_ Git - rust-lightning/blob - lightning/src/blinded_path/payment.rs

   1 //! Data structures and methods for constructing [`BlindedPath`]s to send a payment over.
   2 //!
   3 //! [`BlindedPath`]: crate::blinded_path::BlindedPath
   4
   5 use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
   6
   7 use crate::blinded_path::BlindedHop;
   8 use crate::blinded_path::utils;
   9 use crate::io;
  10 use crate::ln::PaymentSecret;
  11 use crate::ln::channelmanager::CounterpartyForwardingInfo;
  12 use crate::ln::features::BlindedHopFeatures;
  13 use crate::ln::msgs::DecodeError;
  14 use crate::offers::invoice::BlindedPayInfo;
  15 use crate::util::ser::{HighZeroBytesDroppedBigSize, Readable, Writeable, Writer};
  16
  17 #[allow(unused_imports)]
  18 use crate::prelude::*;
  19
  20 use core::convert::TryFrom;
  21
  22 /// An intermediate node, its outbound channel, and relay parameters.
  23 #[derive(Clone, Debug)]
  24 pub struct ForwardNode {
  25         /// The TLVs for this node's [`BlindedHop`], where the fee parameters contained within are also
  26         /// used for [`BlindedPayInfo`] construction.
  27         pub tlvs: ForwardTlvs,
  28         /// This node's pubkey.
  29         pub node_id: PublicKey,
  30         /// The maximum value, in msat, that may be accepted by this node.
  31         pub htlc_maximum_msat: u64,
  32 }
  33
  34 /// Data to construct a [`BlindedHop`] for forwarding a payment.
  35 #[derive(Clone, Debug)]
  36 pub struct ForwardTlvs {
  37         /// The short channel id this payment should be forwarded out over.
  38         pub short_channel_id: u64,
  39         /// Payment parameters for relaying over [`Self::short_channel_id`].
  40         pub payment_relay: PaymentRelay,
  41         /// Payment constraints for relaying over [`Self::short_channel_id`].
  42         pub payment_constraints: PaymentConstraints,
  43         /// Supported and required features when relaying a payment onion containing this object's
  44         /// corresponding [`BlindedHop::encrypted_payload`].
  45         ///
  46         /// [`BlindedHop::encrypted_payload`]: crate::blinded_path::BlindedHop::encrypted_payload
  47         pub features: BlindedHopFeatures,
  48 }
  49
  50 /// Data to construct a [`BlindedHop`] for receiving a payment. This payload is custom to LDK and
  51 /// may not be valid if received by another lightning implementation.
  52 #[derive(Clone, Debug)]
  53 pub struct ReceiveTlvs {
  54         /// Used to authenticate the sender of a payment to the receiver and tie MPP HTLCs together.
  55         pub payment_secret: PaymentSecret,
  56         /// Constraints for the receiver of this payment.
  57         pub payment_constraints: PaymentConstraints,
  58 }
  59
  60 /// Data to construct a [`BlindedHop`] for sending a payment over.
  61 ///
  62 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
  63 pub(crate) enum BlindedPaymentTlvs {
  64         /// This blinded payment data is for a forwarding node.
  65         Forward(ForwardTlvs),
  66         /// This blinded payment data is for the receiving node.
  67         Receive(ReceiveTlvs),
  68 }
  69
  70 // Used to include forward and receive TLVs in the same iterator for encoding.
  71 enum BlindedPaymentTlvsRef<'a> {
  72         Forward(&'a ForwardTlvs),
  73         Receive(&'a ReceiveTlvs),
  74 }
  75
  76 /// Parameters for relaying over a given [`BlindedHop`].
  77 ///
  78 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
  79 #[derive(Clone, Debug)]
  80 pub struct PaymentRelay {
  81         /// Number of blocks subtracted from an incoming HTLC's `cltv_expiry` for this [`BlindedHop`].
  82         pub cltv_expiry_delta: u16,
  83         /// Liquidity fee charged (in millionths of the amount transferred) for relaying a payment over
  84         /// this [`BlindedHop`], (i.e., 10,000 is 1%).
