Support constructing BlindedPaths for payments.

Author: valentinewallace

lightning/src/blinded_path/mod.rs

@@ -9,11 +9,13 @@
 
 //! Creating blinded paths and related utilities live here.
 
+pub mod payment;
 pub(crate) mod message;
 pub(crate) mod utils;
 
 use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
 
+use crate::blinded_path::payment::BlindedPaymentTlvs;
 use crate::sign::EntropySource;
 use crate::ln::msgs::DecodeError;
 use crate::util::ser::{Readable, Writeable, Writer};
@@ -73,6 +75,25 @@ impl BlindedPath {
 			blinded_hops: message::blinded_hops(secp_ctx, node_pks, &blinding_secret).map_err(|_| ())?,
 		})
 	}
+
+	/// Create a blinded path for a payment, to be forwarded along `path`. The last node
+	/// in `path` will be the destination node.
+	///
+	/// Errors if `path` is empty or a node id in `path` is invalid.
+	//  TODO: make all payloads the same size with padding + add dummy hops
+	pub fn new_for_payment<ES: EntropySource, T: secp256k1::Signing + secp256k1::Verification>(
+		path: &[(PublicKey, BlindedPaymentTlvs)], entropy_source: &ES, secp_ctx: &Secp256k1<T>
+	) -> Result<Self, ()> {
+		if path.len() < 1 { return Err(()) }
+		let blinding_secret_bytes = entropy_source.get_secure_random_bytes();
+		let blinding_secret = SecretKey::from_slice(&blinding_secret_bytes[..]).expect("RNG is busted");
+
+		Ok(BlindedPath {
+			introduction_node_id: path[0].0,
+			blinding_point: PublicKey::from_secret_key(secp_ctx, &blinding_secret),
+			blinded_hops: payment::blinded_hops(secp_ctx, path, &blinding_secret).map_err(|_| ())?,
+		})
+	}
 }
 
