--experimental-quick-close to enable quick-close negotiation

Based on a commit by @niftynei, but:
- Separated quickclose logic from main loop.
- I made it indep of anchor_outputs, use and option instead.
- Disable if they've specified how to negotiate.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

closingd/closingd.c

@@ -141,10 +141,12 @@ static void send_offer(struct per_peer_state *pps,
 		       enum side opener,
 		       struct amount_sat our_dust_limit,
 		       struct amount_sat fee_to_offer,
-		       const struct bitcoin_outpoint *wrong_funding)
+		       const struct bitcoin_outpoint *wrong_funding,
+		       const struct tlv_closing_signed_tlvs_fee_range *tlv_fees)
 {
 	struct bitcoin_tx *tx;
 	struct bitcoin_signature our_sig;
+	struct tlv_closing_signed_tlvs *close_tlvs;
 	u8 *msg;
 
 	/* BOLT #2:
@@ -184,8 +186,19 @@ static void send_offer(struct per_peer_state *pps,
 	status_debug("sending fee offer %s",
 		     type_to_string(tmpctx, struct amount_sat, &fee_to_offer));
 
+	/* Add the new close_tlvs with our fee range */
+	if (tlv_fees) {
+		close_tlvs = tlv_closing_signed_tlvs_new(msg);
+		close_tlvs->fee_range
+			= cast_const(struct tlv_closing_signed_tlvs_fee_range *,
+				     tlv_fees);
+	} else
+		close_tlvs = NULL;
+
 	assert(our_sig.sighash_type == SIGHASH_ALL);
-	msg = towire_closing_signed(NULL, channel_id, fee_to_offer, &our_sig.s, NULL);
+	msg = towire_closing_signed(NULL, channel_id, fee_to_offer, &our_sig.s,
+				    close_tlvs);
+
 	sync_crypto_write(pps, take(msg));
 }
 
@@ -222,7 +235,8 @@ receive_offer(struct per_peer_state *pps,
 	      struct amount_sat our_dust_limit,
 	      struct amount_sat min_fee_to_accept,
 	      const struct bitcoin_outpoint *wrong_funding,
-	      struct bitcoin_txid *closing_txid)
+	      struct bitcoin_txid *closing_txid,
+	      struct tlv_closing_signed_tlvs_fee_range **tlv_fees)
 {
 	u8 *msg;
 	struct channel_id their_channel_id;
@@ -330,6 +344,13 @@ receive_offer(struct per_peer_state *pps,
 	status_debug("Received fee offer %s",
 		     type_to_string(tmpctx, struct amount_sat, &received_fee));
 
+	if (tlv_fees) {
+		if (close_tlvs)
+			*tlv_fees = tal_steal(tlv_fees, close_tlvs->fee_range);
+		else
+			*tlv_fees = NULL;
+	}
+
 	/* Master sorts out what is best offer, we just tell it any above min */
 	if (amount_sat_greater_eq(received_fee, min_fee_to_accept)) {
 		status_debug("...offer is reasonable");
@@ -397,6 +418,32 @@ static void adjust_feerange(struct feerange *feerange,
 			      "Overflow in updating fee range");
 }
 
+/* Do these two ranges overlap?  If so, return that range. */
+static bool get_overlap(const struct tlv_closing_signed_tlvs_fee_range *r1,
+			const struct tlv_closing_signed_tlvs_fee_range *r2,
+			struct tlv_closing_signed_tlvs_fee_range *overlap)
+{
+ 	if (amount_sat_greater(r1->min_fee_satoshis, r2->min_fee_satoshis))
+		overlap->min_fee_satoshis = r1->min_fee_satoshis;
+	else
+		overlap->min_fee_satoshis = r2->min_fee_satoshis;
+ 	if (amount_sat_less(r1->max_fee_satoshis, r2->max_fee_satoshis))
+		overlap->max_fee_satoshis = r1->max_fee_satoshis;
+	else
+		overlap->max_fee_satoshis = r2->max_fee_satoshis;
+
+	return amount_sat_less_eq(overlap->min_fee_satoshis,
+				  overlap->max_fee_satoshis);
+}
+
+/* Is this amount in this range? */
+static bool amount_in_range(struct amount_sat amount,
+			    const struct tlv_closing_signed_tlvs_fee_range *r)
+{
+	return amount_sat_greater_eq(amount, r->min_fee_satoshis)
+		&& amount_sat_less_eq(amount, r->max_fee_satoshis);
+}
+
 /* Figure out what we should offer now. */
 static struct amount_sat
 adjust_offer(struct per_peer_state *pps, const struct channel_id *channel_id,
@@ -572,6 +619,177 @@ static void calc_fee_bounds(size_t expected_weight,
 		     type_to_string(tmpctx, struct amount_sat, &maxfee));
 }
 
