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