_ 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         short_channel_id: u64,
  23         /// Payment parameters for relaying over [`Self::short_channel_id`].
  24         payment_relay: PaymentRelay,
  25         /// Payment constraints for relaying over [`Self::short_channel_id`].
  26         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         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         payment_secret: PaymentSecret,
  39         /// Constraints for the receiver of this payment.
  40         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)],
 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)], payee_tlvs: &ReceiveTlvs
 180 ) -> Result<BlindedPayInfo, ()> {
 181         let mut curr_base_fee: u64 = 0;
 182         let mut curr_prop_mil: u64 = 0;
 183         let mut cltv_expiry_delta: u16 = 0;
 184         for (_, tlvs) in intermediate_nodes.iter().rev() {
 185                 // In the future, we'll want to take the intersection of all supported features for the
 186                 // `BlindedPayInfo`, but there are no features in that context right now.
 187                 if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
 188
 189                 let next_base_fee = tlvs.payment_relay.fee_base_msat as u64;
 190                 let next_prop_mil = tlvs.payment_relay.fee_proportional_millionths as u64;
 191                 // Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
 192                 // ((curr_base_fee * (1_000_000 + next_prop_mil)) / 1_000_000) + next_base_fee
 193                 curr_base_fee = curr_base_fee.checked_mul(1_000_000 + next_prop_mil)
 194                         .and_then(|f| f.checked_add(1_000_000 - 1))
 195                         .map(|f| f / 1_000_000)
 196                         .and_then(|f| f.checked_add(next_base_fee))
 197                         .ok_or(())?;
 198                 // ceil(((curr_prop_mil + 1_000_000) * (next_prop_mil + 1_000_000)) / 1_000_000) - 1_000_000
 199                 curr_prop_mil = curr_prop_mil.checked_add(1_000_000)
 200                         .and_then(|f1| next_prop_mil.checked_add(1_000_000).and_then(|f2| f2.checked_mul(f1)))
 201                         .and_then(|f| f.checked_add(1_000_000 - 1))
 202                         .map(|f| f / 1_000_000)
 203                         .and_then(|f| f.checked_sub(1_000_000))
 204                         .ok_or(())?;
 205
 206                 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
 207         }
 208
 209         let mut htlc_minimum_msat: u64 = 1;
 210         for (_, tlvs) in intermediate_nodes.iter() {
 211                 // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
 212                 // following hops for forwarding that min, since that fee amount will automatically be included
 213                 // in the amount that this node receives and contribute towards reaching its min.
 214                 htlc_minimum_msat = amt_to_forward_msat(
 215                         core::cmp::max(tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
 216                         &tlvs.payment_relay
 217                 ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
 218         }
 219         htlc_minimum_msat = core::cmp::max(
 220                 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
 221         );
 222
 223         Ok(BlindedPayInfo {
 224                 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
 225                 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
 226                 cltv_expiry_delta,
 227                 htlc_minimum_msat,
 228                 htlc_maximum_msat: 21_000_000 * 100_000_000 * 1_000, // TODO
 229                 features: BlindedHopFeatures::empty(),
 230         })
 231 }
 232
 233 impl_writeable_msg!(PaymentRelay, {
 234         cltv_expiry_delta,
 235         fee_proportional_millionths,
 236         fee_base_msat
 237 }, {});
 238
 239 impl_writeable_msg!(PaymentConstraints, {
 240         max_cltv_expiry,
 241         htlc_minimum_msat
 242 }, {});
 243
 244 #[cfg(test)]
 245 mod tests {
 246         use bitcoin::secp256k1::PublicKey;
 247         use crate::blinded_path::payment::{ForwardTlvs, ReceiveTlvs, PaymentConstraints, PaymentRelay};
 248         use crate::ln::PaymentSecret;
 249         use crate::ln::features::BlindedHopFeatures;
 250
 251         #[test]
 252         fn compute_payinfo() {
 253                 // Taken from the spec example for aggregating blinded payment info. See
 254                 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments
 255                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 256                 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
 257                         short_channel_id: 0,
 258                         payment_relay: PaymentRelay {
 259                                 cltv_expiry_delta: 144,
 260                                 fee_proportional_millionths: 500,
 261                                 fee_base_msat: 100,
 262                         },
 263                         payment_constraints: PaymentConstraints {
 264                                 max_cltv_expiry: 0,
 265                                 htlc_minimum_msat: 100,
 266                         },
 267                         features: BlindedHopFeatures::empty(),
 268                 }), (dummy_pk, ForwardTlvs {
 269                         short_channel_id: 0,
 270                         payment_relay: PaymentRelay {
 271                                 cltv_expiry_delta: 144,
 272                                 fee_proportional_millionths: 500,
 273                                 fee_base_msat: 100,
 274                         },
 275                         payment_constraints: PaymentConstraints {
 276                                 max_cltv_expiry: 0,
 277                                 htlc_minimum_msat: 1_000,
 278                         },
 279                         features: BlindedHopFeatures::empty(),
