During the first pass of path finding, we seek a single path with the
exact payment amount, and only seek additional paths if (a) no single
path can carry the entire balance of the payment or (b) we found a good
path, but along the way we found candidate paths with the potential to
result in a lower total fee. This commit fixes the behavior of (b) -- we
were previously considering some paths to be candidates for a lower fee
when in fact they never would have worked. This caused us to re-run
Dijkstra's when it might not have been beneficial.
let over_path_minimum_msat = amount_to_transfer_over_msat >= $candidate.htlc_minimum_msat() &&
amount_to_transfer_over_msat >= $next_hops_path_htlc_minimum_msat;
let over_path_minimum_msat = amount_to_transfer_over_msat >= $candidate.htlc_minimum_msat() &&
amount_to_transfer_over_msat >= $next_hops_path_htlc_minimum_msat;
+ #[allow(unused_comparisons)] // $next_hops_path_htlc_minimum_msat is 0 in some calls so rustc complains
+ let may_overpay_to_meet_path_minimum_msat =
+ ((amount_to_transfer_over_msat < $candidate.htlc_minimum_msat() &&
+ recommended_value_msat > $candidate.htlc_minimum_msat()) ||
+ (amount_to_transfer_over_msat < $next_hops_path_htlc_minimum_msat &&
+ recommended_value_msat > $next_hops_path_htlc_minimum_msat));
+
// If HTLC minimum is larger than the amount we're going to transfer, we shouldn't
// If HTLC minimum is larger than the amount we're going to transfer, we shouldn't
- // bother considering this channel.
- // Since we're choosing amount_to_transfer_over_msat as maximum possible, it can
- // be only reduced later (not increased), so this channel should just be skipped
- // as not sufficient.
- if !over_path_minimum_msat && doesnt_exceed_cltv_delta_limit {
+ // bother considering this channel. If retrying with recommended_value_msat may
+ // allow us to hit the HTLC minimum limit, set htlc_minimum_limit so that we go
+ // around again with a higher amount.
+ if contributes_sufficient_value && doesnt_exceed_cltv_delta_limit && may_overpay_to_meet_path_minimum_msat {
hit_minimum_limit = true;
hit_minimum_limit = true;
- } else if contributes_sufficient_value && doesnt_exceed_cltv_delta_limit {
+ } else if contributes_sufficient_value && doesnt_exceed_cltv_delta_limit && over_path_minimum_msat {
// Note that low contribution here (limited by available_liquidity_msat)
// might violate htlc_minimum_msat on the hops which are next along the
// payment path (upstream to the payee). To avoid that, we recompute
// Note that low contribution here (limited by available_liquidity_msat)
// might violate htlc_minimum_msat on the hops which are next along the
// payment path (upstream to the payee). To avoid that, we recompute