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