src/net/http/httputil/reverseproxy.go - go - Git at Google

 // 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 (
 	"io"
 	"log"
 	"net"
 	"net/http"
 	"net/url"
 	"strings"
 	"sync"
 	"time"
 )

 // onExitFlushLoop is a callback set by tests to detect the state of the
 // flushLoop() goroutine.
 var onExitFlushLoop func()

 // ReverseProxy is an HTTP Handler that takes an incoming request and
 // sends it to another server, proxying the response back to the
 // client.
 type ReverseProxy struct {
 	// Director 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.
 	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.
 	FlushInterval time.Duration

 	// ErrorLog specifies an optional logger for errors
 	// that occur when attempting to proxy the request.
 	// If nil, logging goes to os.Stderr 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
 }

 // 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
 }

 // 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 rewrite Host headers, use ReverseProxy directly with a custom
 // Director policy.
 func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {
 	targetQuery := target.RawQuery
 	director := func(req *http.Request) {
 		req.URL.Scheme = target.Scheme
 		req.URL.Host = target.Host
 		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
 		if targetQuery == "" || req.URL.RawQuery == "" {
 			req.URL.RawQuery = targetQuery + req.URL.RawQuery
 		} else {
 			req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
 		}
 		if _, ok := req.Header["User-Agent"]; !ok {
 			// explicitly disable User-Agent so it's not set to default value
 			req.Header.Set("User-Agent", "")
 		}
 	}
 	return &ReverseProxy{Director: director}
 }

 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.
 // http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
 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; http://www.rfc-editor.org/errata_search.php?eid=4522
 	"Transfer-Encoding",
 	"Upgrade",
 }

 type requestCanceler interface {
 	CancelRequest(*http.Request)
 }

 type runOnFirstRead struct {
 	io.Reader // optional; nil means empty body

 	fn func() // Run before first Read, then set to nil
 }

 func (c *runOnFirstRead) Read(bs []byte) (int, error) {
 	if c.fn != nil {
 		c.fn()
 		c.fn = nil
 	}
 	if c.Reader == nil {
 		return 0, io.EOF
 	}
 	return c.Reader.Read(bs)
 }

 func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 	transport := p.Transport
 	if transport == nil {
 		transport = http.DefaultTransport
 	}

 	outreq := new(http.Request)
 	*outreq = *req // includes shallow copies of maps, but okay

 	if closeNotifier, ok := rw.(http.CloseNotifier); ok {
 		if requestCanceler, ok := transport.(requestCanceler); ok {
 			reqDone := make(chan struct{})
 			defer close(reqDone)

 			clientGone := closeNotifier.CloseNotify()

 			outreq.Body = struct {
 				io.Reader
 				io.Closer
 			}{
 				Reader: &runOnFirstRead{
 					Reader: outreq.Body,
 					fn: func() {
 						go func() {
 							select {
 							case <-clientGone:
 								requestCanceler.CancelRequest(outreq)
 							case <-reqDone:
 							}
 						}()
 					},
 				},
 				Closer: outreq.Body,
 			}
 		}
 	}

 	p.Director(outreq)
 	outreq.Proto = "HTTP/1.1"
 	outreq.ProtoMajor = 1
 	outreq.ProtoMinor = 1
 	outreq.Close = false

 	// Remove hop-by-hop headers to the backend. Especially
 	// important is "Connection" because we want a persistent
 	// connection, regardless of what the client sent to us. This
 	// is modifying the same underlying map from req (shallow
 	// copied above) so we only copy it if necessary.
 	copiedHeaders := false
 	for _, h := range hopHeaders {
 		if outreq.Header.Get(h) != "" {
 			if !copiedHeaders {
 				outreq.Header = make(http.Header)
 				copyHeader(outreq.Header, req.Header)
 				copiedHeaders = true
 			}
 			outreq.Header.Del(h)
 		}
 	}

