mqtt_client::async

mqtt_client::async_receive

Asynchronously receive an Application Message.

template <
    typename CompletionToken = typename asio::default_completion_token<executor_type>::type
>
decltype(auto) async_receive(
    CompletionToken && token = {}
);

The Client will receive and complete deliveries for all the PUBLISH packets received from the Broker throughout its lifetime. The Client will store them internally in the order they were delivered. Calling this function will attempt to receive an Application Message from internal storage.

	Note
	It is only recommended to call this function if you have established a successful subscription to a Topic using the `mqtt_client::async_subscribe` function.

Parameters

Name	Description
token	Completion token that will be used to produce a completion handler. The handler will be invoked when the operation completes. On immediate completion, invocation of the handler will be performed in a manner equivalent to using `boost::asio::post`.

Handler signature

The handler signature for this operation:

void (
  async_mqtt5::error_code, // Result of operation.
  std::string,  // Topic, the origin of the Application Message.
  std::string,  // Payload, the content of the Application Message.
  async_mqtt5::publish_props, // Properties received in the PUBLISH packet.
)

Completion condition

The asynchronous operation will complete when one of the following conditions is true:

The Client has a pending Application Message in its internal storage ready to be received.
An error occurred. This is indicated by an associated async_mqtt5::error_code in the handler.

Error codes

The list of all possible error codes that this operation can finish with:

boost::system::errc::errc_t::success
boost::asio::error::operation_aborted
async_mqtt5::client::error::session_expired

Refer to the section on Error handling to find the underlying causes for each error code.

Per-Operation Cancellation

This asynchronous operation supports cancellation for the following boost::asio::cancellation_type values:

cancellation_type::terminal
cancellation_type::partial
cancellation_type::total