Non-blocking MQTT library

Question

Are there any MQTT libraries that do not block while connecting?

I'm currently using PubSubClient, and the connection part contains this code: https://github.com/knolleary/pubsubclient/blob/master/src/PubSubClient.cpp

 while (!_client->available()) {
 unsigned long t = millis();
 if (t-lastInActivity >= ((int32_t) MQTT_SOCKET_TIMEOUT*1000UL)) {
 _state = MQTT_CONNECTION_TIMEOUT;
 _client->stop();
 return false;
 }
 }

I'd like my main loop to continue, or a callback to be called, while the MQTT connection is established, rather than waiting for ages if the MQTT server is unavailable.

Update:

I wrote a modification to take a callback function, and called it in an else clause added to that if statement, and discovered that the blocking delay is not this while loop. I think it's in the _client->connect at the start of the method.

Answer 1

I had the same question and found an mqtt library that is completely non-blocking.

• https://github.com/marvinroger/async-mqtt-client

You need to manually install it and the docs give instructions:

• https://github.com/marvinroger/async-mqtt-client/blob/develop/docs/1.-Getting-started.md

It requires one additional library:

• for esp8266: https://github.com/me-no-dev/ESPAsyncTCP
• for esp32: https://github.com/me-no-dev/AsyncTCP

I also liked the example's use of the Ticker library as a general tool for non-blocking code.