lnworker: fix handle_error_code_from_failed_htlc for private channels

if the last (private) edge of the route errors, we need to try other route hints (if any)

electrum/channel_db.py

@@ -610,12 +610,20 @@ class ChannelDB(SqlDB):
             self.update_counts()
             self.logger.info(f'Deleting {len(orphaned_chans)} orphaned channels')
 
-    def add_channel_update_for_private_channel(self, msg_payload: dict, start_node_id: bytes):
+    def add_channel_update_for_private_channel(self, msg_payload: dict, start_node_id: bytes) -> bool:
+        """Returns True iff the channel update was successfully added and it was different than
+        what we had before (if any).
+        """
         if not verify_sig_for_channel_update(msg_payload, start_node_id):
-            return  # ignore
+            return False  # ignore
         short_channel_id = ShortChannelID(msg_payload['short_channel_id'])
         msg_payload['start_node'] = start_node_id
-        self._channel_updates_for_private_channels[(start_node_id, short_channel_id)] = msg_payload
+        key = (start_node_id, short_channel_id)
+        prev_chanupd = self._channel_updates_for_private_channels.get(key)
+        if prev_chanupd == msg_payload:
+            return False
+        self._channel_updates_for_private_channels[key] = msg_payload
+        return True
 
     def remove_channel(self, short_channel_id: ShortChannelID):
         # FIXME what about rm-ing policies?

electrum/lnworker.py

@@ -1224,8 +1224,8 @@ class LNWallet(LNWorker):
                     # maybe it is a private channel (and data in invoice was outdated)
                     self.logger.info(f"Could not find {short_channel_id}. maybe update is for private channel?")
                     start_node_id = route[sender_idx].node_id
-                    self.channel_db.add_channel_update_for_private_channel(payload, start_node_id)
-                    #update = True  # FIXME: we need to check if we actually updated something
+                    update = self.channel_db.add_channel_update_for_private_channel(payload, start_node_id)
+                    blacklist = not update
                 elif r == UpdateStatus.EXPIRED:
                     blacklist = True
                 elif r == UpdateStatus.DEPRECATED:
@@ -1568,6 +1568,8 @@ class LNWallet(LNWorker):
                     if [edge.short_channel_id for edge in full_path[-len(private_path):]] != [edge[1] for edge in private_path]:
                         continue
                     path = full_path[:-len(private_path)]
+            if any(edge.short_channel_id in blacklist for edge in private_route):
+                continue
             try:
                 route = self.network.path_finder.find_route(
                     self.node_keypair.pubkey, border_node_pubkey, amount_for_node,