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 that is acceptable when relaying a payment over this [`BlindedHop`].
93 pub max_cltv_expiry: u32,
94 /// The minimum value, in msat, that may be accepted by the node corresponding to this
96 pub htlc_minimum_msat: u64,
99 impl Writeable for ForwardTlvs {
100 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
101 encode_tlv_stream!(w, {
102 (2, self.short_channel_id, required),
103 (10, self.payment_relay, required),
104 (12, self.payment_constraints, required),
105 (14, self.features, required)
111 impl Writeable for ReceiveTlvs {
112 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
113 encode_tlv_stream!(w, {
114 (12, self.payment_constraints, required),
115 (65536, self.payment_secret, required)
121 // This will be removed once we support forwarding blinded HTLCs, because we'll always read a
122 // `BlindedPaymentTlvs` instead.
123 impl Readable for ReceiveTlvs {
124 fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
125 _init_and_read_tlv_stream!(r, {
126 (12, payment_constraints, required),
127 (65536, payment_secret, required),
130 payment_secret: payment_secret.0.unwrap(),
131 payment_constraints: payment_constraints.0.unwrap()
136 impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
137 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
138 // TODO: write padding
140 Self::Forward(tlvs) => tlvs.write(w)?,
141 Self::Receive(tlvs) => tlvs.write(w)?,
147 impl Readable for BlindedPaymentTlvs {
148 fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
149 _init_and_read_tlv_stream!(r, {
150 (1, _padding, option),
152 (10, payment_relay, option),
153 (12, payment_constraints, required),
154 (14, features, option),
155 (65536, payment_secret, option),
157 let _padding: Option<utils::Padding> = _padding;
159 if let Some(short_channel_id) = scid {
160 if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
161 Ok(BlindedPaymentTlvs::Forward(ForwardTlvs {
163 payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
164 payment_constraints: payment_constraints.0.unwrap(),
165 features: features.ok_or(DecodeError::InvalidValue)?,
168 if payment_relay.is_some() || features.is_some() { return Err(DecodeError::InvalidValue) }
169 Ok(BlindedPaymentTlvs::Receive(ReceiveTlvs {
170 payment_secret: payment_secret.ok_or(DecodeError::InvalidValue)?,
171 payment_constraints: payment_constraints.0.unwrap(),
177 /// Construct blinded payment hops for the given `intermediate_nodes` and payee info.
178 pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
179 secp_ctx: &Secp256k1<T>, intermediate_nodes: &[ForwardNode],
180 payee_node_id: PublicKey, payee_tlvs: ReceiveTlvs, session_priv: &SecretKey
181 ) -> Result<Vec<BlindedHop>, secp256k1::Error> {
182 let pks = intermediate_nodes.iter().map(|node| &node.node_id)
183 .chain(core::iter::once(&payee_node_id));
184 let tlvs = intermediate_nodes.iter().map(|node| BlindedPaymentTlvsRef::Forward(&node.tlvs))
185 .chain(core::iter::once(BlindedPaymentTlvsRef::Receive(&payee_tlvs)));
186 utils::construct_blinded_hops(secp_ctx, pks, tlvs, session_priv)
189 /// `None` if underflow occurs.
190 fn amt_to_forward_msat(inbound_amt_msat: u64, payment_relay: &PaymentRelay) -> Option<u64> {
191 let inbound_amt = inbound_amt_msat as u128;
192 let base = payment_relay.fee_base_msat as u128;
193 let prop = payment_relay.fee_proportional_millionths as u128;
195 let post_base_fee_inbound_amt =
196 if let Some(amt) = inbound_amt.checked_sub(base) { amt } else { return None };
197 let mut amt_to_forward =
198 (post_base_fee_inbound_amt * 1_000_000 + 1_000_000 + prop - 1) / (prop + 1_000_000);
200 let fee = ((amt_to_forward * prop) / 1_000_000) + base;
201 if inbound_amt - fee < amt_to_forward {
202 // Rounding up the forwarded amount resulted in underpaying this node, so take an extra 1 msat
203 // in fee to compensate.
206 debug_assert_eq!(amt_to_forward + fee, inbound_amt);
207 u64::try_from(amt_to_forward).ok()
210 pub(super) fn compute_payinfo(
211 intermediate_nodes: &[ForwardNode], payee_tlvs: &ReceiveTlvs, payee_htlc_maximum_msat: u64
212 ) -> Result<BlindedPayInfo, ()> {
213 let mut curr_base_fee: u64 = 0;
214 let mut curr_prop_mil: u64 = 0;
215 let mut cltv_expiry_delta: u16 = 0;
216 for tlvs in intermediate_nodes.iter().rev().map(|n| &n.tlvs) {
217 // In the future, we'll want to take the intersection of all supported features for the
218 // `BlindedPayInfo`, but there are no features in that context right now.
