[lwip-devel] [bug #59561] [mqtt] Stop sending a keep-alive if the connection is closed for a previously unacked keep-alive

[Giuseppe Modugno]

URL:
  <https://savannah.nongnu.org/bugs/?59561>

                 Summary: [mqtt] Stop sending a keep-alive if the connection
is closed for a previously unacked keep-alive
                 Project: lwIP - A Lightweight TCP/IP stack
            Submitted by: giusloq
            Submitted on: Fri 27 Nov 2020 05:38:25 PM UTC
                Category: apps
                Severity: 3 - Normal
              Item Group: Faulty Behaviour
                  Status: None
                 Privacy: Public
             Assigned to: None
             Open/Closed: Open
         Discussion Lock: Any
         Planned Release: None
            lwIP version: git head

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Details:

In mqtt_cyclic_timer() I read:

    if (client->keep_alive > 0) {

      client->server_watchdog++;
      /* If reception from server has been idle for 1.5*keep_alive time,
server is considered unresponsive */
      if ((client->server_watchdog * MQTT_CYCLIC_TIMER_INTERVAL) >
(client->keep_alive + client->keep_alive / 2)) {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_cyclic_timer: Server incoming
keep-alive timeout\n"));
        mqtt_close(client, MQTT_CONNECT_TIMEOUT);
        restart_timer = 0;
      }

      /* If time for a keep alive message to be sent, transmission has been
idle for keep_alive time */
      client->cyclic_tick++;
      if ((client->cyclic_tick * MQTT_CYCLIC_TIMER_INTERVAL) >=
client->keep_alive) {
        LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_cyclic_timer: Sending keep-alive
message to server\n"));
        if (mqtt_output_check_space(&client->output, 0) != 0) {
          mqtt_output_append_fixed_header(&client->output,
MQTT_MSG_TYPE_PINGREQ, 0, 0, 0, 0);
          client->cyclic_tick = 0;
        }
      }
    }

If the condition of the first if was true, mqtt_close() has been called. We
can't enqueue a new keep-alive. So I propose to include the second block in an
else statement:

    if (client->keep_alive > 0) {

      client->server_watchdog++;
      /* If reception from server has been idle for 1.5*keep_alive time,
server is considered unresponsive */
      if ((client->server_watchdog * MQTT_CYCLIC_TIMER_INTERVAL) >
(client->keep_alive + client->keep_alive / 2)) {
        LWIP_DEBUGF(MQTT_DEBUG_WARN, ("mqtt_cyclic_timer: Server incoming
keep-alive timeout\n"));
        mqtt_close(client, MQTT_CONNECT_TIMEOUT);
        restart_timer = 0;

      } else {

        /* If time for a keep alive message to be sent, transmission has been
idle for keep_alive time */
        client->cyclic_tick++;
        if ((client->cyclic_tick * MQTT_CYCLIC_TIMER_INTERVAL) >=
client->keep_alive) {
          LWIP_DEBUGF(MQTT_DEBUG_TRACE, ("mqtt_cyclic_timer: Sending
keep-alive message to server\n"));
          if (mqtt_output_check_space(&client->output, 0) != 0) {
            mqtt_output_append_fixed_header(&client->output,
MQTT_MSG_TYPE_PINGREQ, 0, 0, 0, 0);
            client->cyclic_tick = 0;
          }
        }
      }
    }





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