Adding the ability to track responses to subscriptions and unsubscriptions

kmqtt-client/src/commonMain/kotlin/io/github/davidepianca98/MQTTClient.kt

@@ -91,6 +91,7 @@ import kotlinx.coroutines.yield
  * @param onConnected called when the CONNACK packet has been received and the connection has been established
  * @param onDisconnected called when a DISCONNECT packet has been received or if the connection has been terminated
  * @param onSubscribed called when a SUBACK packet has been received
+ * @param onUnsubscribed called when a UNSUBACK packet has been received
  * @param debugLog set to print the hex packets sent and received
  * @param publishReceived called when a PUBLISH packet has been received
  */
@@ -118,6 +119,7 @@ public class MQTTClient(
     private val onConnected: (connack: MQTTConnack) -> Unit = {},
     private val onDisconnected: (disconnect: MQTTDisconnect?) -> Unit = {},
     private val onSubscribed: (suback: MQTTSuback) -> Unit = {},
+    private val onUnsubscribed: (unsuback: MQTTUnsuback) -> Unit = {},
     private val debugLog: Boolean = false,
     private val publishReceived: (publish: MQTTPublish) -> Unit
 ) {
@@ -338,17 +340,20 @@ public class MQTTClient(
      *
      * @param subscriptions the list of topic filters and relative settings (many settings are used only in MQTT5)
      * @param properties the properties to be included in the message (used only in MQTT5)
+     * @return the packet Id
      */
-    public fun subscribe(subscriptions: List<Subscription>, properties: MQTT5Properties = MQTT5Properties()) {
+    public fun subscribe(subscriptions: List<Subscription>, properties: MQTT5Properties = MQTT5Properties()): UInt {
         if (!connackReceived.value && properties.authenticationData != null) {
             throw Exception("Not sending until connection complete")
         }
+        val packetId = generatePacketId()
         val subscribe = if (mqttVersion == MQTTVersion.MQTT3_1_1) {
-            MQTT4Subscribe(generatePacketId(), subscriptions)
+            MQTT4Subscribe(packetId, subscriptions)
         } else {
-            MQTT5Subscribe(generatePacketId(), subscriptions, properties)
+            MQTT5Subscribe(packetId, subscriptions, properties)
         }
         send(subscribe.toByteArray())
+        return packetId
     }
 
     /**
@@ -356,17 +361,20 @@ public class MQTTClient(
      *
      * @param topics the list of topic filters
      * @param properties the properties to be included in the message (used only in MQTT5)
+     * @return the packet Id
      */
-    public fun unsubscribe(topics: List<String>, properties: MQTT5Properties = MQTT5Properties()) {
+    public fun unsubscribe(topics: List<String>, properties: MQTT5Properties = MQTT5Properties()): UInt {
         if (!connackReceived.value && properties.authenticationData != null) {
             throw Exception("Not sending until connection complete")
         }
+        val packetId = generatePacketId()
         val unsubscribe = if (mqttVersion == MQTTVersion.MQTT3_1_1) {
-            MQTT4Unsubscribe(generatePacketId(), topics)
+            MQTT4Unsubscribe(packetId, topics)
         } else {
-            MQTT5Unsubscribe(generatePacketId(), topics, properties)
+            MQTT5Unsubscribe(packetId, topics, properties)
         }
         send(unsubscribe.toByteArray())
+        return packetId
     }
 
     /**
@@ -746,6 +754,7 @@ public class MQTTClient(
         if (packet is MQTT5Unsuback && properties.requestProblemInformation == 0u && (packet.properties.reasonString != null || packet.properties.userProperty.isNotEmpty())) {
             throw MQTTException(ReasonCode.PROTOCOL_ERROR)
         }
+        onUnsubscribed(packet)
     }
 
     private fun handlePingresp() {