fix(docker): agent and socket-proxy docker events not flushing with modified reverse proxy handler

agent/pkg/handler/handler.go

@@ -1,17 +1,14 @@
 package handler
 
 import (
-	"context"
 	"fmt"
-	"net"
 	"net/http"
-	"net/http/httputil"
-	"time"
 
 	"github.com/yusing/go-proxy/agent/pkg/agent"
 	"github.com/yusing/go-proxy/agent/pkg/env"
 	"github.com/yusing/go-proxy/internal/metrics/systeminfo"
 	"github.com/yusing/go-proxy/pkg"
+	socketproxy "github.com/yusing/go-proxy/socketproxy/pkg"
 )
 
 type ServeMux struct{ *http.ServeMux }
@@ -24,26 +21,6 @@ func (mux ServeMux) HandleFunc(endpoint string, handler http.HandlerFunc) {
 	mux.ServeMux.HandleFunc(agent.APIEndpointBase+endpoint, handler)
 }
 
-var dialer = &net.Dialer{KeepAlive: 1 * time.Second}
-
-func dialDockerSocket(ctx context.Context, _, _ string) (net.Conn, error) {
-	return dialer.DialContext(ctx, "unix", env.DockerSocket)
-}
-
-func dockerSocketHandler() http.HandlerFunc {
-	rp := httputil.ReverseProxy{
-		Director: func(r *http.Request) {
-			r.URL.Scheme = "http"
-			r.URL.Host = "api.moby.localhost"
-			r.RequestURI = r.URL.String()
-		},
-		Transport: &http.Transport{
-			DialContext: dialDockerSocket,
-		},
-	}
-	return rp.ServeHTTP
-}
-
 func NewAgentHandler() http.Handler {
 	mux := ServeMux{http.NewServeMux()}
 
@@ -54,6 +31,6 @@ func NewAgentHandler() http.Handler {
 	})
 	mux.HandleEndpoint("GET", agent.EndpointHealth, CheckHealth)
 	mux.HandleEndpoint("GET", agent.EndpointSystemInfo, systeminfo.Poller.ServeHTTP)
-	mux.ServeMux.HandleFunc("/", dockerSocketHandler())
+	mux.ServeMux.HandleFunc("/", socketproxy.DockerSocketHandler(env.DockerSocket))
 	return mux
 }

internal/api/v1/dockerapi/logs.go

@@ -15,6 +15,7 @@ import (
 	"github.com/yusing/go-proxy/internal/task"
 )
 
+// FIXME: agent logs not updating.
 func Logs(w http.ResponseWriter, r *http.Request) {
 	query := r.URL.Query()
 	server := r.PathValue("server")

internal/docker/client.go

@@ -20,6 +20,7 @@ import (
 	"github.com/yusing/go-proxy/internal/task"
 )
 
+// TODO: implement reconnect here.
 type (
 	SharedClient struct {
 		*client.Client

socket-proxy/go.mod

@@ -2,4 +2,19 @@ module github.com/yusing/go-proxy/socketproxy
 
 go 1.24.3
 
-require github.com/gorilla/mux v1.8.1
+replace github.com/yusing/go-proxy/internal/utils => ../internal/utils
+
+require (
+	github.com/gorilla/mux v1.8.1
+	github.com/yusing/go-proxy/internal/utils v0.0.0-00010101000000-000000000000
+	golang.org/x/net v0.40.0
+)
+
+require (
+	github.com/mattn/go-colorable v0.1.14 // indirect
+	github.com/mattn/go-isatty v0.0.20 // indirect
+	github.com/rs/zerolog v1.34.0 // indirect
+	go.uber.org/atomic v1.11.0 // indirect
+	golang.org/x/sys v0.33.0 // indirect
+	golang.org/x/text v0.25.0 // indirect
+)

