Add maybe_fee_related bool to NoPathFound and set it on instanciation in according places

electrum/lnpeer.py

@@ -44,7 +44,7 @@ from .lnutil import (Outpoint, LocalConfig, RECEIVED, UpdateAddHtlc, ChannelConf
                      ln_compare_features, MIN_FINAL_CLTV_DELTA_ACCEPTED,
                      RemoteMisbehaving, ShortChannelID,
                      IncompatibleLightningFeatures, derive_payment_secret_from_payment_preimage,
-                     ChannelType, LNProtocolWarning, validate_features, IncompatibleOrInsaneFeatures)
+                     ChannelType, LNProtocolWarning, validate_features, IncompatibleOrInsaneFeatures, NoPathFound)
 from .lnutil import FeeUpdate, channel_id_from_funding_tx, PaymentFeeBudget
 from .lnutil import serialize_htlc_key, Keypair
 from .lntransport import LNTransport, LNTransportBase, LightningPeerConnectionClosed, HandshakeFailed
@@ -2063,11 +2063,15 @@ class Peer(Logger, EventListener):
             )
         except OnionRoutingFailure as e:
             raise
+        except NoPathFound as e:
+            failure_code = (OnionFailureCode.TRAMPOLINE_FEE_INSUFFICIENT
+                            if e.maybe_fee_related
+                            else OnionFailureCode.UNKNOWN_NEXT_PEER)
+            raise OnionRoutingFailure(code=failure_code, data=b'')
         except PaymentFailure as e:
             self.logger.debug(
                 f"maybe_forward_trampoline. PaymentFailure for {payment_hash.hex()=}, {payment_secret.hex()=}: {e!r}")
-            # FIXME: adapt the error code
-            raise OnionRoutingFailure(code=OnionFailureCode.TRAMPOLINE_FEE_INSUFFICIENT, data=b'')
+            raise OnionRoutingFailure(code=OnionFailureCode.UNKNOWN_NEXT_PEER, data=b'')
 
     def _maybe_refuse_to_forward_htlc_that_corresponds_to_payreq_we_created(self, payment_hash: bytes) -> bool:
         """Returns True if the HTLC should be failed.

electrum/lnutil.py

@@ -450,8 +450,13 @@ class InvalidGossipMsg(Exception):
 
 class PaymentFailure(UserFacingException): pass
 class NoPathFound(PaymentFailure):
+    def __init__(self, message: Optional[str] = None, *, maybe_fee_related: Optional[bool] = False):
+        self.maybe_fee_related = maybe_fee_related
+        self._message = message
+        super().__init__(message)
+
     def __str__(self):
-        return _('No path found')
+        return self._message or _('No path found')
 
 
 class LNProtocolError(Exception):

electrum/lnworker.py

@@ -1880,6 +1880,7 @@ class LNWallet(LNWorker):
         and mpp is supported by the receiver, we will split the payment."""
         trampoline_features = LnFeatures.VAR_ONION_OPT
         local_height = self.network.get_local_height()
+        fee_related_error = False
         if channels:
             my_active_channels = channels
         else:
@@ -1970,8 +1971,9 @@ class LNWallet(LNWorker):
                             )
                             routes.append((shi, per_trampoline_cltv_delta, trampoline_onion))
                         if per_trampoline_fees != 0:
-                            self.logger.info('not enough margin to pay trampoline fee')
-                            raise NoPathFound()
+                            e = 'not enough margin to pay trampoline fee'
+                            self.logger.info(e)
+                            raise NoPathFound(e, maybe_fee_related=True)
                 else:
                     # We atomically loop through a split configuration. If there was
                     # a failure to find a path for a single part, we try the next configuration
@@ -2002,12 +2004,13 @@ class LNWallet(LNWorker):
                                 trampoline_route=None,
                             )
                             routes.append((shi, paysession.min_final_cltv_delta, fwd_trampoline_onion))
-            except NoPathFound:
+            except NoPathFound as e:
+                fee_related_error = e.maybe_fee_related
                 continue
             for route in routes:
                 yield route
             return
-        raise NoPathFound()
+        raise NoPathFound(maybe_fee_related=fee_related_error)
 
     @profiler
     def create_route_for_single_htlc(
@@ -2079,7 +2082,7 @@ class LNWallet(LNWorker):
             route, budget=budget, amount_msat_for_dest=amount_msat, cltv_delta_for_dest=min_final_cltv_delta,
         ):
             self.logger.info(f"rejecting route (exceeds budget): {route=}. {budget=}")
-            raise NoPathFound()
+            raise NoPathFound(maybe_fee_related=True)
         assert len(route) > 0
         if route[-1].end_node != invoice_pubkey:
             raise LNPathInconsistent("last node_id != invoice pubkey")

electrum/trampoline.py

@@ -161,7 +161,7 @@ def _allocate_fee_along_route(
         assert trampoline_fee_level > 0
         MAX_LEVEL = 6
         if trampoline_fee_level > MAX_LEVEL:
-            raise NoPathFound()
+            raise NoPathFound("highest trampoline fee level reached", maybe_fee_related=True)
         budget_to_use = budget.fee_msat // (2 ** (MAX_LEVEL - trampoline_fee_level))
     _logger.debug(f"_allocate_fee_along_route(). {trampoline_fee_level=}, {budget.fee_msat=}, {budget_to_use=}")
     # replace placeholder fees
@@ -264,7 +264,7 @@ def create_trampoline_route(
         amount_msat_for_dest=amount_msat,
         cltv_delta_for_dest=min_final_cltv_delta,
     ):
-        raise NoPathFound("route exceeds budget")
+        raise NoPathFound("route exceeds budget", maybe_fee_related=True)
     return route