/// The maximum number of paths that may be used by (MPP) payments.
/// Defaults to [`DEFAULT_MAX_PATH_COUNT`].
pub max_path_count: u8,
+
+ /// Selects the maximum share of a channel's total capacity which will be sent over a channel,
+ /// as a power of 1/2. A higher value prefers to send the payment using more MPP parts whereas
+ /// a lower value prefers to send larger MPP parts, potentially saturating channels and
+ /// increasing failure probability for those paths.
+ ///
+ /// A value of 0 will allow payments up to and including a channel's total announced usable
+ /// capacity, a value of one will only use up to half its capacity, two 1/4, etc.
+ ///
+ /// Default value: 1
+ pub max_channel_saturation_power_of_half: u8,
}
impl_writeable_tlv_based!(PaymentParameters, {
(2, features, option),
(3, max_path_count, (default_value, DEFAULT_MAX_PATH_COUNT)),
(4, route_hints, vec_type),
+ (5, max_channel_saturation_power_of_half, (default_value, 1)),
(6, expiry_time, option),
});
expiry_time: None,
max_total_cltv_expiry_delta: DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA,
max_path_count: DEFAULT_MAX_PATH_COUNT,
+ #[cfg(test)] // Many tests were written prior to the introduction of this parameter, so
+ // we leave it as 0 by default in tests, and change it for a few.
+ max_channel_saturation_power_of_half: 0,
+ #[cfg(not(test))]
+ max_channel_saturation_power_of_half: 1,
}
}
}
}
- fn htlc_maximum_msat(&self) -> u64 {
- match self {
- CandidateRouteHop::FirstHop { details } => details.next_outbound_htlc_limit_msat,
- CandidateRouteHop::PublicHop { info, .. } => info.htlc_maximum_msat(),
- CandidateRouteHop::PrivateHop { hint } => {
- hint.htlc_maximum_msat.unwrap_or(u64::max_value())
- },
- }
- }
-
fn fees(&self) -> RoutingFees {
match self {
CandidateRouteHop::FirstHop { .. } => RoutingFees {
}
}
+#[inline]
+fn max_htlc_from_capacity(capacity: EffectiveCapacity, max_channel_saturation_power_of_half: u8) -> u64 {
+ let saturation_shift: u32 = max_channel_saturation_power_of_half as u32;
+ match capacity {
+ EffectiveCapacity::ExactLiquidity { liquidity_msat } => liquidity_msat,
+ EffectiveCapacity::Infinite => u64::max_value(),
+ EffectiveCapacity::Unknown => EffectiveCapacity::Unknown.as_msat(),
+ EffectiveCapacity::MaximumHTLC { amount_msat } =>
+ amount_msat.checked_shr(saturation_shift).unwrap_or(0),
+ EffectiveCapacity::Total { capacity_msat, htlc_maximum_msat: None } =>
+ capacity_msat.checked_shr(saturation_shift).unwrap_or(0),
+ EffectiveCapacity::Total { capacity_msat, htlc_maximum_msat: Some(htlc_max) } =>
+ cmp::min(capacity_msat.checked_shr(saturation_shift).unwrap_or(0), htlc_max),
+ }
+}
+
/// It's useful to keep track of the hops associated with the fees required to use them,
/// so that we can choose cheaper paths (as per Dijkstra's algorithm).
/// Fee values should be updated only in the context of the whole path, see update_value_and_recompute_fees.
// - for first and last hops early in get_route
if $src_node_id != $dest_node_id {
let short_channel_id = $candidate.short_channel_id();
- let htlc_maximum_msat = $candidate.htlc_maximum_msat();
+ let effective_capacity = $candidate.effective_capacity();
+ let htlc_maximum_msat = max_htlc_from_capacity(effective_capacity, payment_params.max_channel_saturation_power_of_half);
// It is tricky to subtract $next_hops_fee_msat from available liquidity here.
// It may be misleading because we might later choose to reduce the value transferred
let channel_usage = ChannelUsage {
amount_msat: amount_to_transfer_over_msat,
inflight_htlc_msat: used_liquidity_msat,
- effective_capacity: $candidate.effective_capacity(),
+ effective_capacity,
};
let channel_penalty_msat = scorer.channel_penalty_msat(
short_channel_id, &$src_node_id, &$dest_node_id, channel_usage
.entry((hop.candidate.short_channel_id(), *prev_hop < hop.node_id))
.and_modify(|used_liquidity_msat| *used_liquidity_msat += spent_on_hop_msat)
.or_insert(spent_on_hop_msat);
- if *used_liquidity_msat == hop.candidate.htlc_maximum_msat() {
+ let hop_capacity = hop.candidate.effective_capacity();
+ let hop_max_msat = max_htlc_from_capacity(hop_capacity,
+ payment_params.max_channel_saturation_power_of_half);
+ if *used_liquidity_msat == hop_max_msat {
// If this path used all of this channel's available liquidity, we know
// this path will not be selected again in the next loop iteration.
prevented_redundant_path_selection = true;
}
- debug_assert!(*used_liquidity_msat <= hop.candidate.htlc_maximum_msat());
+ debug_assert!(*used_liquidity_msat <= hop_max_msat);
}
if !prevented_redundant_path_selection {
// If we weren't capped by hitting a liquidity limit on a channel in the path,
projects / rust-lightning / blobdiff