Add int return value to on_frame_send_callback

lib/includes/nghttp2/nghttp2.h

@@ -863,8 +863,13 @@ typedef int (*nghttp2_before_frame_send_callback)
  * @functypedef
  *
  * Callback function invoked after the non-DATA frame |frame| is sent.
+ *
+ * The implementation of this function must return 0 if it
+ * succeeds. If nonzero is returned, it is treated as fatal error and
+ * `nghttp2_session_recv()` and `nghttp2_session_send()` functions
+ * immediately return :enum:`NGHTTP2_ERR_CALLBACK_FAILURE`.
  */
-typedef void (*nghttp2_on_frame_send_callback)
+typedef int (*nghttp2_on_frame_send_callback)
 (nghttp2_session *session, nghttp2_frame *frame, void *user_data);
 
 /**

lib/nghttp2_session.c

@@ -1259,8 +1259,10 @@ static int nghttp2_session_after_frame_sent(nghttp2_session *session)
     nghttp2_frame *frame;
     frame = nghttp2_outbound_item_get_ctrl_frame(session->aob.item);
     if(session->callbacks.on_frame_send_callback) {
-      session->callbacks.on_frame_send_callback(session, frame,
+      if(session->callbacks.on_frame_send_callback(session, frame,
-                                                session->user_data);
+                                                   session->user_data) != 0) {
+        return NGHTTP2_ERR_CALLBACK_FAILURE;
+      }
     }
     switch(frame->hd.type) {
     case NGHTTP2_HEADERS: {

src/HttpServer.cc

@@ -739,7 +739,7 @@ void htdocs_on_request_recv_callback
 }
 
 namespace {
-void hd_on_frame_send_callback
+int hd_on_frame_send_callback
 (nghttp2_session *session, nghttp2_frame *frame,
  void *user_data)
 {
@@ -748,6 +748,7 @@ void hd_on_frame_send_callback
     print_session_id(hd->session_id());
     on_frame_send_callback(session, frame, user_data);
   }
+  return 0;
 }
 } // namespace
 

src/app_helper.cc

@@ -389,13 +389,14 @@ void on_unknown_frame_recv_callback(nghttp2_session *session,
   fflush(stdout);
 }
 
-void on_frame_send_callback
+int on_frame_send_callback
 (nghttp2_session *session, nghttp2_frame *frame, void *user_data)
 {
   print_timer();
   printf(" send ");
   print_frame(PRINT_SEND, frame);
   fflush(stdout);
+  return 0;
 }
 
 namespace {

src/app_helper.h

@@ -61,7 +61,7 @@ void on_unknown_frame_recv_callback(nghttp2_session *session,
                                    size_t payloadlen,
                                    void *user_data);
 
-void on_frame_send_callback
+int on_frame_send_callback
 (nghttp2_session *session, nghttp2_frame *frame, void *user_data);
 
 int on_data_recv_callback

src/nghttp.cc

@@ -978,7 +978,7 @@ void check_stream_id(nghttp2_session *session, int32_t stream_id,
 }
 } // namespace
 
-void on_frame_send_callback2
+int on_frame_send_callback2
 (nghttp2_session *session, nghttp2_frame *frame, void *user_data)
 {
   if(frame->hd.type == NGHTTP2_HEADERS &&
@@ -988,6 +988,7 @@ void on_frame_send_callback2
   if(config.verbose) {
     on_frame_send_callback(session, frame, user_data);
   }
+  return 0;
 }
 
 void check_response_header

tests/nghttp2_session_test.c

@@ -145,13 +145,14 @@ static int on_invalid_frame_recv_callback(nghttp2_session *session,
   return 0;
 }
 
-static void on_frame_send_callback(nghttp2_session *session,
+static int on_frame_send_callback(nghttp2_session *session,
-                                   nghttp2_frame *frame,
+                                  nghttp2_frame *frame,
-                                   void *user_data)
+                                  void *user_data)
 {
   my_user_data *ud = (my_user_data*)user_data;
   ++ud->frame_send_cb_called;
   ud->sent_frame_type = frame->hd.type;
+  return 0;
 }
 
 static void on_frame_not_send_callback(nghttp2_session *session,