Support aggregating htlc_maximum_msat for BlindedPayInfo

diff --git a/lightning/src/blinded_path/mod.rs b/lightning/src/blinded_path/mod.rs
index 4a8f111be2cdad6bd68f95718ea5a5f08bce655d..82d50546ddd6c81f2de149333e1c30ee96754397 100644 (file)
--- a/lightning/src/blinded_path/mod.rs
+++ b/lightning/src/blinded_path/mod.rs
@@ -76,7 +76,8 @@ impl BlindedPath {
                })
        }
 
-       /// Create a blinded path for a payment, to be forwarded along `intermediate_nodes`.
+       /// Create a blinded path for a payment, to be forwarded along `intermediate_nodes`, where each
+       /// node is composed of `(node_id, tlvs, htlc_maximum_msat)`.
        ///
        /// Errors if:
        /// * a provided node id is invalid
@@ -86,13 +87,14 @@ impl BlindedPath {
        /// [`ForwardTlvs`]: crate::blinded_path::payment::ForwardTlvs
        //  TODO: make all payloads the same size with padding + add dummy hops
        pub fn new_for_payment<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
-               intermediate_nodes: &[(PublicKey, payment::ForwardTlvs)], payee_node_id: PublicKey,
-               payee_tlvs: payment::ReceiveTlvs, entropy_source: &ES, secp_ctx: &Secp256k1<T>
+               intermediate_nodes: &[(PublicKey, payment::ForwardTlvs, u64)], payee_node_id: PublicKey,
+               payee_tlvs: payment::ReceiveTlvs, htlc_maximum_msat: u64, entropy_source: &ES,
+               secp_ctx: &Secp256k1<T>
        ) -> Result<(BlindedPayInfo, Self), ()> {
                let blinding_secret_bytes = entropy_source.get_secure_random_bytes();
                let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
 
-               let blinded_payinfo = payment::compute_payinfo(intermediate_nodes, &payee_tlvs)?;
+               let blinded_payinfo = payment::compute_payinfo(intermediate_nodes, &payee_tlvs, htlc_maximum_msat)?;
                Ok((blinded_payinfo, BlindedPath {
                        introduction_node_id: intermediate_nodes.first().map_or(payee_node_id, |n| n.0),
                        blinding_point: PublicKey::from_secret_key(secp_ctx, &blinding_secret),

diff --git a/lightning/src/blinded_path/payment.rs b/lightning/src/blinded_path/payment.rs
index 488bdfee6c2b05f98ce96048aba7430df3fb47d8..779b121cadb2dc7f3e7dff7d26bdd272e4541f0a 100644 (file)
--- a/lightning/src/blinded_path/payment.rs
+++ b/lightning/src/blinded_path/payment.rs
@@ -144,12 +144,12 @@ impl Readable for BlindedPaymentTlvs {
 
 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
-       secp_ctx: &Secp256k1<T>, intermediate_nodes: &[(PublicKey, ForwardTlvs)],
+       secp_ctx: &Secp256k1<T>, intermediate_nodes: &[(PublicKey, ForwardTlvs, u64)],
        payee_node_id: PublicKey, payee_tlvs: ReceiveTlvs, session_priv: &SecretKey
 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
-       let pks = intermediate_nodes.iter().map(|(pk, _)| pk)
+       let pks = intermediate_nodes.iter().map(|(pk, _, _)| pk)
                .chain(core::iter::once(&payee_node_id));
-       let tlvs = intermediate_nodes.iter().map(|(_, tlvs)| BlindedPaymentTlvsRef::Forward(tlvs))
+       let tlvs = intermediate_nodes.iter().map(|(_, tlvs, _)| BlindedPaymentTlvsRef::Forward(tlvs))
                .chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
        utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
 }
@@ -176,12 +176,13 @@ fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> O
 }
 
 pub(super) fn compute_payinfo(
-       intermediate_nodes: &[(PublicKey, ForwardTlvs)], payee_tlvs: &ReceiveTlvs
+       intermediate_nodes: &[(PublicKey, ForwardTlvs, u64)], payee_tlvs: &ReceiveTlvs,
+       payee_htlc_maximum_msat: u64
 ) -> Result<BlindedPayInfo, ()> {
        let mut curr_base_fee: u64 = 0;
        let mut curr_prop_mil: u64 = 0;
        let mut cltv_expiry_delta: u16 = 0;
-       for (_, tlvs) in intermediate_nodes.iter().rev() {
+       for (_, tlvs, _) in intermediate_nodes.iter().rev() {
                // In the future, we'll want to take the intersection of all supported features for the
                // `BlindedPayInfo`, but there are no features in that context right now.
                if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
@@ -207,7 +208,8 @@ pub(super) fn compute_payinfo(
        }
 
        let mut htlc_minimum_msat: u64 = 1;
-       for (_, tlvs) in intermediate_nodes.iter() {
+       let mut htlc_maximum_msat: u64 = 21_000_000 * 100_000_000 * 1_000; // Total bitcoin supply
+       for (_, tlvs, max_htlc_candidate) in intermediate_nodes.iter() {
                // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
                // following hops for forwarding that min, since that fee amount will automatically be included
                // in the amount that this node receives and contribute towards reaching its min.
@@ -215,17 +217,22 @@ pub(super) fn compute_payinfo(
                        core::cmp::max(tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
                        &tlvs.payment_relay
                ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
+               htlc_maximum_msat = amt_to_forward_msat(
+                       core::cmp::min(*max_htlc_candidate, htlc_maximum_msat), &tlvs.payment_relay
+               ).ok_or(())?; // If underflow occurs, we cannot send to this hop without exceeding their max
        }
        htlc_minimum_msat = core::cmp::max(
                payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
        );
+       htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
 
