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 /// 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`].
31 /// [`BlindedHop::encrypted_payload`]: crate::blinded_path::BlindedHop::encrypted_payload
32 pub features: BlindedHopFeatures,
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,
45 /// Data to construct a [`BlindedHop`] for sending a payment over.
47 /// [`BlindedHop`]: crate::blinded_path::BlindedHop
48 pub(crate) enum BlindedPaymentTlvs {
49 /// This blinded payment data is for a forwarding node.
51 /// This blinded payment data is for the receiving node.
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),
61 /// Parameters for relaying over a given [`BlindedHop`].
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,
75 /// Constraints for relaying over a given [`BlindedHop`].
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
82 pub max_cltv_expiry: u32,
83 /// The minimum value, in msat, that may be accepted by the node corresponding to this
85 pub htlc_minimum_msat: u64,
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)
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)
110 impl<'a> Writeable for BlindedPaymentTlvsRef<'a> {
111 fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
112 // TODO: write padding
114 Self::Forward(tlvs) => tlvs.write(w)?,
115 Self::Receive(tlvs) => tlvs.write(w)?,
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),
126 (10, payment_relay, option),
127 (12, payment_constraints, required),
128 (14, features, option),
129 (65536, payment_secret, option),
131 let _padding: Option<utils::Padding> = _padding;
133 if let Some(short_channel_id) = scid {
134 if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
135 Ok(BlindedPaymentTlvs::Forward(ForwardTlvs {
137 payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
138 payment_constraints: payment_constraints.0.unwrap(),
139 features: features.ok_or(DecodeError::InvalidValue)?,
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(),
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)
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;
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);
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.
180 debug_assert_eq!(amt_to_forward + fee, inbound_amt);
181 u64::try_from(amt_to_forward).ok()
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(()) }
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))
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))
213 cltv_expiry_delta = cltv_expiry_delta.checked_add(tlvs.payment_relay.cltv_expiry_delta).ok_or(())?;
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),
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
230 htlc_minimum_msat = core::cmp::max(
231 payee_tlvs.payment_constraints.htlc_minimum_msat, htlc_minimum_msat
233 htlc_maximum_msat = core::cmp::min(payee_htlc_maximum_msat, htlc_maximum_msat);
235 if htlc_maximum_msat < htlc_minimum_msat { return Err(()) }
237 fee_base_msat: u32::try_from(curr_base_fee).map_err(|_| ())?,
238 fee_proportional_millionths: u32::try_from(curr_prop_mil).map_err(|_| ())?,
242 features: BlindedHopFeatures::empty(),
246 impl_writeable_msg!(PaymentRelay, {
248 fee_proportional_millionths,
252 impl_writeable_msg!(PaymentConstraints, {
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;
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 {
271 payment_relay: PaymentRelay {
272 cltv_expiry_delta: 144,
273 fee_proportional_millionths: 500,
276 payment_constraints: PaymentConstraints {
278 htlc_minimum_msat: 100,
280 features: BlindedHopFeatures::empty(),
281 }, u64::max_value()), (dummy_pk, ForwardTlvs {
283 payment_relay: PaymentRelay {
284 cltv_expiry_delta: 144,
285 fee_proportional_millionths: 500,
288 payment_constraints: PaymentConstraints {
290 htlc_minimum_msat: 1_000,
292 features: BlindedHopFeatures::empty(),
293 }, u64::max_value())];
294 let recv_tlvs = ReceiveTlvs {
295 payment_secret: PaymentSecret([0; 32]),
296 payment_constraints: PaymentConstraints {
298 htlc_minimum_msat: 1,
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);
311 fn compute_payinfo_1_hop() {
312 let recv_tlvs = ReceiveTlvs {
313 payment_secret: PaymentSecret([0; 32]),
314 payment_constraints: PaymentConstraints {
316 htlc_minimum_msat: 1,
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);
328 fn simple_aggregated_htlc_min() {
329 // If no hops charge fees, the htlc_minimum_msat should just be the maximum htlc_minimum_msat
331 let dummy_pk = PublicKey::from_slice(&[2; 33]).unwrap();
332 let intermediate_nodes = vec![(dummy_pk, ForwardTlvs {
334 payment_relay: PaymentRelay {
335 cltv_expiry_delta: 0,
336 fee_proportional_millionths: 0,
339 payment_constraints: PaymentConstraints {
341 htlc_minimum_msat: 1,
343 features: BlindedHopFeatures::empty(),
344 }, u64::max_value()), (dummy_pk, ForwardTlvs {
346 payment_relay: PaymentRelay {
347 cltv_expiry_delta: 0,
348 fee_proportional_millionths: 0,
351 payment_constraints: PaymentConstraints {
353 htlc_minimum_msat: 2_000,
355 features: BlindedHopFeatures::empty(),
356 }, u64::max_value())];
357 let recv_tlvs = ReceiveTlvs {
358 payment_secret: PaymentSecret([0; 32]),
359 payment_constraints: PaymentConstraints {
361 htlc_minimum_msat: 3,
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);
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 {
376 payment_relay: PaymentRelay {
377 cltv_expiry_delta: 0,
378 fee_proportional_millionths: 500,
379 fee_base_msat: 1_000,
381 payment_constraints: PaymentConstraints {
383 htlc_minimum_msat: 5_000,
385 features: BlindedHopFeatures::empty(),
386 }, u64::max_value()), (dummy_pk, ForwardTlvs {
388 payment_relay: PaymentRelay {
389 cltv_expiry_delta: 0,
390 fee_proportional_millionths: 500,
393 payment_constraints: PaymentConstraints {
395 htlc_minimum_msat: 2_000,
397 features: BlindedHopFeatures::empty(),
398 }, u64::max_value())];
399 let recv_tlvs = ReceiveTlvs {
400 payment_secret: PaymentSecret([0; 32]),
401 payment_constraints: PaymentConstraints {
403 htlc_minimum_msat: 1,
406 let htlc_minimum_msat = 3798;
407 assert!(super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, htlc_minimum_msat - 1).is_err());
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);
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 {
422 payment_relay: PaymentRelay {
423 cltv_expiry_delta: 0,
424 fee_proportional_millionths: 500,
425 fee_base_msat: 1_000,
427 payment_constraints: PaymentConstraints {
429 htlc_minimum_msat: 1,
431 features: BlindedHopFeatures::empty(),
432 }, 5_000), (dummy_pk, ForwardTlvs {
434 payment_relay: PaymentRelay {
435 cltv_expiry_delta: 0,
436 fee_proportional_millionths: 500,
439 payment_constraints: PaymentConstraints {
441 htlc_minimum_msat: 1,
443 features: BlindedHopFeatures::empty(),
445 let recv_tlvs = ReceiveTlvs {
446 payment_secret: PaymentSecret([0; 32]),
447 payment_constraints: PaymentConstraints {
449 htlc_minimum_msat: 1,
453 let blinded_payinfo = super::compute_payinfo(&intermediate_nodes[..], &recv_tlvs, 10_000).unwrap();
454 assert_eq!(blinded_payinfo.htlc_maximum_msat, 3997);