lnrouter: fix self-payments

electrum/channel_db.py

@@ -826,7 +826,7 @@ class ChannelDB(SqlDB):
             *,
             my_channels: Dict[ShortChannelID, 'Channel'] = None,
             private_route_edges: Dict[ShortChannelID, 'RouteEdge'] = None,
-    ) -> Set[bytes]:
+    ) -> Set[ShortChannelID]:
         """Returns the set of short channel IDs where node_id is one of the channel participants."""
         if not self.data_loaded.is_set():
             raise Exception("channelDB data not loaded yet!")

electrum/lnrouter.py

@@ -25,13 +25,13 @@
 
 import queue
 from collections import defaultdict
-from typing import Sequence, List, Tuple, Optional, Dict, NamedTuple, TYPE_CHECKING, Set
+from typing import Sequence, Tuple, Optional, Dict, TYPE_CHECKING, Set
 import time
 from threading import RLock
 import attr
 from math import inf
 
-from .util import bh2u, profiler, with_lock
+from .util import profiler, with_lock, bh2u
 from .logging import Logger
 from .lnutil import (NUM_MAX_EDGES_IN_PAYMENT_PATH, ShortChannelID, LnFeatures,
                      NBLOCK_CLTV_EXPIRY_TOO_FAR_INTO_FUTURE)
@@ -511,7 +511,7 @@ class LNPathFinder(Logger):
         overall_cost = fee_msat + cltv_cost + liquidity_penalty
         return overall_cost, fee_msat
 
-    def get_distances(
+    def get_shortest_path_hops(
             self,
             *,
             nodeA: bytes,
@@ -529,22 +529,34 @@ class LNPathFinder(Logger):
         blacklist = self.liquidity_hints.get_blacklist()
         distance_from_start = defaultdict(lambda: float('inf'))
         distance_from_start[nodeB] = 0
-        prev_node = {}  # type: Dict[bytes, PathEdge]
+        previous_hops = {}  # type: Dict[bytes, PathEdge]
         nodes_to_explore = queue.PriorityQueue()
         nodes_to_explore.put((0, invoice_amount_msat, nodeB))  # order of fields (in tuple) matters!
 
         # main loop of search
         while nodes_to_explore.qsize() > 0:
             dist_to_edge_endnode, amount_msat, edge_endnode = nodes_to_explore.get()
-            if edge_endnode == nodeA:
+            if edge_endnode == nodeA and previous_hops:  # previous_hops check for circular paths
+                self.logger.info("found a path")
                 break
             if dist_to_edge_endnode != distance_from_start[edge_endnode]:
                 # queue.PriorityQueue does not implement decrease_priority,
                 # so instead of decreasing priorities, we add items again into the queue.
                 # so there are duplicates in the queue, that we discard now:
                 continue
-            for edge_channel_id in self.channel_db.get_channels_for_node(
-                    edge_endnode, my_channels=my_channels, private_route_edges=private_route_edges):
+
+            if nodeA == nodeB:  # we want circular paths
+                if not previous_hops:  # in the first node exploration step, we only take receiving channels
+                    channels_for_endnode = self.channel_db.get_channels_for_node(
+                        edge_endnode, my_channels={}, private_route_edges=private_route_edges)
+                else:  # in the next steps, we only take sending channels
+                    channels_for_endnode = self.channel_db.get_channels_for_node(
+                        edge_endnode, my_channels=my_channels, private_route_edges={})
+            else:
+                channels_for_endnode = self.channel_db.get_channels_for_node(
+                    edge_endnode, my_channels=my_channels, private_route_edges=private_route_edges)
+
+            for edge_channel_id in channels_for_endnode:
                 assert isinstance(edge_channel_id, bytes)
                 if blacklist and edge_channel_id in blacklist:
                     continue
@@ -558,10 +570,6 @@ class LNPathFinder(Logger):
                     if edge_startnode == nodeA:  # payment outgoing, on our channel
                         if not my_channels[edge_channel_id].can_pay(amount_msat, check_frozen=True):
                             continue
-                    else:  # payment incoming, on our channel. (funny business, cycle weirdness)
-                        assert edge_endnode == nodeA, (bh2u(edge_startnode), bh2u(edge_endnode))
-                        if not my_channels[edge_channel_id].can_receive(amount_msat, check_frozen=True):
-                            continue
                 edge_cost, fee_for_edge_msat = self._edge_cost(
                     short_channel_id=edge_channel_id,
                     start_node=edge_startnode,
@@ -574,14 +582,17 @@ class LNPathFinder(Logger):
                 alt_dist_to_neighbour = distance_from_start[edge_endnode] + edge_cost
                 if alt_dist_to_neighbour < distance_from_start[edge_startnode]:
                     distance_from_start[edge_startnode] = alt_dist_to_neighbour
-                    prev_node[edge_startnode] = PathEdge(
+                    previous_hops[edge_startnode] = PathEdge(
                         start_node=edge_startnode,
                         end_node=edge_endnode,
                         short_channel_id=ShortChannelID(edge_channel_id))
                     amount_to_forward_msat = amount_msat + fee_for_edge_msat
                     nodes_to_explore.put((alt_dist_to_neighbour, amount_to_forward_msat, edge_startnode))
-
-        return prev_node
+            # for circular paths, we already explored the end node, but this
+            # is also our start node, so set it to unexplored
+            if edge_endnode == nodeB and nodeA == nodeB:
+                distance_from_start[edge_endnode] = float('inf')
+        return previous_hops
 
     @profiler
     def find_path_for_payment(
@@ -600,22 +611,22 @@ class LNPathFinder(Logger):
         if my_channels is None:
             my_channels = {}
 
-        prev_node = self.get_distances(
+        previous_hops = self.get_shortest_path_hops(
             nodeA=nodeA,
             nodeB=nodeB,
             invoice_amount_msat=invoice_amount_msat,
             my_channels=my_channels,
             private_route_edges=private_route_edges)
 
-        if nodeA not in prev_node:
+        if nodeA not in previous_hops:
             return None  # no path found
 
         # backtrack from search_end (nodeA) to search_start (nodeB)
         # FIXME paths cannot be longer than 20 edges (onion packet)...
         edge_startnode = nodeA
         path = []
-        while edge_startnode != nodeB:
-            edge = prev_node[edge_startnode]
+        while edge_startnode != nodeB or not path:  # second condition for circular paths
+            edge = previous_hops[edge_startnode]
             path += [edge]
             edge_startnode = edge.node_id
         return path