lnchannel: allow deleting unfunded incoming channels

We tried to delete incoming channels that didn't get funded after
lnutil.CHANNEL_OPENING_TIMEOUT, however an assert prevented this:

```
  3.63 | E | lnwatcher.LNWatcher.[default_wallet-LNW] | Exception in check_onchain_situation: AssertionError()
Traceback (most recent call last):
  File "/home/user/code/electrum-fork/electrum/util.py", line 1233, in wrapper
    return await func(*args, **kwargs)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/code/electrum-fork/electrum/lnwatcher.py", line 117, in check_onchain_situation
    await self.update_channel_state(
    ...<5 lines>...
        keep_watching=keep_watching)
  File "/home/user/code/electrum-fork/electrum/lnwatcher.py", line 135, in update_channel_state
    chan.update_onchain_state(
    ~~~~~~~~~~~~~~~~~~~~~~~~~^
        funding_txid=funding_txid,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^
    ...<2 lines>...
        closing_height=closing_height,
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
        keep_watching=keep_watching)
        ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/user/code/electrum-fork/electrum/lnchannel.py", line 341, in update_onchain_state
    self.update_unfunded_state()
    ~~~~~~~~~~~~~~~~~~~~~~~~~~^^
  File "/home/user/code/electrum-fork/electrum/lnchannel.py", line 382, in update_unfunded_state
    self.lnworker.remove_channel(self.channel_id)
    ~~~~~~~~~~~~~~~~~~~~~~~~~~~~^^^^^^^^^^^^^^^^^
  File "/home/user/code/electrum-fork/electrum/lnworker.py", line 3244, in remove_channel
    assert chan.can_be_deleted()
           ~~~~~~~~~~~~~~~~~~~^^
AssertionError
```

electrum/lnchannel.py

@@ -60,7 +60,7 @@ from .lnsweep import sweep_their_ctx_to_remote_backup
 from .lnhtlc import HTLCManager
 from .lnmsg import encode_msg, decode_msg
 from .address_synchronizer import TX_HEIGHT_LOCAL
-from .lnutil import CHANNEL_OPENING_TIMEOUT
+from .lnutil import CHANNEL_OPENING_TIMEOUT_BLOCKS, CHANNEL_OPENING_TIMEOUT_SEC
 from .lnutil import ChannelBackupStorage, ImportedChannelBackupStorage, OnchainChannelBackupStorage
 from .lnutil import format_short_channel_id
 from .fee_policy import FEERATE_PER_KW_MIN_RELAY_LIGHTNING
@@ -356,7 +356,6 @@ class AbstractChannel(Logger, ABC):
         self.delete_closing_height()
         if not self.lnworker:
             return
-        chan_age = now() - self.storage.get('init_timestamp', 0)
         state = self.get_state()
         if state in [ChannelState.PREOPENING, ChannelState.OPENING, ChannelState.FORCE_CLOSING]:
             if self.is_initiator():
@@ -377,11 +376,11 @@ class AbstractChannel(Logger, ABC):
                             self.logger.info(f'channel is double spent {inputs}')
                             self.set_state(ChannelState.REDEEMED)
                             break
-            else:
-                if chan_age > CHANNEL_OPENING_TIMEOUT:
-                    self.lnworker.remove_channel(self.channel_id)
+            elif self.has_funding_timed_out():
+                self.logger.warning(f"dropping incoming channel, funding tx not found in mempool")
+                self.lnworker.remove_channel(self.channel_id)
         elif self.is_zeroconf() and state in [ChannelState.OPEN, ChannelState.CLOSING, ChannelState.FORCE_CLOSING]:
-            assert self.storage.get('init_timestamp') is not None, "init_timestamp not set for zeroconf channel"
+            chan_age = now() - self.storage['init_timestamp']
             # handling zeroconf channels with no funding tx, can happen if broadcasting fails on LSP side
             # or if the LSP did double spent the funding tx/never published it intentionally
             # only remove a timed out OPEN channel if we are connected to the network to prevent removing it if we went
@@ -407,6 +406,10 @@ class AbstractChannel(Logger, ABC):
         if funding_height.conf>0:
             self.set_short_channel_id(ShortChannelID.from_components(
                 funding_height.height(), funding_height.txpos, self.funding_outpoint.output_index))
+        elif self.has_funding_timed_out():
+            self.logger.warning("dropping incoming channel, funding tx took too long to confirm")
+            self.lnworker.remove_channel(self.channel_id)
+            return
         if self.get_state() == ChannelState.OPENING:
             if self.is_funding_tx_mined(funding_height):
                 self.set_state(ChannelState.FUNDED)
@@ -549,6 +552,10 @@ class AbstractChannel(Logger, ABC):
     def can_be_deleted(self) -> bool:
         pass
 
