http2: enforce write deadline per stream

If the writeDeadline elapses RST_STREAM is sent with ErrCodeInternal.

Fixes tests added in https://golang.org/cl/34726

Updates golang/go#18437 (fixes once it's bundled into net/http)

Change-Id: I84e4f76753963c29cd3c06730d6bfbb7f1ee6051
Reviewed-on: https://go-review.googlesource.com/34727
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
Run-TryBot: Brad Fitzpatrick <bradfitz@golang.org>
TryBot-Result: Gobot Gobot <gobot@golang.org>

server.go

@@ -307,10 +307,9 @@ func (s *Server) ServeConn(c net.Conn, opts *ServeConnOpts) {
 
 	// The net/http package sets the write deadline from the
 	// http.Server.WriteTimeout during the TLS handshake, but then
-	// passes the connection off to us with the deadline already
-	// set. Disarm it here so that it is not applied to additional
-	// streams opened on this connection.
-	// TODO: implement WriteTimeout fully. See Issue 18437.
+	// passes the connection off to us with the deadline already set.
+	// Write deadlines are set per stream in serverConn.newStream.
+	// Disarm the net.Conn write deadline here.
 	if sc.hs.WriteTimeout != 0 {
 		sc.conn.SetWriteDeadline(time.Time{})
 	}
@@ -493,9 +492,10 @@ type stream struct {
 	numTrailerValues int64
 	weight           uint8
 	state            streamState
-	resetQueued      bool // RST_STREAM queued for write; set by sc.resetStream
-	gotTrailerHeader bool // HEADER frame for trailers was seen
-	wroteHeaders     bool // whether we wrote headers (not status 100)
+	resetQueued      bool        // RST_STREAM queued for write; set by sc.resetStream
+	gotTrailerHeader bool        // HEADER frame for trailers was seen
+	wroteHeaders     bool        // whether we wrote headers (not status 100)
+	writeDeadline    *time.Timer // nil if unused
 
 	trailer    http.Header // accumulated trailers
 	reqTrailer http.Header // handler's Request.Trailer
@@ -766,6 +766,10 @@ func (sc *serverConn) serve() {
 		loopNum++
 		select {
 		case wr := <-sc.wantWriteFrameCh:
+			if se, ok := wr.write.(StreamError); ok {
+				sc.resetStream(se)
+				break
+			}
 			sc.writeFrame(wr)
 		case spr := <-sc.wantStartPushCh:
 			sc.startPush(spr)
@@ -1336,6 +1340,9 @@ func (sc *serverConn) closeStream(st *stream, err error) {
 		panic(fmt.Sprintf("invariant; can't close stream in state %v", st.state))
 	}
 	st.state = stateClosed
+	if st.writeDeadline != nil {
+		st.writeDeadline.Stop()
+	}
 	if st.isPushed() {
 		sc.curPushedStreams--
 	} else {
@@ -1574,6 +1581,12 @@ func (st *stream) copyTrailersToHandlerRequest() {
 	}
 }
 
+// onWriteTimeout is run on its own goroutine (from time.AfterFunc)
+// when the stream's WriteTimeout has fired.
+func (st *stream) onWriteTimeout() {
+	st.sc.writeFrameFromHandler(FrameWriteRequest{write: streamError(st.id, ErrCodeInternal)})
+}
+
 func (sc *serverConn) processHeaders(f *MetaHeadersFrame) error {
 	sc.serveG.check()
 	id := f.StreamID
@@ -1753,6 +1766,9 @@ func (sc *serverConn) newStream(id, pusherID uint32, state streamState) *stream
 	st.flow.add(sc.initialStreamSendWindowSize)
 	st.inflow.conn = &sc.inflow // link to conn-level counter
 	st.inflow.add(sc.srv.initialStreamRecvWindowSize())
+	if sc.hs.WriteTimeout != 0 {
+		st.writeDeadline = time.AfterFunc(sc.hs.WriteTimeout, st.onWriteTimeout)
+	}
 
 	sc.streams[id] = st
 	sc.writeSched.OpenStream(st.id, OpenStreamOptions{PusherID: pusherID})