_ 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         pub cltv_expiry_delta: u16,
  68         /// Liquidity fee charged (in millionths of the amount transferred) for relaying a payment over
  69         /// this [`BlindedHop`], (i.e., 10,000 is 1%).
  70         pub fee_proportional_millionths: u32,
  71         /// Base fee charged (in millisatoshi) for relaying a payment over this [`BlindedHop`].
  72         pub fee_base_msat: u32,
  73 }
  74
  75 /// Constraints for relaying over a given [`BlindedHop`].
  76 ///
  77 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
  78 #[derive(Clone, Debug)]
  79 pub struct PaymentConstraints {
  80         /// The maximum total CLTV delta that is acceptable when relaying a payment over this
  81         /// [`BlindedHop`].
  82         pub max_cltv_expiry: u32,
  83         /// The minimum value, in msat, that may be accepted by the node corresponding to this
  84         /// [`BlindedHop`].
  85         pub htlc_minimum_msat: u64,
  86 }
  87
  88 impl Writeable for ForwardTlvs {
  89         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
  90                 encode_tlv_stream!(w, {
  91                         (2, self.short_channel_id, required),
  92                         (10, self.payment_relay, required),
  93                         (12, self.payment_constraints, required),
  94                         (14, self.features, required)
  95                 });
  96                 Ok(())
  97         }
  98 }
  99
 100 impl Writeable for ReceiveTlvs {
 101         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 102                 encode_tlv_stream!(w, {
 103                         (12, self.payment_constraints, required),
 104                         (65536, self.payment_secret, required)
 105                 });
 106                 Ok(())
 107         }
 108 }
 109
 110 impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
 111         fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
 112                 // TODO: write padding
 113                 match self {
 114                         Self::Forward(tlvs) => tlvs.write(w)?,
 115                         Self::Receive(tlvs) => tlvs.write(w)?,
 116                 }
 117                 Ok(())
 118         }
 119 }
 120
 121 impl Readable for BlindedPaymentTlvs {
 122         fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
 123                 _init_and_read_tlv_stream!(r, {
 124                         (1, _padding, option),
 125                         (2, scid, option),
 126                         (10, payment_relay, option),
 127                         (12, payment_constraints, required),
 128                         (14, features, option),
 129                         (65536, payment_secret, option),
 130                 });
 131                 let _padding: Option<utils::Padding> = _padding;
 132
 133                 if let Some(short_channel_id) = scid {
 134                         if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
 135                         Ok(BlindedPaymentTlvs::Forward(ForwardTlvs {
 136                                 short_channel_id,
 137                                 payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
 138                                 payment_constraints: payment_constraints.0.unwrap(),
 139                                 features: features.ok_or(DecodeError::InvalidValue)?,
 140                         }))
 141                 } else {
 142                         if payment_relay.is_some() || features.is_some() { return Err(DecodeError::InvalidValue) }
 143                         Ok(BlindedPaymentTlvs::Receive(ReceiveTlvs {
 144                                 payment_secret: payment_secret.ok_or(DecodeError::InvalidValue)?,
 145                                 payment_constraints: payment_constraints.0.unwrap(),
 146                         }))
 147                 }
 148         }
 149 }
 150
 151 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
 152 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
 153         secp_ctx: &Secp256k1<T>, intermediate_nodes: &[(PublicKey, ForwardTlvs, u64)],
 154         payee_node_id: PublicKey, payee_tlvs: ReceiveTlvs, session_priv: &SecretKey
 155 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
 156         let pks = intermediate_nodes.iter().map(|(pk, _, _)| pk)
 157                 .chain(core::iter::once(&payee_node_id));
 158         let tlvs = intermediate_nodes.iter().map(|(_, tlvs, _)| BlindedPaymentTlvsRef::Forward(tlvs))
 159                 .chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
 160         utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
 161 }
 162
 163 /// `None` if underflow occurs.
