trampoline: improve payment success

- better error handling: previously we stopped all attempts on any of
  TRAMPOLINE_EXPIRY_TOO_SOON, UNKNOWN_NEXT_PEER, TEMPORARY_NODE_FAILURE.
  Instead we should retry (but see code comments).
- previously payments failed if ALL of the following criteria applied:
  - sender is paying via trampoline, but not via the ACINQ node (which is
    special cased)
  - receiver only has private channels and has put r_tags into invoice, along
    with setting the trampoline feature bit in the invoice, however the receiver
    is not connected to any trampoline forwarders directly
  The sender would then assume that the private routing hints in the invoice
  correspond to trampoline forwarders.
- also, previously if both the sender and the recipient used trampoline and
  they shared a trampoline forwarder (that they were both connected to), the
  private channels the recipient had (with nodes other than the shared TF)
  would never be attempted.

electrum/tests/test_lnchannel.py

@@ -151,7 +151,7 @@ def create_test_channels(*, feerate=6000, local_msat=None, remote_msat=None,
                 bob_first, other_node_id=bob_pubkey, l_dust=200, r_dust=1300,
                 l_csv=5, r_csv=4
             ),
-            name=bob_name,
+            name=f"{alice_name}->{bob_name}",
             initial_feerate=feerate),
         lnchannel.Channel(
             create_channel_state(
@@ -160,7 +160,7 @@ def create_test_channels(*, feerate=6000, local_msat=None, remote_msat=None,
                 alice_first, other_node_id=alice_pubkey, l_dust=1300, r_dust=200,
                 l_csv=4, r_csv=5
             ),
-            name=alice_name,
+            name=f"{bob_name}->{alice_name}",
             initial_feerate=feerate)
     )
 

electrum/tests/test_lnpeer.py

@@ -12,6 +12,8 @@ from typing import Iterable, NamedTuple, Tuple, List, Dict
 
 from aiorpcx import TaskGroup, timeout_after, TaskTimeout
 
+import electrum
+import electrum.trampoline
 from electrum import bitcoin
 from electrum import constants
 from electrum.network import Network
@@ -152,6 +154,8 @@ class MockLNWallet(Logger, NetworkRetryManager[LNPeerAddr]):
         self.preimages = {}
         self.stopping_soon = False
 
+        self.logger.info(f"created LNWallet[{name}] with nodeID={local_keypair.pubkey.hex()}")
+
     def get_invoice_status(self, key):
         pass
 
@@ -272,8 +276,8 @@ class PutIntoOthersQueueTransport(MockTransport):
         self.other_mock_transport.queue.put_nowait(data)
 
 def transport_pair(k1, k2, name1, name2):
-    t1 = PutIntoOthersQueueTransport(k1, name2)
-    t2 = PutIntoOthersQueueTransport(k2, name1)
+    t1 = PutIntoOthersQueueTransport(k1, name1)
+    t2 = PutIntoOthersQueueTransport(k2, name2)
     t1.other_mock_transport = t2
     t2.other_mock_transport = t1
     return t1, t2
@@ -341,7 +345,7 @@ class TestPeer(TestCaseForTestnet):
         self._loop_thread.join(timeout=1)
         super().tearDown()
 
-    def prepare_peers(self, alice_channel, bob_channel):
+    def prepare_peers(self, alice_channel: Channel, bob_channel: Channel):
         k1, k2 = keypair(), keypair()
         alice_channel.node_id = k2.pubkey
         bob_channel.node_id = k1.pubkey
@@ -424,6 +428,8 @@ class TestPeer(TestCaseForTestnet):
 
         w_b.network.config.set_key('lightning_forward_payments', True)
         w_c.network.config.set_key('lightning_forward_payments', True)
+        w_b.network.config.set_key('lightning_forward_trampoline_payments', True)
+        w_c.network.config.set_key('lightning_forward_trampoline_payments', True)
 
         # forwarding fees, etc
         chan_ab.forwarding_fee_proportional_millionths *= 500
@@ -448,7 +454,7 @@ class TestPeer(TestCaseForTestnet):
         peer_cd.mark_open(chan_cd)
         peer_db.mark_open(chan_db)
         peer_dc.mark_open(chan_dc)
-        return SquareGraph(
+        graph = SquareGraph(
             w_a=w_a,
             w_b=w_b,
             w_c=w_c,
@@ -470,6 +476,7 @@ class TestPeer(TestCaseForTestnet):
             chan_db=chan_db,
             chan_dc=chan_dc,
         )
+        return graph
 
     @staticmethod
     async def prepare_invoice(
@@ -935,7 +942,14 @@ class TestPeer(TestCaseForTestnet):
     def test_multipart_payment_with_trampoline(self):
         # single attempt will fail with insufficient trampoline fee
         graph = self.prepare_chans_and_peers_in_square()
-        self._run_mpp(graph, {'alice_uses_trampoline':True, 'attempts':1}, {'alice_uses_trampoline':True, 'attempts':3})
+        electrum.trampoline._TRAMPOLINE_NODES_UNITTESTS = {
+            graph.w_b.name: LNPeerAddr(host="127.0.0.1", port=9735, pubkey=graph.w_b.node_keypair.pubkey),
+            graph.w_c.name: LNPeerAddr(host="127.0.0.1", port=9735, pubkey=graph.w_c.node_keypair.pubkey),
+        }
+        try:
+            self._run_mpp(graph, {'alice_uses_trampoline':True, 'attempts':1}, {'alice_uses_trampoline':True, 'attempts':30})
+        finally:
+            electrum.trampoline._TRAMPOLINE_NODES_UNITTESTS = {}
 
     @needs_test_with_all_chacha20_implementations
     def test_fail_pending_htlcs_on_shutdown(self):