closing: add option to set closing range.

This affects the range we offer even without quick-close, but it's
more critical for quick-close.

Signed-off-by: Rusty Russell <[email protected]>
Changelog-Added: JSONRPC: `close` now takes a `feerange` parameter to set min/max fee rates for mutual close.

Author: rustyrussell

closingd/closingd.c

@@ -622,6 +622,7 @@ static void calc_fee_bounds(size_t expected_weight,
 		/* option_anchor_outputs sets commitment_fee to max, so this
 		 * doesn't do anything */
 		if (amount_sat_greater(*maxfee, commitment_fee)) {
+			/* FIXME: would be nice to notify close cmd here! */
 			status_unusual("Maximum feerate %u would give fee %s:"
 				       " we must limit it to the final commitment fee %s",
 				       *max_feerate,

contrib/pyln-client/pyln/client/lightning.py

@@ -515,7 +515,7 @@ def check(self, command_to_check, **kwargs):
         payload.update({k: v for k, v in kwargs.items()})
         return self.call("check", payload)
 
-    def close(self, peer_id, unilateraltimeout=None, destination=None, fee_negotiation_step=None):
+    def close(self, peer_id, unilateraltimeout=None, destination=None, fee_negotiation_step=None, feerange=None):
         """
         Close the channel with peer {id}, forcing a unilateral
         close after {unilateraltimeout} seconds if non-zero, and
@@ -525,7 +525,8 @@ def close(self, peer_id, unilateraltimeout=None, destination=None, fee_negotiati
             "id": peer_id,
             "unilateraltimeout": unilateraltimeout,
             "destination": destination,
-            "fee_negotiation_step": fee_negotiation_step
+            "fee_negotiation_step": fee_negotiation_step,
+            "feerange": feerange,
         }
         return self.call("close", payload)
 

doc/lightning-close.7

@@ -4,7 +4,7 @@ lightning-close -- Command for closing channels with direct peers
 SYNOPSIS
 --------
 
-**close** *id* \[*unilateraltimeout*\] \[*destination*\] \[*fee_negotiation_step*\] \[*wrong_funding\*]
+**close** *id* \[*unilateraltimeout*\] \[*destination*\] \[*fee_negotiation_step*\] \[*wrong_funding\*] [\*feerange\*]
 
 DESCRIPTION
 -----------
@@ -33,7 +33,11 @@ friends to upgrade!
 
 The *fee_negotiation_step* parameter controls how closing fee
 negotiation is performed assuming the peer proposes a fee that is
-different than our estimate. On every negotiation step we must give up
+different than our estimate.  (Note that using this option
+prevents **experimental-quick-close**, as the quick-close protocol
+does not allow negotiation).
+
+On every negotiation step we must give up
 some amount from our proposal towards the peer's proposal. This parameter
 can be an integer in which case it is interpreted as number of satoshis
 to step at a time. Or it can be an integer followed by "%" to designate
@@ -56,6 +60,23 @@ 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.
 
+*feerange* is an optional array [ *min*, *max* ], indicating the
+minimum and maximum feerates to offer.  *slow* and *unilateral_close*
+are the defaults.
+
+Rates are one of the strings *urgent* (aim for next block), *normal*
+(next 4 blocks or so) or *slow* (next 100 blocks or so) to use
+lightningd’s internal estimates, or one of the names from
+lightning-feerates(7).  Otherwise, they can be numbers with
+an optional suffix: *perkw* means the number is interpreted as
+satoshi-per-kilosipa (weight), and *perkb* means it is interpreted
+bitcoind-style as satoshi-per-kilobyte. Omitting the suffix is
+equivalent to *perkb*.
+
+Note that the maximum fee will be capped at the final commitment
+transaction fee (unless the experimental anchor-outputs option is
+negotiated).
+
 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.

doc/lightning-close.7.md

@@ -245,6 +245,7 @@ struct channel *new_unsaved_channel(struct peer *peer,
 	channel->closing_fee_negotiation_step_unit
 		= CLOSING_FEE_NEGOTIATION_STEP_UNIT_PERCENTAGE;
 	channel->shutdown_wrong_funding = NULL;
+	channel->closing_feerate_range = NULL;
 
 	/* Channel is connected! */
 	channel->connected = true;
@@ -404,6 +405,7 @@ struct channel *new_channel(struct peer *peer, u64 dbid,
 		= CLOSING_FEE_NEGOTIATION_STEP_UNIT_PERCENTAGE;
 	channel->shutdown_wrong_funding
 		= tal_steal(channel, shutdown_wrong_funding);
+	channel->closing_feerate_range = NULL;
 	if (local_shutdown_scriptpubkey)
 		channel->shutdown_scriptpubkey[LOCAL]
 			= tal_steal(channel, local_shutdown_scriptpubkey);

lightningd/channel.c

@@ -164,6 +164,9 @@ struct channel {
 	/* optional wrong_funding for mutual close */
 	const struct bitcoin_outpoint *shutdown_wrong_funding;
 
+	/* optional feerate min/max for mutual close */
+	u32 *closing_feerate_range;
+
 	/* Reestablishment stuff: last sent commit and revocation details. */
 	bool last_was_revoke;
 	struct changed_htlc *last_sent_commit;

lightningd/channel.h

@@ -197,7 +197,7 @@ void peer_start_closingd(struct channel *channel,
 			 struct per_peer_state *pps)
 {
 	u8 *initmsg;
-	u32 feerate, *max_feerate;
+	u32 min_feerate, feerate, *max_feerate;
 	struct amount_msat their_msat;
 	struct amount_sat feelimit;
 	int hsmfd;
@@ -269,6 +269,14 @@ void peer_start_closingd(struct channel *channel,
 	} else
 		max_feerate = NULL;
 
