lightning/daemon/commit_tx.c

#include "bitcoin/locktime.h"
#include "bitcoin/pubkey.h"
#include "bitcoin/script.h"
#include "bitcoin/shadouble.h"
#include "bitcoin/tx.h"
#include "channel.h"
#include "commit_tx.h"
#include "htlc.h"
#include "lightningd.h"
#include "overflows.h"
#include "peer.h"
#include "permute_tx.h"
#include "remove_dust.h"
#include <assert.h>

u8 *wscript_for_htlc(const tal_t *ctx,
		     const struct peer *peer,
		     const struct htlc *h,
		     const struct sha256 *rhash,
		     enum htlc_side side)
{
	const struct peer_visible_state *this_side, *other_side;
	u8 *(*fn)(const tal_t *, secp256k1_context *,
		  const struct pubkey *, const struct pubkey *,
		  const struct abs_locktime *, const struct rel_locktime *,
		  const struct sha256 *, const struct sha256 *);

	/* scripts are different for htlcs offered vs accepted */
	if (side == htlc_owner(h))
		fn = bitcoin_redeem_htlc_send;
	else
		fn = bitcoin_redeem_htlc_recv;

	if (side == LOCAL) {
		this_side = &peer->local;
		other_side = &peer->remote;
	} else {
		this_side = &peer->remote;
		other_side = &peer->local;
	}

	return fn(ctx, peer->dstate->secpctx,
		  &this_side->finalkey, &other_side->finalkey,
		  &h->expiry, &this_side->locktime, rhash, &h->rhash);
}

static size_t count_htlcs(const struct htlc_map *htlcs, int flag)
{
	struct htlc_map_iter it;
	struct htlc *h;
	size_t n = 0;

	for (h = htlc_map_first(htlcs, &it); h; h = htlc_map_next(htlcs, &it)) {
		if (htlc_has(h, flag))
			n++;
	}
	return n;
}

u8 *commit_output_to_us(const tal_t *ctx,
			const struct peer *peer,
			const struct sha256 *rhash,
			enum htlc_side side,
			u8 **wscript)
{
	u8 *tmp;
	if (!wscript)
		wscript = &tmp;
	
	/* Our output to ourself is encumbered by delay. */
	if (side == LOCAL) {
		*wscript = bitcoin_redeem_secret_or_delay(ctx,
							  peer->dstate->secpctx,
							  &peer->local.finalkey,
							  &peer->remote.locktime,
							  &peer->remote.finalkey,
							  rhash);
		return scriptpubkey_p2wsh(ctx, *wscript);
	} else {
		/* Their output to us is a simple p2wpkh */
		*wscript = NULL;
		return scriptpubkey_p2wpkh(ctx, peer->dstate->secpctx,
					   &peer->local.finalkey);
	}
}

u8 *commit_output_to_them(const tal_t *ctx,
			  const struct peer *peer,
			  const struct sha256 *rhash,
			  enum htlc_side side,
			  u8 **wscript)
{
	u8 *tmp;
	if (!wscript)
		wscript = &tmp;

	/* Their output to themselves is encumbered by delay. */
	if (side == REMOTE) {
		*wscript = bitcoin_redeem_secret_or_delay(ctx,
							  peer->dstate->secpctx,
							  &peer->remote.finalkey,
							  &peer->local.locktime,
							  &peer->local.finalkey,
							  rhash);
		return scriptpubkey_p2wsh(ctx, *wscript);
	} else {
		/* Our output to them is a simple p2wpkh */
		*wscript = NULL;
		return scriptpubkey_p2wpkh(ctx, peer->dstate->secpctx,
					   &peer->remote.finalkey);
	}
}

static bool add_output(struct bitcoin_tx *tx, u8 *script, u64 amount,
		       u64 *total)
{
	assert(tx->output_count < tal_count(tx->output));
	if (is_dust(amount))
		return false;
	tx->output[tx->output_count].script = script;
	tx->output[tx->output_count].script_length = tal_count(script);
	tx->output[tx->output_count].amount = amount;
	tx->output_count++;
	(*total) += amount;
	return true;
}

struct bitcoin_tx *create_commit_tx(const tal_t *ctx,
				    struct peer *peer,
				    const struct sha256 *rhash,
				    const struct channel_state *cstate,
				    enum htlc_side side,
				    bool *otherside_only)
{
	struct bitcoin_tx *tx;
	uint64_t total = 0;
	struct htlc_map_iter it;
	struct htlc *h;
	bool pays_to[2];
	int committed_flag = HTLC_FLAG(side,HTLC_F_COMMITTED);

	/* Now create commitment tx: one input, two outputs (plus htlcs) */
	tx = bitcoin_tx(ctx, 1, 2 + count_htlcs(&peer->htlcs, committed_flag));

	/* Our input spends the anchor tx output. */
	tx->input[0].txid = peer->anchor.txid;
	tx->input[0].index = peer->anchor.index;
	tx->input[0].amount = tal_dup(tx->input, u64, &peer->anchor.satoshis);

	tx->output_count = 0;
	pays_to[LOCAL] = add_output(tx, commit_output_to_us(tx, peer, rhash,
							    side, NULL),
				    cstate->side[OURS].pay_msat / 1000,
				    &total);
	pays_to[REMOTE] = add_output(tx, commit_output_to_them(tx, peer, rhash,
							       side, NULL),
				     cstate->side[THEIRS].pay_msat / 1000,
				     &total);

	/* If their tx doesn't pay to them, or our tx doesn't pay to us... */
	*otherside_only = !pays_to[side];

	/* First two outputs done, now for the HTLCs. */
	for (h = htlc_map_first(&peer->htlcs, &it);
	     h;
	     h = htlc_map_next(&peer->htlcs, &it)) {
		const u8 *wscript;

		if (!htlc_has(h, committed_flag))
			continue;
		wscript = wscript_for_htlc(tx, peer, h, rhash, side);
		/* If we pay any HTLC, it's txout is not just to other side. */
		if (add_output(tx, scriptpubkey_p2wsh(tx, wscript),
			       h->msatoshis / 1000, &total))
			*otherside_only = false;
	}
	assert(total <= peer->anchor.satoshis);

	permute_outputs(tx->output, tx->output_count);
	return tx;
}