Improve ACK logic for responses and repeated packets (#5232)

* Don't send ACKs to responses over multiple hops

* Move repeated sending logic to `wasSeenRecently()`

* Add exception for simulator for duplicate packets from PhoneAPI

* Add short debug message

src/mesh/MeshModule.cpp

@@ -33,7 +33,7 @@ MeshModule::~MeshModule()
 }
 
 meshtastic_MeshPacket *MeshModule::allocAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex,
-                                               uint8_t hopStart, uint8_t hopLimit)
+                                               uint8_t hopLimit)
 {
     meshtastic_Routing c = meshtastic_Routing_init_default;
 
@@ -50,7 +50,7 @@ meshtastic_MeshPacket *MeshModule::allocAckNak(meshtastic_Routing_Error err, Nod
 
     p->priority = meshtastic_MeshPacket_Priority_ACK;
 
-    p->hop_limit = routingModule->getHopLimitForResponse(hopStart, hopLimit); // Flood ACK back to original sender
+    p->hop_limit = hopLimit; // Flood ACK back to original sender
     p->to = to;
     p->decoded.request_id = idFrom;
     p->channel = chIndex;
@@ -181,8 +181,8 @@ void MeshModule::callModules(meshtastic_MeshPacket &mp, RxSource src)
             // SECURITY NOTE! I considered sending back a different error code if we didn't find the psk (i.e. !isDecoded)
             // but opted NOT TO.  Because it is not a good idea to let remote nodes 'probe' to find out which PSKs were "good" vs
             // bad.
-            routingModule->sendAckNak(meshtastic_Routing_Error_NO_RESPONSE, getFrom(&mp), mp.id, mp.channel, mp.hop_start,
-                                      mp.hop_limit);
+            routingModule->sendAckNak(meshtastic_Routing_Error_NO_RESPONSE, getFrom(&mp), mp.id, mp.channel,
+                                      routingModule->getHopLimitForResponse(mp.hop_start, mp.hop_limit));
         }
     }
 
@@ -295,4 +295,4 @@ bool MeshModule::isRequestingFocus()
     } else
         return false;
 }
-#endif
+#endif

src/mesh/MeshModule.h

@@ -162,7 +162,7 @@ class MeshModule
     virtual Observable<const UIFrameEvent *> *getUIFrameObservable() { return NULL; }
 
     meshtastic_MeshPacket *allocAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex,
-                                       uint8_t hopStart = 0, uint8_t hopLimit = 0);
+                                       uint8_t hopLimit = 0);
 
     /// Send an error response for the specified packet.
     meshtastic_MeshPacket *allocErrorResponse(meshtastic_Routing_Error err, const meshtastic_MeshPacket *p);

src/mesh/PacketHistory.cpp

@@ -38,6 +38,13 @@ bool PacketHistory::wasSeenRecently(const meshtastic_MeshPacket *p, bool withUpd
         seenRecently = false;
     }
 
+    /* If the original transmitter is doing retransmissions (hopStart equals hopLimit) for a reliable transmission, e.g., when the
+       ACK got lost, we will handle the packet again to make sure it gets an ACK/response to its packet. */
+    if (seenRecently && p->hop_start > 0 && p->hop_start == p->hop_limit) {
+        LOG_DEBUG("Repeated reliable tx");
+        seenRecently = false;
+    }
+
     if (seenRecently) {
         LOG_DEBUG("Found existing packet record for fr=0x%x,to=0x%x,id=0x%x", p->from, p->to, p->id);
     }

src/mesh/PhoneAPI.cpp

@@ -596,10 +596,13 @@ bool PhoneAPI::handleToRadioPacket(meshtastic_MeshPacket &p)
 {
     printPacket("PACKET FROM PHONE", &p);
 
+// For use with the simulator, we should not ignore duplicate packets
+#if !(defined(ARCH_PORTDUINO) && !HAS_RADIO)
     if (p.id > 0 && wasSeenRecently(p.id)) {
         LOG_DEBUG("Ignoring packet from phone, already seen recently");
         return false;
     }
+#endif
 
     if (p.decoded.portnum == meshtastic_PortNum_TRACEROUTE_APP && lastPortNumToRadio[p.decoded.portnum] &&
         Throttle::isWithinTimespanMs(lastPortNumToRadio[p.decoded.portnum], THIRTY_SECONDS_MS)) {

src/mesh/ReliableRouter.cpp

@@ -1,10 +1,10 @@
 #include "ReliableRouter.h"
 #include "Default.h"
-#include "MeshModule.h"
 #include "MeshTypes.h"
 #include "configuration.h"
 #include "mesh-pb-constants.h"
 #include "modules/NodeInfoModule.h"
+#include "modules/RoutingModule.h"
 
 // ReliableRouter::ReliableRouter() {}
 
@@ -73,18 +73,6 @@ bool ReliableRouter::shouldFilterReceived(const meshtastic_MeshPacket *p)
         i->second.nextTxMsec += iface->getPacketTime(p);
     }
 