+/* We've received one offer; if we're opener, that means we've already sent one
+ * too. */
+static void do_quickclose(struct amount_sat offer[NUM_SIDES],
+			  struct per_peer_state *pps,
+			  const struct channel_id *channel_id,
+			  const struct pubkey funding_pubkey[NUM_SIDES],
+			  const u8 *funding_wscript,
+			  u8 *scriptpubkey[NUM_SIDES],
+			  const struct bitcoin_txid *funding_txid,
+			  unsigned int funding_txout,
+			  struct amount_sat funding,
+			  const struct amount_sat out[NUM_SIDES],
+			  enum side opener,
+			  struct amount_sat our_dust_limit,
+			  const struct bitcoin_outpoint *wrong_funding,
+			  struct bitcoin_txid *closing_txid,
+			  const struct tlv_closing_signed_tlvs_fee_range *our_feerange,
+			  const struct tlv_closing_signed_tlvs_fee_range *their_feerange)
+{
+	struct tlv_closing_signed_tlvs_fee_range overlap;
+
+
+	/* BOLT-closing-fee_range #2:
+	 *   - if the message contains a `fee_range`:
+	 *     - if there is no overlap between that and its own `fee_range`:
+	 *       - SHOULD fail the connection
+	 */
+	if (!get_overlap(our_feerange, their_feerange, &overlap)) {
+		peer_failed_warn(pps, channel_id,
+			       "Unable to agree on a feerate."
+			       " Our range %s-%s, other range %s-%s",
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &our_feerange->min_fee_satoshis),
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &our_feerange->max_fee_satoshis),
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &their_feerange->min_fee_satoshis),
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &their_feerange->max_fee_satoshis));
+		return;
+	}
+
+	status_info("performing quickclose in range %s-%s",
+		    type_to_string(tmpctx, struct amount_sat,
+				   &overlap.min_fee_satoshis),
+		    type_to_string(tmpctx, struct amount_sat,
+				   &overlap.max_fee_satoshis));
+
+	/* BOLT-closing-fee_range #2:
+	 * - otherwise:
+	 *   - if it is the funder:
+	 *     - if `fee_satoshis` is not in the overlap between the sent
+	 *       and received `fee_range`:
+	 *       - SHOULD fail the connection
+	 *     - otherwise:
+	 *       - MUST reply with the same `fee_satoshis`.
+	 */
+	if (opener == LOCAL) {
+		if (!amount_in_range(offer[REMOTE], &overlap)) {
+			peer_failed_warn(pps, channel_id,
+			       "Your fee %s was not in range:"
+			       " Our range %s-%s, other range %s-%s",
+			       type_to_string(tmpctx,
+					      struct amount_sat, &offer[REMOTE]),
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &our_feerange->min_fee_satoshis),
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &our_feerange->max_fee_satoshis),
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &their_feerange->min_fee_satoshis),
+			       type_to_string(tmpctx,
+					      struct amount_sat,
+					      &their_feerange->max_fee_satoshis));
+			return;
+		}
+		/* Only reply if we didn't already completely agree. */
+		if (!amount_sat_eq(offer[LOCAL], offer[REMOTE])) {
+			offer[LOCAL] = offer[REMOTE];
+			send_offer(pps, chainparams,
+				   channel_id, funding_pubkey, funding_wscript,
+				   scriptpubkey, funding_txid, funding_txout,
+				   funding, out, opener,
+				   our_dust_limit,
+				   offer[LOCAL],
+				   wrong_funding,
+				   our_feerange);
+		}
+	} else {
+		/* BOLT-closing-fee_range #2:
+		 * - otherwise (it is not the funder):
+		 *   - if it has already sent a `closing_signed`:
+		 *     - if `fee_satoshis` is not the same as the value it sent:
+		 *       - SHOULD fail the connection.
+		 *   - otherwise:
+		 *     - MUST propose a `fee_satoshis` in the overlap between
+		 *       received and (about-to-be) sent `fee_range`.
+		 */
+		if (!amount_in_range(offer[LOCAL], &overlap)) {
+			/* Hmm, go to edges. */
+			if (amount_sat_greater(offer[LOCAL],
+					       overlap.max_fee_satoshis)) {
+				offer[LOCAL] = overlap.max_fee_satoshis;
+				status_unusual("Lowered offer to max allowable"
+					       " %s",
+					       type_to_string(tmpctx,
+							      struct amount_sat,
+							      &offer[LOCAL]));
+			} else if (amount_sat_less(offer[LOCAL],
+						   overlap.min_fee_satoshis)) {
+				offer[LOCAL] = overlap.min_fee_satoshis;
+				status_unusual("Increased offer to min allowable"
+					       " %s",
+					       type_to_string(tmpctx,
+							      struct amount_sat,
+							      &offer[LOCAL]));
+			}
+		}
+		send_offer(pps, chainparams,
+			   channel_id, funding_pubkey, funding_wscript,
+			   scriptpubkey, funding_txid, funding_txout,
+			   funding, out, opener,
+			   our_dust_limit,
+			   offer[LOCAL],
+			   wrong_funding,
+			   our_feerange);
+
+		/* They will reply unless we completely agreed. */
+		if (!amount_sat_eq(offer[LOCAL], offer[REMOTE])) {
+			offer[REMOTE]
+				= receive_offer(pps, chainparams,
+						channel_id, funding_pubkey,
+						funding_wscript,
+						scriptpubkey, funding_txid,
+						funding_txout, funding,
+						out, opener,
+						our_dust_limit,
+						our_feerange->min_fee_satoshis,
+						wrong_funding,
+						closing_txid,
+						NULL);
+			/* BOLT-closing-fee_range #2:
+			 * - otherwise (it is not the funder):
+			 *   - if it has already sent a `closing_signed`:
+			 *     - if `fee_satoshis` is not the same as the value
+			 *       it sent:
+			 *       - SHOULD fail the connection.
+			 */
+			if (!amount_sat_eq(offer[LOCAL], offer[REMOTE])) {
+				peer_failed_warn(pps, channel_id,
+						 "Your fee %s was not equal to %s",
+			       type_to_string(tmpctx,
+					      struct amount_sat, &offer[REMOTE]),
+			       type_to_string(tmpctx,
+					      struct amount_sat, &offer[LOCAL]));
+				return;
+			}
+		}
+	}
+
+	peer_billboard(true, "We agreed on a closing fee of %"PRIu64" satoshi for tx:%s",
+		       offer[LOCAL],
+		       type_to_string(tmpctx, struct bitcoin_txid, closing_txid));
+}
+
 int main(int argc, char *argv[])
 {
 	setup_locale();
@@ -594,6 +812,8 @@ int main(int argc, char *argv[])
 	char fee_negotiation_step_str[32]; /* fee_negotiation_step + "sat" */
 	struct channel_id channel_id;
 	enum side whose_turn;
+	bool use_quickclose;
+	struct tlv_closing_signed_tlvs_fee_range *our_feerange, **their_feerange;
 	struct bitcoin_outpoint *wrong_funding;
 
