Function grind_htlc_tx_fee

onchaind/onchaind.c:425–476

We vary feerate until signature they offered matches. */

/* We vary feerate until signature they offered matches. */
static bool grind_htlc_tx_fee(struct amount_sat *fee,
			      struct bitcoin_tx *tx,
			      const struct bitcoin_signature *remotesig,
			      const u8 *wscript,
			      u64 weight)
{
	struct amount_sat prev_fee = AMOUNT_SAT(UINT64_MAX), input_amt;
	input_amt = psbt_input_get_amount(tx->psbt, 0);

	for (u64 i = min_possible_feerate; i <= max_possible_feerate; i++) {
		/* BOLT #3:
		 *
		 * The fee for an HTLC-timeout transaction:
		 *   - If `option_anchors_zero_fee_htlc_tx` applies:
		 *     1. MUST be 0.
		 *   - Otherwise, MUST be calculated to match:
		 *     1. Multiply `feerate_per_kw` by 663
		 *        (666 if `option_anchor_outputs` applies)
		 *        and divide by 1000 (rounding down).
		 *
		 * The fee for an HTLC-success transaction:
		 *  - If `option_anchors_zero_fee_htlc_tx` applies:
		 *    1. MUST be 0.
		 *  - Otherwise, MUST be calculated to match:
		 *     1. Multiply `feerate_per_kw` by 703
		 *        (706 if `option_anchor_outputs` applies)
		 *        and divide by 1000 (rounding down).
		 */
		struct amount_sat out;

		*fee = amount_tx_fee(i, weight);

		/* Minor optimization: don't check same fee twice */
		if (amount_sat_eq(*fee, prev_fee))
			continue;

		prev_fee = *fee;
		if (!amount_sat_sub(&out, input_amt, *fee))
			break;

		bitcoin_tx_output_set_amount(tx, 0, out);
		bitcoin_tx_finalize(tx);
		if (!check_tx_sig(tx, 0, NULL, wscript,
				  &keyset->other_htlc_key, remotesig))
			continue;

		status_debug("grind feerate_per_kw for %"PRIu64" = %"PRIu64,
			     weight, i);
		return true;
	}
	return false;
}

static bool set_htlc_timeout_fee(struct bitcoin_tx *tx,
				 const struct bitcoin_signature *remotesig,