Allow multiple HTTP-Headers in Server

log/level/level.go

@@ -177,7 +177,7 @@ func DebugValue() Value { return debugValue }
 
 var (
 	// key is of type interfae{} so that it allocates once during package
-	// initialization and avoids allocating every type the value is added to a
+	// initialization and avoids allocating every time the value is added to a
 	// []interface{} later.
 	key interface{} = "level"
 

transport/http/server.go

@@ -144,8 +144,10 @@ type ServerFinalizerFunc func(ctx context.Context, code int, r *http.Request)
 func EncodeJSONResponse(_ context.Context, w http.ResponseWriter, response interface{}) error {
 	w.Header().Set("Content-Type", "application/json; charset=utf-8")
 	if headerer, ok := response.(Headerer); ok {
-		for k := range headerer.Headers() {
-			w.Header().Set(k, headerer.Headers().Get(k))
+		for k, values := range headerer.Headers() {
+			for _, v := range values {
+				w.Header().Add(k, v)
+			}
 		}
 	}
 	code := http.StatusOK
@@ -175,8 +177,10 @@ func DefaultErrorEncoder(_ context.Context, err error, w http.ResponseWriter) {
 	}
 	w.Header().Set("Content-Type", contentType)
 	if headerer, ok := err.(Headerer); ok {
-		for k := range headerer.Headers() {
-			w.Header().Set(k, headerer.Headers().Get(k))
+		for k, values := range headerer.Headers() {
+			for _, v := range values {
+				w.Header().Add(k, v)
+			}
 		}
 	}
 	code := http.StatusInternalServerError

transport/http/server_test.go

@@ -261,6 +261,77 @@ func TestEncodeJSONResponse(t *testing.T) {
 	}
 }
 
+type multiHeaderResponse struct{}
+
+func (_ multiHeaderResponse) Headers() http.Header {
+	return http.Header{"Vary": []string{"Origin", "User-Agent"}}
+}
+
+func TestAddMultipleHeaders(t *testing.T) {
+	handler := httptransport.NewServer(
+		func(context.Context, interface{}) (interface{}, error) { return multiHeaderResponse{}, nil },
+		func(context.Context, *http.Request) (interface{}, error) { return struct{}{}, nil },
+		httptransport.EncodeJSONResponse,
+	)
+
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	resp, err := http.Get(server.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expect := map[string]map[string]struct{}{"Vary": map[string]struct{}{"Origin": struct{}{}, "User-Agent": struct{}{}}}
+	for k, vls := range resp.Header {
+		for _, v := range vls {
+			delete((expect[k]), v)
+		}
+		if len(expect[k]) != 0 {
+			t.Errorf("Header: unexpected header %s: %v", k, expect[k])
+		}
+	}
+}
+
+type multiHeaderResponseError struct {
+	multiHeaderResponse
+	msg string
+}
+
+func (m multiHeaderResponseError) Error() string {
+	return m.msg
+}
+
+func TestAddMultipleHeadersErrorEncoder(t *testing.T) {
+	errStr := "oh no"
+	handler := httptransport.NewServer(
+		func(context.Context, interface{}) (interface{}, error) {
+			return nil, multiHeaderResponseError{msg: errStr}
+		},
+		func(context.Context, *http.Request) (interface{}, error) { return struct{}{}, nil },
+		httptransport.EncodeJSONResponse,
+	)
+
+	server := httptest.NewServer(handler)
+	defer server.Close()
+
+	resp, err := http.Get(server.URL)
+	if err != nil {
+		t.Fatal(err)
+	}
+	expect := map[string]map[string]struct{}{"Vary": map[string]struct{}{"Origin": struct{}{}, "User-Agent": struct{}{}}}
+	for k, vls := range resp.Header {
+		for _, v := range vls {
+			delete((expect[k]), v)
+		}
+		if len(expect[k]) != 0 {
+			t.Errorf("Header: unexpected header %s: %v", k, expect[k])
+		}
+	}
+	if b, _ := ioutil.ReadAll(resp.Body); errStr != string(b) {
+		t.Errorf("ErrorEncoder: got: %q, expected: %q", b, errStr)
+	}
+}
+
 type noContentResponse struct{}
 
 func (e noContentResponse) StatusCode() int { return http.StatusNoContent }