClientTrace(outreq.Context(), trace))
+
+	res, err := transport.RoundTrip(outreq)
+	if err != nil {
+		p.getErrorHandler()(rw, outreq, err)
+		return
+	}
+
+	// Deal with 101 Switching Protocols responses: (WebSocket, h2c, etc)
+	if res.StatusCode == http.StatusSwitchingProtocols {
+		if !p.modifyResponse(rw, res, outreq) {
+			return
+		}
+		p.handleUpgradeResponse(rw, outreq, res)
+		return
+	}
+
+	removeHopByHopHeaders(res.Header)
+
+	if !p.modifyResponse(rw, res, outreq) {
+		return
+	}
+
+	copyHeader(rw.Header(), res.Header)
+
+	// The "Trailer" header isn't included in the Transport's response,
+	// at least for *http.Transport. Build it up from Trailer.
+	announcedTrailers := len(res.Trailer)
+	if announcedTrailers > 0 {
+		trailerKeys := make([]string, 0, len(res.Trailer))
+		for k := range res.Trailer {
+			trailerKeys = append(trailerKeys, k)
+		}
+		rw.Header().Add("Trailer", strings.Join(trailerKeys, ", "))
+	}
+
+	rw.WriteHeader(res.StatusCode)
+
+	err = p.copyResponse(rw, res.Body, p.flushInterval(res))
+	if err != nil {
+		defer res.Body.Close()
+		// Since we're streaming the response, if we run into an error all we can do
+		// is abort the request. Issue 23643: ReverseProxy should use ErrAbortHandler
+		// on read error while copying body.
+		if !shouldPanicOnCopyError(req) {
+			p.logf("suppressing panic for copyResponse error in test; copy error: %v", err)
+			return
+		}
+		panic(http.ErrAbortHandler)
+	}
+	res.Body.Close() // close now, instead of defer, to populate res.Trailer
+
+	if len(res.Trailer) > 0 {
+		// Force chunking if we saw a response trailer.
+		// This prevents net/http from calculating the length for short
+		// bodies and adding a Content-Length.
+		http.NewResponseController(rw).Flush()
+	}
+
+	if len(res.Trailer) == announcedTrailers {
+		copyHeader(rw.Header(), res.Trailer)
+		return
+	}
+
+	for k, vv := range res.Trailer {
+		k = http.TrailerPrefix + k
+		for _, v := range vv {
+			rw.Header().Add(k, v)
+		}
+	}
+}
+
+var inOurTests bool // whether we're in our own tests
+
+// shouldPanicOnCopyError reports whether the reverse proxy should
+// panic with http.ErrAbortHandler. This is the right thing to do by
+// default, but Go 1.10 and earlier did not, so existing unit tests
+// weren't expecting panics. Only panic in our own tests, or when
+// running under the HTTP server.
+func shouldPanicOnCopyError(req *http.Request) bool {
+	if inOurTests {
+		// Our tests know to handle this panic.
+		return true
+	}
+	if req.Context().Value(http.ServerContextKey) != nil {
+		// We seem to be running under an HTTP server, so
+		// it'll recover the panic.
+		return true
+	}
+	// Otherwise act like Go 1.10 and earlier to not break
+	// existing tests.
+	return false
+}
+
+// removeHopByHopHeaders removes hop-by-hop headers.
+func removeHopByHopHeaders(h http.Header) {
+	// RFC 7230, section 6.1: Remove headers listed in the "Connection" header.
+	for _, f := range h["Connection"] {
+		for _, sf := range strings.Split(f, ",") {
+			if sf = textproto.TrimString(sf); sf != "" {
+				h.Del(sf)
+			}
+		}
+	}
+	// RFC 2616, section 13.5.1: Remove a set of known hop-by-hop headers.
+	// This behavior is superseded by the RFC 7230 Connection header, but
+	// preserve it for backwards compatibility.
+	for _, f := range hopHeaders {
+		h.Del(f)
+	}
+}
+
+// flushInterval returns the p.FlushInterval value, conditionally
+// overriding its value for a specific request/response.
