Function calc_maxfee

plugins/xpay/xpay.c:3294–3372

xpay doesn't have maxfeepercent or exemptfee, so we convert them to * an absolute restriction here. If we can't, fail and let pay handle * it. */

 * an absolute restriction here.  If we can't, fail and let pay handle
 * it. */
static bool calc_maxfee(struct command *cmd,
			const char **maxfeestr,
			const char *buf,
			const jsmntok_t *invstringtok,
			const jsmntok_t *amount_msattok,
			const jsmntok_t *exemptfeetok,
			const jsmntok_t *maxfeepercenttok)
{
	u64 maxfeepercent_ppm;
	struct amount_msat amount, maxfee, exemptfee;

	if (!exemptfeetok && !maxfeepercenttok)
		return true;

	/* Can't have both */
	if (*maxfeestr)
		return false;

	/* If they specify amount easy, otherwise take from invoice */
	if (amount_msattok) {
		if (!parse_amount_msat(&amount, buf + amount_msattok->start,
				       amount_msattok->end - amount_msattok->start))
			return false;
	} else {
		const struct bolt11 *b11;
		const char *invstr, *fail;

		/* We need to know total amount to calc fee */
		if (!invstringtok)
			return false;

		invstr = json_strdup(tmpctx, buf, invstringtok);
		b11 = bolt11_decode(tmpctx, invstr, NULL, NULL, NULL, &fail);
		if (b11 != NULL) {
			if (b11->msat == NULL)
				return false;
			amount = *b11->msat;
		} else {
			const struct tlv_invoice *b12;
			b12 = invoice_decode(tmpctx, invstr, strlen(invstr),
					     NULL, NULL, &fail);
			if (b12 == NULL || b12->invoice_amount == NULL)
				return false;
			amount = amount_msat(*b12->invoice_amount);
		}
	}

	if (maxfeepercenttok) {
		if (!json_to_millionths(buf,
					maxfeepercenttok,
					&maxfeepercent_ppm))
			return false;
	} else
		maxfeepercent_ppm = 500000;

	if (!amount_msat_fee(&maxfee, amount, 0, maxfeepercent_ppm / 100))
		return false;