Imported Upstream version 1.4upstream/1.4

1 files changed, 225 insertions, 0 deletions

diff --git a/src/net/http/httputil/reverseproxy.go b/src/net/http/httputil/reverseproxy.go
new file mode 100644
index 000000000..ab4637018
--- /dev/null
+++ b/src/net/http/httputil/reverseproxy.go
@@ -0,0 +1,225 @@
+// 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
+}
+
+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 rewrites
+// 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.
+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
+		}
+	}
+	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",
+	"Keep-Alive",
+	"Proxy-Authenticate",
+	"Proxy-Authorization",
+	"Te", // canonicalized version of "TE"
+	"Trailers",
+	"Transfer-Encoding",
+	"Upgrade",
+}
+
+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
+
+	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.StatusInternalServerError)
+		return
+	}
+	defer res.Body.Close()
+
+	for _, h := range hopHeaders {
+		res.Header.Del(h)
+	}
+
+	copyHeader(rw.Header(), res.Header)
+
+	rw.WriteHeader(res.StatusCode)
+	p.copyResponse(rw, res.Body)
+}
+
+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
+		}
+	}
+
+	io.Copy(dst, src)
+}
+
+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
+
+	lk   sync.Mutex // protects Write + Flush
+	done chan bool
+}
+
+func (m *maxLatencyWriter) Write(p []byte) (int, error) {
+	m.lk.Lock()
+	defer m.lk.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.lk.Lock()
+			m.dst.Flush()
+			m.lk.Unlock()
+		}
+	}
+}
+
+func (m *maxLatencyWriter) stop() { m.done <- true }