mqtt_client::async_unsubscribe (2 of 2 overloads)

Send an UNSUBSCRIBE packet to Broker to unsubscribe from one Topic.

template <
    typename CompletionToken = typename asio::default_completion_token<executor_type>::type
>
decltype(auto) async_unsubscribe(
    const std::string & topic,
    const unsubscribe_props & props,
    CompletionToken && token = {}
);

Description

	Note
	The Client may still receive residual Application Messages through the `mqtt_client::async_receive` function from Topics the Client just unsubscribed to.

Parameters

Name	Description
topic	Topic to unsubscribe from.
props	An instance of `async_mqtt5::unsubscribe_props`.
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::async_immediate`.

Handler signature

The handler signature for this operation:

void (
  async_mqtt5::error_code, // Result of operation.
  std::vector<async_mqtt5::reason_code>, // Vector of Reason Codes containing
                      // the result of unsubscribe operation
                      // for the Topic in the UNSUBSCRIBE packet.
  async_mqtt5::unsuback_props, // Properties received in the UNSUBACK packet.
)

Completion condition

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

The Client has successfully sent an UNSUBSCRIBE packet and has received an UNSUBACK response from the Broker.
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::no_recovery
boost::asio::error::operation_aborted
async_mqtt5::client::error::malformed_packet
async_mqtt5::client::error::packet_too_large
async_mqtt5::client::error::pid_overrun
async_mqtt5::client::error::invalid_topic

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 - invokes mqtt_client::cancel
cancellation_type::partial & cancellation_type::total - prevents potential resending of the UNSUBSCRIBE packet