/// Maximum total CTLV difference we allow for a full payment path.
pub const DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA: u32 = 1008;
+/// Maximum number of paths we allow an MPP payment to have.
+// The default limit is currently set rather arbitrary - there aren't any real fundamental path-count
+// limits, but for now more than 10 paths likely carries too much one-path failure.
+pub const DEFAULT_MAX_MPP_PATH_COUNT: u8 = 10;
+
// The median hop CLTV expiry delta currently seen in the network.
const MEDIAN_HOP_CLTV_EXPIRY_DELTA: u32 = 40;
pub expiry_time: Option<u64>,
/// The maximum total CLTV delta we accept for the route.
+ /// Defaults to [`DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA`].
pub max_total_cltv_expiry_delta: u32,
+
+ /// The maximum number of paths that may be used by MPP payments.
+ /// Defaults to [`DEFAULT_MAX_MPP_PATH_COUNT`].
+ pub max_mpp_path_count: u8,
}
impl_writeable_tlv_based!(PaymentParameters, {
(0, payee_pubkey, required),
(1, max_total_cltv_expiry_delta, (default_value, DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA)),
(2, features, option),
+ (3, max_mpp_path_count, (default_value, DEFAULT_MAX_MPP_PATH_COUNT)),
(4, route_hints, vec_type),
(6, expiry_time, option),
});
route_hints: vec![],
expiry_time: None,
max_total_cltv_expiry_delta: DEFAULT_MAX_TOTAL_CLTV_EXPIRY_DELTA,
+ max_mpp_path_count: DEFAULT_MAX_MPP_PATH_COUNT,
}
}
pub fn with_max_total_cltv_expiry_delta(self, max_total_cltv_expiry_delta: u32) -> Self {
Self { max_total_cltv_expiry_delta, ..self }
}
+
+ /// Includes a limit for the maximum number of payment paths that may be used by MPP.
+ ///
+ /// (C-not exported) since bindings don't support move semantics
+ pub fn with_max_mpp_path_count(self, max_mpp_path_count: u8) -> Self {
+ Self { max_mpp_path_count, ..self }
+ }
}
/// A list of hops along a payment path terminating with a channel to the recipient.
node_info.features.supports_basic_mpp()
} else { false }
} else { false };
+
+ if allow_mpp && payment_params.max_mpp_path_count == 0 {
+ return Err(LightningError{err: "Can't find an MPP route with no paths allowed.".to_owned(), action: ErrorAction::IgnoreError});
+ }
+
log_trace!(logger, "Searching for a route from payer {} to payee {} {} MPP and {} first hops {}overriding the network graph", our_node_pubkey,
payment_params.payee_pubkey, if allow_mpp { "with" } else { "without" },
first_hops.map(|hops| hops.len()).unwrap_or(0), if first_hops.is_some() { "" } else { "not " });
let recommended_value_msat = final_value_msat * ROUTE_CAPACITY_PROVISION_FACTOR as u64;
let mut path_value_msat = final_value_msat;
+ // Routing Fragmentation Mitigation heuristic:
+ //
+ // Routing fragmentation across many payment paths increases the overall routing
+ // fees as you have irreducible routing fees per-link used (`fee_base_msat`).
+ // Taking too many smaller paths also increases the chance of payment failure.
+ // Thus to avoid this effect, we require from our collected links to provide
+ // at least a minimal contribution to the recommended value yet-to-be-fulfilled.
+ // This requirement is currently set to be 1/max_mpp_path_count of the payment
+ // value to ensure we only ever return routes that do not violate this limit.
+ let minimal_value_contribution_msat: u64 = if allow_mpp {
+ (final_value_msat + (payment_params.max_mpp_path_count as u64 - 1)) / payment_params.max_mpp_path_count as u64
+ } else {
+ final_value_msat
+ };
+
// Keep track of how much liquidity has been used in selected channels. Used to determine
// if the channel can be used by additional MPP paths or to inform path finding decisions. It is
// aware of direction *only* to ensure that the correct htlc_maximum_msat value is used. Hence,
let mut used_channel_liquidities: HashMap<(u64, bool), u64> =
HashMap::with_capacity(network_nodes.len());
- // Keeping track of how much value we already collected across other paths. Helps to decide:
- // - how much a new path should be transferring (upper bound);
- // - whether a channel should be disregarded because
- // it's available liquidity is too small comparing to how much more we need to collect;
- // - when we want to stop looking for new paths.
+ // Keeping track of how much value we already collected across other paths. Helps to decide
+ // when we want to stop looking for new paths.
let mut already_collected_value_msat = 0;
for (_, channels) in first_hop_targets.iter_mut() {
*used_liquidity_msat
});
- // Routing Fragmentation Mitigation heuristic:
- //
- // Routing fragmentation across many payment paths increases the overall routing
- // fees as you have irreducible routing fees per-link used (`fee_base_msat`).
- // Taking too many smaller paths also increases the chance of payment failure.
- // Thus to avoid this effect, we require from our collected links to provide
- // at least a minimal contribution to the recommended value yet-to-be-fulfilled.
- //
- // This requirement is currently 5% of the remaining-to-be-collected value.
- // This means as we successfully advance in our collection,
- // the absolute liquidity contribution is lowered,
- // thus increasing the number of potential channels to be selected.
-
- // Derive the minimal liquidity contribution with a ratio of 20 (5%, rounded up)
- // or 100% if we're not allowed to do multipath payments.
- let minimal_value_contribution_msat: u64 = if allow_mpp {
- (recommended_value_msat - already_collected_value_msat + 19) / 20
- } else {
- final_value_msat
- };
// Verify the liquidity offered by this channel complies to the minimal contribution.
let contributes_sufficient_value = available_value_contribution_msat >= minimal_value_contribution_msat;
// Do not consider candidate hops that would exceed the maximum path length.
*used_channel_liquidities.entry((victim_scid, true)).or_default() = exhausted;
}
- // Track the total amount all our collected paths allow to send so that we:
- // - know when to stop looking for more paths
- // - know which of the hops are useless considering how much more sats we need
- // (contributes_sufficient_value)
+ // Track the total amount all our collected paths allow to send so that we know
+ // when to stop looking for more paths
already_collected_value_msat += value_contribution_msat;
payment_paths.push(payment_path);
});
selected_paths.push(path);
}
+ // Make sure we would never create a route with more paths than we allow.
+ debug_assert!(selected_paths.len() <= payment_params.max_mpp_path_count.into());
if let Some(features) = &payment_params.features {
for path in selected_paths.iter_mut() {
projects / rust-lightning / commitdiff