do right counting for max-streams flow control

transport/control.go

@@ -105,7 +105,9 @@ type quotaPool struct {
 // newQuotaPool creates a quotaPool which has quota q available to consume.
 func newQuotaPool(q int) *quotaPool {
 	qb := &quotaPool{c: make(chan int, 1)}
+	if q > 0 {
 		qb.c <- q
+	}
 	return qb
 }
 

transport/http2_client.go

@@ -196,7 +196,7 @@ func newHTTP2Client(addr string, opts *ConnectOptions) (_ ClientTransport, err e
 	return t, nil
 }
 
-func (t *http2Client) newStream(ctx context.Context, callHdr *CallHdr, sq bool) *Stream {
+func (t *http2Client) newStream(ctx context.Context, callHdr *CallHdr) *Stream {
 	fc := &inFlow{
 		limit: initialWindowSize,
 		conn:  t.fc,
@@ -206,7 +206,6 @@ func (t *http2Client) newStream(ctx context.Context, callHdr *CallHdr, sq bool)
 		id:     t.nextID,
 		method: callHdr.Method,
 		buf:    newRecvBuffer(),
-		updateStreams: sq,
 		fc:            fc,
 		sendQuotaPool: newQuotaPool(int(t.streamSendQuota)),
 		headerChan:    make(chan struct{}),
@@ -267,7 +266,7 @@ func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr) (_ *Strea
 		return nil, err
 	}
 	t.mu.Lock()
-	s := t.newStream(ctx, callHdr, checkStreamsQuota)
+	s := t.newStream(ctx, callHdr)
 	t.activeStreams[s.id] = s
 	t.mu.Unlock()
 	// HPACK encodes various headers. Note that once WriteField(...) is
@@ -336,10 +335,14 @@ func (t *http2Client) NewStream(ctx context.Context, callHdr *CallHdr) (_ *Strea
 // CloseStream clears the footprint of a stream when the stream is not needed any more.
 // This must not be executed in reader's goroutine.
 func (t *http2Client) CloseStream(s *Stream, err error) {
+	var updateStreams bool
 	t.mu.Lock()
+	if t.streamsQuota != nil {
+		updateStreams = true
+	}
 	delete(t.activeStreams, s.id)
 	t.mu.Unlock()
-	if s.updateStreams {
+	if updateStreams {
 		t.streamsQuota.add(1)
 	}
 	s.mu.Lock()
@@ -737,7 +740,7 @@ func (t *http2Client) applySettings(ss []http2.Setting) {
 			t.mu.Lock()
 			reset := t.streamsQuota != nil
 			if !reset {
-				t.streamsQuota = newQuotaPool(int(s.Val))
+				t.streamsQuota = newQuotaPool(int(s.Val) - len(t.activeStreams))
 			}
 			ms := t.maxStreams
 			t.maxStreams = int(s.Val)

transport/transport.go

@@ -172,12 +172,6 @@ type Stream struct {
 	method    string
 	buf       *recvBuffer
 	dec       io.Reader
-
-	// updateStreams indicates whether the transport's streamsQuota needed
-	// to be updated when this stream is closed. It is false when the transport
-	// sticks to the initial infinite value of the number of concurrent streams.
-	// Ture otherwise.
-	updateStreams bool
 	fc        *inFlow
 	recvQuota uint32
 	// The accumulated inbound quota pending for window update.