  85         pub fee_proportional_millionths: u32,
  86         /// Base fee charged (in millisatoshi) for relaying a payment over this [`BlindedHop`].
  87         pub fee_base_msat: u32,
  88 }
  89
  90 /// Constraints for relaying over a given [`BlindedHop`].
  91 ///
  92 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
  93 #[derive(Clone, Debug)]
  94 pub struct PaymentConstraints {
  95         /// The maximum total CLTV that is acceptable when relaying a payment over this [`BlindedHop`].
  96         pub max_cltv_expiry: u32,
  97         /// The minimum value, in msat, that may be accepted by the node corresponding to this
  98         /// [`BlindedHop`].
  99         pub htlc_minimum_msat: u64,
 100 }
 101
 102 impl TryFrom<CounterpartyForwardingInfo> for PaymentRelay {
 103         type Error = ();
 104
 105         fn try_from(info: CounterpartyForwardingInfo) -> Result<Self, ()> {
 106                 let CounterpartyForwardingInfo {
 107                         fee_base_msat, fee_proportional_millionths, cltv_expiry_delta
 108                 } = info;
 109
 110                 // Avoid exposing esoteric CLTV expiry deltas
 111                 let cltv_expiry_delta = match cltv_expiry_delta {
 112                         0..=40 => 40,
 113                         41..=80 => 80,
 114                         81..=144 => 144,
 115                         145..=216 => 216,
 116                         _ => return Err(()),
 117                 };
 118
 119                 Ok(Self { cltv_expiry_delta, fee_proportional_millionths, fee_base_msat })
 120         }
 121 }
 122
 123 impl Writeable for ForwardTlvs {
 124         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 125                 let features_opt =
 126                         if self.features == BlindedHopFeatures::empty() { None }
 127                         else { Some(&self.features) };
 128                 encode_tlv_stream!(w, {
 129                         (2, self.short_channel_id, required),
 130                         (10, self.payment_relay, required),
 131                         (12, self.payment_constraints, required),
 132                         (14, features_opt, option)
 133                 });
 134                 Ok(())
 135         }
 136 }
 137
 138 impl Writeable for ReceiveTlvs {
 139         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 140                 encode_tlv_stream!(w, {
 141                         (12, self.payment_constraints, required),
 142                         (65536, self.payment_secret, required)
 143                 });
 144                 Ok(())
 145         }
 146 }
 147
 148 impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
 149         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 150                 // TODO: write padding
 151                 match self {
 152                         Self::Forward(tlvs) => tlvs.write(w)?,
 153                         Self::Receive(tlvs) => tlvs.write(w)?,
 154                 }
 155                 Ok(())
 156         }
 157 }
 158
 159 impl Readable for BlindedPaymentTlvs {
 160         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 161                 _init_and_read_tlv_stream!(r, {
 162                         (1, _padding, option),
 163                         (2, scid, option),
 164                         (10, payment_relay, option),
 165                         (12, payment_constraints, required),
 166                         (14, features, option),
 167                         (65536, payment_secret, option),
 168                 });
 169                 let _padding: Option<utils::Padding> = _padding;
 170
 171                 if let Some(short_channel_id) = scid {
 172                         if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
 173                         Ok(BlindedPaymentTlvs::Forward(ForwardTlvs {
 174                                 short_channel_id,
 175                                 payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
 176                                 payment_constraints: payment_constraints.0.unwrap(),
 177                                 features: features.unwrap_or_else(BlindedHopFeatures::empty),
 178                         }))
 179                 } else {
 180                         if payment_relay.is_some() || features.is_some() { return Err(DecodeError::InvalidValue) }
 181                         Ok(BlindedPaymentTlvs::Receive(ReceiveTlvs {
 182                                 payment_secret: payment_secret.ok_or(DecodeError::InvalidValue)?,
 183                                 payment_constraints: payment_constraints.0.unwrap(),
 184                         }))
 185                 }
 186         }
 187 }
 188
 189 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
 190 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 191         secp_ctx: &Secp256k1<T>, intermediate_nodes: &[ForwardNode],
 192         payee_node_id: PublicKey, payee_tlvs: ReceiveTlvs, session_priv: &SecretKey
 193 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
 194         let pks = intermediate_nodes.iter().map(|node| &node.node_id)
 195                 .chain(core::iter::once(&payee_node_id));
 196         let tlvs = intermediate_nodes.iter().map(|node| BlindedPaymentTlvsRef::Forward(&node.tlvs))
 197                 .chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
 198         utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
 199 }
 200
 201 /// `None` if underflow occurs.