socket-proxy/go.sum

@@ -1,2 +1,34 @@
+github.com/coreos/go-systemd/v22 v22.5.0/go.mod h1:Y58oyj3AT4RCenI/lSvhwexgC+NSVTIJ3seZv2GcEnc=
+github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc h1:U9qPSI2PIWSS1VwoXQT9A3Wy9MM3WgvqSxFWenqJduM=
+github.com/davecgh/go-spew v1.1.2-0.20180830191138-d8f796af33cc/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/godbus/dbus/v5 v5.0.4/go.mod h1:xhWf0FNVPg57R7Z0UbKHbJfkEywrmjJnf7w5xrFpKfA=
 github.com/gorilla/mux v1.8.1 h1:TuBL49tXwgrFYWhqrNgrUNEY92u81SPhu7sTdzQEiWY=
 github.com/gorilla/mux v1.8.1/go.mod h1:AKf9I4AEqPTmMytcMc0KkNouC66V3BtZ4qD5fmWSiMQ=
+github.com/mattn/go-colorable v0.1.13/go.mod h1:7S9/ev0klgBDR4GtXTXX8a3vIGJpMovkB8vQcUbaXHg=
+github.com/mattn/go-colorable v0.1.14 h1:9A9LHSqF/7dyVVX6g0U9cwm9pG3kP9gSzcuIPHPsaIE=
+github.com/mattn/go-colorable v0.1.14/go.mod h1:6LmQG8QLFO4G5z1gPvYEzlUgJ2wF+stgPZH1UqBm1s8=
+github.com/mattn/go-isatty v0.0.16/go.mod h1:kYGgaQfpe5nmfYZH+SKPsOc2e4SrIfOl2e/yFXSvRLM=
+github.com/mattn/go-isatty v0.0.19/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/mattn/go-isatty v0.0.20 h1:xfD0iDuEKnDkl03q4limB+vH+GxLEtL/jb4xVJSWWEY=
+github.com/mattn/go-isatty v0.0.20/go.mod h1:W+V8PltTTMOvKvAeJH7IuucS94S2C6jfK/D7dTCTo3Y=
+github.com/pkg/errors v0.9.1/go.mod h1:bwawxfHBFNV+L2hUp1rHADufV3IMtnDRdf1r5NINEl0=
+github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2 h1:Jamvg5psRIccs7FGNTlIRMkT8wgtp5eCXdBlqhYGL6U=
+github.com/pmezard/go-difflib v1.0.1-0.20181226105442-5d4384ee4fb2/go.mod h1:iKH77koFhYxTK1pcRnkKkqfTogsbg7gZNVY4sRDYZ/4=
+github.com/rs/xid v1.6.0/go.mod h1:7XoLgs4eV+QndskICGsho+ADou8ySMSjJKDIan90Nz0=
+github.com/rs/zerolog v1.34.0 h1:k43nTLIwcTVQAncfCw4KZ2VY6ukYoZaBPNOE8txlOeY=
+github.com/rs/zerolog v1.34.0/go.mod h1:bJsvje4Z08ROH4Nhs5iH600c3IkWhwp44iRc54W6wYQ=
+github.com/stretchr/testify v1.10.0 h1:Xv5erBjTwe/5IxqUQTdXv5kgmIvbHo3QQyRwhJsOfJA=
+github.com/stretchr/testify v1.10.0/go.mod h1:r2ic/lqez/lEtzL7wO/rwa5dbSLXVDPFyf8C91i36aY=
+go.uber.org/atomic v1.11.0 h1:ZvwS0R+56ePWxUNi+Atn9dWONBPp/AUETXlHW0DxSjE=
+go.uber.org/atomic v1.11.0/go.mod h1:LUxbIzbOniOlMKjJjyPfpl4v+PKK2cNJn91OQbhoJI0=
+golang.org/x/net v0.40.0 h1:79Xs7wF06Gbdcg4kdCCIQArK11Z1hr5POQ6+fIYHNuY=
+golang.org/x/net v0.40.0/go.mod h1:y0hY0exeL2Pku80/zKK7tpntoX23cqL3Oa6njdgRtds=
+golang.org/x/sys v0.0.0-20220811171246-fbc7d0a398ab/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.6.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.12.0/go.mod h1:oPkhp1MJrh7nUepCBck5+mAzfO9JrbApNNgaTdGDITg=
+golang.org/x/sys v0.33.0 h1:q3i8TbbEz+JRD9ywIRlyRAQbM0qF7hu24q3teo2hbuw=
+golang.org/x/sys v0.33.0/go.mod h1:BJP2sWEmIv4KK5OTEluFJCKSidICx8ciO85XgH3Ak8k=
+golang.org/x/text v0.25.0 h1:qVyWApTSYLk/drJRO5mDlNYskwQznZmkpV2c8q9zls4=
+golang.org/x/text v0.25.0/go.mod h1:WEdwpYrmk1qmdHvhkSTNPm3app7v4rsT8F2UD6+VHIA=
+gopkg.in/yaml.v3 v3.0.1 h1:fxVm/GzAzEWqLHuvctI91KS9hhNmmWOoWu0XTYJS7CA=
+gopkg.in/yaml.v3 v3.0.1/go.mod h1:K4uyk7z7BCEPqu6E+C64Yfv1cQ7kz7rIZviUmN+EgEM=

socket-proxy/pkg/handler.go

@@ -4,30 +4,33 @@ import (
 	"context"
 	"net"
 	"net/http"
-	"net/http/httputil"
 	"strings"
 	"time"
 
