Adding zero-length chunk for long-running requests

mongoose.c

@@ -4931,6 +4931,9 @@ static void mg_ev_handler(struct ns_connection *nc, enum ns_event ev, void *p) {
 
     case NS_POLL:
       if (call_user(conn, MG_POLL) == MG_TRUE) {
+        if (conn->ns_conn->flags & MG_HEADERS_SENT) {
+          write_terminating_chunk(conn);
+        }
         close_local_endpoint(conn);
       }