_ 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 /// 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                 let features_opt =
 124                         if self.features == BlindedHopFeatures::empty() { None }
 125                         else { Some(&self.features) };
 126                 encode_tlv_stream!(w, {
 127                         (2, self.short_channel_id, required),
 128                         (10, self.payment_relay, required),
 129                         (12, self.payment_constraints, required),
 130                         (14, features_opt, option)
 131                 });
 132                 Ok(())
 133         }
 134 }
 135
 136 impl Writeable for ReceiveTlvs {
 137         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 138                 encode_tlv_stream!(w, {
 139                         (12, self.payment_constraints, required),
 140                         (65536, self.payment_secret, required)
 141                 });
 142                 Ok(())
 143         }
 144 }
 145
 146 impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
 147         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 148                 // TODO: write padding
 149                 match self {
 150                         Self::Forward(tlvs) => tlvs.write(w)?,
 151                         Self::Receive(tlvs) => tlvs.write(w)?,
 152                 }
 153                 Ok(())
 154         }
 155 }
 156
 157 impl Readable for BlindedPaymentTlvs {
 158         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 159                 _init_and_read_tlv_stream!(r, {
 160                         (1, _padding, option),
 161                         (2, scid, option),
 162                         (10, payment_relay, option),
 163                         (12, payment_constraints, required),
 164                         (14, features, option),
 165                         (65536, payment_secret, option),
 166                 });
 167                 let _padding: Option<utils::Padding> = _padding;
 168
 169                 if let Some(short_channel_id) = scid {
 170                         if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
 171                         Ok(BlindedPaymentTlvs::Forward(ForwardTlvs {
 172                                 short_channel_id,
 173                                 payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
 174                                 payment_constraints: payment_constraints.0.unwrap(),
 175                                 features: features.unwrap_or_else(BlindedHopFeatures::empty),
 176                         }))
 177                 } else {
 178                         if payment_relay.is_some() || features.is_some() { return Err(DecodeError::InvalidValue) }
 179                         Ok(BlindedPaymentTlvs::Receive(ReceiveTlvs {
 180                                 payment_secret: payment_secret.ok_or(DecodeError::InvalidValue)?,
 181                                 payment_constraints: payment_constraints.0.unwrap(),
 182                         }))
 183                 }
 184         }
 185 }
 186
 187 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
 188 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 189         secp_ctx: &Secp256k1<T>, intermediate_nodes: &[ForwardNode],
 190         payee_node_id: PublicKey, payee_tlvs: ReceiveTlvs, session_priv: &SecretKey
 191 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
 192         let pks = intermediate_nodes.iter().map(|node| &node.node_id)
 193                 .chain(core::iter::once(&payee_node_id));
 194         let tlvs = intermediate_nodes.iter().map(|node| BlindedPaymentTlvsRef::Forward(&node.tlvs))
 195                 .chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
 196         utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
 197 }
 198
 199 /// `None` if underflow occurs.
 200 pub(crate) fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> Option<u64> {
 201         let inbound_amt = inbound_amt_msat as u128;
 202         let base = payment_relay.fee_base_msat as u128;
 203         let prop = payment_relay.fee_proportional_millionths as u128;
 204
 205         let post_base_fee_inbound_amt =
 206                 if let Some(amt) = inbound_amt.checked_sub(base) { amt } else { return None };
 207         let mut amt_to_forward =
 208                 (post_base_fee_inbound_amt * 1_000_000 + 1_000_000 + prop - 1) / (prop + 1_000_000);
 209
 210         let fee = ((amt_to_forward * prop) / 1_000_000) + base;
 211         if inbound_amt - fee < amt_to_forward {
 212                 // Rounding up the forwarded amount resulted in underpaying this node, so take an extra 1 msat
 213                 // in fee to compensate.
 214                 amt_to_forward -= 1;
 215         }
 216         debug_assert_eq!(amt_to_forward + fee, inbound_amt);
 217         u64::try_from(amt_to_forward).ok()
 218 }
 219
 220 pub(super) fn compute_payinfo(
 221         intermediate_nodes: &[ForwardNode], payee_tlvs: &ReceiveTlvs, payee_htlc_maximum_msat: u64,
 222         min_final_cltv_expiry_delta: u16
 223 ) -> Result<BlindedPayInfo, ()> {
 224         let mut curr_base_fee: u64 = 0;
 225         let mut curr_prop_mil: u64 = 0;
 226         let mut cltv_expiry_delta: u16 = min_final_cltv_expiry_delta;
 227         for tlvs in intermediate_nodes.iter().rev().map(|n| &n.tlvs) {
 228                 // In the future, we'll want to take the intersection of all supported features for the
 229                 // `BlindedPayInfo`, but there are no features in that context right now.
