Function presplit_cb

plugins/libplugin-pay.c:3530–3654

}

static void presplit_cb(struct presplit_mod_data *d, struct payment *p)
{
	struct payment *root = payment_root(p);

	if (d->disable || p->parent != NULL || !payment_supports_mpp(p))
		return payment_continue(p);

	if (p->step == PAYMENT_STEP_ONION_PAYLOAD) {
		/* We need to tell the last hop the total we're going to
		 * send. Presplit disables amount fuzzing, so we should always
		 * get the exact value through. */
		size_t lastidx = tal_count(p->createonion_request->hops) - 1;
		struct createonion_hop *hop = &p->createonion_request->hops[lastidx];
		struct tlv_field **fields = &hop->tlv_payload->fields;
		tlvstream_set_tlv_payload_data(
			    fields, root->payment_secret,
			    root->amount.millisatoshis); /* Raw: onion payload */
	} else if (p->step == PAYMENT_STEP_INITIALIZED) {
		/* The presplitter only acts on the root and only in the first
		 * step. */
		size_t count = 0;
		u32 htlcs;
		struct amount_msat target, amt = p->amount;
		char *partids = tal_strdup(tmpctx, "");
		u64 target_amount = MPP_TARGET_SIZE;

		/* We aim for at most PRESPLIT_MAX_SPLITS parts, even for
		 * large values. To achieve this we take the base amount and
		 * multiply it by the number of targetted parts until the
		 * total amount divided by part amount gives us at most that
		 * number of parts. */
		while (amount_msat_less(amount_msat(target_amount * PRESPLIT_MAX_SPLITS),
					p->amount))
			target_amount *= PRESPLIT_MAX_SPLITS;

		/* We need to opt-in to the MPP sending facility no matter
		 * what we do. That means setting all partids to a non-zero
		 * value. */
		root->partid++;

		/* Bump the next_partid as well so we don't have duplicate
		 * partids. Not really necessary since the root payment whose
		 * id could be reused will never reach the `sendonion` step,
		 * but makes debugging a bit easier. */
		root->next_partid++;

		htlcs = payment_max_htlcs(p);
		/* Divide it up if we can, but it might be v low already */
		if (htlcs >= PRESPLIT_MAX_HTLC_SHARE)
			htlcs /= PRESPLIT_MAX_HTLC_SHARE;

		int targethtlcs =
		    p->amount.millisatoshis / target_amount; /* Raw: division */
		if (htlcs == 0) {
			p->abort = true;
			return payment_fail(
			    p, "Cannot attempt payment, we have no channel to "
			       "which we can add an HTLC");