core-lightning/lightningd/htlc_tx.c

#include <bitcoin/preimage.h>
#include <bitcoin/script.h>
#include <bitcoin/tx.h>
#include <lightningd/commit_tx.h>
#include <lightningd/htlc_tx.h>

static struct bitcoin_tx *htlc_tx(const tal_t *ctx,
				  const struct sha256_double *commit_txid,
				  unsigned int commit_output_number,
				  const struct htlc *htlc,
				  u16 to_self_delay,
				  const struct pubkey *revocation_pubkey,
				  const struct pubkey *local_delayedkey,
				  u64 htlc_fee_satoshi,
				  u32 locktime)
{
	struct bitcoin_tx *tx = bitcoin_tx(ctx, 1, 1);
	u8 *wscript;
	u64 amount;

	/* BOLT #3:
	 *
	 * ## HTLC-Timeout and HTLC-Success Transactions
	 *
	 * These HTLC transactions are almost identical, except the
	 * HTLC-Timeout transaction is timelocked.  This is also the
	 * transaction which can be spent by a valid penalty transaction.
	 */

	/* BOLT #3:
	 * * version: 2
	 */
	assert(tx->version == 2);

	/* BOLT #3:
	 * * locktime: `0` for HTLC-Success, `htlc-timeout` for HTLC-Timeout.
	 */
	tx->lock_time = locktime;

	/* BOLT #3:
	 * * txin count: 1
	 *    * `txin[0]` outpoint: `txid` of the commitment transaction and
	 *      `output_index` of the matching HTLC output for the HTLC
	 *      transaction.
	 */
	tx->input[0].txid = *commit_txid;
	tx->input[0].index = commit_output_number;

	/* We need amount for signing. */
	amount = htlc->msatoshi / 1000;
	tx->input[0].amount = tal_dup(tx, u64, &amount);

	/* BOLT #3:
	 *    * `txin[0]` sequence: `0`
	 */
	tx->input[0].sequence_number = 0;

	/* BOLT #3:
	 * * txout count: 1
	 *    * `txout[0]` amount: the HTLC amount minus fees
	 *       (see [Fee Calculation](#fee-calculation)).
	 *    * `txout[0]` script: version 0 P2WSH with witness script as shown
	 *       below.
	 */
	tx->output[0].amount = amount - htlc_fee_satoshi;
	wscript = bitcoin_wscript_htlc_tx(tx, to_self_delay,
					  revocation_pubkey, local_delayedkey);
	tx->output[0].script = scriptpubkey_p2wsh(tx, wscript);
	tal_free(wscript);

	return tx;
}

struct bitcoin_tx *htlc_success_tx(const tal_t *ctx,
				   const struct sha256_double *commit_txid,
				   unsigned int commit_output_number,
				   const struct htlc *received_htlc,
				   u16 to_self_delay,
				   const struct pubkey *revocation_pubkey,
				   const struct pubkey *local_delayedkey,
				   u64 feerate_per_kw)
{
	/* BOLT #3:
	 * * locktime: `0` for HTLC-Success, `htlc-timeout` for HTLC-Timeout.
	 */
	return htlc_tx(ctx, commit_txid, commit_output_number, received_htlc,
		       to_self_delay, revocation_pubkey, local_delayedkey,
		       htlc_success_fee(feerate_per_kw), 0);
}

/* Fill in the witness for HTLC-success tx produced above. */
void htlc_success_tx_add_witness(struct bitcoin_tx *htlc_success,
				 const struct abs_locktime *htlc_abstimeout,
				 const struct pubkey *localkey,
				 const struct pubkey *remotekey,
				 const secp256k1_ecdsa_signature *localsig,
				 const secp256k1_ecdsa_signature *remotesig,
				 const struct preimage *payment_preimage,
				 const struct pubkey *revocationkey)
{
	struct sha256 hash;
	u8 *wscript;

	sha256(&hash, payment_preimage, sizeof(*payment_preimage));
	wscript = bitcoin_wscript_htlc_receive(htlc_success,
					       htlc_abstimeout,
					       localkey, remotekey,
					       &hash, revocationkey);

	htlc_success->input[0].witness
		= bitcoin_htlc_receive_spend_preimage(htlc_success->input,
						      localsig, remotesig,
						      payment_preimage,
						      wscript);
	tal_free(wscript);
}

struct bitcoin_tx *htlc_timeout_tx(const tal_t *ctx,
				   const struct sha256_double *commit_txid,
				   unsigned int commit_output_number,
				   const struct htlc *offered_htlc,
				   u16 to_self_delay,
				   const struct pubkey *revocation_pubkey,
				   const struct pubkey *local_delayedkey,
				   u64 feerate_per_kw)
{
	/* BOLT #3:
	 * * locktime: `0` for HTLC-Success, `htlc-timeout` for HTLC-Timeout.
	 */
	return htlc_tx(ctx, commit_txid, commit_output_number, offered_htlc,
		       to_self_delay, revocation_pubkey, local_delayedkey,
		       htlc_timeout_fee(feerate_per_kw),
		       offered_htlc->expiry.locktime);
}

/* Fill in the witness for HTLC-timeout tx produced above. */
void htlc_timeout_tx_add_witness(struct bitcoin_tx *htlc_timeout,
				 const struct pubkey *localkey,
				 const struct pubkey *remotekey,
				 const struct sha256 *payment_hash,
				 const struct pubkey *revocationkey,
				 const secp256k1_ecdsa_signature *localsig,
				 const secp256k1_ecdsa_signature *remotesig)
{
	u8 *wscript = bitcoin_wscript_htlc_offer(htlc_timeout,
						 localkey, remotekey,
						 payment_hash, revocationkey);

	htlc_timeout->input[0].witness
		= bitcoin_htlc_offer_spend_timeout(htlc_timeout->input,
						   localsig, remotesig,
						   wscript);
	tal_free(wscript);
}