diff --git a/lightning/src/blinded_path/payment.rs b/lightning/src/blinded_path/payment.rs index ea887073105..f40111998cb 100644 --- a/lightning/src/blinded_path/payment.rs +++ b/lightning/src/blinded_path/payment.rs @@ -184,11 +184,38 @@ pub(super) fn compute_payinfo( cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?; } + + let mut htlc_minimum_msat = 0; + for (idx, node) in intermediate_nodes.iter().map(|(_, tlvs)| tlvs).enumerate() { + let mut htlc_min_candidate = node.payment_constraints.htlc_minimum_msat as u128; + // Get an iterator over `[curr_hop_tlvs..last_intermediate_hop_tlvs]`. + let next_nodes = intermediate_nodes.iter() + .enumerate() + .skip_while(|(i, _)| *i != idx) + .map(|(_, (_, tlvs))| tlvs); + for node in next_nodes { + // The min htlc for a hop is that hop's htlc_minimum_msat minus the fees paid from that hop to + // the end of the path, because the sender will automatically include that following fee + // amount in the amount that this hop receives. + let prop_fee = node.payment_relay.fee_proportional_millionths as u128; + let base_fee = node.payment_relay.fee_base_msat as u128; + let hop_fee = htlc_min_candidate + .checked_mul(prop_fee) + .and_then(|prop_fee| (prop_fee / 1_000_000).checked_add(base_fee)) + .ok_or(())?; + htlc_min_candidate = htlc_min_candidate.saturating_sub(hop_fee); + if htlc_min_candidate == 0 { break } + } + htlc_minimum_msat = core::cmp::max(htlc_min_candidate, htlc_minimum_msat); + } + htlc_minimum_msat = + core::cmp::max(payee_tlvs.payment_constraints.htlc_minimum_msat as u128, htlc_minimum_msat); + Ok(BlindedPayInfo { fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?, fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?, cltv_expiry_delta, - htlc_minimum_msat: 1, // TODO + htlc_minimum_msat: u64::try_from(htlc_minimum_msat).map_err(|_| ())?, htlc_maximum_msat: 21_000_000 * 100_000_000 * 1_000, // TODO features: BlindedHopFeatures::empty(), }) @@ -253,6 +280,7 @@ mod tests { assert_eq!(blinded_payinfo.fee_base_msat, 201); assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001); assert_eq!(blinded_payinfo.cltv_expiry_delta, 288); + assert_eq!(blinded_payinfo.htlc_minimum_msat, 900); } #[test] @@ -268,5 +296,89 @@ mod tests { assert_eq!(blinded_payinfo.fee_base_msat, 0); assert_eq!(blinded_payinfo.fee_proportional_millionths, 0); assert_eq!(blinded_payinfo.cltv_expiry_delta, 0); + assert_eq!(blinded_payinfo.htlc_minimum_msat, 1); + } + + #[test] + fn simple_aggregated_htlc_min() { + // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat + // along the path. + let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap(); + let intermediate_nodes = vec![(dummy_pk, ForwardTlvs { + short_channel_id: 0, + payment_relay: PaymentRelay { + cltv_expiry_delta: 0, + fee_proportional_millionths: 0, + fee_base_msat: 0, + }, + payment_constraints: PaymentConstraints { + max_cltv_expiry: 0, + htlc_minimum_msat: 1, + }, + features: BlindedHopFeatures::empty(), + }), (dummy_pk, ForwardTlvs { + short_channel_id: 0, + payment_relay: PaymentRelay { + cltv_expiry_delta: 0, + fee_proportional_millionths: 0, + fee_base_msat: 0, + }, + payment_constraints: PaymentConstraints { + max_cltv_expiry: 0, + htlc_minimum_msat: 2_000, + }, + features: BlindedHopFeatures::empty(), + })]; + let recv_tlvs = ReceiveTlvs { + payment_secret: PaymentSecret([0; 32]), + payment_constraints: PaymentConstraints { + max_cltv_expiry: 0, + htlc_minimum_msat: 3, + }, + }; + let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap(); + assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000); + } + + #[test] + fn aggregated_htlc_min() { + // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the + // max (htlc_min - following_fees) along the path. + let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap(); + let intermediate_nodes = vec![(dummy_pk, ForwardTlvs { + short_channel_id: 0, + payment_relay: PaymentRelay { + cltv_expiry_delta: 0, + fee_proportional_millionths: 500, + fee_base_msat: 1_000, + }, + payment_constraints: PaymentConstraints { + max_cltv_expiry: 0, + htlc_minimum_msat: 5_000, + }, + features: BlindedHopFeatures::empty(), + }), (dummy_pk, ForwardTlvs { + short_channel_id: 0, + payment_relay: PaymentRelay { + cltv_expiry_delta: 0, + fee_proportional_millionths: 500, + fee_base_msat: 200, + }, + payment_constraints: PaymentConstraints { + max_cltv_expiry: 0, + htlc_minimum_msat: 2_000, + }, + features: BlindedHopFeatures::empty(), + })]; + let recv_tlvs = ReceiveTlvs { + payment_secret: PaymentSecret([0; 32]), + payment_constraints: PaymentConstraints { + max_cltv_expiry: 0, + htlc_minimum_msat: 1, + }, + }; + + let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap(); + assert_eq!(blinded_payinfo.htlc_minimum_msat, 3797); } }