 	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.
 		if prior, ok := outreq.Header["X-Forwarded-For"]; ok {
 			clientIP = strings.Join(prior, ", ") + ", " + clientIP
 		}
 		outreq.Header.Set("X-Forwarded-For", clientIP)
 	}

 	res, err := transport.RoundTrip(outreq)
 	if err != nil {
 		p.logf("http: proxy error: %v", err)
 		rw.WriteHeader(http.StatusBadGateway)
 		return
 	}

 	for _, h := range hopHeaders {
 		res.Header.Del(h)
 	}

 	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.
 	if len(res.Trailer) > 0 {
 		var trailerKeys []string
 		for k := range res.Trailer {
 			trailerKeys = append(trailerKeys, k)
 		}
 		rw.Header().Add("Trailer", strings.Join(trailerKeys, ", "))
 	}

 	rw.WriteHeader(res.StatusCode)
 	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.
 		if fl, ok := rw.(http.Flusher); ok {
 			fl.Flush()
 		}
 	}
 	p.copyResponse(rw, res.Body)
 	res.Body.Close() // close now, instead of defer, to populate res.Trailer
 	copyHeader(rw.Header(), res.Trailer)
 }

 func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader) {
 	if p.FlushInterval != 0 {
 		if wf, ok := dst.(writeFlusher); ok {
 			mlw := &maxLatencyWriter{
 				dst:     wf,
 				latency: p.FlushInterval,
 				done:    make(chan bool),
 			}
 			go mlw.flushLoop()
 			defer mlw.stop()
 			dst = mlw
 		}
 	}

 	var buf []byte
 	if p.BufferPool != nil {
 		buf = p.BufferPool.Get()
 	}
 	io.CopyBuffer(dst, src, buf)
 	if p.BufferPool != nil {
 		p.BufferPool.Put(buf)
 	}
 }

 func (p *ReverseProxy) logf(format string, args ...interface{}) {
 	if p.ErrorLog != nil {
 		p.ErrorLog.Printf(format, args...)
 	} else {
 		log.Printf(format, args...)
 	}
 }

 type writeFlusher interface {
 	io.Writer
 	http.Flusher
 }

 type maxLatencyWriter struct {
 	dst     writeFlusher
 	latency time.Duration

 	mu   sync.Mutex // protects Write + Flush
 	done chan bool
 }

 func (m *maxLatencyWriter) Write(p []byte) (int, error) {
 	m.mu.Lock()
 	defer m.mu.Unlock()
 	return m.dst.Write(p)
 }

 func (m *maxLatencyWriter) flushLoop() {
 	t := time.NewTicker(m.latency)
 	defer t.Stop()
 	for {
 		select {
 		case <-m.done:
 			if onExitFlushLoop != nil {
 				onExitFlushLoop()
 			}
 			return
 		case <-t.C:
 			m.mu.Lock()
 			m.dst.Flush()
 			m.mu.Unlock()
 		}
 	}
 }

 func (m *maxLatencyWriter) stop() { m.done <- true }
	// 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 (
	"io"
	"log"
	"net"
	"net/http"
	"net/url"
	"strings"
	"sync"
	"time"
	)

	// onExitFlushLoop is a callback set by tests to detect the state of the
	// flushLoop() goroutine.
	var onExitFlushLoop func()

	// ReverseProxy is an HTTP Handler that takes an incoming request and
	// sends it to another server, proxying the response back to the
	// client.
	type ReverseProxy struct {
	// Director 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.
	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.
	FlushInterval time.Duration

	// ErrorLog specifies an optional logger for errors
	// that occur when attempting to proxy the request.
	// If nil, logging goes to os.Stderr 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
	}

	// 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
	}

	// 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 rewrite Host headers, use ReverseProxy directly with a custom
	// Director policy.
	func NewSingleHostReverseProxy(target url.URL) ReverseProxy {
	targetQuery := target.RawQuery
	director := func(req *http.Request) {
	req.URL.Scheme = target.Scheme
	req.URL.Host = target.Host
	req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
	if targetQuery == "" \|\| req.URL.RawQuery == "" {
	req.URL.RawQuery = targetQuery + req.URL.RawQuery
	} else {
	req.URL.RawQuery = targetQuery + "&" + req.URL.RawQuery
	}
	if _, ok := req.Header["User-Agent"]; !ok {
	// explicitly disable User-Agent so it's not set to default value
	req.Header.Set("User-Agent", "")
	}
	}
	return &ReverseProxy{Director: director}
	}

