internal: remove err from ClientTransport.GracefulClose (#2771)

internal/transport/http2_client.go

@@ -794,21 +794,21 @@ func (t *http2Client) Close() error {
 // stream is closed.  If there are no active streams, the transport is closed
 // immediately.  This does nothing if the transport is already draining or
 // closing.
-func (t *http2Client) GracefulClose() error {
+func (t *http2Client) GracefulClose() {
 	t.mu.Lock()
 	// Make sure we move to draining only from active.
 	if t.state == draining || t.state == closing {
 		t.mu.Unlock()
-		return nil
+		return
 	}
 	t.state = draining
 	active := len(t.activeStreams)
 	t.mu.Unlock()
 	if active == 0 {
-		return t.Close()
+		t.Close()
+		return
 	}
 	t.controlBuf.put(&incomingGoAway{})
-	return nil
 }
 
 // Write formats the data into HTTP2 data frame(s) and sends it out. The caller

internal/transport/transport.go

@@ -583,7 +583,7 @@ type ClientTransport interface {
 	// finished, the transport will close.
 	//
 	// It does not block.
-	GracefulClose() error
+	GracefulClose()
 
 	// Write sends the data for the given stream. A nil stream indicates
 	// the write is to be performed on the transport as a whole.

internal/transport/transport_test.go

@@ -1130,9 +1130,7 @@ func TestGracefulClose(t *testing.T) {
 	if _, err := s.Read(recvMsg); err != nil {
 		t.Fatalf("Error while reading: %v", err)
 	}
-	if err = ct.GracefulClose(); err != nil {
-		t.Fatalf("GracefulClose() = %v, want <nil>", err)
-	}
+	ct.GracefulClose()
 	var wg sync.WaitGroup
 	// Expect the failure for all the follow-up streams because ct has been closed gracefully.
 	for i := 0; i < 200; i++ {