 	"github.com/gorilla/mux"
+	"github.com/yusing/go-proxy/socketproxy/pkg/reverseproxy"
 )
 
 var dialer = &net.Dialer{KeepAlive: 1 * time.Second}
 
-func dialDockerSocket(ctx context.Context, _, _ string) (net.Conn, error) {
+func dialDockerSocket(socket string) func(ctx context.Context, _, _ string) (net.Conn, error) {
-	return dialer.DialContext(ctx, "unix", DockerSocket)
+	return func(ctx context.Context, _, _ string) (net.Conn, error) {
+		return dialer.DialContext(ctx, "unix", socket)
+	}
 }
 
 var DockerSocketHandler = dockerSocketHandler
 
-func dockerSocketHandler() http.HandlerFunc {
+func dockerSocketHandler(socket string) http.HandlerFunc {
-	rp := &httputil.ReverseProxy{
+	rp := &reverseproxy.ReverseProxy{
 		Director: func(req *http.Request) {
 			req.URL.Scheme = "http"
 			req.URL.Host = "api.moby.localhost"
 			req.RequestURI = req.URL.String()
 		},
 		Transport: &http.Transport{
-			DialContext: dialDockerSocket,
+			DialContext:        dialDockerSocket(socket),
+			DisableCompression: true,
 		},
 	}
 
@@ -41,7 +44,7 @@ func endpointNotAllowed(w http.ResponseWriter, _ *http.Request) {
 // ref: https://github.com/Tecnativa/docker-socket-proxy/blob/master/haproxy.cfg
 func NewHandler() http.Handler {
 	r := mux.NewRouter()
-	socketHandler := DockerSocketHandler()
+	socketHandler := DockerSocketHandler(DockerSocket)
 
 	const apiVersionPrefix = `/{version:(?:v[\d\.]+)?}`
 	const containerPath = "/containers/{id:[a-zA-Z0-9_.-]+}"

socket-proxy/pkg/handler_test.go

@@ -9,7 +9,7 @@ import (
 	. "github.com/yusing/go-proxy/socketproxy/pkg"
 )
 
-func mockDockerSocketHandler() http.HandlerFunc {
+func mockDockerSocketHandler(_ string) http.HandlerFunc {
 	return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
 		w.WriteHeader(http.StatusOK)
 		w.Write([]byte("mock docker response"))

socket-proxy/pkg/reverseproxy/reverse_proxy.go

@@ -0,0 +1,600 @@
+// 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.
+// License URL: https://cs.opensource.google/go/go/+/master:LICENSE
+
+// HTTP reverse proxy handler
+
+package reverseproxy
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"io"
+	"log"
+	"net"
+	"net/http"
+	"net/http/httptrace"
+	"net/textproto"
+	"net/url"
+	"strings"
+	"sync"
+	"time"
+
+	"github.com/yusing/go-proxy/internal/utils"
+	"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 {
+	// 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
+	ctx := req.Context()
+
+	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
+	}
+
+	p.Director(outreq)
+	if outreq.Form != nil {
+		outreq.URL.RawQuery = cleanQueryParams(outreq.URL.RawQuery)
+	}
+	outreq.Close = false
+
+	reqUpType := upgradeType(outreq.Header)
+	if !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")
+	}
+
+	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", "")
+	}
+
+	var (
+		roundTripMutex sync.Mutex
+		roundTripDone  bool
+	)
+	trace := &httptrace.ClientTrace{
+		Got1xxResponse: func(code int, header textproto.MIMEHeader) error {
+			roundTripMutex.Lock()
+			defer roundTripMutex.Unlock()
+			if roundTripDone {
+				// If RoundTrip has returned, don't try to further modify
+				// the ResponseWriter's header map.
+				return nil
+			}
+			h := rw.Header()
+			copyHeader(h, http.Header(header))
+			rw.WriteHeader(code)
+
+			// Clear headers, it's not automatically done by ResponseWriter.WriteHeader() for 1xx responses
+			clear(h)
+			return nil
+		},
+	}
+	outreq = outreq.WithContext(httptrace.WithClientTrace(outreq.Context(), trace))
+
+	res, err := transport.RoundTrip(outreq)
+	roundTripMutex.Lock()
+	roundTripDone = true
+	roundTripMutex.Unlock()
+	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 = utils.CopyCloseWithContext(ctx, rw, res.Body)
+	if err != nil {
+		if !errors.Is(err, context.Canceled) {
+			p.getErrorHandler()(rw, req, err)
+		}
+		return
+	}
+
+	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)
+		}
+	}
+}
+
+// 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.SplitSeq(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)
+	}
+}
+
+func (p *ReverseProxy) logf(format string, args ...any) {
+	if p.ErrorLog != nil {
+		p.ErrorLog.Printf(format, args...)
+	} else {
+		log.Printf(format, args...)
+	}
+}
+
+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 !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))
+		return
+	}
+	if !strings.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
+}
+
+func IsPrint(s string) bool {
+	for _, r := range s {
+		if r < ' ' || r > '~' {
+			return false
+		}
+	}
+	return true
+}