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 = {}