fix(bigquery/storage/managedwriter): address possible resource leak

bigquery/storage/managedwriter/managed_stream.go

@@ -205,16 +205,13 @@ func (ms *ManagedStream) getStream(arc *storagepb.BigQueryWrite_AppendRowsClient
 	if arc != ms.arc && !forceReconnect {
 		return ms.arc, ms.pending, nil
 	}
-	if arc != ms.arc && forceReconnect && ms.arc != nil {
-		// In this case, we're forcing a close on the existing stream.
-		// This is due to either needing to reconnect to satisfy the needs of
-		// the current request (e.g. to signal a schema change), or because
-		// a previous request on the stream yielded a transient error and we
-		// want to reconnect before issuing a subsequent request.
-		//
-		// TODO: clean this up once internal issue 205756033 is resolved.
+	// We need to (re)open a connection.  Cleanup previous connection and channel if they are present.
+	if ms.arc != nil {
 		(*ms.arc).CloseSend()
 	}
+	if ms.pending != nil {
+		close(ms.pending)
+	}
 
 	ms.arc = new(storagepb.BigQueryWrite_AppendRowsClient)
 	*ms.arc, ms.pending, ms.err = ms.openWithRetry()

bigquery/storage/managedwriter/managed_stream_test.go

@@ -471,6 +471,52 @@ func TestManagedStream_LeakingGoroutines(t *testing.T) {
 	}
 }
 
+// Ensures we don't lose track of channels/connections during reconnects.
+// https://github.com/googleapis/google-cloud-go/issues/6766
+func TestManagedStream_LeakingReconnect(t *testing.T) {
+
+	ctx := context.Background()
+
+	ms := &ManagedStream{
+		ctx:            ctx,
+		streamSettings: defaultStreamSettings(),
+		fc:             newFlowController(10, 0),
+		open: openTestArc(&testAppendRowsClient{},
+			func(req *storagepb.AppendRowsRequest) error {
+				// Append always reports EOF on send.
+				return io.EOF
+			}, nil),
+	}
+	ms.schemaDescriptor = &descriptorpb.DescriptorProto{
+		Name: proto.String("testDescriptor"),
+	}
+
+	var chans []chan *pendingWrite
+
+	for i := 0; i < 10; i++ {
+		_, ch, err := ms.getStream(nil, true)
+		if err != nil {
+			t.Fatalf("failed openWithRetry(%d): %v", i, err)
+		}
+		chans = append(chans, ch)
+	}
+	var closedCount int
+	for _, ch := range chans {
+		select {
+		case _, ok := <-ch:
+			if !ok {
+				closedCount = closedCount + 1
+			}
+		case <-time.After(time.Second):
+			// we blocked, likely indicative that the channel is open.
+			continue
+		}
+	}
+	if wantClosed := len(chans) - 1; wantClosed != closedCount {
+		t.Errorf("closed count mismatch, got %d want %d", closedCount, wantClosed)
+	}
+}
+
 // Ensures we're propagating call options as expected.
 // Background: https://github.com/googleapis/google-cloud-go/issues/6487
 func TestOpenCallOptionPropagation(t *testing.T) {