219 if tlvs.features.requires_unknown_bits_from(&BlindedHopFeatures::empty()) { return Err(()) }
221 let next_base_fee = tlvs.payment_relay.fee_base_msat as u64;
222 let next_prop_mil = tlvs.payment_relay.fee_proportional_millionths as u64;
223 // Use integer arithmetic to compute `ceil(a/b)` as `(a+b-1)/b`
224 // ((curr_base_fee * (1_000_000 + next_prop_mil)) / 1_000_000) + next_base_fee
225 curr_base_fee = curr_base_fee.checked_mul(1_000_000 + next_prop_mil)
226 .and_then(|f| f.checked_add(1_000_000 - 1))
227 .map(|f| f / 1_000_000)
228 .and_then(|f| f.checked_add(next_base_fee))
230 // ceil(((curr_prop_mil + 1_000_000) * (next_prop_mil + 1_000_000)) / 1_000_000) - 1_000_000
231 curr_prop_mil = curr_prop_mil.checked_add(1_000_000)
232 .and_then(|f1| next_prop_mil.checked_add(1_000_000).and_then(|f2| f2.checked_mul(f1)))
233 .and_then(|f| f.checked_add(1_000_000 - 1))
234 .map(|f| f / 1_000_000)
235 .and_then(|f| f.checked_sub(1_000_000))
238 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
241 let mut htlc_minimum_msat: u64 = 1;
242 let mut htlc_maximum_msat: u64 = 21_000_000 * 100_000_000 * 1_000; // Total bitcoin supply
243 for node in intermediate_nodes.iter() {
244 // The min htlc for an intermediate node is that node's min minus the fees charged by all of the
245 // following hops for forwarding that min, since that fee amount will automatically be included
246 // in the amount that this node receives and contribute towards reaching its min.
247 htlc_minimum_msat = amt_to_forward_msat(
248 core::cmp::max(node.tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat),
249 &node.tlvs.payment_relay
250 ).unwrap_or(1); // If underflow occurs, we definitely reached this node's min
251 htlc_maximum_msat = amt_to_forward_msat(
252 core::cmp::min(node.htlc_maximum_msat, htlc_maximum_msat), &node.tlvs.payment_relay
253 ).ok_or(())?; // If underflow occurs, we cannot send to this hop without exceeding their max
255 htlc_minimum_msat = core::cmp::max(
256 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
258 htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
260 if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
262 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
263 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
267 features: BlindedHopFeatures::empty(),
271 impl_writeable_msg!(PaymentRelay, {
273 fee_proportional_millionths,
277 impl_writeable_msg!(PaymentConstraints, {
284 use bitcoin::secp256k1::PublicKey;
285 use crate::blinded_path::payment::{ForwardNode, ForwardTlvs, ReceiveTlvs, PaymentConstraints, PaymentRelay};
286 use crate::ln::PaymentSecret;
287 use crate::ln::features::BlindedHopFeatures;
290 fn compute_payinfo() {
291 // Taken from the spec example for aggregating blinded payment info. See
292 // https://github.com/lightning/bolts/blob/master/proposals/route-blinding.md#blinded-payments
293 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
294 let intermediate_nodes = vec![ForwardNode {
298 payment_relay: PaymentRelay {
299 cltv_expiry_delta: 144,
300 fee_proportional_millionths: 500,
303 payment_constraints: PaymentConstraints {
305 htlc_minimum_msat: 100,
307 features: BlindedHopFeatures::empty(),
309 htlc_maximum_msat: u64::max_value(),
314 payment_relay: PaymentRelay {
315 cltv_expiry_delta: 144,
316 fee_proportional_millionths: 500,
319 payment_constraints: PaymentConstraints {
321 htlc_minimum_msat: 1_000,
323 features: BlindedHopFeatures::empty(),
325 htlc_maximum_msat: u64::max_value(),
327 let recv_tlvs = ReceiveTlvs {
328 payment_secret: PaymentSecret([0; 32]),
329 payment_constraints: PaymentConstraints {
331 htlc_minimum_msat: 1,
334 let htlc_maximum_msat = 100_000;
335 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
336 assert_eq!(blinded_payinfo.fee_base_msat, 201);
337 assert_eq!(blinded_payinfo.fee_proportional_millionths, 1001);
338 assert_eq!(blinded_payinfo.cltv_expiry_delta, 288);
339 assert_eq!(blinded_payinfo.htlc_minimum_msat, 900);
340 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
