LN cooperative close: avoid address-reuse (#6590)

Previously if we coop-closed multiple channels in the same session,
they would reuse the wallet address.

electrum/lnchannel.py

@@ -145,7 +145,7 @@ class AbstractChannel(Logger, ABC):
     config: Dict[HTLCOwner, Union[LocalConfig, RemoteConfig]]
     _sweep_info: Dict[str, Dict[str, 'SweepInfo']]
     lnworker: Optional['LNWallet']
-    sweep_address: str
+    _fallback_sweep_address: str
     channel_id: bytes
     funding_outpoint: Outpoint
     node_id: bytes
@@ -307,6 +307,20 @@ class AbstractChannel(Logger, ABC):
         if self.get_state() == ChannelState.CLOSED and not keep_watching:
             self.set_state(ChannelState.REDEEMED)
 
+    @property
+    def sweep_address(self) -> str:
+        # TODO: in case of unilateral close with pending HTLCs, this address will be reused
+        addr = None
+        if self.is_static_remotekey_enabled():
+            our_payment_pubkey = self.config[LOCAL].payment_basepoint.pubkey
+            addr = make_commitment_output_to_remote_address(our_payment_pubkey)
+        if addr is None:
+            addr = self._fallback_sweep_address
+        assert addr
+        if self.lnworker:
+            assert self.lnworker.wallet.is_mine(addr)
+        return addr
+
     @abstractmethod
     def is_initiator(self) -> bool:
         pass
@@ -367,6 +381,10 @@ class AbstractChannel(Logger, ABC):
         """
         pass
 
+    @abstractmethod
+    def is_static_remotekey_enabled(self) -> bool:
+        pass
+
 
 class ChannelBackup(AbstractChannel):
     """
@@ -383,7 +401,7 @@ class ChannelBackup(AbstractChannel):
         Logger.__init__(self)
         self.cb = cb
         self._sweep_info = {}
-        self.sweep_address = sweep_address
+        self._fallback_sweep_address = sweep_address
         self.storage = {} # dummy storage
         self._state = ChannelState.OPENING
         self.config = {}
@@ -485,7 +503,7 @@ class Channel(AbstractChannel):
         self.name = name
         Logger.__init__(self)
         self.lnworker = lnworker
-        self.sweep_address = sweep_address
+        self._fallback_sweep_address = sweep_address
         self.storage = state
         self.db_lock = self.storage.db.lock if self.storage.db else threading.RLock()
         self.config = {}

electrum/lnworker.py

@@ -494,7 +494,8 @@ class LNWallet(LNWorker):
         self.features |= LnFeatures.OPTION_STATIC_REMOTEKEY_REQ
         self.payments = self.db.get_dict('lightning_payments')     # RHASH -> amount, direction, is_paid  # FIXME amt should be msat
         self.preimages = self.db.get_dict('lightning_preimages')   # RHASH -> preimage
-        self.sweep_address = wallet.get_new_sweep_address_for_channel()  # TODO possible address-reuse
+        # note: this sweep_address is only used as fallback; as it might result in address-reuse
+        self.sweep_address = wallet.get_new_sweep_address_for_channel()
         self.logs = defaultdict(list)  # type: Dict[str, List[PaymentAttemptLog]]  # key is RHASH  # (not persisted)
         self.is_routing = set()        # (not persisted) keys of invoices that are in PR_ROUTING state
         # used in tests

electrum/tests/test_lnchannel.py

@@ -172,9 +172,8 @@ def create_test_channels(*, feerate=6000, local_msat=None, remote_msat=None,
     alice.config[REMOTE].next_per_commitment_point = bob_second
     bob.config[REMOTE].next_per_commitment_point = alice_second
 
-    # TODO: sweep_address in lnchannel.py should use static_remotekey
-    alice.sweep_address = bitcoin.pubkey_to_address('p2wpkh', alice.config[LOCAL].payment_basepoint.pubkey.hex())
-    bob.sweep_address = bitcoin.pubkey_to_address('p2wpkh', bob.config[LOCAL].payment_basepoint.pubkey.hex())
+    alice._fallback_sweep_address = bitcoin.pubkey_to_address('p2wpkh', alice.config[LOCAL].payment_basepoint.pubkey.hex())
+    bob._fallback_sweep_address = bitcoin.pubkey_to_address('p2wpkh', bob.config[LOCAL].payment_basepoint.pubkey.hex())
 
     alice._ignore_max_htlc_value = True
     bob._ignore_max_htlc_value = True

electrum/tests/test_lnpeer.py

@@ -103,6 +103,9 @@ class MockWallet:
     def is_lightning_backup(self):
         return False
 
+    def is_mine(self, addr):
+        return True
+
 
 class MockLNWallet(Logger, NetworkRetryManager[LNPeerAddr]):
     def __init__(self, *, local_keypair: Keypair, chans: Iterable['Channel'], tx_queue):