Only write Content-Length if the runtime.WithWriteContentLength() opt…

…ion is specified (#5151)

runtime/handler.go

@@ -196,7 +196,7 @@ func ForwardResponseMessage(ctx context.Context, mux *ServeMux, marshaler Marsha
 		return
 	}
 
-	if !doForwardTrailers {
+	if !doForwardTrailers && mux.writeContentLength {
 		w.Header().Set("Content-Length", strconv.Itoa(len(buf)))
 	}
 

runtime/handler_test.go

@@ -377,6 +377,77 @@ func TestForwardResponseMessage(t *testing.T) {
 }
 
 func TestOutgoingHeaderMatcher(t *testing.T) {
+	t.Parallel()
+	msg := &pb.SimpleMessage{Id: "foo"}
+	for _, tc := range []struct {
+		name    string
+		md      runtime.ServerMetadata
+		headers http.Header
+		matcher runtime.HeaderMatcherFunc
+	}{
+		{
+			name: "default matcher",
+			md: runtime.ServerMetadata{
+				HeaderMD: metadata.Pairs(
+					"foo", "bar",
+					"baz", "qux",
+				),
+			},
+			headers: http.Header{
+				"Content-Type":      []string{"application/json"},
+				"Grpc-Metadata-Foo": []string{"bar"},
+				"Grpc-Metadata-Baz": []string{"qux"},
+			},
+		},
+		{
+			name: "custom matcher",
+			md: runtime.ServerMetadata{
+				HeaderMD: metadata.Pairs(
+					"foo", "bar",
+					"baz", "qux",
+				),
+			},
+			headers: http.Header{
+				"Content-Type": []string{"application/json"},
+				"Custom-Foo":   []string{"bar"},
+			},
+			matcher: func(key string) (string, bool) {
+				switch key {
+				case "foo":
+					return "custom-foo", true
+				default:
+					return "", false
+				}
+			},
+		},
+	} {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			ctx := runtime.NewServerMetadataContext(context.Background(), tc.md)
+
+			req := httptest.NewRequest("GET", "http://example.com/foo", nil)
+			resp := httptest.NewRecorder()
+
+			mux := runtime.NewServeMux(
+				runtime.WithOutgoingHeaderMatcher(tc.matcher),
+			)
+			runtime.ForwardResponseMessage(ctx, mux, &runtime.JSONPb{}, resp, req, msg)
+
+			w := resp.Result()
+			defer w.Body.Close()
+			if w.StatusCode != http.StatusOK {
+				t.Fatalf("StatusCode %d want %d", w.StatusCode, http.StatusOK)
+			}
+
+			if !reflect.DeepEqual(w.Header, tc.headers) {
+				t.Fatalf("Header %v want %v", w.Header, tc.headers)
+			}
+		})
+	}
+}
+
+func TestOutgoingHeaderMatcherWithContentLength(t *testing.T) {
 	t.Parallel()
 	msg := &pb.SimpleMessage{Id: "foo"}
 	for _, tc := range []struct {
@@ -431,7 +502,11 @@ func TestOutgoingHeaderMatcher(t *testing.T) {
 			req := httptest.NewRequest("GET", "http://example.com/foo", nil)
 			resp := httptest.NewRecorder()
 
-			runtime.ForwardResponseMessage(ctx, runtime.NewServeMux(runtime.WithOutgoingHeaderMatcher(tc.matcher)), &runtime.JSONPb{}, resp, req, msg)
+			mux := runtime.NewServeMux(
+				runtime.WithOutgoingHeaderMatcher(tc.matcher),
+				runtime.WithWriteContentLength(),
+			)
+			runtime.ForwardResponseMessage(ctx, mux, &runtime.JSONPb{}, resp, req, msg)
 
 			w := resp.Result()
 			defer w.Body.Close()
@@ -529,7 +604,11 @@ func TestOutgoingTrailerMatcher(t *testing.T) {
 			req.Header = tc.caller
 			resp := httptest.NewRecorder()
 
-			runtime.ForwardResponseMessage(ctx, runtime.NewServeMux(runtime.WithOutgoingTrailerMatcher(tc.matcher)), &runtime.JSONPb{}, resp, req, msg)
+			mux := runtime.NewServeMux(
+				runtime.WithOutgoingTrailerMatcher(tc.matcher),
+				runtime.WithWriteContentLength(),
+			)
+			runtime.ForwardResponseMessage(ctx, mux, &runtime.JSONPb{}, resp, req, msg)
 
 			w := resp.Result()
 			_, _ = io.Copy(io.Discard, w.Body)

runtime/mux.go

@@ -71,6 +71,7 @@ type ServeMux struct {
 	routingErrorHandler       RoutingErrorHandlerFunc
 	disablePathLengthFallback bool
 	unescapingMode            UnescapingMode
+	writeContentLength        bool
 }
 
 // ServeMuxOption is an option that can be given to a ServeMux on construction.
@@ -258,6 +259,13 @@ func WithDisablePathLengthFallback() ServeMuxOption {
 	}
 }
 
+// WithWriteContentLength returns a ServeMuxOption to enable writing content length on non-streaming responses
+func WithWriteContentLength() ServeMuxOption {
+	return func(serveMux *ServeMux) {
+		serveMux.writeContentLength = true
+	}
+}
+
 // WithHealthEndpointAt returns a ServeMuxOption that will add an endpoint to the created ServeMux at the path specified by endpointPath.
 // When called the handler will forward the request to the upstream grpc service health check (defined in the
 // gRPC Health Checking Protocol).