 	subdaemon_setup(argc, argv);
@@ -619,6 +839,7 @@ int main(int argc, char *argv[])
 				    &scriptpubkey[REMOTE],
 				    &fee_negotiation_step,
 				    &fee_negotiation_step_unit,
+				    &use_quickclose,
 				    &dev_fast_gossip,
 				    &wrong_funding))
 		master_badmsg(WIRE_CLOSINGD_INIT, msg);
@@ -637,6 +858,29 @@ int main(int argc, char *argv[])
 			min_feerate, initial_feerate, commitment_fee,
 			&min_fee_to_accept, &offer[LOCAL]);
 
+	/* Write values into tlv for updated closing fee neg */
+	their_feerange = tal(ctx, struct tlv_closing_signed_tlvs_fee_range *);
+	*their_feerange = NULL;
+
+	if (use_quickclose) {
+		our_feerange = tal(ctx, struct tlv_closing_signed_tlvs_fee_range);
+		our_feerange->min_fee_satoshis = min_fee_to_accept;
+
+		/* BOLT-closing-fee_range #2:
+		 * - if it is not the funder:
+		 *  - SHOULD set `max_fee_satoshis` to at least the
+		 *    `max_fee_satoshis` received
+		 *...
+		 * Note that the non-funder is not paying the fee, so there is
+		 * no reason for it to have a maximum feerate.
+		 */
+		if (opener == REMOTE)
+			our_feerange->max_fee_satoshis = funding;
+		else
+			our_feerange->max_fee_satoshis = commitment_fee;
+	} else
+		our_feerange = NULL;
+
 	snprintf(fee_negotiation_step_str, sizeof(fee_negotiation_step_str),
 		 "%" PRIu64 "%s", fee_negotiation_step,
 		 fee_negotiation_step_unit ==
@@ -683,7 +927,8 @@ int main(int argc, char *argv[])
 				   funding, out, opener,
 				   our_dust_limit,
 				   offer[LOCAL],
-				   wrong_funding);
+				   wrong_funding,
+				   our_feerange);
 		} else {
 			if (i == 0)
 				peer_billboard(false, "Waiting for their initial"
@@ -705,7 +950,22 @@ int main(int argc, char *argv[])
 						our_dust_limit,
 						min_fee_to_accept,
 						wrong_funding,
-						&closing_txid);
+						&closing_txid,
+						their_feerange);
+
+			if (our_feerange && *their_feerange) {
+				do_quickclose(offer,
+					      pps, &channel_id, funding_pubkey,
+					      funding_wscript,
+					      scriptpubkey,
+					      &funding_txid, funding_txout,
+					      funding, out, opener,
+					      our_dust_limit,
+					      wrong_funding,
+					      &closing_txid,
+					      our_feerange, *their_feerange);
+				goto exit_thru_the_giftshop;
+			}
 		}
 	}
 
