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Don't consider a path as having hit HTLC-min if it isn't sufficient

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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.
This commit is contained in:
Matt Corallo 2022-03-24 18:38:43 +00:00 • committed by Jeffrey Czyz
parent f9cdf93da0
commit 8ddfe66046
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1 changed files with 12 additions and 6 deletions
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18
lightning/src/routing/router.rs
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@ -916,14 +916,20 @@ where L::Target: Logger {
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
// 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;
} 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