fix confusion re max path length

electrum/lnonion.py

@@ -33,7 +33,7 @@ from cryptography.hazmat.backends import default_backend
 from . import ecc
 from .crypto import sha256, hmac_oneshot
 from .util import bh2u, profiler, xor_bytes, bfh
-from .lnutil import get_ecdh, PaymentFailure, NUM_MAX_HOPS_IN_PAYMENT_PATH
+from .lnutil import get_ecdh, PaymentFailure, NUM_MAX_HOPS_IN_PAYMENT_PATH, NUM_MAX_EDGES_IN_PAYMENT_PATH
 from .lnrouter import RouteEdge
 
 
@@ -191,8 +191,8 @@ def calc_hops_data_for_payment(route: List[RouteEdge], amount_msat: int, final_c
     """Returns the hops_data to be used for constructing an onion packet,
     and the amount_msat and cltv to be used on our immediate channel.
     """
-    if len(route) > NUM_MAX_HOPS_IN_PAYMENT_PATH:
-        raise PaymentFailure(f"too long route ({len(route)} hops)")
+    if len(route) > NUM_MAX_EDGES_IN_PAYMENT_PATH:
+        raise PaymentFailure(f"too long route ({len(route)} edges)")
 
     amt = amount_msat
     cltv = final_cltv

electrum/lnrouter.py

@@ -39,7 +39,7 @@ from .storage import JsonDB
 from .lnchannelverifier import LNChannelVerifier, verify_sig_for_channel_update
 from .crypto import Hash
 from . import ecc
-from .lnutil import LN_GLOBAL_FEATURES_KNOWN_SET, LNPeerAddr, NUM_MAX_HOPS_IN_PAYMENT_PATH
+from .lnutil import LN_GLOBAL_FEATURES_KNOWN_SET, LNPeerAddr, NUM_MAX_EDGES_IN_PAYMENT_PATH
 
 
 class UnknownEvenFeatureBits(Exception): pass
@@ -535,7 +535,7 @@ def is_route_sane_to_use(route: List[RouteEdge], invoice_amount_msat: int, min_f
     """Run some sanity checks on the whole route, before attempting to use it.
     called when we are paying; so e.g. lower cltv is better
     """
-    if len(route) > NUM_MAX_HOPS_IN_PAYMENT_PATH:
+    if len(route) > NUM_MAX_EDGES_IN_PAYMENT_PATH:
         return False
     amt = invoice_amount_msat
     cltv = min_final_cltv_expiry
@@ -606,7 +606,7 @@ class LNPathFinder(PrintError):
         unable_channels = set(map(lambda x: x.short_channel_id, filter(lambda x: not x.can_pay(amount_msat), my_channels)))
 
         # TODO find multiple paths??
-        # FIXME paths cannot be longer than 20 (onion packet)...
+        # FIXME paths cannot be longer than 21 edges (onion packet)...
 
         # run Dijkstra
         distance_from_start = defaultdict(lambda: float('inf'))

electrum/lnutil.py

@@ -614,4 +614,5 @@ class EncumberedTransaction(NamedTuple("EncumberedTransaction", [('tx', Transact
 
 
 NUM_MAX_HOPS_IN_PAYMENT_PATH = 20
+NUM_MAX_EDGES_IN_PAYMENT_PATH = NUM_MAX_HOPS_IN_PAYMENT_PATH + 1
 

electrum/lnworker.py

@@ -26,7 +26,7 @@ from .lnutil import (Outpoint, calc_short_channel_id, LNPeerAddr,
                      PaymentFailure, split_host_port, ConnStringFormatError,
                      generate_keypair, LnKeyFamily, LOCAL, REMOTE,
                      UnknownPaymentHash, MIN_FINAL_CLTV_EXPIRY_FOR_INVOICE,
-                     NUM_MAX_HOPS_IN_PAYMENT_PATH)
+                     NUM_MAX_EDGES_IN_PAYMENT_PATH)
 from .lnaddr import lndecode
 from .i18n import _
 from .lnrouter import RouteEdge, is_route_sane_to_use
@@ -286,7 +286,7 @@ class LNWorker(PrintError):
             channels = list(self.channels.values())
         for private_route in r_tags:
             if len(private_route) == 0: continue
-            if len(private_route) > NUM_MAX_HOPS_IN_PAYMENT_PATH: continue
+            if len(private_route) > NUM_MAX_EDGES_IN_PAYMENT_PATH: continue
             border_node_pubkey = private_route[0][0]
             path = self.network.path_finder.find_path_for_payment(self.node_keypair.pubkey, border_node_pubkey, amount_msat, channels)
             if not path: continue