close: accept wrong_funding outpoint arg if we negotiated the feature.

Changelog-Added: lightningd: experimental-shutdown-wrong-funding to allow remote nodes to close incorrectly opened channels.
Changelog-Added: JSON-RPC: close has a new `wrong_funding` option to try to close out unused channels where we messed up the funding tx.
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

doc/lightning-close.7.md

@@ -4,7 +4,7 @@ lightning-close -- Command for closing channels with direct peers
 SYNOPSIS
 --------
 
-**close** *id* \[*unilateraltimeout*\] \[*destination*\] \[*fee_negotiation_step*\]
+**close** *id* \[*unilateraltimeout*\] \[*destination*\] \[*fee_negotiation_step*\] \[*wrong_funding\*]
 
 DESCRIPTION
 -----------
@@ -44,6 +44,15 @@ insist on our fee as much as possible.
 we quickly accept the peer's proposal.
 The default is "50%".
 
+*wrong_funding_txid* can only be specified if both sides have offered
+the "shutdown_wrong_funding" feature (enabled by the
+**experimental-shutdown-wrong-funding** option): it must be a
+transaction id followed by a colon then the output number.  Instead of
+negotiating a shutdown to spend the expected funding transaction, the
+shutdown transaction will spend this output instead.  This is only
+allowed if this peer opened the channel and the channel is unused: it
+can rescue openings which have been manually miscreated.
+
 The peer needs to be live and connected in order to negotiate a mutual
 close. The default of unilaterally closing after 48 hours is usually a
 reasonable indication that you can no longer contact the peer.
@@ -87,7 +96,7 @@ ZmnSCPxj <<ZmnSCPxj@protonmail.com>> is mainly responsible.
 SEE ALSO
 --------
 
-lightning-disconnect(7), lightning-fundchannel(7)
+lightning-disconnect(7), lightning-fundchannel(7), lightningd-config(5).
 
 RESOURCES
 ---------

lightningd/peer_control.c

@@ -1492,6 +1492,19 @@ command_find_channel(struct command *cmd,
 	}
 }
 
+static struct command_result *param_outpoint(struct command *cmd,
+					     const char *name,
+					     const char *buffer,
+					     const jsmntok_t *tok,
+					     struct bitcoin_outpoint **outp)
+{
+	*outp = tal(cmd, struct bitcoin_outpoint);
+	if (json_to_outpoint(buffer, tok, *outp))
+		return NULL;
+	return command_fail_badparam(cmd, name, buffer, tok,
+				     "should be a txid:outnum");
+}
+
 static struct command_result *json_close(struct command *cmd,
 					 const char *buffer,
 					 const jsmntok_t *obj UNNEEDED,
@@ -1502,8 +1515,9 @@ static struct command_result *json_close(struct command *cmd,
 	struct channel *channel COMPILER_WANTS_INIT("gcc 7.3.0 fails, 8.3 OK");
 	unsigned int *timeout;
 	const u8 *close_to_script = NULL;
-	bool close_script_set;
+	bool close_script_set, wrong_funding_changed;
 	const char *fee_negotiation_step_str;
+	struct bitcoin_outpoint *wrong_funding;
 	char* end;
 
 	if (!param(cmd, buffer, params,
@@ -1513,6 +1527,7 @@ static struct command_result *json_close(struct command *cmd,
 		   p_opt("destination", param_bitcoin_address, &close_to_script),
 		   p_opt("fee_negotiation_step", param_string,
 			 &fee_negotiation_step_str),
+		   p_opt("wrong_funding", param_outpoint, &wrong_funding),
 		   NULL))
 		return command_param_failed();
 
@@ -1544,7 +1559,6 @@ static struct command_result *json_close(struct command *cmd,
 				    "Peer has no active channel");
 	}
 
-
 	/* If we've set a local shutdown script for this peer, and it's not the
 	 * default upfront script, try to close to a different channel.
 	 * Error is an operator error */
@@ -1618,6 +1632,33 @@ static struct command_result *json_close(struct command *cmd,
 			    fee_negotiation_step_str);
 	}
 
