allow to response with different content-type

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

handler.go

@@ -243,7 +243,22 @@ func (h *httpServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	}
 
 	scode := int(200)
-	if appErr := fn(ctx, hr, replyv.Interface()); appErr != nil {
+	appErr := fn(ctx, hr, replyv.Interface())
+
+	w.Header().Set("Content-Type", ct)
+	if md, ok := metadata.FromOutgoingContext(ctx); ok {
+		for k, v := range md {
+			w.Header().Set(k, v)
+		}
+	}
+	if ct != w.Header().Get("Content-Type") {
+		if cf, err = h.newCodec(ct); err != nil {
+			h.errorHandler(ctx, nil, w, r, err, http.StatusBadRequest)
+			return
+		}
+	}
+
+	if appErr != nil {
 		switch verr := appErr.(type) {
 		case *errors.Error:
 			scode = int(verr.Code)
@@ -256,19 +271,12 @@ func (h *httpServer) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	} else {
 		b, err = cf.Marshal(replyv.Interface())
 	}
+
 	if err != nil && handler.sopts.Logger.V(logger.ErrorLevel) {
 		handler.sopts.Logger.Errorf(handler.sopts.Context, "handler err: %v", err)
 		return
 	}
 
-	w.Header().Set("Content-Type", ct)
-
-	if md, ok := metadata.FromOutgoingContext(ctx); ok {
-		for k, v := range md {
-			w.Header().Set(k, v)
-		}
-	}
-
 	if nscode := GetRspCode(ctx); nscode != 0 {
 		scode = nscode
 	}