+	min_feerate = feerate_min(ld, NULL);
+
+	/* If they specified feerates in `close`, they apply now! */
+	if (channel->closing_feerate_range) {
+		min_feerate = channel->closing_feerate_range[0];
+		max_feerate = &channel->closing_feerate_range[1];
+	}
+
 	/* BOLT #3:
 	 *
 	 * Each node offering a signature:
@@ -301,8 +309,7 @@ void peer_start_closingd(struct channel *channel,
 				       amount_msat_to_sat_round_down(channel->our_msat),
 				       amount_msat_to_sat_round_down(their_msat),
 				       channel->our_config.dust_limit,
-				       feerate_min(ld, NULL), feerate,
-				       max_feerate,
+				       min_feerate, feerate, max_feerate,
 				       feelimit,
 				       channel->shutdown_scriptpubkey[LOCAL],
 				       channel->shutdown_scriptpubkey[REMOTE],

lightningd/closing_control.c

@@ -1648,6 +1648,31 @@ static struct command_result *param_outpoint(struct command *cmd,
 				     "should be a txid:outnum");
 }
 
+static struct command_result *param_feerate_range(struct command *cmd,
+						  const char *name,
+						  const char *buffer,
+						  const jsmntok_t *tok,
+						  u32 **feerate_range)
+{
+	struct command_result *ret;
+	u32 *rate;
+
+	*feerate_range = tal_arr(cmd, u32, 2);
+	if (tok->type != JSMN_ARRAY || tok->size != 2)
+		return command_fail_badparam(cmd, name, buffer, tok,
+					     "should be an array of 2 entries");
+
+	ret = param_feerate(cmd, name, buffer, tok+1, &rate);
+	if (ret)
+		return ret;
+	(*feerate_range)[0] = *rate;
+	ret = param_feerate(cmd, name, buffer, tok+2, &rate);
+	if (ret)
+		return ret;
+	(*feerate_range)[1] = *rate;
+	return NULL;
+}
+
 static struct command_result *json_close(struct command *cmd,
 					 const char *buffer,
 					 const jsmntok_t *obj UNNEEDED,
@@ -1661,6 +1686,7 @@ static struct command_result *json_close(struct command *cmd,
 	bool close_script_set, wrong_funding_changed;
 	const char *fee_negotiation_step_str;
 	struct bitcoin_outpoint *wrong_funding;
+	u32 *feerate_range;
 	char* end;
 	bool anysegwit;
 
@@ -1672,6 +1698,7 @@ static struct command_result *json_close(struct command *cmd,
 		   p_opt("fee_negotiation_step", param_string,
 			 &fee_negotiation_step_str),
 		   p_opt("wrong_funding", param_outpoint, &wrong_funding),
+		   p_opt("feerange", param_feerate_range, &feerate_range),
 		   NULL))
 		return command_param_failed();
 
@@ -1821,6 +1848,9 @@ static struct command_result *json_close(struct command *cmd,
 			wrong_funding_changed = false;
 	}
 
+	/* Works fine if feerate_range is NULL */
+	channel->closing_feerate_range = tal_steal(channel, feerate_range);
+
 	/* Normal case.
 	 * We allow states shutting down and sigexchange; a previous
 	 * close command may have timed out, and this current command

lightningd/peer_control.c

@@ -524,6 +524,11 @@ struct command_result *param_escaped_string(struct command *cmd UNNEEDED,
 					    const jsmntok_t *tok UNNEEDED,
 					    const char **str UNNEEDED)
 { fprintf(stderr, "param_escaped_string called!\n"); abort(); }
+/* Generated stub for param_feerate */
+struct command_result *param_feerate(struct command *cmd UNNEEDED, const char *name UNNEEDED,
+				     const char *buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,
+				     u32 **feerate UNNEEDED)
+{ fprintf(stderr, "param_feerate called!\n"); abort(); }
 /* Generated stub for param_label */
 struct command_result *param_label(struct command *cmd UNNEEDED, const char *name UNNEEDED,
 				   const char * buffer UNNEEDED, const jsmntok_t *tok UNNEEDED,

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

@@ -2942,3 +2942,25 @@ def test_anysegwit_close_needs_feature(node_factory, bitcoind):
     l1.rpc.close(l2.info['id'], destination='bcrt1pw508d6qejxtdg4y5r3zarvary0c5xw7kw508d6qejxtdg4y5r3zarvary0c5xw7k0ylj56')
     wait_for(lambda: only_one(only_one(l1.rpc.listpeers()['peers'])['channels'])['state'] == 'CLOSINGD_COMPLETE')
     bitcoind.generate_block(1, wait_for_mempool=1)
+
+
+def test_close_feerate_range(node_factory, bitcoind, chainparams):
+    """Test the quick-close fee range negotiation"""
+    l1, l2 = node_factory.line_graph(2, opts={'experimental-quick-close': None})
+
+    # Lowball the range here.
+    l1.rpc.close(l2.info['id'], feerange=['253perkw', 'normal'])
+
+    if not chainparams['elements']:
+        l1_range = [138, 4110]
+        l2_range = [1027, 1000000]
+    else:
+        # That fee output is a little chunky.
+        l1_range = [175, 5212]
+        l2_range = [1303, 1000000]
+
+    l1.daemon.wait_for_log('Negotiating closing fee between {}sat and {}sat satoshi'.format(l1_range[0], l1_range[1]))
+    l2.daemon.wait_for_log('Negotiating closing fee between {}sat and {}sat satoshi'.format(l2_range[0], l2_range[1]))
+
+    overlap = [max(l1_range[0], l2_range[0]), min(l1_range[1], l2_range[1])]
+    l1.daemon.wait_for_log('performing quickclose in range {}sat-{}sat'.format(overlap[0], overlap[1]))