+	if (wrong_funding) {
+		if (!feature_negotiated(cmd->ld->our_features,
+					peer->their_features,
+					OPT_SHUTDOWN_WRONG_FUNDING)) {
+			return command_fail(cmd, JSONRPC2_INVALID_PARAMS,
+					    "wrong_funding feature not negotiated"
+					    " (we said %s, they said %s: try experimental-shutdown-wrong-funding?)",
+					    feature_offered(cmd->ld->our_features
+							    ->bits[INIT_FEATURE],
+							    OPT_SHUTDOWN_WRONG_FUNDING)
+					    ? "yes" : "no",
+					    feature_offered(peer->their_features,
+							    OPT_SHUTDOWN_WRONG_FUNDING)
+					    ? "yes" : "no");
+		}
+
+		wrong_funding_changed = true;
+		channel->shutdown_wrong_funding
+			= tal_steal(channel, wrong_funding);
+	} else {
+		if (channel->shutdown_wrong_funding) {
+			channel->shutdown_wrong_funding
+				= tal_free(channel->shutdown_wrong_funding);
+			wrong_funding_changed = true;
+		}
+	}
+
 	/* Normal case.
 	 * We allow states shutting down and sigexchange; a previous
 	 * close command may have timed out, and this current command
@@ -1663,8 +1704,9 @@ static struct command_result *json_close(struct command *cmd,
 	/* Register this command for later handling. */
 	register_close_command(cmd->ld, cmd, channel, *timeout);
 
-	/* If we set `channel->shutdown_scriptpubkey[LOCAL]`, save it. */
-	if (close_script_set)
+	/* If we set `channel->shutdown_scriptpubkey[LOCAL]` or
+	 * changed shutdown_wrong_funding, save it. */
+	if (close_script_set || wrong_funding_changed)
 		wallet_channel_save(cmd->ld->wallet, channel);
 
 	/* Wait until close drops down to chain. */

lightningd/test/run-invoice-select-inchan.c

@@ -172,6 +172,9 @@ bool feature_is_set(const u8 *features UNNEEDED, size_t bit UNNEEDED)
 bool feature_negotiated(const struct feature_set *our_features UNNEEDED,
 			const u8 *their_features UNNEEDED, size_t f UNNEEDED)
 { fprintf(stderr, "feature_negotiated called!\n"); abort(); }
+/* Generated stub for feature_offered */
+bool feature_offered(const u8 *features UNNEEDED, size_t f UNNEEDED)
+{ fprintf(stderr, "feature_offered called!\n"); abort(); }
 /* Generated stub for fixup_htlcs_out */
 void fixup_htlcs_out(struct lightningd *ld UNNEEDED)
 { fprintf(stderr, "fixup_htlcs_out called!\n"); abort(); }
@@ -374,6 +377,10 @@ enum address_parse_result json_to_address_scriptpubkey(const tal_t *ctx UNNEEDED
 bool json_to_node_id(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
 			       struct node_id *id UNNEEDED)
 { fprintf(stderr, "json_to_node_id called!\n"); abort(); }
+/* Generated stub for json_to_outpoint */
+bool json_to_outpoint(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
+		      struct bitcoin_outpoint *op UNNEEDED)
+{ fprintf(stderr, "json_to_outpoint called!\n"); abort(); }
 /* Generated stub for json_to_short_channel_id */
 bool json_to_short_channel_id(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
 			      struct short_channel_id *scid UNNEEDED)

tests/test_closing.py

@@ -1,12 +1,12 @@
 from fixtures import *  # noqa: F401,F403
 from flaky import flaky
-from pyln.client import RpcError
+from pyln.client import RpcError, Millisatoshi
 from shutil import copyfile
 from pyln.testing.utils import SLOW_MACHINE
 from utils import (
     only_one, sync_blockheight, wait_for, DEVELOPER, TIMEOUT,
     account_balance, first_channel_id, basic_fee, TEST_NETWORK,
-    EXPERIMENTAL_FEATURES,
+    EXPERIMENTAL_FEATURES, EXPERIMENTAL_DUAL_FUND,
 )
 
