Add extra state to distinguish shutdown negotiation from post-

negotiation, where channel should not be reestablished. See #6182

electrum/lnchannel.py

@@ -77,10 +77,11 @@ class ChannelState(IntEnum):
                          #  - Non-funding node: has sent the funding_signed message.
     FUNDED          = 2  # Funding tx was mined (requires min_depth and tx verification)
     OPEN            = 3  # both parties have sent funding_locked
-    CLOSING         = 4  # shutdown has been sent, and closing tx is unconfirmed.
-    FORCE_CLOSING   = 5  # we force-closed, and closing tx is unconfirmed. (otherwise we remain OPEN)
-    CLOSED          = 6  # closing tx has been mined
-    REDEEMED        = 7  # we can stop watching
+    SHUTDOWN        = 4  # shutdown has been sent.
+    CLOSING         = 5  # closing negotiation done. we have a fully signed tx.
+    FORCE_CLOSING   = 6  # we force-closed, and closing tx is unconfirmed. (otherwise we remain OPEN)
+    CLOSED          = 7  # closing tx has been mined
+    REDEEMED        = 8  # we can stop watching
 
 
 class PeerState(IntEnum):
@@ -95,18 +96,25 @@ state_transitions = [
     (cs.PREOPENING, cs.OPENING),
     (cs.OPENING, cs.FUNDED),
     (cs.FUNDED, cs.OPEN),
-    (cs.OPENING, cs.CLOSING),
-    (cs.FUNDED, cs.CLOSING),
-    (cs.OPEN, cs.CLOSING),
+    (cs.OPENING, cs.SHUTDOWN),
+    (cs.FUNDED, cs.SHUTDOWN),
+    (cs.OPEN, cs.SHUTDOWN),
+    (cs.SHUTDOWN, cs.SHUTDOWN),  # if we reestablish
+    (cs.SHUTDOWN, cs.CLOSING),
+    (cs.CLOSING, cs.CLOSING),
+    # we can force close almost any time
     (cs.OPENING,  cs.FORCE_CLOSING),
     (cs.FUNDED,   cs.FORCE_CLOSING),
     (cs.OPEN,     cs.FORCE_CLOSING),
+    (cs.SHUTDOWN, cs.FORCE_CLOSING),
     (cs.CLOSING,  cs.FORCE_CLOSING),
+    # we can get force closed almost any time
     (cs.OPENING,  cs.CLOSED),
     (cs.FUNDED,   cs.CLOSED),
     (cs.OPEN,     cs.CLOSED),
-    (cs.CLOSING, cs.CLOSING),  # if we reestablish
+    (cs.SHUTDOWN, cs.CLOSED),
     (cs.CLOSING,  cs.CLOSED),
+    #
     (cs.FORCE_CLOSING, cs.FORCE_CLOSING),  # allow multiple attempts
     (cs.FORCE_CLOSING, cs.CLOSED),
     (cs.FORCE_CLOSING, cs.REDEEMED),
@@ -174,11 +182,11 @@ class AbstractChannel(Logger, ABC):
         return self.get_state() == ChannelState.OPEN
 
     def is_closing(self):
-        return self.get_state() in [ChannelState.CLOSING, ChannelState.FORCE_CLOSING]
+        return ChannelState.SHUTDOWN <= self.get_state() <= ChannelState.FORCE_CLOSING
 
     def is_closed(self):
         # the closing txid has been saved
-        return self.get_state() >= ChannelState.CLOSED
+        return self.get_state() >= ChannelState.CLOSING
 
     def is_redeemed(self):
         return self.get_state() == ChannelState.REDEEMED
@@ -707,8 +715,6 @@ class Channel(AbstractChannel):
         #       and the constraints are the ones imposed by their config
         ctn = self.get_next_ctn(htlc_receiver)
         chan_config = self.config[htlc_receiver]
-        if self.is_closed():
-            raise PaymentFailure('Channel closed')
         if self.get_state() != ChannelState.OPEN:
             raise PaymentFailure('Channel not open', self.get_state())
         if htlc_proposer == LOCAL:
@@ -777,7 +783,7 @@ class Channel(AbstractChannel):
         return True
 