 202 pub(crate) fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> Option<u64> {
 203         let inbound_amt = inbound_amt_msat as u128;
 204         let base = payment_relay.fee_base_msat as u128;
 205         let prop = payment_relay.fee_proportional_millionths as u128;
 206
 207         let post_base_fee_inbound_amt =
 208                 if let Some(amt) = inbound_amt.checked_sub(base) { amt } else { return None };
 209         let mut amt_to_forward =
 210                 (post_base_fee_inbound_amt * 1_000_000 + 1_000_000 + prop - 1) / (prop + 1_000_000);
 211
 212         let fee = ((amt_to_forward * prop) / 1_000_000) + base;
 213         if inbound_amt - fee < amt_to_forward {
 214                 // Rounding up the forwarded amount resulted in underpaying this node, so take an extra 1 msat
 215                 // in fee to compensate.
 216                 amt_to_forward -= 1;
 217         }
 218         debug_assert_eq!(amt_to_forward + fee, inbound_amt);
 219         u64::try_from(amt_to_forward).ok()
 220 }
 221
 222 pub(super) fn compute_payinfo(
 223         intermediate_nodes: &[ForwardNode], payee_tlvs: &ReceiveTlvs, payee_htlc_maximum_msat: u64,
 224         min_final_cltv_expiry_delta: u16
 225 ) -> Result<BlindedPayInfo, ()> {
 226         let mut curr_base_fee: u64 = 0;
 227         let mut curr_prop_mil: u64 = 0;
 228         let mut cltv_expiry_delta: u16 = min_final_cltv_expiry_delta;
 229         for tlvs in intermediate_nodes.iter().rev().map(|n| &n.tlvs) {
 230                 // In the future, we'll want to take the intersection of all supported features for the
 231                 // `BlindedPayInfo`, but there are no features in that context right now.
 232                 if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
 233
 234                 let next_base_fee = tlvs.payment_relay.fee_base_msat as u64;
 235                 let next_prop_mil = tlvs.payment_relay.fee_proportional_millionths as u64;
 236                 // Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
 237                 // ((curr_base_fee * (1_000_000 + next_prop_mil)) / 1_000_000) + next_base_fee
 238                 curr_base_fee = curr_base_fee.checked_mul(1_000_000 + next_prop_mil)
 239                         .and_then(|f| f.checked_add(1_000_000 - 1))
 240                         .map(|f| f / 1_000_000)
 241                         .and_then(|f| f.checked_add(next_base_fee))
 242                         .ok_or(())?;
 243                 // ceil(((curr_prop_mil + 1_000_000) * (next_prop_mil + 1_000_000)) / 1_000_000) - 1_000_000
 244                 curr_prop_mil = curr_prop_mil.checked_add(1_000_000)
 245                         .and_then(|f1| next_prop_mil.checked_add(1_000_000).and_then(|f2| f2.checked_mul(f1)))
 246                         .and_then(|f| f.checked_add(1_000_000 - 1))
 247                         .map(|f| f / 1_000_000)
 248                         .and_then(|f| f.checked_sub(1_000_000))
 249                         .ok_or(())?;
 250
 251                 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
 252         }
 253
 254         let mut htlc_minimum_msat: u64 = 1;
 255         let mut htlc_maximum_msat: u64 = 21_000_000 * 100_000_000 * 1_000; // Total bitcoin supply
 256         for node in intermediate_nodes.iter() {
 257                 // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
 258                 // following hops for forwarding that min, since that fee amount will automatically be included
 259                 // in the amount that this node receives and contribute towards reaching its min.