 230                 if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
 231
 232                 let next_base_fee = tlvs.payment_relay.fee_base_msat as u64;
 233                 let next_prop_mil = tlvs.payment_relay.fee_proportional_millionths as u64;
 234                 // Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
 235                 // ((curr_base_fee * (1_000_000 + next_prop_mil)) / 1_000_000) + next_base_fee
 236                 curr_base_fee = curr_base_fee.checked_mul(1_000_000 + next_prop_mil)
 237                         .and_then(|f| f.checked_add(1_000_000 - 1))
 238                         .map(|f| f / 1_000_000)
 239                         .and_then(|f| f.checked_add(next_base_fee))
 240                         .ok_or(())?;
 241                 // ceil(((curr_prop_mil + 1_000_000) * (next_prop_mil + 1_000_000)) / 1_000_000) - 1_000_000
 242                 curr_prop_mil = curr_prop_mil.checked_add(1_000_000)
 243                         .and_then(|f1| next_prop_mil.checked_add(1_000_000).and_then(|f2| f2.checked_mul(f1)))
 244                         .and_then(|f| f.checked_add(1_000_000 - 1))
 245                         .map(|f| f / 1_000_000)
 246                         .and_then(|f| f.checked_sub(1_000_000))
 247                         .ok_or(())?;
 248
 249                 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
 250         }
 251
 252         let mut htlc_minimum_msat: u64 = 1;
 253         let mut htlc_maximum_msat: u64 = 21_000_000 * 100_000_000 * 1_000; // Total bitcoin supply
 254         for node in intermediate_nodes.iter() {
 255                 // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
 256                 // following hops for forwarding that min, since that fee amount will automatically be included
 257                 // in the amount that this node receives and contribute towards reaching its min.
 258                 htlc_minimum_msat = amt_to_forward_msat(
 259                         core::cmp::max(node.tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
 260                         &node.tlvs.payment_relay
 261                 ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
 262                 htlc_maximum_msat = amt_to_forward_msat(
 263                         core::cmp::min(node.htlc_maximum_msat, htlc_maximum_msat), &node.tlvs.payment_relay
 264                 ).ok_or(())?; // If underflow occurs, we cannot send to this hop without exceeding their max
 265         }
 266         htlc_minimum_msat = core::cmp::max(
 267                 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
 268         );
 269         htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
 270
 271         if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
 272         Ok(BlindedPayInfo {
 273                 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
 274                 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
 275                 cltv_expiry_delta,
 276                 htlc_minimum_msat,
 277                 htlc_maximum_msat,
 278                 features: BlindedHopFeatures::empty(),
 279         })
 280 }
 281
 282 impl Writeable for PaymentRelay {
 283         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 284                 self.cltv_expiry_delta.write(w)?;
 285                 self.fee_proportional_millionths.write(w)?;
 286                 HighZeroBytesDroppedBigSize(self.fee_base_msat).write(w)
 287         }
 288 }
 289 impl Readable for PaymentRelay {
 290         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 291                 let cltv_expiry_delta: u16 = Readable::read(r)?;
 292                 let fee_proportional_millionths: u32 = Readable::read(r)?;
 293                 let fee_base_msat: HighZeroBytesDroppedBigSize<u32> = Readable::read(r)?;
 294                 Ok(Self { cltv_expiry_delta, fee_proportional_millionths, fee_base_msat: fee_base_msat.0 })
 295         }
 296 }
 297
 298 impl Writeable for PaymentConstraints {
 299         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 300                 self.max_cltv_expiry.write(w)?;
 301                 HighZeroBytesDroppedBigSize(self.htlc_minimum_msat).write(w)
 302         }
 303 }
 304 impl Readable for PaymentConstraints {
 305         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 306                 let max_cltv_expiry: u32 = Readable::read(r)?;
 307                 let htlc_minimum_msat: HighZeroBytesDroppedBigSize<u64> = Readable::read(r)?;
 308                 Ok(Self { max_cltv_expiry, htlc_minimum_msat: htlc_minimum_msat.0 })
 309         }
 310 }
 311
 312 #[cfg(test)]
 313 mod tests {
 314         use bitcoin::secp256k1::PublicKey;
 315         use crate::blinded_path::payment::{ForwardNode, ForwardTlvs, ReceiveTlvs, PaymentConstraints, PaymentRelay};
 316         use crate::ln::PaymentSecret;
 317         use crate::ln::features::BlindedHopFeatures;
 318         use crate::ln::functional_test_utils::TEST_FINAL_CLTV;
 319
 320         #[test]
 321         fn compute_payinfo() {
 322                 // Taken from the spec example for aggregating blinded payment info. See
 323                 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments
 324                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 325                 let intermediate_nodes = vec![ForwardNode {
 326                         node_id: dummy_pk,
 327                         tlvs: ForwardTlvs {
 328                                 short_channel_id: 0,
 329                                 payment_relay: PaymentRelay {
 330                                         cltv_expiry_delta: 144,
 331                                         fee_proportional_millionths: 500,
 332                                         fee_base_msat: 100,
 333                                 },
 334                                 payment_constraints: PaymentConstraints {
 335                                         max_cltv_expiry: 0,
 336                                         htlc_minimum_msat: 100,
