From 24458a73d6cbdba9f4d731eb0be3f07ffd0973f1 Mon Sep 17 00:00:00 2001
From: GUVWAF <78759985+GUVWAF@users.noreply.github.com>
Date: Sun, 9 Jun 2024 23:03:53 +0200
Subject: [PATCH] Add missing hops in traceroute as "unkown" (#4056)

E.g. in case a node couldn't decrypt the packet
---
 src/modules/TraceRouteModule.cpp | 28 ++++++++++++++++++++++++----
 src/modules/TraceRouteModule.h   |  3 +++
 2 files changed, 27 insertions(+), 4 deletions(-)

diff --git a/src/modules/TraceRouteModule.cpp b/src/modules/TraceRouteModule.cpp
index aa0b6a1ebd..f390aafcd6 100644
--- a/src/modules/TraceRouteModule.cpp
+++ b/src/modules/TraceRouteModule.cpp
@@ -16,17 +16,37 @@ bool TraceRouteModule::handleReceivedProtobuf(const meshtastic_MeshPacket &mp, m
 void TraceRouteModule::alterReceivedProtobuf(meshtastic_MeshPacket &p, meshtastic_RouteDiscovery *r)
 {
     auto &incoming = p.decoded;
-    // Only append an ID for the request (one way) and if we are not the destination (the reply will have our NodeNum already)
-    if (!incoming.request_id && p.to != nodeDB->getNodeNum()) {
-        appendMyID(r);
-        printRoute(r, p.from, NODENUM_BROADCAST);
+    // Only append IDs for the request (one way)
+    if (!incoming.request_id) {
+        // Insert unknown hops if necessary
+        insertUnknownHops(p, r);
 
+        // Don't add ourselves if we are the destination (the reply will have our NodeNum already)
+        if (p.to != nodeDB->getNodeNum()) {
+            appendMyID(r);
+            printRoute(r, p.from, NODENUM_BROADCAST);
+        }
         // Set updated route to the payload of the to be flooded packet
         p.decoded.payload.size =
             pb_encode_to_bytes(p.decoded.payload.bytes, sizeof(p.decoded.payload.bytes), &meshtastic_RouteDiscovery_msg, r);
     }
 }
 
+void TraceRouteModule::insertUnknownHops(meshtastic_MeshPacket &p, meshtastic_RouteDiscovery *r)
+{
+    // Only insert unknown hops if hop_start is valid
+    if (p.hop_start != 0 && p.hop_limit <= p.hop_start) {
+        uint8_t hopsTaken = p.hop_start - p.hop_limit;
+        int8_t diff = hopsTaken - r->route_count;
+        for (uint8_t i = 0; i < diff; i++) {
+            if (r->route_count < sizeof(r->route) / sizeof(r->route[0])) {
+                r->route[r->route_count] = NODENUM_BROADCAST; // This will represent an unknown hop
+                r->route_count += 1;
+            }
+        }
+    }
+}
+
 void TraceRouteModule::appendMyID(meshtastic_RouteDiscovery *updated)
 {
     // Length of route array can normally not be exceeded due to the max. hop_limit of 7
diff --git a/src/modules/TraceRouteModule.h b/src/modules/TraceRouteModule.h
index 15e01debd8..18a5ac0cb7 100644
--- a/src/modules/TraceRouteModule.h
+++ b/src/modules/TraceRouteModule.h
@@ -19,6 +19,9 @@ class TraceRouteModule : public ProtobufModule<meshtastic_RouteDiscovery>
     void alterReceivedProtobuf(meshtastic_MeshPacket &p, meshtastic_RouteDiscovery *r) override;
 
   private:
+    // Call to add unknown hops (e.g. when a node couldn't decrypt it) to the route based on hopStart and current hopLimit
+    void insertUnknownHops(meshtastic_MeshPacket &p, meshtastic_RouteDiscovery *r);
+
     // Call to add your ID to the route array of a RouteDiscovery message
     void appendMyID(meshtastic_RouteDiscovery *r);