@@ -734,7 +994,8 @@ int main(int argc, char *argv[])
 				   funding, out, opener,
 				   our_dust_limit,
 				   offer[LOCAL],
-				   wrong_funding);
+				   wrong_funding,
+				   our_feerange);
 		} else {
 			peer_billboard(false, "Waiting for another"
 				       " closing fee offer:"
@@ -751,7 +1012,8 @@ int main(int argc, char *argv[])
 						our_dust_limit,
 						min_fee_to_accept,
 						wrong_funding,
-						&closing_txid);
+						&closing_txid,
+						their_feerange);
 		}
 
 		whose_turn = !whose_turn;
@@ -761,9 +1023,12 @@ int main(int argc, char *argv[])
 		       offer[LOCAL],
 		       type_to_string(tmpctx, struct bitcoin_txid, &closing_txid));
 
+exit_thru_the_giftshop:
 #if DEVELOPER
 	/* We don't listen for master commands, so always check memleak here */
 	tal_free(wrong_funding);
+	tal_free(our_feerange);
+	tal_free(their_feerange);
 	closing_dev_memleak(ctx, scriptpubkey, funding_wscript);
 #endif
 

closingd/closingd_wire.csv

@@ -26,6 +26,7 @@ msgdata,closingd_init,remote_scriptpubkey_len,u16,
 msgdata,closingd_init,remote_scriptpubkey,u8,remote_scriptpubkey_len
 msgdata,closingd_init,fee_negotiation_step,u64,
 msgdata,closingd_init,fee_negotiation_step_unit,u8,
+msgdata,closingd_init,use_quickclose,bool,
 msgdata,closingd_init,dev_fast_gossip,bool,
 msgdata,closingd_init,shutdown_wrong_funding,?bitcoin_outpoint,
 

closingd/closingd_wiregen.c

@@ -48,7 +48,7 @@ bool closingd_wire_is_defined(u16 type)
 
 /* WIRE: CLOSINGD_INIT */
 /* Begin!  (passes peer fd */
-u8 *towire_closingd_init(const tal_t *ctx, const struct chainparams *chainparams, const struct per_peer_state *pps, const struct channel_id *channel_id, const struct bitcoin_txid *funding_txid, u16 funding_txout, struct amount_sat funding_satoshi, const struct pubkey *local_fundingkey, const struct pubkey *remote_fundingkey, enum side opener, struct amount_sat local_sat, struct amount_sat remote_sat, struct amount_sat our_dust_limit, u32 min_feerate_perksipa, u32 preferred_feerate_perksipa, struct amount_sat fee_limit_satoshi, const u8 *local_scriptpubkey, const u8 *remote_scriptpubkey, u64 fee_negotiation_step, u8 fee_negotiation_step_unit, bool dev_fast_gossip, const struct bitcoin_outpoint *shutdown_wrong_funding)
+u8 *towire_closingd_init(const tal_t *ctx, const struct chainparams *chainparams, const struct per_peer_state *pps, const struct channel_id *channel_id, const struct bitcoin_txid *funding_txid, u16 funding_txout, struct amount_sat funding_satoshi, const struct pubkey *local_fundingkey, const struct pubkey *remote_fundingkey, enum side opener, struct amount_sat local_sat, struct amount_sat remote_sat, struct amount_sat our_dust_limit, u32 min_feerate_perksipa, u32 preferred_feerate_perksipa, struct amount_sat fee_limit_satoshi, const u8 *local_scriptpubkey, const u8 *remote_scriptpubkey, u64 fee_negotiation_step, u8 fee_negotiation_step_unit, bool use_quickclose, bool dev_fast_gossip, const struct bitcoin_outpoint *shutdown_wrong_funding)
 {
 	u16 local_scriptpubkey_len = tal_count(local_scriptpubkey);
 	u16 remote_scriptpubkey_len = tal_count(remote_scriptpubkey);
@@ -76,6 +76,7 @@ u8 *towire_closingd_init(const tal_t *ctx, const struct chainparams *chainparams
 	towire_u8_array(&p, remote_scriptpubkey, remote_scriptpubkey_len);
 	towire_u64(&p, fee_negotiation_step);
 	towire_u8(&p, fee_negotiation_step_unit);
+	towire_bool(&p, use_quickclose);
 	towire_bool(&p, dev_fast_gossip);
 	if (!shutdown_wrong_funding)
 		towire_bool(&p, false);
@@ -86,7 +87,7 @@ u8 *towire_closingd_init(const tal_t *ctx, const struct chainparams *chainparams
 
