Function get_htlc_success_fee

onchaind/onchaind.c:497–556

}

static struct amount_sat get_htlc_success_fee(struct tracked_output *out)
{
	static struct amount_sat fee = AMOUNT_SAT_INIT(UINT64_MAX);
	size_t weight;
	struct amount_msat htlc_amount;
	struct bitcoin_tx *tx;

	/* We only grind once, since they're all equiv. */
	if (!amount_sat_eq(fee, AMOUNT_SAT(UINT64_MAX)))
		return fee;

	if (option_anchors_zero_fee_htlc_tx) {
		fee = AMOUNT_SAT(0);
		return fee;
	}

	if (!amount_sat_to_msat(&htlc_amount, out->sat))
		status_failed(STATUS_FAIL_INTERNAL_ERROR,
			      "Overflow in get_htlc_success_fee %s",
			      fmt_amount_sat(tmpctx, out->sat));
	tx = htlc_success_tx(tmpctx, chainparams,
			     &out->outpoint,
			     out->wscript,
			     htlc_amount,
			     to_self_delay[LOCAL],
			     0,
			     keyset,
			     option_anchor_outputs,
			     option_anchors_zero_fee_htlc_tx);

	/* BOLT #3:
	 *
	 * The fee for an HTLC-success transaction:
	 * - If `option_anchors` applies:
	 *   1. MUST be 0.
	 * - Otherwise, MUST be calculated to match:
	 *   1. Multiply `feerate_per_kw` by 703 and divide by 1000 (rounding down).
	 */
	/* FIXME: Older bolt used to say (706 if `option_anchor_outputs` applies) */
	if (option_anchor_outputs)
		weight = 706;
	else
		weight = 703;

	weight += elements_tx_overhead(chainparams, 1, 1);
	if (!grind_htlc_tx_fee(&fee, tx, out->remote_htlc_sig,
			       out->wscript, weight)) {
		status_failed(STATUS_FAIL_INTERNAL_ERROR,
			      "htlc_success_fee can't be found "
			      "for tx %s (weight %zu, feerate %u-%u), signature %s, wscript %s",
			      fmt_bitcoin_tx(tmpctx, tx),
			      weight,
			      min_possible_feerate, max_possible_feerate,
			      fmt_bitcoin_signature(tmpctx,
					     out->remote_htlc_sig),
			      tal_hex(tmpctx, out->wscript));
	}