 164 fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> Option<u64> {
 165         let inbound_amt = inbound_amt_msat as u128;
 166         let base = payment_relay.fee_base_msat as u128;
 167         let prop = payment_relay.fee_proportional_millionths as u128;
 168
 169         let post_base_fee_inbound_amt =
 170                 if let Some(amt) = inbound_amt.checked_sub(base) { amt } else { return None };
 171         let mut amt_to_forward =
 172                 (post_base_fee_inbound_amt * 1_000_000 + 1_000_000 + prop - 1) / (prop + 1_000_000);
 173
 174         let fee = ((amt_to_forward * prop) / 1_000_000) + base;
 175         if inbound_amt - fee < amt_to_forward {
 176                 // Rounding up the forwarded amount resulted in underpaying this node, so take an extra 1 msat
 177                 // in fee to compensate.
 178                 amt_to_forward -= 1;
 179         }
 180         debug_assert_eq!(amt_to_forward + fee, inbound_amt);
 181         u64::try_from(amt_to_forward).ok()
 182 }
 183
 184 pub(super) fn compute_payinfo(
 185         intermediate_nodes: &[(PublicKey, ForwardTlvs, u64)], payee_tlvs: &ReceiveTlvs,
 186         payee_htlc_maximum_msat: u64
 187 ) -> Result<BlindedPayInfo, ()> {
 188         let mut curr_base_fee: u64 = 0;
 189         let mut curr_prop_mil: u64 = 0;
 190         let mut cltv_expiry_delta: u16 = 0;
 191         for (_, tlvs, _) in intermediate_nodes.iter().rev() {
 192                 // In the future, we'll want to take the intersection of all supported features for the
 193                 // `BlindedPayInfo`, but there are no features in that context right now.
 194                 if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
 195
 196                 let next_base_fee = tlvs.payment_relay.fee_base_msat as u64;
 197                 let next_prop_mil = tlvs.payment_relay.fee_proportional_millionths as u64;
 198                 // Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
 199                 // ((curr_base_fee * (1_000_000 + next_prop_mil)) / 1_000_000) + next_base_fee
 200                 curr_base_fee = curr_base_fee.checked_mul(1_000_000 + next_prop_mil)
 201                         .and_then(|f| f.checked_add(1_000_000 - 1))
 202                         .map(|f| f / 1_000_000)
 203                         .and_then(|f| f.checked_add(next_base_fee))
 204                         .ok_or(())?;
 205                 // ceil(((curr_prop_mil + 1_000_000) * (next_prop_mil + 1_000_000)) / 1_000_000) - 1_000_000
 206                 curr_prop_mil = curr_prop_mil.checked_add(1_000_000)
 207                         .and_then(|f1| next_prop_mil.checked_add(1_000_000).and_then(|f2| f2.checked_mul(f1)))
 208                         .and_then(|f| f.checked_add(1_000_000 - 1))
 209                         .map(|f| f / 1_000_000)
 210                         .and_then(|f| f.checked_sub(1_000_000))
 211                         .ok_or(())?;
 212
 213                 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
 214         }
 215
 216         let mut htlc_minimum_msat: u64 = 1;
 217         let mut htlc_maximum_msat: u64 = 21_000_000 * 100_000_000 * 1_000; // Total bitcoin supply
 218         for (_, tlvs, max_htlc_candidate) in intermediate_nodes.iter() {
 219                 // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
 220                 // following hops for forwarding that min, since that fee amount will automatically be included
 221                 // in the amount that this node receives and contribute towards reaching its min.
