Mark implicit ACK for MQTT as MQTT transport (#8939)

* Mark implicit ACK for MQTT as MQTT transport

* TRUNK

* Fix build

* Make sure implicit ACKs from MQTT do not stop retransmissions in ReliableRouter

---------

Co-authored-by: Ben Meadors <benmmeadors@gmail.com>

src/mesh/ReliableRouter.cpp

@@ -150,7 +150,9 @@ void ReliableRouter::sniffReceived(const meshtastic_MeshPacket *p, const meshtas
         PacketId nakId = (c && c->error_reason != meshtastic_Routing_Error_NONE) ? p->decoded.request_id : 0;
 
         // We intentionally don't check wasSeenRecently, because it is harmless to delete non existent retransmission records
-        if (ackId || nakId) {
+        if ((ackId || nakId) &&
+            // Implicit ACKs from MQTT should not stop retransmissions
+            !(isFromUs(p) && p->transport_mechanism == meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MQTT)) {
             LOG_DEBUG("Received a %s for 0x%x, stopping retransmissions", ackId ? "ACK" : "NAK", ackId);
             if (ackId) {
                 stopRetransmission(p->to, ackId);

src/modules/RoutingModule.cpp

@@ -75,6 +75,12 @@ uint8_t RoutingModule::getHopLimitForResponse(uint8_t hopStart, uint8_t hopLimit
     return Default::getConfiguredOrDefaultHopLimit(config.lora.hop_limit); // Use the default hop limit
 }
 
+meshtastic_MeshPacket *RoutingModule::allocAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex,
+                                                  uint8_t hopLimit)
+{
+    return MeshModule::allocAckNak(err, to, idFrom, chIndex, hopLimit);
+}
+
 RoutingModule::RoutingModule() : ProtobufModule("routing", meshtastic_PortNum_ROUTING_APP, &meshtastic_Routing_msg)
 {
     isPromiscuous = true;

src/modules/RoutingModule.h

@@ -16,6 +16,9 @@ class RoutingModule : public ProtobufModule<meshtastic_Routing>
     virtual void sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopLimit = 0,
                             bool ackWantsAck = false);
 
+    meshtastic_MeshPacket *allocAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex,
+                                       uint8_t hopLimit = 0);
+
     // Given the hopStart and hopLimit upon reception of a request, return the hop limit to use for the response
     uint8_t getHopLimitForResponse(uint8_t hopStart, uint8_t hopLimit);
 

src/mqtt/MQTT.cpp

@@ -87,10 +87,13 @@ inline void onReceiveProto(char *topic, byte *payload, size_t length)
         // Generate an implicit ACK towards ourselves (handled and processed only locally!) for this message.
         // We do this because packets are not rebroadcasted back into MQTT anymore and we assume that at least one node
         // receives it when we get our own packet back. Then we'll stop our retransmissions.
-        if (isFromUs(e.packet))
+        if (isFromUs(e.packet)) {
-            routingModule->sendAckNak(meshtastic_Routing_Error_NONE, getFrom(e.packet), e.packet->id, ch.index);
+            auto pAck = routingModule->allocAckNak(meshtastic_Routing_Error_NONE, getFrom(e.packet), e.packet->id, ch.index);
-        else
+            pAck->transport_mechanism = meshtastic_MeshPacket_TransportMechanism_TRANSPORT_MQTT;
+            router->sendLocal(pAck);
+        } else {
             LOG_INFO("Ignore downlink message we originally sent");
+        }
         return;
     }
     if (isFromUs(e.packet)) {