mosquitto_pub now handles the MQTT v5 retain-available property

It will not set the retain bit if retain-available is false.

ChangeLog.txt

@@ -15,6 +15,8 @@ Client library:
   identifier integer to the corresponding property name string.
 - Add `mosquitto_property_next()` to retrieve the next property in a list, for
   iterating over property lists.
+- mosquitto_pub now handles the MQTT v5 retain-available property by never
+  setting the retain bit.
 
 Clients:
 - Add timeout return code (27) for `mosquitto_sub -W <secs>` and

lib/actions.c

@@ -51,6 +51,10 @@ int mosquitto_publish_v5(struct mosquitto *mosq, int *mid, const char *topic, in
 	if(mosq->protocol != mosq_p_mqtt5 && properties) return MOSQ_ERR_NOT_SUPPORTED;
 	if(qos > mosq->maximum_qos) return MOSQ_ERR_QOS_NOT_SUPPORTED;
 
+	if(!mosq->retain_available){
+		retain = false;
+	}
+
 	if(properties){
 		if(properties->client_generated){
 			outgoing_properties = properties;

lib/connect.c

@@ -78,6 +78,7 @@ static int mosquitto__connect_init(struct mosquitto *mosq, const char *host, int
 	mosq->keepalive = keepalive;
 	mosq->msgs_in.inflight_quota = mosq->msgs_in.inflight_maximum;
 	mosq->msgs_out.inflight_quota = mosq->msgs_out.inflight_maximum;
+	mosq->retain_available = 1;
 
 	if(mosq->sockpairR != INVALID_SOCKET){
 		COMPAT_CLOSE(mosq->sockpairR);

lib/handle_connack.c

@@ -97,6 +97,7 @@ int handle__connack(struct mosquitto *mosq)
 		}
 	}
 
+	mosquitto_property_read_byte(properties, MQTT_PROP_RETAIN_AVAILABLE, &mosq->retain_available, false);
 	mosquitto_property_read_byte(properties, MQTT_PROP_MAXIMUM_QOS, &mosq->maximum_qos, false);
 	mosquitto_property_read_int16(properties, MQTT_PROP_RECEIVE_MAXIMUM, &mosq->msgs_out.inflight_maximum, false);
 	mosquitto_property_read_int16(properties, MQTT_PROP_SERVER_KEEP_ALIVE, &mosq->keepalive, false);

lib/mosquitto_internal.h

@@ -329,6 +329,7 @@ struct mosquitto {
 	unsigned int reconnect_delay;
 	unsigned int reconnect_delay_max;
 	bool reconnect_exponential_backoff;
+	uint8_t retain_available;
 	char threaded;
 	struct mosquitto__packet *out_packet_last;
 #  ifdef WITH_SRV