     def should_try_to_reestablish_peer(self) -> bool:
-        return ChannelState.PREOPENING < self._state < ChannelState.FORCE_CLOSING and self.peer_state == PeerState.DISCONNECTED
+        return ChannelState.PREOPENING < self._state < ChannelState.CLOSING and self.peer_state == PeerState.DISCONNECTED
 
     def get_funding_address(self):
         script = funding_output_script(self.config[LOCAL], self.config[REMOTE])

electrum/lnpeer.py

@@ -87,7 +87,7 @@ class Peer(Logger):
         self.temp_id_to_id = {}   # to forward error messages
         self.funding_created_sent = set() # for channels in PREOPENING
         self.funding_signed_sent = set()  # for channels in PREOPENING
-        self.shutdown_received = {}
+        self.shutdown_received = {} # chan_id -> asyncio.Future()
         self.announcement_signatures = defaultdict(asyncio.Queue)
         self.orphan_channel_updates = OrderedDict()
         Logger.__init__(self)
@@ -933,7 +933,8 @@ class Peer(Logger):
         if chan.is_funded() and chan.config[LOCAL].funding_locked_received:
             self.mark_open(chan)
         util.trigger_callback('channel', chan)
-        if chan.get_state() == ChannelState.CLOSING:
+        # if we have sent a previous shutdown, it must be retransmitted (Bolt2)
+        if chan.get_state() == ChannelState.SHUTDOWN:
             await self.send_shutdown(chan)
 
     def send_funding_locked(self, chan: Channel):
@@ -1429,7 +1430,7 @@ class Peer(Logger):
         while chan.has_pending_changes(REMOTE):
             await asyncio.sleep(0.1)
         self.send_message('shutdown', channel_id=chan.channel_id, len=len(scriptpubkey), scriptpubkey=scriptpubkey)
-        chan.set_state(ChannelState.CLOSING)
+        chan.set_state(ChannelState.SHUTDOWN)
         # can fullfill or fail htlcs. cannot add htlcs, because of CLOSING state
         chan.set_can_send_ctx_updates(True)
 
@@ -1492,12 +1493,17 @@ class Peer(Logger):
         if not chan.constraints.is_initiator:
             send_closing_signed()
         # add signatures
-        closing_tx.add_signature_to_txin(txin_idx=0,
+        closing_tx.add_signature_to_txin(
+            txin_idx=0,
             signing_pubkey=chan.config[LOCAL].multisig_key.pubkey.hex(),
             sig=bh2u(der_sig_from_sig_string(our_sig) + b'\x01'))
-        closing_tx.add_signature_to_txin(txin_idx=0,
+        closing_tx.add_signature_to_txin(
+            txin_idx=0,
             signing_pubkey=chan.config[REMOTE].multisig_key.pubkey.hex(),
             sig=bh2u(der_sig_from_sig_string(their_sig) + b'\x01'))
+        # save local transaction and set state
+        self.lnworker.wallet.add_transaction(closing_tx)
+        chan.set_state(ChannelState.CLOSING)
         # broadcast
         await self.network.try_broadcasting(closing_tx, 'closing')
         return closing_tx.txid()

electrum/tests/test_lnpeer.py

@@ -90,13 +90,20 @@ class MockBlockchain:
 
 
 class MockWallet:
+
     def set_label(self, x, y):
         pass
+
     def save_db(self):
         pass
+
+    def add_transaction(self, tx):
+        pass
+
     def is_lightning_backup(self):
         return False
 
+
 class MockLNWallet(Logger, NetworkRetryManager[LNPeerAddr]):
     def __init__(self, *, local_keypair: Keypair, chans: Iterable['Channel'], tx_queue):
         Logger.__init__(self)