344 fn compute_payinfo_1_hop() {
345 let recv_tlvs = ReceiveTlvs {
346 payment_secret: PaymentSecret([0; 32]),
347 payment_constraints: PaymentConstraints {
349 htlc_minimum_msat: 1,
352 let blinded_payinfo = super::compute_payinfo(&[], &recv_tlvs, 4242).unwrap();
353 assert_eq!(blinded_payinfo.fee_base_msat, 0);
354 assert_eq!(blinded_payinfo.fee_proportional_millionths, 0);
355 assert_eq!(blinded_payinfo.cltv_expiry_delta, 0);
356 assert_eq!(blinded_payinfo.htlc_minimum_msat, 1);
357 assert_eq!(blinded_payinfo.htlc_maximum_msat, 4242);
361 fn simple_aggregated_htlc_min() {
362 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
364 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
365 let intermediate_nodes = vec![ForwardNode {
369 payment_relay: PaymentRelay {
370 cltv_expiry_delta: 0,
371 fee_proportional_millionths: 0,
374 payment_constraints: PaymentConstraints {
376 htlc_minimum_msat: 1,
378 features: BlindedHopFeatures::empty(),
380 htlc_maximum_msat: u64::max_value()
385 payment_relay: PaymentRelay {
386 cltv_expiry_delta: 0,
387 fee_proportional_millionths: 0,
390 payment_constraints: PaymentConstraints {
392 htlc_minimum_msat: 2_000,
394 features: BlindedHopFeatures::empty(),
396 htlc_maximum_msat: u64::max_value()
398 let recv_tlvs = ReceiveTlvs {
399 payment_secret: PaymentSecret([0; 32]),
400 payment_constraints: PaymentConstraints {
402 htlc_minimum_msat: 3,
405 let htlc_maximum_msat = 100_000;
406 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
407 assert_eq!(blinded_payinfo.htlc_minimum_msat, 2_000);
411 fn aggregated_htlc_min() {
412 // Create a path with varying fees and htlc_mins, and make sure htlc_minimum_msat ends up as the
413 // max (htlc_min - following_fees) along the path.
414 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
415 let intermediate_nodes = vec![ForwardNode {
419 payment_relay: PaymentRelay {
420 cltv_expiry_delta: 0,
421 fee_proportional_millionths: 500,
422 fee_base_msat: 1_000,
424 payment_constraints: PaymentConstraints {
426 htlc_minimum_msat: 5_000,
428 features: BlindedHopFeatures::empty(),
430 htlc_maximum_msat: u64::max_value()
435 payment_relay: PaymentRelay {
436 cltv_expiry_delta: 0,
437 fee_proportional_millionths: 500,
440 payment_constraints: PaymentConstraints {
442 htlc_minimum_msat: 2_000,
444 features: BlindedHopFeatures::empty(),
446 htlc_maximum_msat: u64::max_value()
448 let recv_tlvs = ReceiveTlvs {
449 payment_secret: PaymentSecret([0; 32]),
450 payment_constraints: PaymentConstraints {
452 htlc_minimum_msat: 1,
455 let htlc_minimum_msat = 3798;
456 assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1).is_err());
458 let htlc_maximum_msat = htlc_minimum_msat + 1;
459 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_maximum_msat).unwrap();
460 assert_eq!(blinded_payinfo.htlc_minimum_msat, htlc_minimum_msat);
461 assert_eq!(blinded_payinfo.htlc_maximum_msat, htlc_maximum_msat);
465 fn aggregated_htlc_max() {
466 // Create a path with varying fees and `htlc_maximum_msat`s, and make sure the aggregated max
467 // htlc ends up as the min (htlc_max - following_fees) along the path.
468 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
469 let intermediate_nodes = vec![ForwardNode {
473 payment_relay: PaymentRelay {
474 cltv_expiry_delta: 0,
475 fee_proportional_millionths: 500,
476 fee_base_msat: 1_000,
478 payment_constraints: PaymentConstraints {
480 htlc_minimum_msat: 1,
482 features: BlindedHopFeatures::empty(),
484 htlc_maximum_msat: 5_000,
489 payment_relay: PaymentRelay {
490 cltv_expiry_delta: 0,
491 fee_proportional_millionths: 500,
494 payment_constraints: PaymentConstraints {
496 htlc_minimum_msat: 1,
498 features: BlindedHopFeatures::empty(),
500 htlc_maximum_msat: 10_000
502 let recv_tlvs = ReceiveTlvs {
503 payment_secret: PaymentSecret([0; 32]),
504 payment_constraints: PaymentConstraints {
506 htlc_minimum_msat: 1,
510 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, 10_000).unwrap();
511 assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);