 import os
@@ -2695,3 +2695,49 @@ def test_segwit_shutdown_script(node_factory, bitcoind, executor):
         l1.rpc.connect(l2.info['id'], 'localhost', l2.port)
         with pytest.raises(RpcError, match=r'Unacceptable upfront_shutdown_script'):
             l1.rpc.fundchannel(l2.info['id'], 10**6)
+
+
+@unittest.skipIf(EXPERIMENTAL_DUAL_FUND, "Uses fundchannel_start")
+def test_shutdown_alternate_txid(node_factory, bitcoind):
+    l1, l2 = node_factory.line_graph(2, fundchannel=False,
+                                     opts={'experimental-shutdown-wrong-funding': None})
+
+    amount = 1000000
+    amount_msat = Millisatoshi(amount * 1000)
+
+    # Let's make a classic fundchannel mistake (wrong txid!)
+    addr = l1.rpc.fundchannel_start(l2.info['id'], amount_msat)['funding_address']
+    txid = bitcoind.rpc.sendtoaddress(addr, amount / 10**8)
+    bitcoind.generate_block(1, wait_for_mempool=1)
+
+    # Gotta figure out which output manually :(
+    tx = bitcoind.rpc.getrawtransaction(txid, 1)
+    for n, out in enumerate(tx['vout']):
+        if out['scriptPubKey']['addresses'][0] == addr:
+            txout = n
+
+    # Wrong txid, wrong txout!
+    wrong_txid = txid[16:] + txid[:16]
+    wrong_txout = txout ^ 1
+    l1.rpc.fundchannel_complete(l2.info['id'], wrong_txid, wrong_txout)
+
+    wait_for(lambda: only_one(l2.rpc.listpeers()['peers'])['channels'] != [])
+    wait_for(lambda: only_one(l2.rpc.listpeers()['peers'])['channels'][0]['state'] == 'CHANNELD_AWAITING_LOCKIN')
+
+    closeaddr = l1.rpc.newaddr()['bech32']
+
+    # Oops, try rescuing it!
+    l1.rpc.call('close', {'id': l2.info['id'], 'destination': closeaddr, 'wrong_funding': txid + ':' + str(txout)})
+
+    # Just make sure node has no funds.
+    assert l1.rpc.listfunds()['outputs'] == []
+
+    bitcoind.generate_block(100, wait_for_mempool=1)
+    sync_blockheight(bitcoind, [l1, l2])
+
+    # We will see our funds return.
+    assert len(l1.rpc.listfunds()['outputs']) == 1
+
+    # FIXME: we should close channels, but we don't!
+    # wait_for(lambda: l2.rpc.listpeers()['peers'] == [])
+    # wait_for(lambda: l1.rpc.listpeers()['peers'] == [])

wallet/test/run-wallet.c

@@ -119,6 +119,9 @@ void   fatal(const char *fmt UNNEEDED, ...)
 bool feature_negotiated(const struct feature_set *our_features UNNEEDED,
 			const u8 *their_features UNNEEDED, size_t f UNNEEDED)
 { fprintf(stderr, "feature_negotiated called!\n"); abort(); }
+/* Generated stub for feature_offered */
+bool feature_offered(const u8 *features UNNEEDED, size_t f UNNEEDED)
+{ fprintf(stderr, "feature_offered called!\n"); abort(); }
 /* Generated stub for fromwire_channeld_dev_memleak_reply */
 bool fromwire_channeld_dev_memleak_reply(const void *p UNNEEDED, bool *leak UNNEEDED)
 { fprintf(stderr, "fromwire_channeld_dev_memleak_reply called!\n"); abort(); }
@@ -400,6 +403,10 @@ bool json_to_node_id(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
 bool json_to_number(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
 		    unsigned int *num UNNEEDED)
 { fprintf(stderr, "json_to_number called!\n"); abort(); }
+/* Generated stub for json_to_outpoint */
+bool json_to_outpoint(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
+		      struct bitcoin_outpoint *op UNNEEDED)
+{ fprintf(stderr, "json_to_outpoint called!\n"); abort(); }
 /* Generated stub for json_to_preimage */
 bool json_to_preimage(const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED, struct preimage *preimage UNNEEDED)
 { fprintf(stderr, "json_to_preimage called!\n"); abort(); }