 260                 htlc_minimum_msat = amt_to_forward_msat(
 261                         core::cmp::max(node.tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
 262                         &node.tlvs.payment_relay
 263                 ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
 264                 htlc_maximum_msat = amt_to_forward_msat(
 265                         core::cmp::min(node.htlc_maximum_msat, htlc_maximum_msat), &node.tlvs.payment_relay
 266                 ).ok_or(())?; // If underflow occurs, we cannot send to this hop without exceeding their max
 267         }
 268         htlc_minimum_msat = core::cmp::max(
 269                 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
 270         );
 271         htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
 272
 273         if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
 274         Ok(BlindedPayInfo {
 275                 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
 276                 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
 277                 cltv_expiry_delta,
 278                 htlc_minimum_msat,
 279                 htlc_maximum_msat,
 280                 features: BlindedHopFeatures::empty(),
 281         })
 282 }
 283
 284 impl Writeable for PaymentRelay {
 285         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 286                 self.cltv_expiry_delta.write(w)?;
 287                 self.fee_proportional_millionths.write(w)?;
 288                 HighZeroBytesDroppedBigSize(self.fee_base_msat).write(w)
 289         }
 290 }
 291 impl Readable for PaymentRelay {
 292         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 293                 let cltv_expiry_delta: u16 = Readable::read(r)?;
 294                 let fee_proportional_millionths: u32 = Readable::read(r)?;
 295                 let fee_base_msat: HighZeroBytesDroppedBigSize<u32> = Readable::read(r)?;
 296                 Ok(Self { cltv_expiry_delta, fee_proportional_millionths, fee_base_msat: fee_base_msat.0 })
 297         }
 298 }
 299
 300 impl Writeable for PaymentConstraints {
 301         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 302                 self.max_cltv_expiry.write(w)?;
 303                 HighZeroBytesDroppedBigSize(self.htlc_minimum_msat).write(w)
 304         }
 305 }
 306 impl Readable for PaymentConstraints {
 307         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 308                 let max_cltv_expiry: u32 = Readable::read(r)?;
 309                 let htlc_minimum_msat: HighZeroBytesDroppedBigSize<u64> = Readable::read(r)?;
 310                 Ok(Self { max_cltv_expiry, htlc_minimum_msat: htlc_minimum_msat.0 })
 311         }
 312 }
 313
 314 #[cfg(test)]
 315 mod tests {
 316         use bitcoin::secp256k1::PublicKey;
 317         use crate::blinded_path::payment::{ForwardNode, ForwardTlvs, ReceiveTlvs, PaymentConstraints, PaymentRelay};
 318         use crate::ln::PaymentSecret;
 319         use crate::ln::features::BlindedHopFeatures;
 320         use crate::ln::functional_test_utils::TEST_FINAL_CLTV;
 321
 322         #[test]
 323         fn compute_payinfo() {
 324                 // Taken from the spec example for aggregating blinded payment info. See
 325                 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments
 326                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 327                 let intermediate_nodes = vec![ForwardNode {
 328                         node_id: dummy_pk,
 329                         tlvs: ForwardTlvs {
 330                                 short_channel_id: 0,
 331                                 payment_relay: PaymentRelay {
 332                                         cltv_expiry_delta: 144,
 333                                         fee_proportional_millionths: 500,
 334                                         fee_base_msat: 100,
 335                                 },
 336                                 payment_constraints: PaymentConstraints {
 337                                         max_cltv_expiry: 0,
 338                                         htlc_minimum_msat: 100,
 339                                 },
 340                                 features: BlindedHopFeatures::empty(),
 341                         },
 342                         htlc_maximum_msat: u64::max_value(),
 343                 }, ForwardNode {
 344                         node_id: dummy_pk,
 345                         tlvs: ForwardTlvs {
 346                                 short_channel_id: 0,
 347                                 payment_relay: PaymentRelay {
 348                                         cltv_expiry_delta: 144,
 349                                         fee_proportional_millionths: 500,
 350                                         fee_base_msat: 100,
 351                                 },
 352                                 payment_constraints: PaymentConstraints {
 353                                         max_cltv_expiry: 0,
 354                                         htlc_minimum_msat: 1_000,
