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