Add int return value to nghttp2_before_frame_send_callback

lib/includes/nghttp2/nghttp2.h

@@ -850,8 +850,13 @@ typedef int (*nghttp2_on_data_recv_callback)
  * HEADERS and PUSH_PROMISE frame (see also
  * `nghttp2_session_get_stream_user_data()`), which is not assigned
  * when it was queued.
+ *
+ * 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_before_frame_send_callback)
+typedef int (*nghttp2_before_frame_send_callback)
 (nghttp2_session *session, nghttp2_frame *frame, void *user_data);
 
 /**

lib/nghttp2_session.c

@@ -1496,10 +1496,12 @@ int nghttp2_session_send(nghttp2_session *session)
       /* Call before_send callback */
       if(item->frame_cat == NGHTTP2_CAT_CTRL &&
          session->callbacks.before_frame_send_callback) {
-        session->callbacks.before_frame_send_callback
+        if(session->callbacks.before_frame_send_callback
            (session,
             nghttp2_outbound_item_get_ctrl_frame(item),
-           session->user_data);
+            session->user_data) != 0) {
+          return NGHTTP2_ERR_CALLBACK_FAILURE;
+        }
       }
     }
     data = session->aob.framebuf + session->aob.framebufoff;

src/shrpx_spdy_session.cc

@@ -945,7 +945,7 @@ int on_data_chunk_recv_callback(nghttp2_session *session,
 } // namespace
 
 namespace {
-void before_frame_send_callback(nghttp2_session *session,
+int before_frame_send_callback(nghttp2_session *session,
                                nghttp2_frame *frame,
                                void *user_data)
 {
@@ -956,7 +956,7 @@ void before_frame_send_callback(nghttp2_session *session,
     if(!sd || !sd->dconn) {
       nghttp2_submit_rst_stream(session, frame->hd.stream_id,
                                 NGHTTP2_CANCEL);
-      return;
+      return 0;
     }
     auto downstream = sd->dconn->get_downstream();
     if(downstream) {
@@ -965,6 +965,7 @@ void before_frame_send_callback(nghttp2_session *session,
       nghttp2_submit_rst_stream(session, frame->hd.stream_id, NGHTTP2_CANCEL);
     }
   }
+  return 0;
 }
 } // namespace