 impl Writeable for BlindedPath {

lightning/src/blinded_path/payment.rs

@@ -0,0 +1,150 @@
+//! Data structures and methods for constructing [`BlindedPath`]s to send a payment over.
+//!
+//! [`BlindedPath`]: crate::blinded_path::BlindedPath
+
+use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
+
+use crate::blinded_path::BlindedHop;
+use crate::blinded_path::utils;
+use crate::io;
+use crate::ln::PaymentSecret;
+use crate::ln::features::BlindedHopFeatures;
+use crate::ln::msgs::DecodeError;
+use crate::prelude::*;
+use crate::util::ser::{Readable, Writeable, Writer};
+
+/// Data to construct a [`BlindedHop`] for sending a payment over.
+///
+/// [`BlindedHop`]: crate::blinded_path::BlindedHop
+pub enum BlindedPaymentTlvs {
+	/// This blinded payment data is to be forwarded.
+	Forward {
+		/// The short channel id this payment is being forwarded over.
+		short_channel_id: u64,
+		/// Payment parameters for relaying over this channel.
+		payment_relay: PaymentRelay,
+		/// Payment constraints when relaying over this channel.
+		payment_constraints: PaymentConstraints,
+		/// Supported and required features when relaying a payment onion containing this object's
+		/// corresponding [`BlindedHop`].
+		///
+		/// [`BlindedHop`]: crate::blinded_path::BlindedHop
+		features: BlindedHopFeatures,
+	},
+	/// This blinded payment data is to be received.
+	Receive {
+		/// Used to authenticate the sender of a payment to the receiver and tie MPP HTLCs together.
+		payment_secret: PaymentSecret,
+		/// Constraints for the receiver of this payment.
+		payment_constraints: PaymentConstraints,
+		/// Supported and required features when receiving a payment containing this object's
+		/// corresponding [`BlindedHop`].
+		///
+		/// [`BlindedHop`]: crate::blinded_path::BlindedHop
+		features: BlindedHopFeatures,
+	},
+}
+
+/// Parameters for relaying over a given [`BlindedHop`].
+///
+/// [`BlindedHop`]: crate::blinded_path::BlindedHop
+pub struct PaymentRelay {
+	/// Number of blocks subtracted from an incoming HTLC's `cltv_expiry` for this [`BlindedHop`].
+	///
+	///[`BlindedHop`]: crate::blinded_path::BlindedHop
+	pub cltv_expiry_delta: u16,
+	/// Liquidity fee charged (in millionths of the amount transferred) for relaying a payment over
+	/// this [`BlindedHop`], (i.e., 10,000 is 1%).
+	///
+	///[`BlindedHop`]: crate::blinded_path::BlindedHop
+	pub fee_proportional_millionths: u32,
+	/// Base fee charged (in millisatoshi) for relaying a payment over this [`BlindedHop`].
+	///
+	///[`BlindedHop`]: crate::blinded_path::BlindedHop
+	pub fee_base_msat: u32,
+}
+
+/// Constraints for relaying over a given [`BlindedHop`].
+///
+/// [`BlindedHop`]: crate::blinded_path::BlindedHop
+pub struct PaymentConstraints {
+	/// The maximum total CLTV delta that is acceptable when relaying a payment over this
+	/// [`BlindedHop`].
+	///
+	///[`BlindedHop`]: crate::blinded_path::BlindedHop
+	pub max_cltv_expiry: u32,
+	/// The minimum value, in msat, that may be relayed over this [`BlindedHop`].
+	pub htlc_minimum_msat: u64,
+}
+
+impl Writeable for BlindedPaymentTlvs {
+	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
+		// TODO: write padding
+		match self {
+			Self::Forward { short_channel_id, payment_relay, payment_constraints, features } => {
+				encode_tlv_stream!(w, {
+					(2, short_channel_id, required),
+					(10, payment_relay, required),
+					(12, payment_constraints, required),
+					(14, features, required),
+				});
+			},
+			Self::Receive { payment_secret, payment_constraints, features } => {
+				encode_tlv_stream!(w, {
+					(6, payment_secret, required),
+					(12, payment_constraints, required),
+					(14, features, required),
+				});
+			}
+		}
+		Ok(())
+	}
+}
+
+impl Readable for BlindedPaymentTlvs {
+	fn read<R: io::Read>(r: &mut R) -> Result<Self, DecodeError> {
+		_init_and_read_tlv_stream!(r, {
+			(1, _padding, option),
+			(2, scid, option),
+			(6, payment_secret, option),
+			(10, payment_relay, option),
+			(12, payment_constraints, required),
+			(14, features, required),
+		});
+		if let Some(short_channel_id) = scid {
+			if payment_secret.is_some() { return Err(DecodeError::InvalidValue) }
+			Ok(BlindedPaymentTlvs::Forward {
+				short_channel_id,
+				payment_relay: payment_relay.ok_or(DecodeError::InvalidValue)?,
+				payment_constraints: payment_constraints.0.unwrap(),
+				features: features.0.unwrap(),
+			})
+		} else {
+			if payment_relay.is_some() { return Err(DecodeError::InvalidValue) }
+			Ok(BlindedPaymentTlvs::Receive {
+				payment_secret: payment_secret.ok_or(DecodeError::InvalidValue)?,
+				payment_constraints: payment_constraints.0.unwrap(),
+				features: features.0.unwrap(),
+			})
+		}
+	}
+}
+
+/// Construct blinded payment hops for the given `unblinded_path`.
+pub(super) fn blinded_hops<T: secp256k1::Signing + secp256k1::Verification>(
+	secp_ctx: &Secp256k1<T>, unblinded_path: &[(PublicKey, BlindedPaymentTlvs)], session_priv: &SecretKey
+) -> Result<Vec<BlindedHop>, secp256k1::Error> {
+	utils::construct_blinded_hops(secp_ctx, unblinded_path.iter().map(|(pk, _)| pk),
+		unblinded_path.iter().map(|(_, tlvs)| tlvs), session_priv)
+}
+
+impl_writeable_msg!(PaymentRelay, {
+	cltv_expiry_delta,
+	fee_proportional_millionths,
+	fee_base_msat
+}, {});
+
+impl_writeable_msg!(PaymentConstraints, {
+	max_cltv_expiry,
+	htlc_minimum_msat
+}, {});