 280                 })];
 281                 let recv_tlvs = ReceiveTlvs {
 282                         payment_secret: PaymentSecret([0; 32]),
 283                         payment_constraints: PaymentConstraints {
 284                                 max_cltv_expiry: 0,
 285                                 htlc_minimum_msat: 1,
 286                         },
 287                 };
 288                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap();
 289                 assert_eq!(blinded_payinfo.fee_base_msat, 201);
 290                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001);
 291                 assert_eq!(blinded_payinfo.cltv_expiry_delta, 288);
 292                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 900);
 293         }
 294
 295         #[test]
 296         fn compute_payinfo_1_hop() {
 297                 let recv_tlvs = ReceiveTlvs {
 298                         payment_secret: PaymentSecret([0; 32]),
 299                         payment_constraints: PaymentConstraints {
 300                                 max_cltv_expiry: 0,
 301                                 htlc_minimum_msat: 1,
 302                         },
 303                 };
 304                 let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs).unwrap();
 305                 assert_eq!(blinded_payinfo.fee_base_msat, 0);
 306                 assert_eq!(blinded_payinfo.fee_proportional_millionths, 0);
 307                 assert_eq!(blinded_payinfo.cltv_expiry_delta, 0);
 308                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 1);
 309         }
 310
 311         #[test]
 312         fn simple_aggregated_htlc_min() {
 313                 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
 314                 // along the path.
 315                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 316                 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
 317                         short_channel_id: 0,
 318                         payment_relay: PaymentRelay {
 319                                 cltv_expiry_delta: 0,
 320                                 fee_proportional_millionths: 0,
 321                                 fee_base_msat: 0,
 322                         },
 323                         payment_constraints: PaymentConstraints {
 324                                 max_cltv_expiry: 0,
 325                                 htlc_minimum_msat: 1,
 326                         },
 327                         features: BlindedHopFeatures::empty(),
 328                 }), (dummy_pk, ForwardTlvs {
 329                         short_channel_id: 0,
 330                         payment_relay: PaymentRelay {
 331                                 cltv_expiry_delta: 0,
 332                                 fee_proportional_millionths: 0,
 333                                 fee_base_msat: 0,
 334                         },
 335                         payment_constraints: PaymentConstraints {
 336                                 max_cltv_expiry: 0,
 337                                 htlc_minimum_msat: 2_000,
 338                         },
 339                         features: BlindedHopFeatures::empty(),
 340                 })];
 341                 let recv_tlvs = ReceiveTlvs {
 342                         payment_secret: PaymentSecret([0; 32]),
 343                         payment_constraints: PaymentConstraints {
 344                                 max_cltv_expiry: 0,
 345                                 htlc_minimum_msat: 3,
 346                         },
 347                 };
 348                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap();
 349                 assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
 350         }
 351
 352         #[test]
 353         fn aggregated_htlc_min() {
 354                 // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the
 355                 // max (htlc_min - following_fees) along the path.
 356                 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
 357                 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
 358                         short_channel_id: 0,
 359                         payment_relay: PaymentRelay {
 360                                 cltv_expiry_delta: 0,
 361                                 fee_proportional_millionths: 500,
 362                                 fee_base_msat: 1_000,
 363                         },
 364                         payment_constraints: PaymentConstraints {
 365                                 max_cltv_expiry: 0,
 366                                 htlc_minimum_msat: 5_000,
 367                         },
 368                         features: BlindedHopFeatures::empty(),
 369                 }), (dummy_pk, ForwardTlvs {
 370                         short_channel_id: 0,
 371                         payment_relay: PaymentRelay {
 372                                 cltv_expiry_delta: 0,
 373                                 fee_proportional_millionths: 500,
 374                                 fee_base_msat: 200,
 375                         },
 376                         payment_constraints: PaymentConstraints {
 377                                 max_cltv_expiry: 0,
 378                                 htlc_minimum_msat: 2_000,
 379                         },
 380                         features: BlindedHopFeatures::empty(),
 381                 })];
 382                 let recv_tlvs = ReceiveTlvs {
 383                         payment_secret: PaymentSecret([0; 32]),
 384                         payment_constraints: PaymentConstraints {
 385                                 max_cltv_expiry: 0,
 386                                 htlc_minimum_msat: 1,
 387                         },
 388                 };
 389                 let htlc_minimum_msat = 3798;
 390                 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs).unwrap();
 391                 assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
 392         }
 393 }