 	return memcheck(p, tal_count(p));
 }
-bool fromwire_closingd_init(const tal_t *ctx, const void *p, const struct chainparams **chainparams, struct per_peer_state **pps, struct channel_id *channel_id, struct bitcoin_txid *funding_txid, u16 *funding_txout, struct amount_sat *funding_satoshi, struct pubkey *local_fundingkey, struct pubkey *remote_fundingkey, enum side *opener, struct amount_sat *local_sat, struct amount_sat *remote_sat, struct amount_sat *our_dust_limit, u32 *min_feerate_perksipa, u32 *preferred_feerate_perksipa, struct amount_sat *fee_limit_satoshi, u8 **local_scriptpubkey, u8 **remote_scriptpubkey, u64 *fee_negotiation_step, u8 *fee_negotiation_step_unit, bool *dev_fast_gossip, struct bitcoin_outpoint **shutdown_wrong_funding)
+bool fromwire_closingd_init(const tal_t *ctx, const void *p, const struct chainparams **chainparams, struct per_peer_state **pps, struct channel_id *channel_id, struct bitcoin_txid *funding_txid, u16 *funding_txout, struct amount_sat *funding_satoshi, struct pubkey *local_fundingkey, struct pubkey *remote_fundingkey, enum side *opener, struct amount_sat *local_sat, struct amount_sat *remote_sat, struct amount_sat *our_dust_limit, u32 *min_feerate_perksipa, u32 *preferred_feerate_perksipa, struct amount_sat *fee_limit_satoshi, u8 **local_scriptpubkey, u8 **remote_scriptpubkey, u64 *fee_negotiation_step, u8 *fee_negotiation_step_unit, bool *use_quickclose, bool *dev_fast_gossip, struct bitcoin_outpoint **shutdown_wrong_funding)
 {
 	u16 local_scriptpubkey_len;
 	u16 remote_scriptpubkey_len;
@@ -121,6 +122,7 @@ bool fromwire_closingd_init(const tal_t *ctx, const void *p, const struct chainp
 	fromwire_u8_array(&cursor, &plen, *remote_scriptpubkey, remote_scriptpubkey_len);
  	*fee_negotiation_step = fromwire_u64(&cursor, &plen);
  	*fee_negotiation_step_unit = fromwire_u8(&cursor, &plen);
+ 	*use_quickclose = fromwire_bool(&cursor, &plen);
  	*dev_fast_gossip = fromwire_bool(&cursor, &plen);
  	if (!fromwire_bool(&cursor, &plen))
 		*shutdown_wrong_funding = NULL;
@@ -195,4 +197,4 @@ bool fromwire_closingd_complete(const void *p)
 		return false;
 	return cursor != NULL;
 }
-// SHA256STAMP:961ca5ceef03f911684ba0e7863d69993e692b9b418108e6038a567cb7cc7b3e
+// SHA256STAMP:b736e1d2c03a883962558ddcd5675d26cb09dcf3462c0cf82b3d49f1fd980c8a

closingd/closingd_wiregen.h

@@ -37,8 +37,8 @@ bool closingd_wire_is_defined(u16 type);
 
