proxy: Added support for HTTP trailers

caddyhttp/proxy/proxy.go

@@ -247,12 +247,28 @@ func createUpstreamRequest(r *http.Request) *http.Request {
 		outreq.URL.Opaque = outreq.URL.RawPath
 	}
 
+	// We are modifying the same underlying map from req (shallow
+	// copied above) so we only copy it if necessary.
+	copiedHeaders := false
+
+	// Remove hop-by-hop headers listed in the "Connection" header.
+	// See RFC 2616, section 14.10.
+	if c := outreq.Header.Get("Connection"); c != "" {
+		for _, f := range strings.Split(c, ",") {
+			if f = strings.TrimSpace(f); f != "" {
+				if !copiedHeaders {
+					outreq.Header = make(http.Header)
+					copyHeader(outreq.Header, r.Header)
+					copiedHeaders = true
+				}
+				outreq.Header.Del(f)
+			}
+		}
+	}
+
 	// 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 r (shallow
-	// copied above) so we only copy it if necessary.
-	var copiedHeaders bool
+	// connection, regardless of what the client sent to us.
 	for _, h := range hopHeaders {
 		if outreq.Header.Get(h) != "" {
 			if !copiedHeaders {

caddyhttp/proxy/proxy_test.go

@@ -42,10 +42,32 @@ func TestReverseProxy(t *testing.T) {
 	log.SetOutput(ioutil.Discard)
 	defer log.SetOutput(os.Stderr)
 
+	verifyHeaders := func(headers http.Header, trailers http.Header) {
+		if headers.Get("X-Header") != "header-value" {
+			t.Error("Expected header 'X-Header' to be proxied properly")
+		}
+
+		if trailers == nil {
+			t.Error("Expected to receive trailers")
+		}
+		if trailers.Get("X-Trailer") != "trailer-value" {
+			t.Error("Expected header 'X-Trailer' to be proxied properly")
+		}
+	}
+
 	var requestReceived bool
 	backend := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+		// read the body (even if it's empty) to make Go parse trailers
+		io.Copy(ioutil.Discard, r.Body)
+		verifyHeaders(r.Header, r.Trailer)
+
 		requestReceived = true
+
+		w.Header().Set("Trailer", "X-Trailer")
+		w.Header().Set("X-Header", "header-value")
+		w.WriteHeader(http.StatusOK)
 		w.Write([]byte("Hello, client"))
+		w.Header().Set("X-Trailer", "trailer-value")
 	}))
 	defer backend.Close()
 
@@ -59,12 +81,21 @@ func TestReverseProxy(t *testing.T) {
 	r := httptest.NewRequest("GET", "/", nil)
 	w := httptest.NewRecorder()
 
+	r.ContentLength = -1 // force chunked encoding (required for trailers)
+	r.Header.Set("X-Header", "header-value")
+	r.Trailer = map[string][]string{
+		"X-Trailer": {"trailer-value"},
+	}
+
 	p.ServeHTTP(w, r)
 
 	if !requestReceived {
 		t.Error("Expected backend to receive request, but it didn't")
 	}
 
+	res := w.Result()
+	verifyHeaders(res.Header, res.Trailer)
+
 	// Make sure {upstream} placeholder is set
 	rr := httpserver.NewResponseRecorder(httptest.NewRecorder())
 	rr.Replacer = httpserver.NewReplacer(r, rr, "-")

caddyhttp/proxy/reverseproxy.go

@@ -211,10 +211,27 @@ func (rp *ReverseProxy) ServeHTTP(rw http.ResponseWriter, outreq *http.Request,
 		return err
 	}
 
+	isWebsocket := res.StatusCode == http.StatusSwitchingProtocols && strings.ToLower(res.Header.Get("Upgrade")) == "websocket"
+
+	// Remove hop-by-hop headers listed in the
+	// "Connection" header of the response.
+	if c := res.Header.Get("Connection"); c != "" {
+		for _, f := range strings.Split(c, ",") {
+			if f = strings.TrimSpace(f); f != "" {
+				res.Header.Del(f)
+			}
+		}
+	}
+
+	for _, h := range hopHeaders {
+		res.Header.Del(h)
+	}
+
 	if respUpdateFn != nil {
 		respUpdateFn(res)
 	}
-	if res.StatusCode == http.StatusSwitchingProtocols && strings.ToLower(res.Header.Get("Upgrade")) == "websocket" {
+
+	if isWebsocket {
 		res.Body.Close()
 		hj, ok := rw.(http.Hijacker)
 		if !ok {
@@ -246,13 +263,30 @@ func (rp *ReverseProxy) ServeHTTP(rw http.ResponseWriter, outreq *http.Request,
 		go pooledIoCopy(backendConn, conn) // write tcp stream to backend
 		pooledIoCopy(conn, backendConn)    // read tcp stream from backend
 	} else {
-		defer res.Body.Close()
-		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 {
+			trailerKeys := make([]string, 0, len(res.Trailer))
+			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()
+			}
+		}
 		rp.copyResponse(rw, res.Body)
+		res.Body.Close() // close now, instead of defer, to populate res.Trailer
+		copyHeader(rw.Header(), res.Trailer)
 	}
 
 	return nil
@@ -305,16 +339,17 @@ func copyHeader(dst, src http.Header) {
 // Hop-by-hop headers. These are removed when sent to the backend.
 // http://www.w3.org/Protocols/rfc2616/rfc2616-sec13.html
 var hopHeaders = []string{
+	"Alt-Svc",
+	"Alternate-Protocol",
 	"Connection",
 	"Keep-Alive",
 	"Proxy-Authenticate",
 	"Proxy-Authorization",
-	"Te", // canonicalized version of "TE"
-	"Trailers",
+	"Proxy-Connection", // non-standard but still sent by libcurl and rejected by e.g. google
+	"Te",               // canonicalized version of "TE"
+	"Trailer",          // not Trailers per URL above; http://www.rfc-editor.org/errata_search.php?eid=4522
 	"Transfer-Encoding",
 	"Upgrade",
-	"Alternate-Protocol",
-	"Alt-Svc",
 }
 
 type respUpdateFn func(resp *http.Response)