DISCONNECT properties

The last field in the Variable header of DISCONNECT packet is a set of Properties. A set contains a Property Length followed by the Properties. A Property consists of an Identifier and a value.

This section lists all possible DISCONNECT Properties and describes their usage:

Table 1.16. DISCONNECT properties

Identifier	Value type	Description
session_expiry_interval	`uint32_t`	Represents the Session Expiry Internal in seconds. Can only be sent by the Client.
reason_string	`std::string`	A UTF-8 Encoded String representing the reason associated with this response.
user_property	`std::pair<std::string, std::string>`	Name, value pair (`UTF-8 String Pair`) defining User Property. There can be multiple pairs in one packet. This property may be used to provide additional diagnostic or other information.
server_reference	`std::string`	A UTF-8 Encoded String which can be used by the Client to identfy another Server to use.

Usage

After obtaining an instance of async_mqtt5::disconnect_props, the subscript operator can be used to access a Property.

The Identifiers listed in the table above are available within the async_mqtt5::prop namespace for Property access.

	Note
	When accessing a property value, the subscript operator will return a `std::optional` of the value type for all properties, except for `async_mqtt5::prop::user_property`, where it will return an instance of `std::vector<std::pair<std::string, std::string>>`.

Example

The following example shows how to set a Property value:

async_mqtt5::disconnect_props props;
props[async_mqtt5::prop::reason_string] = "Lost connection!";
props[async_mqtt5::prop::user_property].emplace_back("name", "value");

The following example shows how to retrieve a Property value:

std::optional<std::string> reason_string = props[async_mqtt5::prop::reason_string];
if (reason_string.has_value())
	// reason string property was previously set
else
	// reason string property was not set

std::vector<std::pair<std::string, std::string>>& user_props = props[async_mqtt5::prop::user_property];
if (!user_props.empty())
	// user property was previously set
else
	// user property was not set