 /* WIRE: CLOSINGD_INIT */
 /*  Begin!  (passes peer fd */
-u8 *towire_closingd_init(const tal_t *ctx, const struct chainparams *chainparams, const struct per_peer_state *pps, const struct channel_id *channel_id, const struct bitcoin_txid *funding_txid, u16 funding_txout, struct amount_sat funding_satoshi, const struct pubkey *local_fundingkey, const struct pubkey *remote_fundingkey, enum side opener, struct amount_sat local_sat, struct amount_sat remote_sat, struct amount_sat our_dust_limit, u32 min_feerate_perksipa, u32 preferred_feerate_perksipa, struct amount_sat fee_limit_satoshi, const u8 *local_scriptpubkey, const u8 *remote_scriptpubkey, u64 fee_negotiation_step, u8 fee_negotiation_step_unit, bool dev_fast_gossip, const struct bitcoin_outpoint *shutdown_wrong_funding);
+u8 *towire_closingd_init(const tal_t *ctx, const struct chainparams *chainparams, const struct per_peer_state *pps, const struct channel_id *channel_id, const struct bitcoin_txid *funding_txid, u16 funding_txout, struct amount_sat funding_satoshi, const struct pubkey *local_fundingkey, const struct pubkey *remote_fundingkey, enum side opener, struct amount_sat local_sat, struct amount_sat remote_sat, struct amount_sat our_dust_limit, u32 min_feerate_perksipa, u32 preferred_feerate_perksipa, struct amount_sat fee_limit_satoshi, const u8 *local_scriptpubkey, const u8 *remote_scriptpubkey, u64 fee_negotiation_step, u8 fee_negotiation_step_unit, bool use_quickclose, bool dev_fast_gossip, const struct bitcoin_outpoint *shutdown_wrong_funding);
-bool fromwire_closingd_init(const tal_t *ctx, const void *p, const struct chainparams **chainparams, struct per_peer_state **pps, struct channel_id *channel_id, struct bitcoin_txid *funding_txid, u16 *funding_txout, struct amount_sat *funding_satoshi, struct pubkey *local_fundingkey, struct pubkey *remote_fundingkey, enum side *opener, struct amount_sat *local_sat, struct amount_sat *remote_sat, struct amount_sat *our_dust_limit, u32 *min_feerate_perksipa, u32 *preferred_feerate_perksipa, struct amount_sat *fee_limit_satoshi, u8 **local_scriptpubkey, u8 **remote_scriptpubkey, u64 *fee_negotiation_step, u8 *fee_negotiation_step_unit, bool *dev_fast_gossip, struct bitcoin_outpoint **shutdown_wrong_funding);
+bool fromwire_closingd_init(const tal_t *ctx, const void *p, const struct chainparams **chainparams, struct per_peer_state **pps, struct channel_id *channel_id, struct bitcoin_txid *funding_txid, u16 *funding_txout, struct amount_sat *funding_satoshi, struct pubkey *local_fundingkey, struct pubkey *remote_fundingkey, enum side *opener, struct amount_sat *local_sat, struct amount_sat *remote_sat, struct amount_sat *our_dust_limit, u32 *min_feerate_perksipa, u32 *preferred_feerate_perksipa, struct amount_sat *fee_limit_satoshi, u8 **local_scriptpubkey, u8 **remote_scriptpubkey, u64 *fee_negotiation_step, u8 *fee_negotiation_step_unit, bool *use_quickclose, bool *dev_fast_gossip, struct bitcoin_outpoint **shutdown_wrong_funding);
 
 /* WIRE: CLOSINGD_RECEIVED_SIGNATURE */
 /*  We received an offer */
@@ -56,4 +56,4 @@ bool fromwire_closingd_complete(const void *p);
 
 
 #endif /* LIGHTNING_CLOSINGD_CLOSINGD_WIREGEN_H */
-// SHA256STAMP:961ca5ceef03f911684ba0e7863d69993e692b9b418108e6038a567cb7cc7b3e
+// SHA256STAMP:b736e1d2c03a883962558ddcd5675d26cb09dcf3462c0cf82b3d49f1fd980c8a

doc/lightning-listconfigs.7

@@ -90,6 +90,8 @@ On success, an object is returned, containing:
 .IP \[bu]
 \fBexperimental-offers\fR (boolean, optional): \fBexperimental-offers\fR field from config or cmdline, or default
 .IP \[bu]
+\fBexperimental-quick-close\fR (boolean, optional): \fBexperimental-quick-close\fR field from config or cmdline, or default
+.IP \[bu]
 \fBexperimental-shutdown-wrong-funding\fR (boolean, optional): \fBexperimental-shutdown-wrong-funding\fR field from config or cmdline, or default
 .IP \[bu]
 \fBrgb\fR (hex, optional): \fBrgb\fR field from config or cmdline, or default (always 6 characters)
@@ -270,4 +272,4 @@ Vincenzo Palazzo \fI<vincenzo.palazzo@protonmail.com\fR> wrote the initial versi
 
 Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 
-\" SHA256STAMP:b6e48314de5642ec61a3e2c989ac0197630c2a3c0e8e6d86020b597679049400
+\" SHA256STAMP:fd8f2ae862627712b6baf51741670a6d60db8342f839580871617deed0c75317

doc/lightning-listconfigs.7.md

@@ -55,6 +55,7 @@ On success, an object is returned, containing:
 - **experimental-dual-fund** (boolean, optional): `experimental-dual-fund` field from config or cmdline, or default
 - **experimental-onion-messages** (boolean, optional): `experimental-onion-messages` field from config or cmdline, or default
 - **experimental-offers** (boolean, optional): `experimental-offers` field from config or cmdline, or default
+- **experimental-quick-close** (boolean, optional): `experimental-quick-close` field from config or cmdline, or default
 - **experimental-shutdown-wrong-funding** (boolean, optional): `experimental-shutdown-wrong-funding` field from config or cmdline, or default
 - **rgb** (hex, optional): `rgb` field from config or cmdline, or default (always 6 characters)
 - **alias** (string, optional): `alias` field from config or cmdline, or default
@@ -205,4 +206,4 @@ RESOURCES
 ---------
 
 Main web site: <https://github.com/ElementsProject/lightning>
-[comment]: # ( SHA256STAMP:7bb40fc8fac201b32d9701b02596d0fa59eb14a3baf606439cbf96dc11548ed4)
+[comment]: # ( SHA256STAMP:8b198154e70e1c0acb6c9ccdbe9e41e35ddab55738be9ea9076c5384da965cb8)

doc/lightningd-config.5

@@ -625,6 +625,16 @@ about whether to add funds or not to a proposed channel is handled
 automatically by a plugin that implements the appropriate logic for
 your needs\. The default behavior is to not contribute funds\.
 