 337                                 },
 338                                 features: BlindedHopFeatures::empty(),
 339                         },
 340                         htlc_maximum_msat: u64::max_value(),
 341                 }, ForwardNode {
 342                         node_id: dummy_pk,
 343                         tlvs: ForwardTlvs {
 344                                 short_channel_id: 0,
 345                                 payment_relay: PaymentRelay {
 346                                         cltv_expiry_delta: 144,
 347                                         fee_proportional_millionths: 500,
 348                                         fee_base_msat: 100,
 349                                 },
 350                                 payment_constraints: PaymentConstraints {
 351                                         max_cltv_expiry: 0,
 352                                         htlc_minimum_msat: 1_000,
 353                                 },
 354                                 features: BlindedHopFeatures::empty(),
 355                         },
 356                         htlc_maximum_msat: u64::max_value(),
 357                 }];
 358                 let recv_tlvs = ReceiveTlvs {
 359                         payment_secret: PaymentSecret([0; 32]),
 360                         payment_constraints: PaymentConstraints {
 361                                 max_cltv_expiry: 0,
 362                                 htlc_minimum_msat: 1,
 363                         },
 364                 };
 365                 let htlc_maximum_msat = 100_000;
 366                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, 12).unwrap();
 367                 assert_eq!(blinded_payinfo.fee_base_msat, 201);
 368                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001);
 369                 assert_eq!(blinded_payinfo.cltv_expiry_delta, 300);
 370                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 900);
 371                 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
 372         }
 373
 374         #[test]
 375         fn compute_payinfo_1_hop() {
 376                 let recv_tlvs = ReceiveTlvs {
 377                         payment_secret: PaymentSecret([0; 32]),
 378                         payment_constraints: PaymentConstraints {
 379                                 max_cltv_expiry: 0,
 380                                 htlc_minimum_msat: 1,
 381                         },
 382                 };
 383                 let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs, 4242, TEST_FINAL_CLTV as u16).unwrap();
 384                 assert_eq!(blinded_payinfo.fee_base_msat, 0);
 385                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 0);
 386                 assert_eq!(blinded_payinfo.cltv_expiry_delta, TEST_FINAL_CLTV as u16);
 387                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 1);
 388                 assert_eq!(blinded_payinfo.htlc_maximum_msat, 4242);
 389         }
 390
 391         #[test]
 392         fn simple_aggregated_htlc_min() {
 393                 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
 394                 // along the path.
 395                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 396                 let intermediate_nodes = vec![ForwardNode {
 397                         node_id: dummy_pk,
 398                         tlvs: ForwardTlvs {
 399                                 short_channel_id: 0,
 400                                 payment_relay: PaymentRelay {
 401                                         cltv_expiry_delta: 0,
 402                                         fee_proportional_millionths: 0,
 403                                         fee_base_msat: 0,
 404                                 },
 405                                 payment_constraints: PaymentConstraints {
 406                                         max_cltv_expiry: 0,
 407                                         htlc_minimum_msat: 1,
 408                                 },
 409                                 features: BlindedHopFeatures::empty(),
 410                         },
 411                         htlc_maximum_msat: u64::max_value()
 412                 }, ForwardNode {
 413                         node_id: dummy_pk,
 414                         tlvs: ForwardTlvs {
 415                                 short_channel_id: 0,
 416                                 payment_relay: PaymentRelay {
 417                                         cltv_expiry_delta: 0,
 418                                         fee_proportional_millionths: 0,
 419                                         fee_base_msat: 0,
 420                                 },
 421                                 payment_constraints: PaymentConstraints {
 422                                         max_cltv_expiry: 0,
 423                                         htlc_minimum_msat: 2_000,
 424                                 },
 425                                 features: BlindedHopFeatures::empty(),
 426                         },
 427                         htlc_maximum_msat: u64::max_value()
 428                 }];
 429                 let recv_tlvs = ReceiveTlvs {
 430                         payment_secret: PaymentSecret([0; 32]),
 431                         payment_constraints: PaymentConstraints {
 432                                 max_cltv_expiry: 0,
 433                                 htlc_minimum_msat: 3,
 434                         },
 435                 };
 436                 let htlc_maximum_msat = 100_000;
 437                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, TEST_FINAL_CLTV as u16).unwrap();
 438                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
 439         }
 440
 441         #[test]
 442         fn aggregated_htlc_min() {
 443                 // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the
 444                 // max (htlc_min - following_fees) along the path.
