Fix #198 (#781)

* Add new function to Render interface for writing content type only

* Add support for the new function in Render interface for writing content-type only

* Fix unhandled merge conflict in context_test.go

* Update vendor.json

render/json.go

@@ -21,18 +21,15 @@ type (
 
 var jsonContentType = []string{"application/json; charset=utf-8"}
 
-func (r JSON) Render(w http.ResponseWriter) error {
-	return WriteJSON(w, r.Data)
+func (r JSON) Render(w http.ResponseWriter) (err error) {
+	if err = WriteJSON(w, r.Data); err != nil {
+		panic(err)
+	}
+	return
 }
 
-func (r IndentedJSON) Render(w http.ResponseWriter) error {
+func (r JSON) WriteContentType(w http.ResponseWriter) {
 	writeContentType(w, jsonContentType)
-	jsonBytes, err := json.MarshalIndent(r.Data, "", "    ")
-	if err != nil {
-		return err
-	}
-	w.Write(jsonBytes)
-	return nil
 }
 
 func WriteJSON(w http.ResponseWriter, obj interface{}) error {
@@ -44,3 +41,17 @@ func WriteJSON(w http.ResponseWriter, obj interface{}) error {
 	w.Write(jsonBytes)
 	return nil
 }
+
+func (r IndentedJSON) Render(w http.ResponseWriter) error {
+	r.WriteContentType(w)
+	jsonBytes, err := json.MarshalIndent(r.Data, "", "    ")
+	if err != nil {
+		return err
+	}
+	w.Write(jsonBytes)
+	return nil
+}
+
+func (r IndentedJSON) WriteContentType(w http.ResponseWriter) {
+	writeContentType(w, jsonContentType)
+}