net/http/httputil: ReverseProxy should pass on unannounced Trailers

Trailers that are not announced in the Trailer must be passed on to
the downstream client.

Rather than iterate over each and find missing trailer values,
this re-adds all trailers to the headers if there is a disparity
between the number of announced trailers and the final number.

This fixes #20437

Change-Id: I867e85f45feff68616a9a9bd6f65f12d73825eb7
Reviewed-on: https://go-review.googlesource.com/43712
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

diff --git a/src/net/http/httputil/reverseproxy.go b/src/net/http/httputil/reverseproxy.go
index 488db9731330f3f4d8eac3e0f9554f8d36eeacab..fd78d45602d8cec3498f185aaa824c5b26b36ba8 100644 (file)
--- a/src/net/http/httputil/reverseproxy.go
+++ b/src/net/http/httputil/reverseproxy.go
@@ -233,7 +233,8 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
 
        // 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 {
+       announcedTrailers := len(res.Trailer)
+       if announcedTrailers > 0 {
                trailerKeys := make([]string, 0, len(res.Trailer))
                for k := range res.Trailer {
                        trailerKeys = append(trailerKeys, k)
@@ -252,7 +253,18 @@ func (p *ReverseProxy) ServeHTTP(rw http.ResponseWriter, req *http.Request) {
        }
        p.copyResponse(rw, res.Body)
        res.Body.Close() // close now, instead of defer, to populate res.Trailer
-       copyHeader(rw.Header(), res.Trailer)
+
+       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)
+               }
+       }
 }
 
 func (p *ReverseProxy) copyResponse(dst io.Writer, src io.Reader) {

diff --git a/src/net/http/httputil/reverseproxy_test.go b/src/net/http/httputil/reverseproxy_test.go
index 008e4e717fbad0a2eac460514f4325a22970b04b..04ac6b4059141c9526ee0a983e775136fb184e58 100644 (file)
--- a/src/net/http/httputil/reverseproxy_test.go
+++ b/src/net/http/httputil/reverseproxy_test.go
@@ -69,6 +69,7 @@ func TestReverseProxy(t *testing.T) {
                w.WriteHeader(backendStatus)
                w.Write([]byte(backendResponse))
                w.Header().Set("X-Trailer", "trailer_value")
+               w.Header().Set(http.TrailerPrefix+"X-Unannounced-Trailer", "unannounced_trailer_value")
        }))
        defer backend.Close()
        backendURL, err := url.Parse(backend.URL)
@@ -122,6 +123,9 @@ func TestReverseProxy(t *testing.T) {
        if g, e := res.Trailer.Get("X-Trailer"), "trailer_value"; g != e {
                t.Errorf("Trailer(X-Trailer) = %q ; want %q", g, e)
        }
+       if g, e := res.Trailer.Get("X-Unannounced-Trailer"), "unannounced_trailer_value"; g != e {
+               t.Errorf("Trailer(X-Unannounced-Trailer) = %q ; want %q", g, e)
+       }
 
        // Test that a backend failing to be reached or one which doesn't return
        // a response results in a StatusBadGateway.