+func (p *ReverseProxy) flushInterval(res *http.Response) time.Duration {
+	resCT := res.Header.Get("Content-Type")
+
+	// For Server-Sent Events responses, flush immediately.
+	// The MIME type is defined in https://www.w3.org/TR/eventsource/#text-event-stream
+	if baseCT, _, _ := mime.ParseMediaType(resCT); baseCT == "text/event-stream" {
+		return -1 // negative means immediately
+	}
+
+	// We might have the case of streaming for which Content-Length might be unset.
+	if res.ContentLength == -1 {
+		return -1
+	}
+
+	return p.FlushInterval
+}
+
+func (p *ReverseProxy) copyResponse(dst http.ResponseWriter, src io.Reader, flushInterval time.Duration) error {
+	var w io.Writer = dst
+
+	if flushInterval != 0 {
+		mlw := &maxLatencyWriter{
+			dst:     dst,
+			flush:   http.NewResponseController(dst).Flush,
+			latency: flushInterval,
+		}
+		defer mlw.stop()
+
+		// set up initial timer so headers get flushed even if body writes are delayed
+		mlw.flushPending = true
+		mlw.t = time.AfterFunc(flushInterval, mlw.delayedFlush)
+
+		w = mlw
+	}
+
+	var buf []byte
+	if p.BufferPool != nil {
+		buf = p.BufferPool.Get()
+		defer p.BufferPool.Put(buf)
+	}
+	_, err := p.copyBuffer(w, src, buf)
+	return err
+}
+
+// copyBuffer returns any write errors or non-EOF read errors, and the amount
+// of bytes written.
+func (p *ReverseProxy) copyBuffer(dst io.Writer, src io.Reader, buf []byte) (int64, error) {
+	if len(buf) == 0 {
+		buf = make([]byte, 32*1024)
+	}
+	var written int64
+	for {
+		nr, rerr := src.Read(buf)
+		if rerr != nil && rerr != io.EOF && rerr != context.Canceled {
+			p.logf("httputil: ReverseProxy read error during body copy: %v", rerr)
+		}
+		if nr > 0 {
+			nw, werr := dst.Write(buf[:nr])
+			if nw > 0 {
+				written += int64(nw)
+			}
+			if werr != nil {
+				return written, werr
+			}
+			if nr != nw {
+				return written, io.ErrShortWrite
+			}
+		}
+		if rerr != nil {
+			if rerr == io.EOF {
+				rerr = nil
+			}
+			return written, rerr
+		}
+	}
+}
+
+func (p *ReverseProxy) logf(format string, args ...any) {
+	if p.ErrorLog != nil {
+		p.ErrorLog.Printf(format, args...)
+	} else {
+		log.Printf(format, args...)
+	}
+}
+
+type maxLatencyWriter struct {
+	dst     io.Writer
+	flush   func() error
+	latency time.Duration // non-zero; negative means to flush immediately
+
+	mu           sync.Mutex // protects t, flushPending, and dst.Flush
+	t            *time.Timer
+	flushPending bool
+}
+
+func (m *maxLatencyWriter) Write(p []byte) (n int, err error) {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	n, err = m.dst.Write(p)
+	if m.latency < 0 {
+		m.flush()
+		return
+	}
+	if m.flushPending {
+		return
+	}
+	if m.t == nil {
+		m.t = time.AfterFunc(m.latency, m.delayedFlush)
+	} else {
+		m.t.Reset(m.latency)
+	}
+	m.flushPending = true
+	return
+}
+
+func (m *maxLatencyWriter) delayedFlush() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	if !m.flushPending { // if stop was called but AfterFunc already started this goroutine
+		return
+	}
+	m.flush()
+	m.flushPending = false
+}
+
+func (m *maxLatencyWriter) stop() {
+	m.mu.Lock()
+	defer m.mu.Unlock()
+	m.flushPending = false
+	if m.t != nil {
+		m.t.Stop()
+	}
+}
+
+func upgradeType(h http.Header) string {
+	if !httpguts.HeaderValuesContainsToken(h["Connection"], "Upgrade") {
+		return ""
+	}
+	return h.Get("Upgrade")
+}
+
+func (p *ReverseProxy) handleUpgradeResponse(rw http.ResponseWriter, req *http.Request, res *http.Response) {
+	reqUpType := upgradeType(req.Header)
+	resUpType := upgradeType(res.Header)
+	if !ascii.IsPrint(resUpType) { // We know reqUpType is ASCII, it's checked by the caller.
