✨ Add ability to publish DUP packets (marvinroger#61)

* Added ability to publish DUP packets

* Added DUP retry feature to subscibe messages

* Reverted previous commit

* Revert "Reverted previous commit"

This reverts commit 337314b.

* Revert "Added DUP retry feature to subscibe messages"

This reverts commit 3f7170c.

* Updated docs

Author: UHSL-Marcus

docs/2.-API-reference.md

@@ -145,7 +145,7 @@ Return the packet ID or 0 if failed.
 
 * **`topic`**: Topic
 
-#### uint16_t publish(const char\* `topic`, uint8_t `qos`, bool `retain`, const char\* `payload` = nullptr, size_t `length` = 0)
+#### uint16_t publish(const char\* `topic`, uint8_t `qos`, bool `retain`, const char\* `payload` = nullptr, size_t `length` = 0, bool dup = false, uint16_t message_id = 0)
 
 Publish a packet.
 
@@ -156,3 +156,5 @@ Return the packet ID (or 1 if QoS 0) or 0 if failed.
 * **`retain`**: Retain flag
 * **`payload`**: Payload. If unset, the payload will be empty
 * **`length`**: Payload length. If unset or set to 0, the payload will be considered as a string and its size will be calculated using `strlen(payload)`
+* **`dup`**: Duplicate flag. If set or set to 1, the payload will be flagged as a duplicate
+* **`message_id`**: The message ID. If unset or set to 0, the message ID will be automtaically assigned. Use this with the DUP flag to identify which message is being duplicated

src/AsyncMqttClient.cpp

@@ -786,13 +786,13 @@ uint16_t AsyncMqttClient::unsubscribe(const char* topic) {
   return packetId;
 }
 
-uint16_t AsyncMqttClient::publish(const char* topic, uint8_t qos, bool retain, const char* payload, size_t length) {
+uint16_t AsyncMqttClient::publish(const char* topic, uint8_t qos, bool retain, const char* payload, size_t length, bool dup, uint16_t message_id) {
   if (!_connected) return 0;
 
   char fixedHeader[5];
   fixedHeader[0] = AsyncMqttClientInternals::PacketType.PUBLISH;
   fixedHeader[0] = fixedHeader[0] << 4;
-  fixedHeader[0] = fixedHeader[0] | AsyncMqttClientInternals::HeaderFlag.CONNECT_RESERVED;
+  fixedHeader[0] = fixedHeader[0] | (dup ? 0x01 : 0x00);
   if (retain) fixedHeader[0] |= AsyncMqttClientInternals::HeaderFlag.PUBLISH_RETAIN;
   switch (qos) {
     case 0:
@@ -829,7 +829,11 @@ uint16_t AsyncMqttClient::publish(const char* topic, uint8_t qos, bool retain, c
   uint16_t packetId = 0;
   char packetIdBytes[2];
   if (qos != 0) {
-    packetId = _getNextPacketId();
+    if (dup && message_id > 0) {
+		packetId = message_id;
+	} else {
+		packetId = _getNextPacketId();
+	}
     packetIdBytes[0] = packetId >> 8;
     packetIdBytes[1] = packetId & 0xFF;
   }

src/AsyncMqttClient.hpp

@@ -67,7 +67,7 @@ class AsyncMqttClient {
   void disconnect(bool force = false);
   uint16_t subscribe(const char* topic, uint8_t qos);
   uint16_t unsubscribe(const char* topic);
-  uint16_t publish(const char* topic, uint8_t qos, bool retain, const char* payload = nullptr, size_t length = 0);
+  uint16_t publish(const char* topic, uint8_t qos, bool retain, const char* payload = nullptr, size_t length = 0, bool dup = false, uint16_t message_id = 0);
 
  private:
   AsyncClient _client;