x/net/http2: allow sending 1xx responses

http2/server.go

@@ -2611,8 +2611,7 @@ func checkWriteHeaderCode(code int) {
 	// Issue 22880: require valid WriteHeader status codes.
 	// For now we only enforce that it's three digits.
 	// In the future we might block things over 599 (600 and above aren't defined
-	// at http://httpwg.org/specs/rfc7231.html#status.codes)
-	// and we might block under 200 (once we have more mature 1xx support).
+	// at http://httpwg.org/specs/rfc7231.html#status.codes).
 	// But for now any three digits.
 	//
 	// We used to send "HTTP/1.1 000 0" on the wire in responses but there's
@@ -2633,13 +2632,36 @@ func (w *responseWriter) WriteHeader(code int) {
 }
 
 func (rws *responseWriterState) writeHeader(code int) {
-	if !rws.wroteHeader {
-		checkWriteHeaderCode(code)
-		rws.wroteHeader = true
-		rws.status = code
-		if len(rws.handlerHeader) > 0 {
-			rws.snapHeader = cloneHeader(rws.handlerHeader)
+	if rws.wroteHeader {
+		return
+	}
+
+	checkWriteHeaderCode(code)
+
+	// Handle informational headers, except 100 (Continue) which is handled automatically
+	if code > 100 && code < 200 {
+		var h http.Header
+		if code == 103 {
+			// Per RFC 8297 we must not clear the current header map
+			h = rws.handlerHeader
+		}
+
+		if rws.conn.writeHeaders(rws.stream, &writeResHeaders{
+			streamID:    rws.stream.id,
+			httpResCode: code,
+			h:           h,
+			endStream:   rws.handlerDone && !rws.hasTrailers(),
+		}) != nil {
+			rws.dirty = true
 		}
+
+		return
+	}
+
+	rws.wroteHeader = true
+	rws.status = code
+	if len(rws.handlerHeader) > 0 {
+		rws.snapHeader = cloneHeader(rws.handlerHeader)
 	}
 }
 

http2/server_test.go

@@ -4267,3 +4267,92 @@ func TestServerWindowUpdateOnBodyClose(t *testing.T) {
 		t.Error(err)
 	}
 }
+
+func TestServerSendsEarlyHints(t *testing.T) {
+	testServerResponse(t, func(w http.ResponseWriter, r *http.Request) error {
+		h := w.Header()
+		h.Add("Link", "</style.css>; rel=preload; as=style")
+		h.Add("Link", "</script.js>; rel=preload; as=script")
+		w.WriteHeader(http.StatusEarlyHints)
+
+		h.Add("Link", "</foo.js>; rel=preload; as=script")
+		w.WriteHeader(http.StatusEarlyHints)
+
+		w.Write([]byte("stuff"))
+
+		return nil
+	}, func(st *serverTester) {
+		getSlash(st)
+		hf := st.wantHeaders()
+		goth := st.decodeHeader(hf.HeaderBlockFragment())
+		wanth := [][2]string{
+			{":status", "103"},
+			{"link", "</style.css>; rel=preload; as=style"},
+			{"link", "</script.js>; rel=preload; as=script"},
+		}
+
+		if !reflect.DeepEqual(goth, wanth) {
+			t.Errorf("Got = %q; want %q", goth, wanth)
+		}
+
+		hf = st.wantHeaders()
+		goth = st.decodeHeader(hf.HeaderBlockFragment())
+		wanth = [][2]string{
+			{":status", "103"},
+			{"link", "</style.css>; rel=preload; as=style"},
+			{"link", "</script.js>; rel=preload; as=script"},
+			{"link", "</foo.js>; rel=preload; as=script"},
+		}
+
+		if !reflect.DeepEqual(goth, wanth) {
+			t.Errorf("Got = %q; want %q", goth, wanth)
+		}
+
+		hf = st.wantHeaders()
+		goth = st.decodeHeader(hf.HeaderBlockFragment())
+		wanth = [][2]string{
+			{":status", "200"},
+			{"link", "</style.css>; rel=preload; as=style"},
+			{"link", "</script.js>; rel=preload; as=script"},
+			{"link", "</foo.js>; rel=preload; as=script"},
+			{"content-type", "text/plain; charset=utf-8"},
+			{"content-length", "5"},
+		}
+
+		if !reflect.DeepEqual(goth, wanth) {
+			t.Errorf("Got = %q; want %q", goth, wanth)
+		}
+	})
+}
+
+func TestServerSendsProcessing(t *testing.T) {
+	testServerResponse(t, func(w http.ResponseWriter, r *http.Request) error {
+		w.WriteHeader(http.StatusProcessing)
+		w.Write([]byte("stuff"))
+
+		return nil
+	}, func(st *serverTester) {
+		getSlash(st)
+		hf := st.wantHeaders()
+		goth := st.decodeHeader(hf.HeaderBlockFragment())
+		wanth := [][2]string{
+			{":status", "102"},
+		}
+
+		if !reflect.DeepEqual(goth, wanth) {
+			t.Errorf("Got = %q; want %q", goth, wanth)
+		}
+
+		hf = st.wantHeaders()
+		goth = st.decodeHeader(hf.HeaderBlockFragment())
+		wanth = [][2]string{
+			{":status", "200"},
+			{"content-type", "text/plain; charset=utf-8"},
+			{"content-length", "5"},
+		}
+
+		if !reflect.DeepEqual(goth, wanth) {
+			t.Errorf("Got = %q; want %q", goth, wanth)
+		}
+	})
+}