+		p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch to invalid protocol %q", resUpType))
+	}
+	if !ascii.EqualFold(reqUpType, resUpType) {
+		p.getErrorHandler()(rw, req, fmt.Errorf("backend tried to switch protocol %q when %q was requested", resUpType, reqUpType))
+		return
+	}
+
+	backConn, ok := res.Body.(io.ReadWriteCloser)
+	if !ok {
+		p.getErrorHandler()(rw, req, fmt.Errorf("internal error: 101 switching protocols response with non-writable body"))
+		return
+	}
+
+	rc := http.NewResponseController(rw)
+	conn, brw, hijackErr := rc.Hijack()
+	if errors.Is(hijackErr, http.ErrNotSupported) {
+		p.getErrorHandler()(rw, req, fmt.Errorf("can't switch protocols using non-Hijacker ResponseWriter type %T", rw))
+		return
+	}
+
+	backConnCloseCh := make(chan bool)
+	go func() {
+		// Ensure that the cancellation of a request closes the backend.
+		// See issue https://golang.org/issue/35559.
+		select {
+		case <-req.Context().Done():
+		case <-backConnCloseCh:
+		}
+		backConn.Close()
+	}()
+	defer close(backConnCloseCh)
+
+	if hijackErr != nil {
+		p.getErrorHandler()(rw, req, fmt.Errorf("Hijack failed on protocol switch: %v", hijackErr))
+		return
+	}
+	defer conn.Close()
+
+	copyHeader(rw.Header(), res.Header)
+
+	res.Header = rw.Header()
+	res.Body = nil // so res.Write only writes the headers; we have res.Body in backConn above
+	if err := res.Write(brw); err != nil {
+		p.getErrorHandler()(rw, req, fmt.Errorf("response write: %v", err))
+		return
+	}
+	if err := brw.Flush(); err != nil {
+		p.getErrorHandler()(rw, req, fmt.Errorf("response flush: %v", err))
+		return
+	}
+	errc := make(chan error, 1)
+	spc := switchProtocolCopier{user: conn, backend: backConn}
+	go spc.copyToBackend(errc)
+	go spc.copyFromBackend(errc)
+	<-errc
+}
+
+// switchProtocolCopier exists so goroutines proxying data back and
+// forth have nice names in stacks.
+type switchProtocolCopier struct {
+	user, backend io.ReadWriter
+}
+
+func (c switchProtocolCopier) copyFromBackend(errc chan<- error) {
+	_, err := io.Copy(c.user, c.backend)
+	errc <- err
+}
+
+func (c switchProtocolCopier) copyToBackend(errc chan<- error) {
+	_, err := io.Copy(c.backend, c.user)
+	errc <- err
+}
+
+func cleanQueryParams(s string) string {
+	reencode := func(s string) string {
+		v, _ := url.ParseQuery(s)
+		return v.Encode()
+	}
+	for i := 0; i < len(s); {
+		switch s[i] {
+		case ';':
+			return reencode(s)
+		case '%':
+			if i+2 >= len(s) || !ishex(s[i+1]) || !ishex(s[i+2]) {
+				return reencode(s)
+			}
+			i += 3
+		default:
+			i++
+		}
+	}
+	return s
+}
+
+func ishex(c byte) bool {
+	switch {
+	case '0' <= c && c <= '9':
+		return true
+	case 'a' <= c && c <= 'f':
+		return true
+	case 'A' <= c && c <= 'F':
+		return true
+	}
+	return false
+}