+
+ \fBexperimental-quick-close\fR
+
+
+Specifying this means we send our range of acceptable fees to the peer
+on mutual close\.  If they support it too, we'll simply use that for
+closing (unless \fIfee_negotiation_step\fR is set, see \fBlightning-close\fR(7))\.
+We always use this on channels which negotiation \fBoption_anchor_outputs\fR,
+as the spec requires that\.
+
 .SH BUGS
 
 You should report bugs on our github issues page, and maybe submit a fix
@@ -650,4 +660,4 @@ Main web site: \fIhttps://github.com/ElementsProject/lightning\fR
 Note: the modules in the ccan/ directory have their own licenses, but
 the rest of the code is covered by the BSD-style MIT license\.
 
-\" SHA256STAMP:1c392f3fee66dc6c1fc2c34200204a9be1d79e53fd5fb1720ad169fc671f71c0
+\" SHA256STAMP:0d2474276b325cb002191211fb1d0da2409ebc859ff3ccc6dd3e688b10d4550c

doc/lightningd-config.5.md

@@ -517,6 +517,14 @@ about whether to add funds or not to a proposed channel is handled
 automatically by a plugin that implements the appropriate logic for
 your needs. The default behavior is to not contribute funds.
 
+ **experimental-quick-close**
+ 
+Specifying this means we send our range of acceptable fees to the peer
+on mutual close.  If they support it too, we'll simply use that for
+closing (unless *fee_negotiation_step* is set, see lightning-close(7)).
+We always use this on channels which negotiation `option_anchor_outputs`,
+as the spec requires that.
+
 BUGS
 ----
 

doc/schemas/listconfigs.schema.json

@@ -117,6 +117,10 @@
 	    "type": "boolean",
 	    "description": "`experimental-offers` field from config or cmdline, or default"
 	},
+	"experimental-quick-close": {
+	    "type": "boolean",
+	    "description": "`experimental-quick-close` field from config or cmdline, or default"
+	},
 	"experimental-shutdown-wrong-funding": {
 	    "type": "boolean",
 	    "description": "`experimental-shutdown-wrong-funding` field from config or cmdline, or default"

lightningd/closing_control.c

@@ -2,6 +2,7 @@
 #include <bitcoin/script.h>
 #include <closingd/closingd_wiregen.h>
 #include <common/close_tx.h>
+#include <common/closing_fee.h>
 #include <common/fee_states.h>
 #include <common/initial_commit_tx.h>
 #include <common/per_peer_state.h>
@@ -289,6 +290,12 @@ void peer_start_closingd(struct channel *channel,
 				       channel->shutdown_scriptpubkey[REMOTE],
 				       channel->closing_fee_negotiation_step,
 				       channel->closing_fee_negotiation_step_unit,
+				       (ld->use_quickclose
+					/* Don't quickclose if they specified how to negotiate! */
+					&& channel->closing_fee_negotiation_step == 50
+					&& channel->closing_fee_negotiation_step_unit == CLOSING_FEE_NEGOTIATION_STEP_UNIT_PERCENTAGE)
+				       /* Always use quickclose with anchors */
+				       || channel->option_anchor_outputs,
 				       IFDEV(ld->dev_fast_gossip, false),
 				       channel->shutdown_wrong_funding);
 

lightningd/lightningd.c

@@ -295,6 +295,11 @@ static struct lightningd *new_lightningd(const tal_t *ctx)
 	 * case this is a pointer to an enum feerate-indexed array of values */
 	ld->force_feerates = NULL;
 
+	/*~ We don't enable new network features until they've been approved
+	 * and tested in the spec (i.e. some other implementation has also
+	 * implemented and tested!).  Until then we use a flag: */
+	ld->use_quickclose = false;
+
 	return ld;
 }
 

lightningd/lightningd.h

@@ -283,6 +283,9 @@ struct lightningd {
 	/* Should we re-exec ourselves instead of just exiting? */
 	bool try_reexec;
 
+	/* --experimental-quick-close */
+	bool use_quickclose;
+
 	/* Array of (even) TLV types that we should allow. This is required
 	 * since we otherwise would outright reject them. */
 	u64 *accept_extra_tlv_types;

lightningd/options.c

@@ -1062,6 +1062,10 @@ static void register_opts(struct lightningd *ld)
 			 "--subdaemon=hsmd:remote_signer "
 			 "would use a hypothetical remote signing subdaemon.");
 
