Classes authority_path mqtt_client reason_code subscribe_options subscribe_topic will Concepts ExecutionContext StreamType TlsContext is_authenticator Type aliases error_code Enumerations auth_step_e client::error disconnect_rc_e qos_e retain_e Functions get_error_code_category make_error_code Properties will_props connect_props connack_props publish_props puback_props pubrec_props pubrel_props pubcomp_props subscribe_props suback_props unsubscribe_props unsuback_props disconnect_props auth_props Reference tables Reason codes Error handling