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::channelmanager::CounterpartyForwardingInfo;
12 use crate::ln::features::BlindedHopFeatures;
13 use crate::ln::msgs::DecodeError;
14 use crate::offers::invoice::BlindedPayInfo;
15 use crate::prelude::*;
16 use crate::util::ser::{HighZeroBytesDroppedBigSize, Readable, Writeable, Writer};
18 use core::convert::TryFrom;
20 /// An intermediate node, its outbound channel, and relay parameters.
21 #[derive(Clone, Debug)]
22 pub struct ForwardNode {
23 /// The TLVs for this node's [`BlindedHop`], where the fee parameters contained within are also
24 /// used for [`BlindedPayInfo`] construction.
25 pub tlvs: ForwardTlvs,
26 /// This node's pubkey.
27 pub node_id: PublicKey,
28 /// The maximum value, in msat, that may be accepted by this node.
29 pub htlc_maximum_msat: u64,
32 /// Data to construct a [`BlindedHop`] for forwarding a payment.
33 #[derive(Clone, Debug)]
34 pub struct ForwardTlvs {
35 /// The short channel id this payment should be forwarded out over.
36 pub short_channel_id: u64,
37 /// Payment parameters for relaying over [`Self::short_channel_id`].
38 pub payment_relay: PaymentRelay,
39 /// Payment constraints for relaying over [`Self::short_channel_id`].
40 pub payment_constraints: PaymentConstraints,
41 /// Supported and required features when relaying a payment onion containing this object's
42 /// corresponding [`BlindedHop::encrypted_payload`].
44 /// [`BlindedHop::encrypted_payload`]: crate::blinded_path::BlindedHop::encrypted_payload
45 pub features: BlindedHopFeatures,
48 /// Data to construct a [`BlindedHop`] for receiving a payment. This payload is custom to LDK and
49 /// may not be valid if received by another lightning implementation.
50 #[derive(Clone, Debug)]
51 pub struct ReceiveTlvs {
52 /// Used to authenticate the sender of a payment to the receiver and tie MPP HTLCs together.
53 pub payment_secret: PaymentSecret,
54 /// Constraints for the receiver of this payment.
55 pub payment_constraints: PaymentConstraints,
58 /// Data to construct a [`BlindedHop`] for sending a payment over.
60 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
61 pub(crate) enum BlindedPaymentTlvs {
62 /// This blinded payment data is for a forwarding node.
64 /// This blinded payment data is for the receiving node.
68 // Used to include forward and receive TLVs in the same iterator for encoding.
69 enum BlindedPaymentTlvsRef<'a> {
70 Forward(&'a ForwardTlvs),
71 Receive(&'a ReceiveTlvs),
74 /// Parameters for relaying over a given [`BlindedHop`].
76 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
77 #[derive(Clone, Debug)]
78 pub struct PaymentRelay {
79 /// Number of blocks subtracted from an incoming HTLC's `cltv_expiry` for this [`BlindedHop`].
80 pub cltv_expiry_delta: u16,
81 /// Liquidity fee charged (in millionths of the amount transferred) for relaying a payment over
82 /// this [`BlindedHop`], (i.e., 10,000 is 1%).
83 pub fee_proportional_millionths: u32,
84 /// Base fee charged (in millisatoshi) for relaying a payment over this [`BlindedHop`].
85 pub fee_base_msat: u32,
88 /// Constraints for relaying over a given [`BlindedHop`].
90 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
91 #[derive(Clone, Debug)]
92 pub struct PaymentConstraints {
93 /// The maximum total CLTV that is acceptable when relaying a payment over this [`BlindedHop`].