-    /* Resend implicit ACKs for repeated packets (hopStart equals hopLimit);
-     * this way if an implicit ACK is dropped and a packet is resent we'll rebroadcast again.
-     * Resending real ACKs is omitted, as you might receive a packet multiple times due to flooding and
-     * flooding this ACK back to the original sender already adds redundancy. */
-    bool isRepeated = p->hop_start == 0 ? (p->hop_limit == HOP_RELIABLE) : (p->hop_start == p->hop_limit);
-    if (wasSeenRecently(p, false) && isRepeated && !MeshModule::currentReply && !isToUs(p)) {
-        LOG_DEBUG("Resending implicit ack for a repeated floodmsg");
-        meshtastic_MeshPacket *tosend = packetPool.allocCopy(*p);
-        tosend->hop_limit--; // bump down the hop count
-        Router::send(tosend);
-    }
-
     return FloodingRouter::shouldFilterReceived(p);
 }
 
@@ -107,16 +95,22 @@ void ReliableRouter::sniffReceived(const meshtastic_MeshPacket *p, const meshtas
             if (MeshModule::currentReply) {
                 LOG_DEBUG("Another module replied to this message, no need for 2nd ack");
             } else if (p->which_payload_variant == meshtastic_MeshPacket_decoded_tag) {
-                sendAckNak(meshtastic_Routing_Error_NONE, getFrom(p), p->id, p->channel, p->hop_start, p->hop_limit);
+                // A response may be set to want_ack for retransmissions, but we don't need to ACK a response if it received an
+                // implicit ACK already. If we received it directly, only ACK with a hop limit of 0
+                if (!p->decoded.request_id)
+                    sendAckNak(meshtastic_Routing_Error_NONE, getFrom(p), p->id, p->channel,
+                               routingModule->getHopLimitForResponse(p->hop_start, p->hop_limit));
+                else if (p->hop_start > 0 && p->hop_start == p->hop_limit)
+                    sendAckNak(meshtastic_Routing_Error_NONE, getFrom(p), p->id, p->channel, 0);
             } else if (p->which_payload_variant == meshtastic_MeshPacket_encrypted_tag && p->channel == 0 &&
                        (nodeDB->getMeshNode(p->from) == nullptr || nodeDB->getMeshNode(p->from)->user.public_key.size == 0)) {
                 LOG_INFO("PKI packet from unknown node, send PKI_UNKNOWN_PUBKEY");
                 sendAckNak(meshtastic_Routing_Error_PKI_UNKNOWN_PUBKEY, getFrom(p), p->id, channels.getPrimaryIndex(),
-                           p->hop_start, p->hop_limit);
+                           routingModule->getHopLimitForResponse(p->hop_start, p->hop_limit));
             } else {
                 // Send a 'NO_CHANNEL' error on the primary channel if want_ack packet destined for us cannot be decoded
-                sendAckNak(meshtastic_Routing_Error_NO_CHANNEL, getFrom(p), p->id, channels.getPrimaryIndex(), p->hop_start,
-                           p->hop_limit);
+                sendAckNak(meshtastic_Routing_Error_NO_CHANNEL, getFrom(p), p->id, channels.getPrimaryIndex(),
+                           routingModule->getHopLimitForResponse(p->hop_start, p->hop_limit));
             }
         }
         if (p->which_payload_variant == meshtastic_MeshPacket_decoded_tag && c &&

src/mesh/Router.cpp

@@ -136,10 +136,9 @@ meshtastic_MeshPacket *Router::allocForSending()
 /**
  * Send an ack or a nak packet back towards whoever sent idFrom
  */
-void Router::sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopStart,
-                        uint8_t hopLimit)
+void Router::sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopLimit)
 {
-    routingModule->sendAckNak(err, to, idFrom, chIndex, hopStart, hopLimit);
+    routingModule->sendAckNak(err, to, idFrom, chIndex, hopLimit);
 }
 
 void Router::abortSendAndNak(meshtastic_Routing_Error err, meshtastic_MeshPacket *p)

src/mesh/Router.h

@@ -108,8 +108,7 @@ class Router : protected concurrency::OSThread
     /**
      * Send an ack or a nak packet back towards whoever sent idFrom
      */
-    void sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopStart = 0,
-                    uint8_t hopLimit = 0);
+    void sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopLimit = 0);
 
   private:
     /**

src/modules/RoutingModule.cpp

@@ -49,10 +49,9 @@ meshtastic_MeshPacket *RoutingModule::allocReply()
     return NULL;
 }
 
-void RoutingModule::sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopStart,
-                               uint8_t hopLimit)
+void RoutingModule::sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopLimit)
 {
-    auto p = allocAckNak(err, to, idFrom, chIndex, hopStart, hopLimit);
+    auto p = allocAckNak(err, to, idFrom, chIndex, hopLimit);
 
     router->sendLocal(p); // we sometimes send directly to the local node
 }

src/modules/RoutingModule.h

@@ -13,8 +13,7 @@ class RoutingModule : public ProtobufModule<meshtastic_Routing>
      */
     RoutingModule();
 
-    void sendAckNak(meshtastic_Routing_Error err, NodeNum to, PacketId idFrom, ChannelIndex chIndex, uint8_t hopStart = 0,
-                    uint8_t hopLimit = 0);
+    void sendAckNak(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);
@@ -36,4 +35,4 @@ class RoutingModule : public ProtobufModule<meshtastic_Routing>
     virtual bool wantPacket(const meshtastic_MeshPacket *p) override { return true; }
 };
 
-extern RoutingModule *routingModule;
+extern RoutingModule *routingModule;