 355                                 },
 356                                 features: BlindedHopFeatures::empty(),
 357                         },
 358                         htlc_maximum_msat: u64::max_value(),
 359                 }];
 360                 let recv_tlvs = ReceiveTlvs {
 361                         payment_secret: PaymentSecret([0; 32]),
 362                         payment_constraints: PaymentConstraints {
 363                                 max_cltv_expiry: 0,
 364                                 htlc_minimum_msat: 1,
 365                         },
 366                 };
 367                 let htlc_maximum_msat = 100_000;
 368                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, 12).unwrap();
 369                 assert_eq!(blinded_payinfo.fee_base_msat, 201);
 370                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001);
 371                 assert_eq!(blinded_payinfo.cltv_expiry_delta, 300);
 372                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 900);
 373                 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
 374         }
 375
 376         #[test]
 377         fn compute_payinfo_1_hop() {
 378                 let recv_tlvs = ReceiveTlvs {
 379                         payment_secret: PaymentSecret([0; 32]),
 380                         payment_constraints: PaymentConstraints {
 381                                 max_cltv_expiry: 0,
 382                                 htlc_minimum_msat: 1,
 383                         },
 384                 };
 385                 let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs, 4242, TEST_FINAL_CLTV as u16).unwrap();
 386                 assert_eq!(blinded_payinfo.fee_base_msat, 0);
 387                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 0);
 388                 assert_eq!(blinded_payinfo.cltv_expiry_delta, TEST_FINAL_CLTV as u16);
 389                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 1);
 390                 assert_eq!(blinded_payinfo.htlc_maximum_msat, 4242);
 391         }
 392
 393         #[test]
 394         fn simple_aggregated_htlc_min() {
 395                 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
 396                 // along the path.
 397                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 398                 let intermediate_nodes = vec![ForwardNode {
 399                         node_id: dummy_pk,
 400                         tlvs: ForwardTlvs {
 401                                 short_channel_id: 0,
 402                                 payment_relay: PaymentRelay {
 403                                         cltv_expiry_delta: 0,
 404                                         fee_proportional_millionths: 0,
 405                                         fee_base_msat: 0,
 406                                 },
 407                                 payment_constraints: PaymentConstraints {
 408                                         max_cltv_expiry: 0,
 409                                         htlc_minimum_msat: 1,
 410                                 },
 411                                 features: BlindedHopFeatures::empty(),
 412                         },
 413                         htlc_maximum_msat: u64::max_value()
 414                 }, ForwardNode {
 415                         node_id: dummy_pk,
 416                         tlvs: ForwardTlvs {
 417                                 short_channel_id: 0,
 418                                 payment_relay: PaymentRelay {
 419                                         cltv_expiry_delta: 0,
 420                                         fee_proportional_millionths: 0,
 421                                         fee_base_msat: 0,
 422                                 },
 423                                 payment_constraints: PaymentConstraints {
 424                                         max_cltv_expiry: 0,
 425                                         htlc_minimum_msat: 2_000,
 426                                 },
 427                                 features: BlindedHopFeatures::empty(),
 428                         },
 429                         htlc_maximum_msat: u64::max_value()
 430                 }];
 431                 let recv_tlvs = ReceiveTlvs {
 432                         payment_secret: PaymentSecret([0; 32]),
 433                         payment_constraints: PaymentConstraints {
 434                                 max_cltv_expiry: 0,
 435                                 htlc_minimum_msat: 3,
 436                         },
 437                 };
 438                 let htlc_maximum_msat = 100_000;
 439                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, TEST_FINAL_CLTV as u16).unwrap();
 440                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
 441         }
 442
 443         #[test]
 444         fn aggregated_htlc_min() {
 445                 // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the
 446                 // max (htlc_min - following_fees) along the path.