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 TryFrom<CounterpartyForwardingInfo> for PaymentRelay {
103 fn try_from(info: CounterpartyForwardingInfo) -> Result<Self, ()> {
104 let CounterpartyForwardingInfo {
105 fee_base_msat, fee_proportional_millionths, cltv_expiry_delta
108 // Avoid exposing esoteric CLTV expiry deltas
109 let cltv_expiry_delta = match cltv_expiry_delta {
117 Ok(Self { cltv_expiry_delta, fee_proportional_millionths, fee_base_msat })
121 impl Writeable for ForwardTlvs {
122 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
123 encode_tlv_stream!(w, {
124 (2, self.short_channel_id, required),
125 (10, self.payment_relay, required),
126 (12, self.payment_constraints, required),
127 (14, self.features, required)
133 impl Writeable for ReceiveTlvs {
134 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
135 encode_tlv_stream!(w, {
136 (12, self.payment_constraints, required),
137 (65536, self.payment_secret, required)
143 impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
144 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
145 // TODO: write padding
147 Self::Forward(tlvs) => tlvs.write(w)?,
148 Self::Receive(tlvs) => tlvs.write(w)?,
154 impl Readable for BlindedPaymentTlvs {
155 fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
156 _init_and_read_tlv_stream!(r, {
157 (1, _padding, option),
159 (10, payment_relay, option),
160 (12, payment_constraints, required),
161 (14, features, option),
162 (65536, payment_secret, option),
164 let _padding: Option<utils::Padding> = _padding;
166 if let Some(short_channel_id) = scid {
167 if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
168 Ok(BlindedPaymentTlvs::Forward(ForwardTlvs {
170 payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
171 payment_constraints: payment_constraints.0.unwrap(),
172 features: features.ok_or(DecodeError::InvalidValue)?,
175 if payment_relay.is_some() || features.is_some() { return Err(DecodeError::InvalidValue) }
176 Ok(BlindedPaymentTlvs::Receive(ReceiveTlvs {
177 payment_secret: payment_secret.ok_or(DecodeError::InvalidValue)?,
178 payment_constraints: payment_constraints.0.unwrap(),
184 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
185 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
186 secp_ctx: &Secp256k1<T>, intermediate_nodes: &[ForwardNode],
187 payee_node_id: PublicKey, payee_tlvs: ReceiveTlvs, session_priv: &SecretKey
188 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
189 let pks = intermediate_nodes.iter().map(|node| &node.node_id)
190 .chain(core::iter::once(&payee_node_id));
191 let tlvs = intermediate_nodes.iter().map(|node| BlindedPaymentTlvsRef::Forward(&node.tlvs))
192 .chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
193 utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
196 /// `None` if underflow occurs.
197 pub(crate) fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> Option<u64> {
198 let inbound_amt = inbound_amt_msat as u128;
199 let base = payment_relay.fee_base_msat as u128;
200 let prop = payment_relay.fee_proportional_millionths as u128;
202 let post_base_fee_inbound_amt =
203 if let Some(amt) = inbound_amt.checked_sub(base) { amt } else { return None };
204 let mut amt_to_forward =
205 (post_base_fee_inbound_amt * 1_000_000 + 1_000_000 + prop - 1) / (prop + 1_000_000);
207 let fee = ((amt_to_forward * prop) / 1_000_000) + base;
208 if inbound_amt - fee < amt_to_forward {
209 // Rounding up the forwarded amount resulted in underpaying this node, so take an extra 1 msat
210 // in fee to compensate.
213 debug_assert_eq!(amt_to_forward + fee, inbound_amt);
214 u64::try_from(amt_to_forward).ok()
217 pub(super) fn compute_payinfo(
218 intermediate_nodes: &[ForwardNode], payee_tlvs: &ReceiveTlvs, payee_htlc_maximum_msat: u64,
219 min_final_cltv_expiry_delta: u16
220 ) -> Result<BlindedPayInfo, ()> {
221 let mut curr_base_fee: u64 = 0;
222 let mut curr_prop_mil: u64 = 0;
223 let mut cltv_expiry_delta: u16 = min_final_cltv_expiry_delta;
224 for tlvs in intermediate_nodes.iter().rev().map(|n| &n.tlvs) {
225 // In the future, we'll want to take the intersection of all supported features for the
226 // `BlindedPayInfo`, but there are no features in that context right now.
227 if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
229 let next_base_fee = tlvs.payment_relay.fee_base_msat as u64;
230 let next_prop_mil = tlvs.payment_relay.fee_proportional_millionths as u64;
231 // Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
232 // ((curr_base_fee * (1_000_000 + next_prop_mil)) / 1_000_000) + next_base_fee
233 curr_base_fee = curr_base_fee.checked_mul(1_000_000 + next_prop_mil)
234 .and_then(|f| f.checked_add(1_000_000 - 1))
235 .map(|f| f / 1_000_000)
236 .and_then(|f| f.checked_add(next_base_fee))
238 // ceil(((curr_prop_mil + 1_000_000) * (next_prop_mil + 1_000_000)) / 1_000_000) - 1_000_000
239 curr_prop_mil = curr_prop_mil.checked_add(1_000_000)
240 .and_then(|f1| next_prop_mil.checked_add(1_000_000).and_then(|f2| f2.checked_mul(f1)))
241 .and_then(|f| f.checked_add(1_000_000 - 1))
242 .map(|f| f / 1_000_000)
243 .and_then(|f| f.checked_sub(1_000_000))
246 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
249 let mut htlc_minimum_msat: u64 = 1;
250 let mut htlc_maximum_msat: u64 = 21_000_000 * 100_000_000 * 1_000; // Total bitcoin supply
251 for node in intermediate_nodes.iter() {
252 // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
253 // following hops for forwarding that min, since that fee amount will automatically be included
254 // in the amount that this node receives and contribute towards reaching its min.
255 htlc_minimum_msat = amt_to_forward_msat(
256 core::cmp::max(node.tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
257 &node.tlvs.payment_relay
258 ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
259 htlc_maximum_msat = amt_to_forward_msat(
260 core::cmp::min(node.htlc_maximum_msat, htlc_maximum_msat), &node.tlvs.payment_relay
261 ).ok_or(())?; // If underflow occurs, we cannot send to this hop without exceeding their max
263 htlc_minimum_msat = core::cmp::max(
264 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
266 htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
268 if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
270 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
271 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
275 features: BlindedHopFeatures::empty(),
279 impl Writeable for PaymentRelay {
280 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
281 self.cltv_expiry_delta.write(w)?;
282 self.fee_proportional_millionths.write(w)?;
283 HighZeroBytesDroppedBigSize(self.fee_base_msat).write(w)
286 impl Readable for PaymentRelay {
287 fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
288 let cltv_expiry_delta: u16 = Readable::read(r)?;
289 let fee_proportional_millionths: u32 = Readable::read(r)?;
290 let fee_base_msat: HighZeroBytesDroppedBigSize<u32> = Readable::read(r)?;
291 Ok(Self { cltv_expiry_delta, fee_proportional_millionths, fee_base_msat: fee_base_msat.0 })
295 impl Writeable for PaymentConstraints {
296 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
297 self.max_cltv_expiry.write(w)?;
298 HighZeroBytesDroppedBigSize(self.htlc_minimum_msat).write(w)
301 impl Readable for PaymentConstraints {
302 fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
303 let max_cltv_expiry: u32 = Readable::read(r)?;
304 let htlc_minimum_msat: HighZeroBytesDroppedBigSize<u64> = Readable::read(r)?;
305 Ok(Self { max_cltv_expiry, htlc_minimum_msat: htlc_minimum_msat.0 })
311 use bitcoin::secp256k1::PublicKey;
312 use crate::blinded_path::payment::{ForwardNode, ForwardTlvs, ReceiveTlvs, PaymentConstraints, PaymentRelay};
313 use crate::ln::PaymentSecret;
314 use crate::ln::features::BlindedHopFeatures;
315 use crate::ln::functional_test_utils::TEST_FINAL_CLTV;
318 fn compute_payinfo() {
319 // Taken from the spec example for aggregating blinded payment info. See
320 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments
321 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
322 let intermediate_nodes = vec![ForwardNode {
326 payment_relay: PaymentRelay {
327 cltv_expiry_delta: 144,
328 fee_proportional_millionths: 500,
331 payment_constraints: PaymentConstraints {
333 htlc_minimum_msat: 100,
335 features: BlindedHopFeatures::empty(),
337 htlc_maximum_msat: u64::max_value(),
342 payment_relay: PaymentRelay {
343 cltv_expiry_delta: 144,
344 fee_proportional_millionths: 500,
347 payment_constraints: PaymentConstraints {
349 htlc_minimum_msat: 1_000,
351 features: BlindedHopFeatures::empty(),
353 htlc_maximum_msat: u64::max_value(),
355 let recv_tlvs = ReceiveTlvs {
356 payment_secret: PaymentSecret([0; 32]),
357 payment_constraints: PaymentConstraints {
359 htlc_minimum_msat: 1,
362 let htlc_maximum_msat = 100_000;
363 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, 12).unwrap();
364 assert_eq!(blinded_payinfo.fee_base_msat, 201);
365 assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001);
366 assert_eq!(blinded_payinfo.cltv_expiry_delta, 300);
367 assert_eq!(blinded_payinfo.htlc_minimum_msat, 900);
368 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
372 fn compute_payinfo_1_hop() {
373 let recv_tlvs = ReceiveTlvs {
374 payment_secret: PaymentSecret([0; 32]),
375 payment_constraints: PaymentConstraints {
377 htlc_minimum_msat: 1,
380 let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs, 4242, TEST_FINAL_CLTV as u16).unwrap();
381 assert_eq!(blinded_payinfo.fee_base_msat, 0);
382 assert_eq!(blinded_payinfo.fee_proportional_millionths, 0);
383 assert_eq!(blinded_payinfo.cltv_expiry_delta, TEST_FINAL_CLTV as u16);
384 assert_eq!(blinded_payinfo.htlc_minimum_msat, 1);
385 assert_eq!(blinded_payinfo.htlc_maximum_msat, 4242);
389 fn simple_aggregated_htlc_min() {
390 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
392 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
393 let intermediate_nodes = vec![ForwardNode {
397 payment_relay: PaymentRelay {
398 cltv_expiry_delta: 0,
399 fee_proportional_millionths: 0,
402 payment_constraints: PaymentConstraints {
404 htlc_minimum_msat: 1,
406 features: BlindedHopFeatures::empty(),
408 htlc_maximum_msat: u64::max_value()
413 payment_relay: PaymentRelay {
414 cltv_expiry_delta: 0,
415 fee_proportional_millionths: 0,
418 payment_constraints: PaymentConstraints {
420 htlc_minimum_msat: 2_000,
422 features: BlindedHopFeatures::empty(),
424 htlc_maximum_msat: u64::max_value()
426 let recv_tlvs = ReceiveTlvs {
427 payment_secret: PaymentSecret([0; 32]),
428 payment_constraints: PaymentConstraints {
430 htlc_minimum_msat: 3,
433 let htlc_maximum_msat = 100_000;
434 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, TEST_FINAL_CLTV as u16).unwrap();
435 assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
439 fn aggregated_htlc_min() {
440 // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the
441 // max (htlc_min - following_fees) along the path.
442 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
443 let intermediate_nodes = vec![ForwardNode {
447 payment_relay: PaymentRelay {
448 cltv_expiry_delta: 0,
449 fee_proportional_millionths: 500,
450 fee_base_msat: 1_000,
452 payment_constraints: PaymentConstraints {
454 htlc_minimum_msat: 5_000,
456 features: BlindedHopFeatures::empty(),
458 htlc_maximum_msat: u64::max_value()
463 payment_relay: PaymentRelay {
464 cltv_expiry_delta: 0,
465 fee_proportional_millionths: 500,
468 payment_constraints: PaymentConstraints {
470 htlc_minimum_msat: 2_000,
472 features: BlindedHopFeatures::empty(),
474 htlc_maximum_msat: u64::max_value()
476 let recv_tlvs = ReceiveTlvs {
477 payment_secret: PaymentSecret([0; 32]),
478 payment_constraints: PaymentConstraints {
480 htlc_minimum_msat: 1,
483 let htlc_minimum_msat = 3798;
484 assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1, TEST_FINAL_CLTV as u16).is_err());
486 let htlc_maximum_msat = htlc_minimum_msat + 1;
487 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat, TEST_FINAL_CLTV as u16).unwrap();
488 assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
489 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
493 fn aggregated_htlc_max() {
494 // Create a path with varying fees and `htlc_maximum_msat`s, and make sure the aggregated max
495 // htlc ends up as the min (htlc_max - following_fees) along the path.
496 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
497 let intermediate_nodes = vec![ForwardNode {
501 payment_relay: PaymentRelay {
502 cltv_expiry_delta: 0,
503 fee_proportional_millionths: 500,
504 fee_base_msat: 1_000,
506 payment_constraints: PaymentConstraints {
508 htlc_minimum_msat: 1,
510 features: BlindedHopFeatures::empty(),
512 htlc_maximum_msat: 5_000,
517 payment_relay: PaymentRelay {
518 cltv_expiry_delta: 0,
519 fee_proportional_millionths: 500,
522 payment_constraints: PaymentConstraints {
524 htlc_minimum_msat: 1,
526 features: BlindedHopFeatures::empty(),
528 htlc_maximum_msat: 10_000
530 let recv_tlvs = ReceiveTlvs {
531 payment_secret: PaymentSecret([0; 32]),
532 payment_constraints: PaymentConstraints {
534 htlc_minimum_msat: 1,
538 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, 10_000, TEST_FINAL_CLTV as u16).unwrap();
539 assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);