 445                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 446                 let intermediate_nodes = vec![ForwardNode {
 447                         node_id: dummy_pk,
 448                         tlvs: ForwardTlvs {
 449                                 short_channel_id: 0,
 450                                 payment_relay: PaymentRelay {
 451                                         cltv_expiry_delta: 0,
 452                                         fee_proportional_millionths: 500,
 453                                         fee_base_msat: 1_000,
 454                                 },
 455                                 payment_constraints: PaymentConstraints {
 456                                         max_cltv_expiry: 0,
 457                                         htlc_minimum_msat: 5_000,
 458                                 },
 459                                 features: BlindedHopFeatures::empty(),
 460                         },
 461                         htlc_maximum_msat: u64::max_value()
 462                 }, ForwardNode {
 463                         node_id: dummy_pk,
 464                         tlvs: ForwardTlvs {
 465                                 short_channel_id: 0,
 466                                 payment_relay: PaymentRelay {
 467                                         cltv_expiry_delta: 0,
 468                                         fee_proportional_millionths: 500,
 469                                         fee_base_msat: 200,
 470                                 },
 471                                 payment_constraints: PaymentConstraints {
 472                                         max_cltv_expiry: 0,
 473                                         htlc_minimum_msat: 2_000,
 474                                 },
 475                                 features: BlindedHopFeatures::empty(),
 476                         },
 477                         htlc_maximum_msat: u64::max_value()
 478                 }];
 479                 let recv_tlvs = ReceiveTlvs {
 480                         payment_secret: PaymentSecret([0; 32]),
 481                         payment_constraints: PaymentConstraints {
 482                                 max_cltv_expiry: 0,
 483                                 htlc_minimum_msat: 1,
 484                         },
 485                 };
 486                 let htlc_minimum_msat = 3798;
 487                 assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1, TEST_FINAL_CLTV as u16).is_err());
 488
 489                 let htlc_maximum_msat = htlc_minimum_msat + 1;
 490                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, TEST_FINAL_CLTV as u16).unwrap();
 491                 assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
 492                 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
 493         }
 494
 495         #[test]
 496         fn aggregated_htlc_max() {
 497                 // Create a path with varying fees and `htlc_maximum_msat`s, and make sure the aggregated max
 498                 // htlc ends up as the min (htlc_max - following_fees) along the path.
 499                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 500                 let intermediate_nodes = vec![ForwardNode {
 501                         node_id: dummy_pk,
 502                         tlvs: ForwardTlvs {
 503                                 short_channel_id: 0,
 504                                 payment_relay: PaymentRelay {
 505                                         cltv_expiry_delta: 0,
 506                                         fee_proportional_millionths: 500,
 507                                         fee_base_msat: 1_000,
 508                                 },
 509                                 payment_constraints: PaymentConstraints {
 510                                         max_cltv_expiry: 0,
 511                                         htlc_minimum_msat: 1,
 512                                 },
 513                                 features: BlindedHopFeatures::empty(),
 514                         },
 515                         htlc_maximum_msat: 5_000,
 516                 }, ForwardNode {
 517                         node_id: dummy_pk,
 518                         tlvs: ForwardTlvs {
 519                                 short_channel_id: 0,
 520                                 payment_relay: PaymentRelay {
 521                                         cltv_expiry_delta: 0,
 522                                         fee_proportional_millionths: 500,
 523                                         fee_base_msat: 1,
 524                                 },
 525                                 payment_constraints: PaymentConstraints {
 526                                         max_cltv_expiry: 0,
 527                                         htlc_minimum_msat: 1,
 528                                 },
 529                                 features: BlindedHopFeatures::empty(),
 530                         },
 531                         htlc_maximum_msat: 10_000
 532                 }];
 533                 let recv_tlvs = ReceiveTlvs {
 534                         payment_secret: PaymentSecret([0; 32]),
 535                         payment_constraints: PaymentConstraints {
 536                                 max_cltv_expiry: 0,
 537                                 htlc_minimum_msat: 1,
 538                         },
 539                 };
 540
 541                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, 10_000, TEST_FINAL_CLTV as u16).unwrap();
 542                 assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);
 543         }
 544 }