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