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