	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.
	// http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
	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; http://www.rfc-editor.org/errata_search.php?eid=4522
	"Transfer-Encoding",
	"Upgrade",
	}

	type requestCanceler interface {
	CancelRequest(*http.Request)
	}

	type runOnFirstRead struct {
	io.Reader // optional; nil means empty body

	fn func() // Run before first Read, then set to nil
	}

	func (c *runOnFirstRead) Read(bs []byte) (int, error) {
	if c.fn != nil {
	c.fn()
	c.fn = nil
	}
	if c.Reader == nil {
	return 0, io.EOF
	}
	return c.Reader.Read(bs)
	}

	func (p ReverseProxy) ServeHTTP(rw http.ResponseWriter, req http.Request) {
	transport := p.Transport
	if transport == nil {
	transport = http.DefaultTransport
	}

	outreq := new(http.Request)
	outreq = req // includes shallow copies of maps, but okay

	if closeNotifier, ok := rw.(http.CloseNotifier); ok {
	if requestCanceler, ok := transport.(requestCanceler); ok {
	reqDone := make(chan struct{})
	defer close(reqDone)

	clientGone := closeNotifier.CloseNotify()

	outreq.Body = struct {
	io.Reader
	io.Closer
	}{
	Reader: &runOnFirstRead{
	Reader: outreq.Body,
	fn: func() {
	go func() {
	select {
	case <-clientGone:
	requestCanceler.CancelRequest(outreq)
	case <-reqDone:
	}
	}()
	},
	},
	Closer: outreq.Body,
	}
	}
	}

	p.Director(outreq)
	outreq.Proto = "HTTP/1.1"
	outreq.ProtoMajor = 1
	outreq.ProtoMinor = 1
	outreq.Close = false

	// Remove hop-by-hop headers to the backend. Especially
	// important is "Connection" because we want a persistent
	// connection, regardless of what the client sent to us. This
	// is modifying the same underlying map from req (shallow
	// copied above) so we only copy it if necessary.
	copiedHeaders := false
	for _, h := range hopHeaders {
	if outreq.Header.Get(h) != "" {
	if !copiedHeaders {
	outreq.Header = make(http.Header)
	copyHeader(outreq.Header, req.Header)
	copiedHeaders = true
	}
	outreq.Header.Del(h)
	}
	}

	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.
	if prior, ok := outreq.Header["X-Forwarded-For"]; ok {
	clientIP = strings.Join(prior, ", ") + ", " + clientIP
	}
	outreq.Header.Set("X-Forwarded-For", clientIP)
	}

	res, err := transport.RoundTrip(outreq)
	if err != nil {
	p.logf("http: proxy error: %v", err)
	rw.WriteHeader(http.StatusBadGateway)
	return
	}

	for _, h := range hopHeaders {
	res.Header.Del(h)
	}

	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.
	if len(res.Trailer) > 0 {
	var trailerKeys []string
	for k := range res.Trailer {
	trailerKeys = append(trailerKeys, k)
	}
	rw.Header().Add("Trailer", strings.Join(trailerKeys, ", "))
	}

	rw.WriteHeader(res.StatusCode)
	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.
	if fl, ok := rw.(http.Flusher); ok {
	fl.Flush()
	}
	}
	p.copyResponse(rw, res.Body)
	res.Body.Close() // close now, instead of defer, to populate res.Trailer
	copyHeader(rw.Header(), res.Trailer)
	}

	func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader) {
	if p.FlushInterval != 0 {
	if wf, ok := dst.(writeFlusher); ok {
	mlw := &maxLatencyWriter{
	dst: wf,
	latency: p.FlushInterval,
	done: make(chan bool),
	}
	go mlw.flushLoop()
	defer mlw.stop()
	dst = mlw
	}
	}

	var buf []byte
	if p.BufferPool != nil {
	buf = p.BufferPool.Get()
	}
	io.CopyBuffer(dst, src, buf)
	if p.BufferPool != nil {
	p.BufferPool.Put(buf)
	}
	}

	func (p *ReverseProxy) logf(format string, args ...interface{}) {
	if p.ErrorLog != nil {
	p.ErrorLog.Printf(format, args...)
	} else {
	log.Printf(format, args...)
	}
	}

	type writeFlusher interface {
	io.Writer
	http.Flusher
	}

	type maxLatencyWriter struct {
	dst writeFlusher
	latency time.Duration

	mu sync.Mutex // protects Write + Flush
	done chan bool
	}

	func (m *maxLatencyWriter) Write(p []byte) (int, error) {
	m.mu.Lock()
	defer m.mu.Unlock()
	return m.dst.Write(p)
	}

	func (m *maxLatencyWriter) flushLoop() {
	t := time.NewTicker(m.latency)
	defer t.Stop()
	for {
	select {
	case <-m.done:
	if onExitFlushLoop != nil {
	onExitFlushLoop()
	}
	return
	case <-t.C:
	m.mu.Lock()
	m.dst.Flush()
	m.mu.Unlock()
	}
	}
	}

	func (m *maxLatencyWriter) stop() { m.done <- true }