 222                 htlc_minimum_msat = amt_to_forward_msat(
 223                         core::cmp::max(tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
 224                         &tlvs.payment_relay
 225                 ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
 226                 htlc_maximum_msat = amt_to_forward_msat(
 227                         core::cmp::min(*max_htlc_candidate, htlc_maximum_msat), &tlvs.payment_relay
 228                 ).ok_or(())?; // If underflow occurs, we cannot send to this hop without exceeding their max
 229         }
 230         htlc_minimum_msat = core::cmp::max(
 231                 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
 232         );
 233         htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
 234
 235         if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
 236         Ok(BlindedPayInfo {
 237                 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
 238                 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
 239                 cltv_expiry_delta,
 240                 htlc_minimum_msat,
 241                 htlc_maximum_msat,
 242                 features: BlindedHopFeatures::empty(),
 243         })
 244 }
 245
 246 impl_writeable_msg!(PaymentRelay, {
 247         cltv_expiry_delta,
 248         fee_proportional_millionths,
 249         fee_base_msat
 250 }, {});
 251
 252 impl_writeable_msg!(PaymentConstraints, {
 253         max_cltv_expiry,
 254         htlc_minimum_msat
 255 }, {});
 256
 257 #[cfg(test)]
 258 mod tests {
 259         use bitcoin::secp256k1::PublicKey;
 260         use crate::blinded_path::payment::{ForwardTlvs, ReceiveTlvs, PaymentConstraints, PaymentRelay};
 261         use crate::ln::PaymentSecret;
 262         use crate::ln::features::BlindedHopFeatures;
 263
 264         #[test]
 265         fn compute_payinfo() {
 266                 // Taken from the spec example for aggregating blinded payment info. See
 267                 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments
 268                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 269                 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
 270                         short_channel_id: 0,
 271                         payment_relay: PaymentRelay {
 272                                 cltv_expiry_delta: 144,
 273                                 fee_proportional_millionths: 500,
 274                                 fee_base_msat: 100,
 275                         },
 276                         payment_constraints: PaymentConstraints {
 277                                 max_cltv_expiry: 0,
 278                                 htlc_minimum_msat: 100,
 279                         },
 280                         features: BlindedHopFeatures::empty(),
 281                 }, u64::max_value()), (dummy_pk, ForwardTlvs {
 282                         short_channel_id: 0,
 283                         payment_relay: PaymentRelay {
 284                                 cltv_expiry_delta: 144,
 285                                 fee_proportional_millionths: 500,
 286                                 fee_base_msat: 100,
 287                         },
 288                         payment_constraints: PaymentConstraints {
 289                                 max_cltv_expiry: 0,
 290                                 htlc_minimum_msat: 1_000,
 291                         },
 292                         features: BlindedHopFeatures::empty(),
 293                 }, u64::max_value())];
 294                 let recv_tlvs = ReceiveTlvs {
 295                         payment_secret: PaymentSecret([0; 32]),
 296                         payment_constraints: PaymentConstraints {
 297                                 max_cltv_expiry: 0,
 298                                 htlc_minimum_msat: 1,
 299                         },
 300                 };
 301                 let htlc_maximum_msat = 100_000;
 302                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
 303                 assert_eq!(blinded_payinfo.fee_base_msat, 201);
 304                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001);
 305                 assert_eq!(blinded_payinfo.cltv_expiry_delta, 288);
 306                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 900);
 307                 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
 308         }
 309
 310         #[test]
 311         fn compute_payinfo_1_hop() {
 312                 let recv_tlvs = ReceiveTlvs {
 313                         payment_secret: PaymentSecret([0; 32]),
 314                         payment_constraints: PaymentConstraints {
 315                                 max_cltv_expiry: 0,
 316                                 htlc_minimum_msat: 1,
 317                         },
 318                 };
 319                 let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs, 4242).unwrap();
 320                 assert_eq!(blinded_payinfo.fee_base_msat, 0);
 321                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 0);
 322                 assert_eq!(blinded_payinfo.cltv_expiry_delta, 0);
 323                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 1);
 324                 assert_eq!(blinded_payinfo.htlc_maximum_msat, 4242);
 325         }
 326
 327         #[test]
 328         fn simple_aggregated_htlc_min() {
 329                 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
 330                 // along the path.
