Function sign_last_tx

lightningd/peer_control.c:239–272

BOLT #2: * A node: * - MUST NOT broadcast old (revoked) commitment transactions, * - Note: doing so will allow the other node to seize all channel funds. * - SHOULD NOT sign commitment transactions, unless it's about to broadcast * them (due to a failed connection), * - Note: this is to reduce the above risk. */

 *     - Note: this is to reduce the above risk.
 */
static struct bitcoin_tx *sign_last_tx(const tal_t *ctx,
				       const struct channel *channel,
				       const struct bitcoin_tx *last_tx,
				       const struct bitcoin_signature *last_sig)
{
	struct lightningd *ld = channel->peer->ld;
	struct bitcoin_signature sig;
	const u8 *msg;
	u8 **witness;
	u64 commit_index = channel->next_index[LOCAL] - 1;
	struct bitcoin_tx *tx = clone_bitcoin_tx(ctx, last_tx);

	assert(!tx->wtx->inputs[0].witness);
	msg = towire_hsmd_sign_commitment_tx(NULL,
					     &channel->peer->id,
					     channel->dbid,
					     tx,
					     &channel->channel_info
					     .remote_fundingkey,
					     commit_index);

	msg = hsm_sync_req(tmpctx, ld, take(msg));
	if (!fromwire_hsmd_sign_commitment_tx_reply(msg, &sig))
		fatal("HSM gave bad sign_commitment_tx_reply %s",
		      tal_hex(tmpctx, msg));

	witness =
	    bitcoin_witness_2of2(tx, last_sig,
				 &sig, &channel->channel_info.remote_fundingkey,
				 &channel->local_funding_pubkey);

	bitcoin_tx_input_set_witness(tx, 0, take(witness));
	return tx;
}

bool invalid_last_tx(const struct bitcoin_tx *tx)
{