public onion utils, create/peel payment

lightning/src/ln/mod.rs

@@ -39,6 +39,7 @@ pub(crate) mod onion_utils;
 mod outbound_payment;
 pub mod wire;
 
+pub use onion_utils::create_payment_onion;
 // Older rustc (which we support) refuses to let us call the get_payment_preimage_hash!() macro
 // without the node parameter being mut. This is incorrect, and thus newer rustcs will complain
 // about an unnecessary mut. Thus, we silence the unused_mut warning in two test modules below.

lightning/src/ln/msgs.rs

@@ -1674,17 +1674,21 @@ pub use self::fuzzy_internal_msgs::*;
 #[cfg(not(fuzzing))]
 pub(crate) use self::fuzzy_internal_msgs::*;
 
+/// Bolt04 OnionPacket including hop data for the next peer
 #[derive(Clone)]
-pub(crate) struct OnionPacket {
-	pub(crate) version: u8,
+pub struct OnionPacket {
+	/// Bolt 04 version number
+	pub version: u8,
 	/// In order to ensure we always return an error on onion decode in compliance with [BOLT
 	/// #4](https://github.com/lightning/bolts/blob/master/04-onion-routing.md), we have to
 	/// deserialize `OnionPacket`s contained in [`UpdateAddHTLC`] messages even if the ephemeral
 	/// public key (here) is bogus, so we hold a [`Result`] instead of a [`PublicKey`] as we'd
 	/// like.
-	pub(crate) public_key: Result<PublicKey, secp256k1::Error>,
-	pub(crate) hop_data: [u8; 20*65],
-	pub(crate) hmac: [u8; 32],
+	pub public_key: Result<PublicKey, secp256k1::Error>,
+	/// 1300 bytes encrypted payload for the next hop
+	pub hop_data: [u8; 20*65],
+	/// HMAC to verify the integrity of hop_data
+	pub hmac: [u8; 32],
 }
 
 impl onion_utils::Packet for OnionPacket {

lightning/src/ln/onion_utils.rs

@@ -935,6 +935,29 @@ pub(crate) fn decode_next_payment_hop<NS: Deref>(
 	}
 }
 
+/// Build a payment onion, returning the first hop msat and cltv values as well.
+pub fn create_payment_onion<T>(
+	secp_ctx: &Secp256k1<T>, path: &Path, session_priv: &SecretKey, total_msat: u64, 
+	recipient_onion: RecipientOnionFields, best_block_height: u32, payment_hash: PaymentHash,
+	keysend_preimage: Option<PaymentPreimage>, prng_seed: [u8; 32]
+) -> Result<(u64, u32, msgs::OnionPacket), ()>
+where
+	T: secp256k1::Signing
+{
+	let onion_keys = construct_onion_keys(&secp_ctx, &path, &session_priv).map_err(|_| ())?;
+	let (onion_payloads, htlc_msat, htlc_cltv) = build_onion_payloads(
+		&path,
+		total_msat,
+		recipient_onion,
+		best_block_height + 1,
+		&keysend_preimage,
+	).map_err(|_| ())?;
+	let onion_packet = construct_onion_packet(
+		onion_payloads, onion_keys, prng_seed, &payment_hash
+	)?;
+	Ok((htlc_msat, htlc_cltv, onion_packet))
+}
+
 pub(crate) fn decode_next_untagged_hop<T, R: ReadableArgs<T>, N: NextPacketBytes>(shared_secret: [u8; 32], hop_data: &[u8], hmac_bytes: [u8; 32], read_args: T) -> