1 //! Data structures and methods for constructing [`BlindedPath`]s to send a payment over.
3 //! [`BlindedPath`]: crate::blinded_path::BlindedPath
5 use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
7 use crate::blinded_path::BlindedHop;
8 use crate::blinded_path::utils;
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};
17 use core::convert::TryFrom;
19 /// An intermediate node, its outbound channel, and relay parameters.
20 #[derive(Clone, Debug)]
21 pub struct ForwardNode {
22 /// The TLVs for this node's [`BlindedHop`], where the fee parameters contained within are also
23 /// used for [`BlindedPayInfo`] construction.
24 pub tlvs: ForwardTlvs,
25 /// This node's pubkey.
26 pub node_id: PublicKey,
27 /// The maximum value, in msat, that may be accepted by this node.
28 pub htlc_maximum_msat: u64,
31 /// Data to construct a [`BlindedHop`] for forwarding a payment.
32 #[derive(Clone, Debug)]
33 pub struct ForwardTlvs {
34 /// The short channel id this payment should be forwarded out over.
35 pub short_channel_id: u64,
36 /// Payment parameters for relaying over [`Self::short_channel_id`].
37 pub payment_relay: PaymentRelay,
38 /// Payment constraints for relaying over [`Self::short_channel_id`].
39 pub payment_constraints: PaymentConstraints,
40 /// Supported and required features when relaying a payment onion containing this object's
41 /// corresponding [`BlindedHop::encrypted_payload`].
43 /// [`BlindedHop::encrypted_payload`]: crate::blinded_path::BlindedHop::encrypted_payload
44 pub features: BlindedHopFeatures,
47 /// Data to construct a [`BlindedHop`] for receiving a payment. This payload is custom to LDK and
48 /// may not be valid if received by another lightning implementation.
49 #[derive(Clone, Debug)]
50 pub struct ReceiveTlvs {
51 /// Used to authenticate the sender of a payment to the receiver and tie MPP HTLCs together.
52 pub payment_secret: PaymentSecret,
53 /// Constraints for the receiver of this payment.
54 pub payment_constraints: PaymentConstraints,
57 /// Data to construct a [`BlindedHop`] for sending a payment over.
59 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
60 pub(crate) enum BlindedPaymentTlvs {
61 /// This blinded payment data is for a forwarding node.
63 /// This blinded payment data is for the receiving node.
67 // Used to include forward and receive TLVs in the same iterator for encoding.
68 enum BlindedPaymentTlvsRef<'a> {
69 Forward(&'a ForwardTlvs),
70 Receive(&'a ReceiveTlvs),
73 /// Parameters for relaying over a given [`BlindedHop`].
75 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
76 #[derive(Clone, Debug)]
77 pub struct PaymentRelay {
78 /// Number of blocks subtracted from an incoming HTLC's `cltv_expiry` for this [`BlindedHop`].
79 pub cltv_expiry_delta: u16,
80 /// Liquidity fee charged (in millionths of the amount transferred) for relaying a payment over
81 /// this [`BlindedHop`], (i.e., 10,000 is 1%).
82 pub fee_proportional_millionths: u32,
83 /// Base fee charged (in millisatoshi) for relaying a payment over this [`BlindedHop`].
84 pub fee_base_msat: u32,
87 /// Constraints for relaying over a given [`BlindedHop`].
89 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
90 #[derive(Clone, Debug)]
91 pub struct PaymentConstraints {
92 /// The maximum total CLTV delta that is acceptable when relaying a payment over this
94 pub max_cltv_expiry: u32,
95 /// The minimum value, in msat, that may be accepted by the node corresponding to this
97 pub htlc_minimum_msat: u64,
100 impl Writeable for ForwardTlvs {
101 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
102 encode_tlv_stream!(w, {
103 (2, self.short_channel_id, required),
104 (10, self.payment_relay, required),
105 (12, self.payment_constraints, required),
106 (14, self.features, required)
112 impl Writeable for ReceiveTlvs {
113 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
114 encode_tlv_stream!(w, {
115 (12, self.payment_constraints, required),
116 (65536, self.payment_secret, required)
122 // This will be removed once we support forwarding blinded HTLCs, because we'll always read a
123 // `BlindedPaymentTlvs` instead.
124 impl Readable for ReceiveTlvs {
125 fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
126 _init_and_read_tlv_stream!(r, {
127 (12, payment_constraints, required),
128 (65536, payment_secret, required),
131 payment_secret: payment_secret.0.unwrap(),
132 payment_constraints: payment_constraints.0.unwrap()
137 impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
138 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
139 // TODO: write padding
141 Self::Forward(tlvs) => tlvs.write(w)?,
142 Self::Receive(tlvs) => tlvs.write(w)?,
148 impl Readable for BlindedPaymentTlvs {
149 fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
150 _init_and_read_tlv_stream!(r, {
151 (1, _padding, option),
153 (10, payment_relay, option),
154 (12, payment_constraints, required),
155 (14, features, option),
156 (65536, payment_secret, option),
158 let _padding: Option<utils::Padding> = _padding;
160 if let Some(short_channel_id) = scid {
161 if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
162 Ok(BlindedPaymentTlvs::Forward(ForwardTlvs {
164 payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
165 payment_constraints: payment_constraints.0.unwrap(),
166 features: features.ok_or(DecodeError::InvalidValue)?,
169 if payment_relay.is_some() || features.is_some() { return Err(DecodeError::InvalidValue) }
170 Ok(BlindedPaymentTlvs::Receive(ReceiveTlvs {
171 payment_secret: payment_secret.ok_or(DecodeError::InvalidValue)?,
172 payment_constraints: payment_constraints.0.unwrap(),
178 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
179 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
180 secp_ctx: &Secp256k1<T>, intermediate_nodes: &[ForwardNode],
181 payee_node_id: PublicKey, payee_tlvs: ReceiveTlvs, session_priv: &SecretKey
182 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
183 let pks = intermediate_nodes.iter().map(|node| &node.node_id)
184 .chain(core::iter::once(&payee_node_id));
185 let tlvs = intermediate_nodes.iter().map(|node| BlindedPaymentTlvsRef::Forward(&node.tlvs))
186 .chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
187 utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
190 /// `None` if underflow occurs.
191 fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> Option<u64> {
192 let inbound_amt = inbound_amt_msat as u128;
193 let base = payment_relay.fee_base_msat as u128;
194 let prop = payment_relay.fee_proportional_millionths as u128;
196 let post_base_fee_inbound_amt =
197 if let Some(amt) = inbound_amt.checked_sub(base) { amt } else { return None };
198 let mut amt_to_forward =
199 (post_base_fee_inbound_amt * 1_000_000 + 1_000_000 + prop - 1) / (prop + 1_000_000);
201 let fee = ((amt_to_forward * prop) / 1_000_000) + base;
202 if inbound_amt - fee < amt_to_forward {
203 // Rounding up the forwarded amount resulted in underpaying this node, so take an extra 1 msat
204 // in fee to compensate.
207 debug_assert_eq!(amt_to_forward + fee, inbound_amt);
208 u64::try_from(amt_to_forward).ok()
211 pub(super) fn compute_payinfo(
212 intermediate_nodes: &[ForwardNode], payee_tlvs: &ReceiveTlvs, payee_htlc_maximum_msat: u64
213 ) -> Result<BlindedPayInfo, ()> {
214 let mut curr_base_fee: u64 = 0;
215 let mut curr_prop_mil: u64 = 0;
216 let mut cltv_expiry_delta: u16 = 0;
217 for tlvs in intermediate_nodes.iter().rev().map(|n| &n.tlvs) {
218 // In the future, we'll want to take the intersection of all supported features for the
219 // `BlindedPayInfo`, but there are no features in that context right now.
220 if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
222 let next_base_fee = tlvs.payment_relay.fee_base_msat as u64;
223 let next_prop_mil = tlvs.payment_relay.fee_proportional_millionths as u64;
224 // Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
225 // ((curr_base_fee * (1_000_000 + next_prop_mil)) / 1_000_000) + next_base_fee
226 curr_base_fee = curr_base_fee.checked_mul(1_000_000 + next_prop_mil)
227 .and_then(|f| f.checked_add(1_000_000 - 1))
228 .map(|f| f / 1_000_000)
229 .and_then(|f| f.checked_add(next_base_fee))
231 // ceil(((curr_prop_mil + 1_000_000) * (next_prop_mil + 1_000_000)) / 1_000_000) - 1_000_000
232 curr_prop_mil = curr_prop_mil.checked_add(1_000_000)
233 .and_then(|f1| next_prop_mil.checked_add(1_000_000).and_then(|f2| f2.checked_mul(f1)))
234 .and_then(|f| f.checked_add(1_000_000 - 1))
235 .map(|f| f / 1_000_000)
236 .and_then(|f| f.checked_sub(1_000_000))
239 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
242 let mut htlc_minimum_msat: u64 = 1;
243 let mut htlc_maximum_msat: u64 = 21_000_000 * 100_000_000 * 1_000; // Total bitcoin supply
244 for node in intermediate_nodes.iter() {
245 // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
246 // following hops for forwarding that min, since that fee amount will automatically be included
247 // in the amount that this node receives and contribute towards reaching its min.
248 htlc_minimum_msat = amt_to_forward_msat(
249 core::cmp::max(node.tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
250 &node.tlvs.payment_relay
251 ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
252 htlc_maximum_msat = amt_to_forward_msat(
253 core::cmp::min(node.htlc_maximum_msat, htlc_maximum_msat), &node.tlvs.payment_relay
254 ).ok_or(())?; // If underflow occurs, we cannot send to this hop without exceeding their max
256 htlc_minimum_msat = core::cmp::max(
257 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
259 htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
261 if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
263 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
264 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
268 features: BlindedHopFeatures::empty(),
272 impl_writeable_msg!(PaymentRelay, {
274 fee_proportional_millionths,
278 impl_writeable_msg!(PaymentConstraints, {
285 use bitcoin::secp256k1::PublicKey;
286 use crate::blinded_path::payment::{ForwardNode, ForwardTlvs, ReceiveTlvs, PaymentConstraints, PaymentRelay};
287 use crate::ln::PaymentSecret;
288 use crate::ln::features::BlindedHopFeatures;
291 fn compute_payinfo() {
292 // Taken from the spec example for aggregating blinded payment info. See
293 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments
294 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
295 let intermediate_nodes = vec![ForwardNode {
299 payment_relay: PaymentRelay {
300 cltv_expiry_delta: 144,
301 fee_proportional_millionths: 500,
304 payment_constraints: PaymentConstraints {
306 htlc_minimum_msat: 100,
308 features: BlindedHopFeatures::empty(),
310 htlc_maximum_msat: u64::max_value(),
315 payment_relay: PaymentRelay {
316 cltv_expiry_delta: 144,
317 fee_proportional_millionths: 500,
320 payment_constraints: PaymentConstraints {
322 htlc_minimum_msat: 1_000,
324 features: BlindedHopFeatures::empty(),
326 htlc_maximum_msat: u64::max_value(),
328 let recv_tlvs = ReceiveTlvs {
329 payment_secret: PaymentSecret([0; 32]),
330 payment_constraints: PaymentConstraints {
332 htlc_minimum_msat: 1,
335 let htlc_maximum_msat = 100_000;
336 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
337 assert_eq!(blinded_payinfo.fee_base_msat, 201);
338 assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001);
339 assert_eq!(blinded_payinfo.cltv_expiry_delta, 288);
340 assert_eq!(blinded_payinfo.htlc_minimum_msat, 900);
341 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
345 fn compute_payinfo_1_hop() {