 331                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 332                 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
 333                         short_channel_id: 0,
 334                         payment_relay: PaymentRelay {
 335                                 cltv_expiry_delta: 0,
 336                                 fee_proportional_millionths: 0,
 337                                 fee_base_msat: 0,
 338                         },
 339                         payment_constraints: PaymentConstraints {
 340                                 max_cltv_expiry: 0,
 341                                 htlc_minimum_msat: 1,
 342                         },
 343                         features: BlindedHopFeatures::empty(),
 344                 }, u64::max_value()), (dummy_pk, ForwardTlvs {
 345                         short_channel_id: 0,
 346                         payment_relay: PaymentRelay {
 347                                 cltv_expiry_delta: 0,
 348                                 fee_proportional_millionths: 0,
 349                                 fee_base_msat: 0,
 350                         },
 351                         payment_constraints: PaymentConstraints {
 352                                 max_cltv_expiry: 0,
 353                                 htlc_minimum_msat: 2_000,
 354                         },
 355                         features: BlindedHopFeatures::empty(),
 356                 }, u64::max_value())];
 357                 let recv_tlvs = ReceiveTlvs {
 358                         payment_secret: PaymentSecret([0; 32]),
 359                         payment_constraints: PaymentConstraints {
 360                                 max_cltv_expiry: 0,
 361                                 htlc_minimum_msat: 3,
 362                         },
 363                 };
 364                 let htlc_maximum_msat = 100_000;
 365                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
 366                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
 367         }
 368
 369         #[test]
 370         fn aggregated_htlc_min() {
 371                 // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the
 372                 // max (htlc_min - following_fees) along the path.
 373                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 374                 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
 375                         short_channel_id: 0,
 376                         payment_relay: PaymentRelay {
 377                                 cltv_expiry_delta: 0,
 378                                 fee_proportional_millionths: 500,
 379                                 fee_base_msat: 1_000,
 380                         },
 381                         payment_constraints: PaymentConstraints {
 382                                 max_cltv_expiry: 0,
 383                                 htlc_minimum_msat: 5_000,
 384                         },
 385                         features: BlindedHopFeatures::empty(),
 386                 }, u64::max_value()), (dummy_pk, ForwardTlvs {
 387                         short_channel_id: 0,
 388                         payment_relay: PaymentRelay {
 389                                 cltv_expiry_delta: 0,
 390                                 fee_proportional_millionths: 500,
 391                                 fee_base_msat: 200,
 392                         },
 393                         payment_constraints: PaymentConstraints {
 394                                 max_cltv_expiry: 0,
 395                                 htlc_minimum_msat: 2_000,
 396                         },
 397                         features: BlindedHopFeatures::empty(),
 398                 }, u64::max_value())];
 399                 let recv_tlvs = ReceiveTlvs {
 400                         payment_secret: PaymentSecret([0; 32]),
 401                         payment_constraints: PaymentConstraints {
 402                                 max_cltv_expiry: 0,
 403                                 htlc_minimum_msat: 1,
 404                         },
 405                 };
 406                 let htlc_minimum_msat = 3798;
 407                 assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1).is_err());
 408
 409                 let htlc_maximum_msat = htlc_minimum_msat + 1;
 410                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
 411                 assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
 412                 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
 413         }
 414
 415         #[test]
 416         fn aggregated_htlc_max() {
 417                 // Create a path with varying fees and `htlc_maximum_msat`s, and make sure the aggregated max
 418                 // htlc ends up as the min (htlc_max - following_fees) along the path.
 419                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 420                 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
 421                         short_channel_id: 0,
 422                         payment_relay: PaymentRelay {
 423                                 cltv_expiry_delta: 0,
 424                                 fee_proportional_millionths: 500,
 425                                 fee_base_msat: 1_000,
 426                         },
 427                         payment_constraints: PaymentConstraints {
 428                                 max_cltv_expiry: 0,
 429                                 htlc_minimum_msat: 1,
 430                         },
 431                         features: BlindedHopFeatures::empty(),
 432                 }, 5_000), (dummy_pk, ForwardTlvs {
 433                         short_channel_id: 0,
 434                         payment_relay: PaymentRelay {
 435                                 cltv_expiry_delta: 0,
 436                                 fee_proportional_millionths: 500,
 437                                 fee_base_msat: 1,
 438                         },
 439                         payment_constraints: PaymentConstraints {
 440                                 max_cltv_expiry: 0,
 441                                 htlc_minimum_msat: 1,
 442                         },
 443                         features: BlindedHopFeatures::empty(),
 444                 }, 10_000)];
 445                 let recv_tlvs = ReceiveTlvs {
 446                         payment_secret: PaymentSecret([0; 32]),
 447                         payment_constraints: PaymentConstraints {
 448                                 max_cltv_expiry: 0,
 449                                 htlc_minimum_msat: 1,
 450                         },
 451                 };
 452
 453                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, 10_000).unwrap();
 454                 assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);
 455         }
 456 }