http: remove Connection header in ReverseProxy

Fixes #2342

R=golang-dev, adg
CC=golang-dev
https://golang.org/cl/5302057

src/pkg/http/reverseproxy.go

@@ -69,6 +69,14 @@ func NewSingleHostReverseProxy(target *url.URL) *ReverseProxy {
 	return &ReverseProxy{Director: director}
 }
 
+func copyHeader(dst, src Header) {
+	for k, vv := range src {
+		for _, v := range vv {
+			dst.Add(k, v)
+		}
+	}
+}
+
 func (p *ReverseProxy) ServeHTTP(rw ResponseWriter, req *Request) {
 	transport := p.Transport
 	if transport == nil {
@@ -84,6 +92,16 @@ func (p *ReverseProxy) ServeHTTP(rw ResponseWriter, req *Request) {
 	outreq.ProtoMinor = 1
 	outreq.Close = false
 
+	// Remove the connection header to the backend.  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.
+	if outreq.Header.Get("Connection") != "" {
+		outreq.Header = make(Header)
+		copyHeader(outreq.Header, req.Header)
+		outreq.Header.Del("Connection")
+	}
+
 	if clientIp, _, err := net.SplitHostPort(req.RemoteAddr); err == nil {
 		outreq.Header.Set("X-Forwarded-For", clientIp)
 	}
@@ -95,12 +113,7 @@ func (p *ReverseProxy) ServeHTTP(rw ResponseWriter, req *Request) {
 		return
 	}
 
-	hdr := rw.Header()
-	for k, vv := range res.Header {
-		for _, v := range vv {
-			hdr.Add(k, v)
-		}
-	}
+	copyHeader(rw.Header(), res.Header)
 
 	rw.WriteHeader(res.StatusCode)
 

src/pkg/http/reverseproxy_test.go

@@ -24,6 +24,9 @@ func TestReverseProxy(t *testing.T) {
 		if r.Header.Get("X-Forwarded-For") == "" {
 			t.Errorf("didn't get X-Forwarded-For header")
 		}
+		if c := r.Header.Get("Connection"); c != "" {
+			t.Errorf("handler got Connection header value %q", c)
+		}
 		if g, e := r.Host, "some-name"; g != e {
 			t.Errorf("backend got Host header %q, want %q", g, e)
 		}
@@ -43,6 +46,8 @@ func TestReverseProxy(t *testing.T) {
 
 	getReq, _ := NewRequest("GET", frontend.URL, nil)
 	getReq.Host = "some-name"
+	getReq.Header.Set("Connection", "close")
+	getReq.Close = true
 	res, err := DefaultClient.Do(getReq)
 	if err != nil {
 		t.Fatalf("Get: %v", err)