+    @abstractmethod
+    def has_funding_timed_out(self) -> bool:
+        pass
+
     @abstractmethod
     def get_wallet_addresses_channel_might_want_reserved(self) -> Sequence[str]:
         """Returns a list of addrs that the wallet should not use, to avoid address-reuse.
@@ -651,6 +658,9 @@ class ChannelBackup(AbstractChannel):
     def can_be_deleted(self):
         return self.is_imported or self.is_redeemed()
 
+    def has_funding_timed_out(self):
+        return False
+
     def get_capacity(self):
         lnwatcher = self.lnworker.lnwatcher
         if lnwatcher:
@@ -769,7 +779,7 @@ class Channel(AbstractChannel):
         self,
         state: 'StoredDict', *,
         name=None,
-        lnworker=None,
+        lnworker=None,  # None only in unittests
         initial_feerate=None,
         jit_opening_fee: Optional[int] = None,
     ):
@@ -833,9 +843,23 @@ class Channel(AbstractChannel):
     def has_onchain_backup(self):
         return self.storage.get('has_onchain_backup', False)
 
-    def can_be_deleted(self):
+    def can_be_deleted(self) -> bool:
+        if self.has_funding_timed_out():
+            return True
         return self.is_redeemed()
 
+    def has_funding_timed_out(self):
+        if self.is_initiator() or self.is_funded():
+            return False
+        if self.lnworker.network.blockchain().is_tip_stale() or not self.lnworker.wallet.is_up_to_date():
+            return False
+        init_height = self.storage.get('init_height', 0)
+        init_timestamp = self.storage.get('init_timestamp', 0)
+        age_blocks = self.lnworker.network.get_local_height() - init_height
+        age_sec = now() - init_timestamp
+        # some channels might not have init_height set so we check both time and block based timeouts
+        return age_blocks > CHANNEL_OPENING_TIMEOUT_BLOCKS and age_sec > CHANNEL_OPENING_TIMEOUT_SEC
+
     def get_capacity(self):
         return self.constraints.capacity
 

electrum/lnpeer.py

@@ -1216,6 +1216,7 @@ class Peer(Logger, EventListener):
         )
         chan.storage['funding_inputs'] = [txin.prevout.to_json() for txin in funding_tx.inputs()]
         chan.storage['has_onchain_backup'] = has_onchain_backup
+        chan.storage['init_height'] = self.lnworker.network.get_local_height()
         chan.storage['init_timestamp'] = int(time.time())
         if isinstance(self.transport, LNTransport):
             chan.add_or_update_peer_addr(self.transport.peer_addr)
@@ -1438,6 +1439,7 @@ class Peer(Logger, EventListener):
             initial_feerate=feerate,
             jit_opening_fee = channel_opening_fee,
         )
+        chan.storage['init_height'] = self.lnworker.network.get_local_height()
         chan.storage['init_timestamp'] = int(time.time())
         if isinstance(self.transport, LNTransport):
             chan.add_or_update_peer_addr(self.transport.peer_addr)

electrum/lnutil.py

@@ -489,7 +489,10 @@ class LNProtocolWarning(Exception):
 # TODO make some of these values configurable?
 REDEEM_AFTER_DOUBLE_SPENT_DELAY = 30
 
-CHANNEL_OPENING_TIMEOUT = 24*60*60
+# timeout after which we forget incoming channels if the funding tx has no confirmation
+# https://github.com/lightning/bolts/commit/ba00bf8f4cd85f21bacfc03adcafd4acc7d68382
+CHANNEL_OPENING_TIMEOUT_BLOCKS = 2016
+CHANNEL_OPENING_TIMEOUT_SEC = 14*24*60*60  # 2 weeks
 
 # Small capacity channels are problematic for many reasons. As the onchain fees start to become
 # significant compared to the capacity, things start to break down. e.g. the counterparty