core-lightning/lightningd/closing_control.c

#include <bitcoin/script.h>
#include <closingd/gen_closing_wire.h>
#include <common/close_tx.h>
#include <common/initial_commit_tx.h>
#include <common/utils.h>
#include <errno.h>
#include <inttypes.h>
#include <lightningd/chaintopology.h>
#include <lightningd/channel.h>
#include <lightningd/closing_control.h>
#include <lightningd/lightningd.h>
#include <lightningd/log.h>
#include <lightningd/options.h>
#include <lightningd/peer_control.h>
#include <lightningd/subd.h>

/* Is this better than the last tx we were holding?  This can happen
 * even without closingd misbehaving, if we have multiple,
 * interrupted, rounds of negotiation. */
static bool better_closing_fee(struct lightningd *ld,
			       struct channel *channel,
			       const struct bitcoin_tx *tx)
{
	u64 weight, fee, last_fee, ideal_fee, min_fee;
	s64 old_diff, new_diff;
	size_t i;

	/* Calculate actual fee (adds in eliminated outputs) */
	fee = channel->funding_satoshi;
	for (i = 0; i < tal_count(tx->output); i++)
		fee -= tx->output[i].amount;

	last_fee = channel->funding_satoshi;
	for (i = 0; i < tal_count(channel->last_tx); i++)
		last_fee -= channel->last_tx->output[i].amount;

	log_debug(channel->log, "Their actual closing tx fee is %"PRIu64
		 " vs previous %"PRIu64, fee, last_fee);

	/* Weight once we add in sigs. */
	weight = measure_tx_weight(tx) + 74 * 2;

	min_fee = get_feerate(ld->topology, FEERATE_SLOW) * weight / 1000;
	if (fee < min_fee) {
		log_debug(channel->log, "... That's below our min %"PRIu64
			 " for weight %"PRIu64" at feerate %u",
			 min_fee, weight,
			 get_feerate(ld->topology, FEERATE_SLOW));
		return false;
	}

	ideal_fee = get_feerate(ld->topology, FEERATE_NORMAL) * weight / 1000;

	/* We prefer fee which is closest to our ideal. */
	old_diff = imaxabs((s64)ideal_fee - (s64)last_fee);
	new_diff = imaxabs((s64)ideal_fee - (s64)fee);

	/* In case of a tie, prefer new over old: this covers the preference
	 * for a mutual close over a unilateral one. */
	log_debug(channel->log, "... That's %s our ideal %"PRIu64,
		 new_diff < old_diff
		 ? "closer to"
		 : new_diff > old_diff
		 ? "further from"
		 : "same distance to",
		 ideal_fee);

	return new_diff <= old_diff;
}

static void peer_received_closing_signature(struct channel *channel,
					    const u8 *msg)
{
	secp256k1_ecdsa_signature sig;
	struct bitcoin_tx *tx;
	struct lightningd *ld = channel->peer->ld;

	if (!fromwire_closing_received_signature(msg, msg, &sig, &tx)) {
		channel_internal_error(channel, "Bad closing_received_signature %s",
				       tal_hex(msg, msg));
		return;
	}

	/* FIXME: Make sure signature is correct! */
	if (better_closing_fee(ld, channel, tx)) {
		channel_set_last_tx(channel, tx, &sig);
		/* TODO(cdecker) Selectively save updated fields to DB */
		wallet_channel_save(ld->wallet, channel);
	}

	/* OK, you can continue now. */
	subd_send_msg(channel->owner,
		      take(towire_closing_received_signature_reply(channel)));
}

static void peer_closing_complete(struct channel *channel, const u8 *msg)
{
	/* FIXME: We should save this, to return to gossipd */
	u64 gossip_index;

	if (!fromwire_closing_complete(msg, &gossip_index)) {
		channel_internal_error(channel, "Bad closing_complete %s",
				       tal_hex(msg, msg));
		return;
	}

