post review updates

test/end2end_test.go

@@ -2673,21 +2673,24 @@ func testExceedMaxStreamsLimit(t *testing.T, e env) {
 
 const defaultMaxStreamsClient = 100
 
-func TestClientExceedMaxStreamsLimit(t *testing.T) {
+func TestExceedDefaultMaxStreamsLimit(t *testing.T) {
 	defer leakCheck(t)()
 	for _, e := range listTestEnv() {
-		testClientExceedMaxStreamsLimit(t, e)
+		testExceedDefaultMaxStreamsLimit(t, e)
 	}
 }
 
-func testClientExceedMaxStreamsLimit(t *testing.T, e env) {
+func testExceedDefaultMaxStreamsLimit(t *testing.T, e env) {
 	te := newTest(t, e)
 	te.declareLogNoise(
 		"http2Client.notifyError got notified that the client transport was broken",
 		"Conn.resetTransport failed to create client transport",
 		"grpc: the connection is closing",
 	)
-	te.maxStream = 0 // Server allows infinite streams. The cap should be on client side.
+	// When masStream is set to 0 the server doesn't send a settings frame for
+	// MaxConcurrentStreams, essentially allowing infinite (math.MaxInt32) streams.
+	// In such a case, there should be a default cap on the client-side.
+	te.maxStream = 0
 	te.startServer(&testServer{security: e.security})
 	defer te.tearDown()
 

transport/http2_client.go

@@ -491,8 +491,17 @@ func (t *http2Client) CloseStream(s *Stream, err error) {
 		return
 	}
 	t.mu.Unlock()
+	// rstStream is true in case the stream is being closed at the client-side
+	// and the server needs to be intimated about it by sending a RST_STREAM
+	// frame.
+	// To make sure this frame is written to the wire before the headers of the
+	// next stream waiting for streamsQuota, we add to streamsQuota pool only
+	// after having acquired the writableChan to send RST_STREAM out (look at
+	// the controller() routine).
 	var rstStream bool
 	defer func() {
+		// In case, the client doesn't have to send RST_STREAM to server
+		// we can safely add back to streamsQuota pool now.
 		if !rstStream {
 			t.streamsQuota.add(1)
 			return
@@ -1068,6 +1077,11 @@ func (t *http2Client) controller() {
 						t.framer.writeSettings(true, i.ss...)
 					}
 				case *resetStream:
+					// If the server needs to be to intimated about stream closing,
+					// then we need to make sure the RST_STREAM frame is written to
+					// the wire before the headers of the next stream waiting on
+					// streamQuota. We ensure this by adding to the streamsQuota pool
+					// only after having acquired the writableChan to send RST_STREAM.
 					t.streamsQuota.add(1)
 					t.framer.writeRSTStream(true, i.streamID, i.code)
 				case *flushIO:

transport/transport.go

@@ -213,8 +213,8 @@ type Stream struct {
 	// the status received from the server.
 	statusCode codes.Code
 	statusDesc string
-	// rstStream is a flag that is true when a RST stream frame
-	// is sent to the server signifying that this stream is closing.
+	// rstStream indicates whether a RST_STREAM frame needs to be sent
+	// to the server to signify that this stream is closing.
 	rstStream bool
 }