+       if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
        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,
-               htlc_maximum_msat: 21_000_000 * 100_000_000 * 1_000, // TODO
+               htlc_maximum_msat,
                features: BlindedHopFeatures::empty(),
        })
 }
@@ -265,7 +272,7 @@ mod tests {
                                htlc_minimum_msat: 100,
                        },
                        features: BlindedHopFeatures::empty(),
-               }), (dummy_pk, ForwardTlvs {
+               }, u64::max_value()), (dummy_pk, ForwardTlvs {
                        short_channel_id: 0,
                        payment_relay: PaymentRelay {
                                cltv_expiry_delta: 144,
@@ -277,7 +284,7 @@ mod tests {
                                htlc_minimum_msat: 1_000,
                        },
                        features: BlindedHopFeatures::empty(),
-               })];
+               }, u64::max_value())];
                let recv_tlvs = ReceiveTlvs {
                        payment_secret: PaymentSecret([0; 32]),
                        payment_constraints: PaymentConstraints {
@@ -285,11 +292,13 @@ mod tests {
                                htlc_minimum_msat: 1,
                        },
                };
-               let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap();
+               let htlc_maximum_msat = 100_000;
+               let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
                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);
+               assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
        }
 
        #[test]
@@ -301,11 +310,12 @@ mod tests {
                                htlc_minimum_msat: 1,
                        },
                };
-               let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs).unwrap();
+               let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs, 4242).unwrap();
                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);
+               assert_eq!(blinded_payinfo.htlc_maximum_msat, 4242);
        }
 
        #[test]
@@ -325,7 +335,7 @@ mod tests {
                                htlc_minimum_msat: 1,
                        },
                        features: BlindedHopFeatures::empty(),
-               }), (dummy_pk, ForwardTlvs {
+               }, u64::max_value()), (dummy_pk, ForwardTlvs {
                        short_channel_id: 0,
                        payment_relay: PaymentRelay {
                                cltv_expiry_delta: 0,
@@ -337,7 +347,7 @@ mod tests {
                                htlc_minimum_msat: 2_000,
                        },
                        features: BlindedHopFeatures::empty(),
-               })];
+               }, u64::max_value())];
                let recv_tlvs = ReceiveTlvs {
                        payment_secret: PaymentSecret([0; 32]),
                        payment_constraints: PaymentConstraints {
@@ -345,7 +355,8 @@ mod tests {
                                htlc_minimum_msat: 3,
                        },
                };
-               let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap();
+               let htlc_maximum_msat = 100_000;
+               let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
                assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
        }
 
@@ -366,7 +377,7 @@ mod tests {
                                htlc_minimum_msat: 5_000,
                        },
                        features: BlindedHopFeatures::empty(),
-               }), (dummy_pk, ForwardTlvs {
+               }, u64::max_value()), (dummy_pk, ForwardTlvs {
                        short_channel_id: 0,
                        payment_relay: PaymentRelay {
                                cltv_expiry_delta: 0,
@@ -378,7 +389,7 @@ mod tests {
                                htlc_minimum_msat: 2_000,
                        },
                        features: BlindedHopFeatures::empty(),
-               })];
+               }, u64::max_value())];
                let recv_tlvs = ReceiveTlvs {
                        payment_secret: PaymentSecret([0; 32]),
                        payment_constraints: PaymentConstraints {
@@ -387,7 +398,53 @@ mod tests {
                        },
                };
                let htlc_minimum_msat = 3798;
-               let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap();
+               assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1).is_err());
+
+               let htlc_maximum_msat = htlc_minimum_msat + 1;
+               let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
                assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
+               assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
+       }
+
+       #[test]
+       fn aggregated_htlc_max() {
+               // Create a path with varying fees and `htlc_maximum_msat`s, and make sure the aggregated max
+               // htlc ends up as the min (htlc_max - 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: 1,
+                       },
+                       features: BlindedHopFeatures::empty(),
+               }, 5_000), (dummy_pk, ForwardTlvs {
+                       short_channel_id: 0,
+                       payment_relay: PaymentRelay {
+                               cltv_expiry_delta: 0,
+                               fee_proportional_millionths: 500,
+                               fee_base_msat: 1,
+                       },
+                       payment_constraints: PaymentConstraints {
+                               max_cltv_expiry: 0,
+                               htlc_minimum_msat: 1,
+                       },
+                       features: BlindedHopFeatures::empty(),
+               }, 10_000)];
+               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, 10_000).unwrap();
+               assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);
        }
 }