 447                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 448                 let intermediate_nodes = vec![ForwardNode {
 449                         node_id: dummy_pk,
 450                         tlvs: ForwardTlvs {
 451                                 short_channel_id: 0,
 452                                 payment_relay: PaymentRelay {
 453                                         cltv_expiry_delta: 0,
 454                                         fee_proportional_millionths: 500,
 455                                         fee_base_msat: 1_000,
 456                                 },
 457                                 payment_constraints: PaymentConstraints {
 458                                         max_cltv_expiry: 0,
 459                                         htlc_minimum_msat: 5_000,
 460                                 },
 461                                 features: BlindedHopFeatures::empty(),
 462                         },
 463                         htlc_maximum_msat: u64::max_value()
 464                 }, ForwardNode {
 465                         node_id: dummy_pk,
 466                         tlvs: ForwardTlvs {
 467                                 short_channel_id: 0,
 468                                 payment_relay: PaymentRelay {
 469                                         cltv_expiry_delta: 0,
 470                                         fee_proportional_millionths: 500,
 471                                         fee_base_msat: 200,
 472                                 },
 473                                 payment_constraints: PaymentConstraints {
 474                                         max_cltv_expiry: 0,
 475                                         htlc_minimum_msat: 2_000,
 476                                 },
 477                                 features: BlindedHopFeatures::empty(),
 478                         },
 479                         htlc_maximum_msat: u64::max_value()
 480                 }];
 481                 let recv_tlvs = ReceiveTlvs {
 482                         payment_secret: PaymentSecret([0; 32]),
 483                         payment_constraints: PaymentConstraints {
 484                                 max_cltv_expiry: 0,
 485                                 htlc_minimum_msat: 1,
 486                         },
 487                 };
 488                 let htlc_minimum_msat = 3798;
 489                 assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1, TEST_FINAL_CLTV as u16).is_err());
 490
 491                 let htlc_maximum_msat = htlc_minimum_msat + 1;
 492                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, TEST_FINAL_CLTV as u16).unwrap();
 493                 assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
 494                 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
 495         }
 496
 497         #[test]
 498         fn aggregated_htlc_max() {
 499                 // Create a path with varying fees and `htlc_maximum_msat`s, and make sure the aggregated max
 500                 // htlc ends up as the min (htlc_max - following_fees) along the path.
 501                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 502                 let intermediate_nodes = vec![ForwardNode {
 503                         node_id: dummy_pk,
 504                         tlvs: ForwardTlvs {
 505                                 short_channel_id: 0,
 506                                 payment_relay: PaymentRelay {
 507                                         cltv_expiry_delta: 0,
 508                                         fee_proportional_millionths: 500,
 509                                         fee_base_msat: 1_000,
 510                                 },
 511                                 payment_constraints: PaymentConstraints {
 512                                         max_cltv_expiry: 0,
 513                                         htlc_minimum_msat: 1,
 514                                 },
 515                                 features: BlindedHopFeatures::empty(),
 516                         },
 517                         htlc_maximum_msat: 5_000,
 518                 }, ForwardNode {
 519                         node_id: dummy_pk,
 520                         tlvs: ForwardTlvs {
 521                                 short_channel_id: 0,
 522                                 payment_relay: PaymentRelay {
 523                                         cltv_expiry_delta: 0,
 524                                         fee_proportional_millionths: 500,
 525                                         fee_base_msat: 1,
 526                                 },
 527                                 payment_constraints: PaymentConstraints {
 528                                         max_cltv_expiry: 0,
 529                                         htlc_minimum_msat: 1,
 530                                 },
 531                                 features: BlindedHopFeatures::empty(),
 532                         },
 533                         htlc_maximum_msat: 10_000
 534                 }];
 535                 let recv_tlvs = ReceiveTlvs {
 536                         payment_secret: PaymentSecret([0; 32]),
 537                         payment_constraints: PaymentConstraints {
 538                                 max_cltv_expiry: 0,
 539                                 htlc_minimum_msat: 1,
 540                         },
 541                 };
 542
 543                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, 10_000, TEST_FINAL_CLTV as u16).unwrap();
 544                 assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);
 545         }
 546 }