Function trim_maximum_feerate

onchaind/onchaind.c:167–211

The feerate for the HTLC txs (which we grind) are the same as the * feerate for the main tx. However, there may be dust HTLCs which * were added to the fee, so we can only estimate a maximum feerate */

 * feerate for the main tx.  However, there may be dust HTLCs which
 * were added to the fee, so we can only estimate a maximum feerate */
static void trim_maximum_feerate(struct amount_sat funding,
				 const struct tx_parts *commitment)
{
	size_t weight;
	struct amount_sat fee = funding;

	/* FIXME: This doesn't work for elements? */
	if (chainparams->is_elements)
		return;

	weight = bitcoin_tx_core_weight(tal_count(commitment->inputs),
					tal_count(commitment->outputs));

	/* BOLT #3:
	 * ## Commitment Transaction
	 *...
	 *   * `txin[0]` script bytes: 0
	 *   * `txin[0]` witness: `0 <signature_for_pubkey1> <signature_for_pubkey2>`
	 */
	/* Account for witness (1 empty + sig + sig) */
	assert(tal_count(commitment->inputs) == 1);
	weight += bitcoin_tx_input_weight(false, 1 + 2 * bitcoin_tx_input_sig_weight());

	for (size_t i = 0; i < tal_count(commitment->outputs); i++) {
		struct amount_asset amt;
		weight += bitcoin_tx_output_weight(commitment->outputs[i]
						   ->script_len);

		amt = wally_tx_output_get_amount(commitment->outputs[i]);
		if (!amount_asset_is_main(&amt))
			continue;
		if (!amount_sat_sub(&fee, fee, amount_asset_to_sat(&amt))) {
			status_failed(STATUS_FAIL_INTERNAL_ERROR,
				      "Unable to subtract fee");
		}
	}

	status_debug("reducing max_possible_feerate from %u...",
		     max_possible_feerate);
	/* This is naive, but simple. */
	while (amount_sat_greater(amount_tx_fee(max_possible_feerate, weight),
				  fee))
		max_possible_feerate--;
	status_debug("... to %u", max_possible_feerate);
}

static void send_coin_mvt(struct chain_coin_mvt *mvt TAKES)
{