PUBACK properties

The last field in the Variable header of PUBACK 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 PUBACK Properties and describes their usage:

Table 1.8. PUBACK properties

Identifier	Value type	Description
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.

Usage

After obtaining an instance of async_mqtt5::puback_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::puback_props props;
props[async_mqtt5::prop::reason_string] = "Some reason...";
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