1 files changed, 159 insertions, 0 deletions
diff --git a/src/pkg/http/reverseproxy.go b/src/pkg/http/reverseproxy.go
new file mode 100644
index 000000000..3f8bfdc80
--- /dev/null
+++ b/src/pkg/http/reverseproxy.go
@@ -0,0 +1,159 @@
+// 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 http
+
+import (
+	"io"
+	"log"
+	"net"
+	"os"
+	"strings"
+	"sync"
+	"time"
+	"url"
+)
+
+// 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(*Request)
+
+	// The Transport used to perform proxy requests.
+	// If nil, DefaultTransport is used.
+	Transport RoundTripper
+
+	// FlushInterval specifies the flush interval, in
+	// nanoseconds, to flush to the client while
+	// coping the response body.
+	// If zero, no periodic flushing is done.
+	FlushInterval int64
+}
+
+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 {
+	director := func(req *Request) {
+		req.URL.Scheme = target.Scheme
+		req.URL.Host = target.Host
+		req.URL.Path = singleJoiningSlash(target.Path, req.URL.Path)
+		if q := req.URL.RawQuery; q != "" {
+			req.URL.RawPath = req.URL.Path + "?" + q
+		} else {
+			req.URL.RawPath = req.URL.Path
+		}
+		req.URL.RawQuery = target.RawQuery
+	}
+	return &ReverseProxy{Director: director}
+}
+
+func (p *ReverseProxy) ServeHTTP(rw ResponseWriter, req *Request) {
+	transport := p.Transport
+	if transport == nil {
+		transport = DefaultTransport
+	}
+
+	outreq := new(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
+
+	if clientIp, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
+		outreq.Header.Set("X-Forwarded-For", clientIp)
+	}
+
+	res, err := transport.RoundTrip(outreq)
+	if err != nil {
+		log.Printf("http: proxy error: %v", err)
+		rw.WriteHeader(StatusInternalServerError)
+		return
+	}
+
+	hdr := rw.Header()
+	for k, vv := range res.Header {
+		for _, v := range vv {
+			hdr.Add(k, v)
+		}
+	}
+
+	rw.WriteHeader(res.StatusCode)
+
+	if res.Body != nil {
+		var dst io.Writer = rw
+		if p.FlushInterval != 0 {
+			if wf, ok := rw.(writeFlusher); ok {
+				dst = &maxLatencyWriter{dst: wf, latency: p.FlushInterval}
+			}
+		}
+		io.Copy(dst, res.Body)
+	}
+}
+
+type writeFlusher interface {
+	io.Writer
+	Flusher
+}
+
+type maxLatencyWriter struct {
+	dst     writeFlusher
+	latency int64 // nanos
+
+	lk   sync.Mutex // protects init of done, as well Write + Flush
+	done chan bool
+}
+
+func (m *maxLatencyWriter) Write(p []byte) (n int, err os.Error) {
+	m.lk.Lock()
+	defer m.lk.Unlock()
+	if m.done == nil {
+		m.done = make(chan bool)
+		go m.flushLoop()
+	}
+	n, err = m.dst.Write(p)
+	if err != nil {
+		m.done <- true
+	}
+	return
+}
+
+func (m *maxLatencyWriter) flushLoop() {
+	t := time.NewTicker(m.latency)
+	defer t.Stop()
+	for {
+		select {
+		case <-t.C:
+			m.lk.Lock()
+			m.dst.Flush()
+			m.lk.Unlock()
+		case <-m.done:
+			return
+		}
+	}
+	panic("unreached")
+}