add mechanism to block htlcs from settling back

Author: f321x

electrum/lnpeer.py

@@ -1943,6 +1943,7 @@ def log_fail_reason(reason: str):
         except BaseException as e:
             log_fail_reason(f"error sending message to next_peer={next_chan.node_id.hex()}")
             raise OnionRoutingFailure(code=OnionFailureCode.TEMPORARY_CHANNEL_FAILURE, data=outgoing_chan_upd_message)
+
         htlc_key = serialize_htlc_key(next_chan.get_scid_or_local_alias(), next_htlc.htlc_id)
         return htlc_key
 
@@ -2297,6 +2298,9 @@ def log_fail_reason(reason: str):
             else:
                 return None, None
 
+        if payment_hash.hex() in self.lnworker.dont_settle_htlcs:
+            return None, None
+
         chan.opening_fee = None
         self.logger.info(f"maybe_fulfill_htlc. will FULFILL HTLC: chan {chan.short_channel_id}. htlc={str(htlc)}")
         return preimage, None

electrum/lnworker.py

@@ -812,6 +812,7 @@ def __init__(self, wallet: 'Abstract_Wallet', xprv):
         self.active_forwardings = self.db.get_dict('active_forwardings')    # type: Dict[str, List[str]]        # Dict: payment_key -> list of htlc_keys
         self.forwarding_failures = self.db.get_dict('forwarding_failures')  # type: Dict[str, Tuple[str, str]]  # Dict: payment_key -> (error_bytes, error_message)
         self.downstream_to_upstream_htlc = {}                               # type: Dict[str, str]              # Dict: htlc_key -> htlc_key (not persisted)
+        self.dont_settle_htlcs = self.db.get_dict('dont_settle_htlcs')      # type: Dict[str, None]             # payment_hashes of htlcs that we should not settle back yet even if we have the preimage
 
         # payment_hash -> callback:
         self.hold_invoice_callbacks = {}                # type: Dict[bytes, Callable[[bytes], Awaitable[None]]]
@@ -1176,6 +1177,9 @@ async def open_channel_just_in_time(
     ) -> str:
         # if an exception is raised during negotiation, we raise an OnionRoutingFailure.
         # this will cancel the incoming HTLC
+
+        # prevent settling the htlc until the channel opening was successfull so we can fail it if needed
+        self.dont_settle_htlcs[payment_hash.hex()] = None
         try:
             funding_sat = 2 * (next_amount_msat_htlc // 1000) # try to fully spend htlcs
             password = self.wallet.get_unlocked_password() if self.wallet.has_password() else None
@@ -1210,13 +1214,17 @@ async def wait_for_preimage():
                 while self.get_preimage(payment_hash) is None:
                     await asyncio.sleep(1)
             await util.wait_for2(wait_for_preimage(), LN_P2P_NETWORK_TIMEOUT)
+
+            # We have been paid and can broadcast
+            # todo: if broadcasting raise an exception, we should try to rebroadcast
+            await self.network.broadcast_transaction(funding_tx)
         except OnionRoutingFailure:
             raise
         except Exception:
             raise OnionRoutingFailure(code=OnionFailureCode.TEMPORARY_NODE_FAILURE, data=b'')
-        # We have been paid and can broadcast
-        # todo: if broadcasting raise an exception, we should try to rebroadcast
-        await self.network.broadcast_transaction(funding_tx)
+        finally:
+            del self.dont_settle_htlcs[payment_hash.hex()]
+
         htlc_key = serialize_htlc_key(next_chan.get_scid_or_local_alias(), htlc.htlc_id)
         return htlc_key
 

tests/test_lnpeer.py

@@ -197,6 +197,7 @@ def __init__(self, *, local_keypair: Keypair, chans: Iterable['Channel'], tx_que
         self.preimages = {}
         self.stopping_soon = False
         self.downstream_to_upstream_htlc = {}
+        self.dont_settle_htlcs = {}
         self.hold_invoice_callbacks = {}
         self.payment_bundles = [] # lists of hashes. todo:persist
         self.config.INITIAL_TRAMPOLINE_FEE_LEVEL = 0