+	opt_register_noarg("--experimental-quick-close",
+			   opt_set_bool, &ld->use_quickclose,
+			   "EXPERIMENTAL: offer range to mutual close");
+
 	opt_register_logging(ld);
 	opt_register_version();
 

tests/test_closing.py

@@ -6,7 +6,7 @@ from pyln.testing.utils import SLOW_MACHINE
 from utils import (
     only_one, sync_blockheight, wait_for, TIMEOUT,
     account_balance, first_channel_id, closing_fee, TEST_NETWORK,
-    scriptpubkey_addr, calc_lease_fee
+    scriptpubkey_addr, calc_lease_fee, EXPERIMENTAL_FEATURES
 )
 
 import os
@@ -446,6 +446,7 @@ def closing_negotiation_step(node_factory, bitcoind, chainparams, opts):
     assert opts['expected_close_fee'] == fee_mempool
 
 
+@unittest.skipIf(EXPERIMENTAL_FEATURES, "anchors uses quick-close, not negotiation")
 def test_closing_negotiation_step_30pct(node_factory, bitcoind, chainparams):
     """Test that the closing fee negotiation step works, 30%"""
     opts = {}
@@ -460,6 +461,7 @@ def test_closing_negotiation_step_30pct(node_factory, bitcoind, chainparams):
     closing_negotiation_step(node_factory, bitcoind, chainparams, opts)
 
 
+@unittest.skipIf(EXPERIMENTAL_FEATURES, "anchors uses quick-close, not negotiation")
 def test_closing_negotiation_step_50pct(node_factory, bitcoind, chainparams):
     """Test that the closing fee negotiation step works, 50%, the default"""
     opts = {}
@@ -474,6 +476,7 @@ def test_closing_negotiation_step_50pct(node_factory, bitcoind, chainparams):
     closing_negotiation_step(node_factory, bitcoind, chainparams, opts)
 
 
+@unittest.skipIf(EXPERIMENTAL_FEATURES, "anchors uses quick-close, not negotiation")
 def test_closing_negotiation_step_100pct(node_factory, bitcoind, chainparams):
     """Test that the closing fee negotiation step works, 100%"""
     opts = {}
@@ -493,6 +496,7 @@ def test_closing_negotiation_step_100pct(node_factory, bitcoind, chainparams):
     closing_negotiation_step(node_factory, bitcoind, chainparams, opts)
 
 
+@unittest.skipIf(EXPERIMENTAL_FEATURES, "anchors uses quick-close, not negotiation")
 def test_closing_negotiation_step_1sat(node_factory, bitcoind, chainparams):
     """Test that the closing fee negotiation step works, 1sat"""
     opts = {}
@@ -507,6 +511,7 @@ def test_closing_negotiation_step_1sat(node_factory, bitcoind, chainparams):
     closing_negotiation_step(node_factory, bitcoind, chainparams, opts)
 
 
+@unittest.skipIf(EXPERIMENTAL_FEATURES, "anchors uses quick-close, not negotiation")
 def test_closing_negotiation_step_700sat(node_factory, bitcoind, chainparams):
     """Test that the closing fee negotiation step works, 700sat"""
     opts = {}

wallet/db_postgres_sqlgen.c

@@ -2074,4 +2074,4 @@ struct db_query db_postgres_queries[] = {
 
 #endif /* LIGHTNINGD_WALLET_GEN_DB_POSTGRES */
 
-// SHA256STAMP:219fccaaf2391eeabadd4cc15b4a3431c7ecab9d17755582e6962a34c74982c5
+// SHA256STAMP:56ce3adfaa2de5ef901e32e7f698b9500859a0015d869470ea1be779847b32e3

wallet/db_sqlite3_sqlgen.c

@@ -2074,4 +2074,4 @@ struct db_query db_sqlite3_queries[] = {
 
 #endif /* LIGHTNINGD_WALLET_GEN_DB_SQLITE3 */
 
-// SHA256STAMP:219fccaaf2391eeabadd4cc15b4a3431c7ecab9d17755582e6962a34c74982c5
+// SHA256STAMP:56ce3adfaa2de5ef901e32e7f698b9500859a0015d869470ea1be779847b32e3

wallet/statements_gettextgen.po

@@ -1369,4 +1369,4 @@ msgstr ""
 #: wallet/test/run-wallet.c:1753
 msgid "INSERT INTO channels (id) VALUES (1);"
 msgstr ""
-#  SHA256STAMP:d098fea63dcba84aefff5cf924cbc455caf9d2ec13cb28ad9ab929bb001a12e6
+#  SHA256STAMP:a433fb1866ae16a28b87177ef67fc99669c03a6cd47a0433e1460884367bbf34