346 let recv_tlvs = ReceiveTlvs {
347 payment_secret: PaymentSecret([0; 32]),
348 payment_constraints: PaymentConstraints {
350 htlc_minimum_msat: 1,
353 let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs, 4242).unwrap();
354 assert_eq!(blinded_payinfo.fee_base_msat, 0);
355 assert_eq!(blinded_payinfo.fee_proportional_millionths, 0);
356 assert_eq!(blinded_payinfo.cltv_expiry_delta, 0);
357 assert_eq!(blinded_payinfo.htlc_minimum_msat, 1);
358 assert_eq!(blinded_payinfo.htlc_maximum_msat, 4242);
362 fn simple_aggregated_htlc_min() {
363 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
365 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
366 let intermediate_nodes = vec![ForwardNode {
370 payment_relay: PaymentRelay {
371 cltv_expiry_delta: 0,
372 fee_proportional_millionths: 0,
375 payment_constraints: PaymentConstraints {
377 htlc_minimum_msat: 1,
379 features: BlindedHopFeatures::empty(),
381 htlc_maximum_msat: u64::max_value()
386 payment_relay: PaymentRelay {
387 cltv_expiry_delta: 0,
388 fee_proportional_millionths: 0,
391 payment_constraints: PaymentConstraints {
393 htlc_minimum_msat: 2_000,
395 features: BlindedHopFeatures::empty(),
397 htlc_maximum_msat: u64::max_value()
399 let recv_tlvs = ReceiveTlvs {
400 payment_secret: PaymentSecret([0; 32]),
401 payment_constraints: PaymentConstraints {
403 htlc_minimum_msat: 3,
406 let htlc_maximum_msat = 100_000;
407 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
408 assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
412 fn aggregated_htlc_min() {
413 // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the
414 // max (htlc_min - following_fees) along the path.
415 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
416 let intermediate_nodes = vec![ForwardNode {
420 payment_relay: PaymentRelay {
421 cltv_expiry_delta: 0,
422 fee_proportional_millionths: 500,
423 fee_base_msat: 1_000,
425 payment_constraints: PaymentConstraints {
427 htlc_minimum_msat: 5_000,
429 features: BlindedHopFeatures::empty(),
431 htlc_maximum_msat: u64::max_value()
436 payment_relay: PaymentRelay {
437 cltv_expiry_delta: 0,
438 fee_proportional_millionths: 500,
441 payment_constraints: PaymentConstraints {
443 htlc_minimum_msat: 2_000,
445 features: BlindedHopFeatures::empty(),
447 htlc_maximum_msat: u64::max_value()
449 let recv_tlvs = ReceiveTlvs {
450 payment_secret: PaymentSecret([0; 32]),
451 payment_constraints: PaymentConstraints {
453 htlc_minimum_msat: 1,
456 let htlc_minimum_msat = 3798;
457 assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1).is_err());
459 let htlc_maximum_msat = htlc_minimum_msat + 1;
460 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
461 assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
462 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
466 fn aggregated_htlc_max() {
467 // Create a path with varying fees and `htlc_maximum_msat`s, and make sure the aggregated max
468 // htlc ends up as the min (htlc_max - following_fees) along the path.
469 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
470 let intermediate_nodes = vec![ForwardNode {
474 payment_relay: PaymentRelay {
475 cltv_expiry_delta: 0,
476 fee_proportional_millionths: 500,
477 fee_base_msat: 1_000,
479 payment_constraints: PaymentConstraints {
481 htlc_minimum_msat: 1,
483 features: BlindedHopFeatures::empty(),
485 htlc_maximum_msat: 5_000,
490 payment_relay: PaymentRelay {
491 cltv_expiry_delta: 0,
492 fee_proportional_millionths: 500,
495 payment_constraints: PaymentConstraints {
497 htlc_minimum_msat: 1,
499 features: BlindedHopFeatures::empty(),
501 htlc_maximum_msat: 10_000
503 let recv_tlvs = ReceiveTlvs {
504 payment_secret: PaymentSecret([0; 32]),
505 payment_constraints: PaymentConstraints {
507 htlc_minimum_msat: 1,
511 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, 10_000).unwrap();
512 assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);