async_mqtt

• I/O independent (as known as Sans-I/O) MQTT protocol library for C++17.
• Asynchronous MQTT communication library using the MQTT protocol library and Boost.Asio.

Version 10.1.0

Document

See Document

I/O independent protocol library

• connection
  • Protocol state machine for MQTT connection.
  • All APIs are implemented as synchronous member functions.
  • State machine events are implemented as pure virtual functions.
• rv_connection
  • Inherits connection.
  • State machine events are implemented as the return value of APIs.
    • The type of return value is vector of event_variant.

Boost.Asio style asynchronous APIs support

Completion Token is supported

• Callbacks
  • Can wait mutiple events
  • High performance
  • Deep callback nesting
  • For simple and continuous multiple waiting usecases
  • example/ep_cb_mqtt_client.cpp
• boost::asio::use_future
  • Can’t wait multiple events
  • Less performance than callbacks and stackless coroutines
  • Easy to read
  • For simple and straight usecases
  • example/ep_future_mqtt_client.cpp
• Stackless Coroutine (boost::asio::coroutine)
  • Can wait multiple event. You can distinguish which event is invoked by operator()’s overloaded parameter.
  • High performance
  • Easy to read but difficult to learn yield notation
  • example/ep_slcoro_mqtt_client.cpp
• C++20Coroutine
  • Can wait multiple event.
  • High performance. (But a little bit slower than Stackless Coroutine)
  • Easy to read.
  • example/ep_slcoro_mqtt_client.cpp
• and more

I recommend using Stackless Coroutine (boost::asio::coroutine) because it can avoid deep nested callbacks and higher performance than boost::asio::use_future. C++20 Coroutine is also a good choice. It requires C++20 support. It is more elegant than Stackless Coroutine but a little bit slower than Stackless coroutine.

High level MQTT client APIs support (since 5.1.0)

See document and example.

Features

• Not only client but also server is supported.
  • endpoint(basic_endpoint) can be used to implement MQTT client application and/or server application like MQTT broker.
• Both MQTT v3.1.1 and v5.0 are supported.
  • In addition, undetermined is supported for server implementation. In this case, the protocol version is decided when you receive CONNECT packet.
• Continuous packet sending
  • You can send MQTT packets before the previous sending is not completed.
• Auto acquiring/mapping topic alias is supported.
  • In addition, when resend PUBLISH packet after reconnecting, topic alias is removed and original topic is restored. It is required by MQTT v5.0 spec.

Requirement

• Compiler: C++17 or later
• Boost Libraries: 1.84.0 or later
  • If you don’t build tests, 1.82.0 or later