	/* Retransmission only, ignore closing. */
	if (channel->state == CLOSINGD_COMPLETE)
		return;

	drop_to_chain(channel->peer->ld, channel);
	channel_set_state(channel, CLOSINGD_SIGEXCHANGE, CLOSINGD_COMPLETE);
}

static unsigned closing_msg(struct subd *sd, const u8 *msg, const int *fds UNUSED)
{
	enum closing_wire_type t = fromwire_peektype(msg);

	switch (t) {
	case WIRE_CLOSING_RECEIVED_SIGNATURE:
		peer_received_closing_signature(sd->channel, msg);
		break;

	case WIRE_CLOSING_COMPLETE:
		peer_closing_complete(sd->channel, msg);
		break;

	/* We send these, not receive them */
	case WIRE_CLOSING_INIT:
	case WIRE_CLOSING_RECEIVED_SIGNATURE_REPLY:
		break;
	}

	return 0;
}

void peer_start_closingd(struct channel *channel,
			 struct crypto_state *cs,
			 u64 gossip_index,
			 int peer_fd, int gossip_fd,
			 bool reconnected)
{
	u8 *initmsg;
	u64 minfee, startfee, feelimit;
	u64 num_revocations;
	u64 funding_msatoshi, our_msatoshi, their_msatoshi;
	struct lightningd *ld = channel->peer->ld;

	if (!channel->remote_shutdown_scriptpubkey) {
		channel_internal_error(channel,
				       "Can't start closing: no remote info");
		return;
	}

	channel_set_owner(channel, new_channel_subd(ld,
					   "lightning_closingd",
					   channel, channel->log,
					   closing_wire_type_name, closing_msg,
					   channel_errmsg,
					   channel_set_billboard,
					   take(&peer_fd), take(&gossip_fd),
					   NULL));
	if (!channel->owner) {
		log_unusual(channel->log, "Could not subdaemon closing: %s",
			    strerror(errno));
		channel_fail_transient(channel, "Failed to subdaemon closing");
		return;
	}

	/* BOLT #2:
	 *
	 * A sending node MUST set `fee_satoshis` lower than or equal
	 * to the base fee of the final commitment transaction as
	 * calculated in [BOLT
	 * #3](03-transactions.md#fee-calculation).
	 */
	feelimit = commit_tx_base_fee(channel->channel_info.feerate_per_kw[LOCAL],
				      0);

	minfee = commit_tx_base_fee(get_feerate(ld->topology, FEERATE_SLOW), 0);
	startfee = commit_tx_base_fee(get_feerate(ld->topology, FEERATE_NORMAL),
				      0);

	if (startfee > feelimit)
		startfee = feelimit;
	if (minfee > feelimit)
		minfee = feelimit;

	num_revocations
		= revocations_received(&channel->their_shachain.chain);

	/* BOLT #3:
	 *
	 * The amounts for each output MUST BE rounded down to whole satoshis.
	 */
	/* Convert unit */
	funding_msatoshi = channel->funding_satoshi * 1000;
	/* What is not ours is theirs */
	our_msatoshi = channel->our_msatoshi;
	their_msatoshi = funding_msatoshi - our_msatoshi;
	initmsg = towire_closing_init(tmpctx,
				      cs,
				      gossip_index,
				      &channel->seed,
				      &channel->funding_txid,
				      channel->funding_outnum,
				      channel->funding_satoshi,
				      &channel->channel_info.remote_fundingkey,
				      channel->funder,
				      our_msatoshi / 1000, /* Rounds down */
				      their_msatoshi / 1000, /* Rounds down */
				      channel->our_config.dust_limit_satoshis,
				      minfee, feelimit, startfee,
				      p2wpkh_for_keyidx(tmpctx, ld,
							channel->final_key_idx),
				      channel->remote_shutdown_scriptpubkey,
				      reconnected,
				      channel->next_index[LOCAL],
				      channel->next_index[REMOTE],
				      num_revocations,
				      deprecated_apis);

	/* We don't expect a response: it will give us feedback on
	 * signatures sent and received, then closing_complete. */
	subd_send_msg(channel->owner, take(initmsg));
}