acquire header mutex while copying trailers

internal/transport/handler_server.go

@@ -277,11 +277,13 @@ func (ht *serverHandlerTransport) writeStatus(s *ServerStream, st *status.Status
 	if err == nil { // transport has not been closed
 		// Note: The trailer fields are compressed with hpack after this call returns.
 		// No WireLength field is set here.
+		s.hdrMu.Lock()
 		for _, sh := range ht.stats {
 			sh.HandleRPC(s.Context(), &stats.OutTrailer{
 				Trailer: s.trailer.Copy(),
 			})
 		}
+		s.hdrMu.Unlock()
 	}
 	ht.Close(errors.New("finished writing status"))
 	return err

internal/transport/handler_server_test.go

@@ -35,6 +35,7 @@ import (
 	"google.golang.org/grpc/codes"
 	"google.golang.org/grpc/mem"
 	"google.golang.org/grpc/metadata"
+	"google.golang.org/grpc/stats"
 	"google.golang.org/grpc/status"
 	"google.golang.org/protobuf/proto"
 	"google.golang.org/protobuf/protoadapt"
@@ -246,6 +247,22 @@ type handleStreamTest struct {
 	ht    *serverHandlerTransport
 }
 
+type mockStatsHandler struct{}
+
+func (h *mockStatsHandler) TagRPC(ctx context.Context, _ *stats.RPCTagInfo) context.Context {
+	return ctx
+}
+
+func (h *mockStatsHandler) HandleRPC(context.Context, stats.RPCStats) {
+}
+
+func (h *mockStatsHandler) TagConn(ctx context.Context, _ *stats.ConnTagInfo) context.Context {
+	return ctx
+}
+
+func (h *mockStatsHandler) HandleConn(context.Context, stats.ConnStats) {
+}
+
 func newHandleStreamTest(t *testing.T) *handleStreamTest {
 	bodyr, bodyw := io.Pipe()
 	req := &http.Request{
@@ -260,7 +277,12 @@ func newHandleStreamTest(t *testing.T) *handleStreamTest {
 		Body: bodyr,
 	}
 	rw := newTestHandlerResponseWriter().(testHandlerResponseWriter)
-	ht, err := NewServerHandlerTransport(rw, req, nil, mem.DefaultBufferPool())
+	// Add mock stats handlers to exercise the stats handler code path.
+	statsHandlers := make([]stats.Handler, 0, 5)
+	for range 5 {
+		statsHandlers = append(statsHandlers, &mockStatsHandler{})
+	}
+	ht, err := NewServerHandlerTransport(rw, req, statsHandlers, mem.DefaultBufferPool())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -485,6 +507,12 @@ func (s) TestHandlerTransport_HandleStreams_ErrDetails(t *testing.T) {
 
 	hst := newHandleStreamTest(t)
 	handleStream := func(s *ServerStream) {
+		if err := s.SendHeader(metadata.New(map[string]string{})); err != nil {
+			t.Error(err)
+		}
+		if err := s.SetTrailer(metadata.Pairs("custom-trailer", "Custom trailer value")); err != nil {
+			t.Error(err)
+		}
 		s.WriteStatus(st)
 	}
 	ctx, cancel := context.WithTimeout(context.Background(), defaultTestTimeout)
@@ -501,6 +529,7 @@ func (s) TestHandlerTransport_HandleStreams_ErrDetails(t *testing.T) {
 		"Grpc-Status":             {fmt.Sprint(uint32(statusCode))},
 		"Grpc-Message":            {encodeGrpcMessage(msg)},
 		"Grpc-Status-Details-Bin": {encodeBinHeader(stBytes)},
+		"Custom-Trailer":          []string{"Custom trailer value"},
 	}
 
 	checkHeaderAndTrailer(t, hst.rw, wantHeader, wantTrailer)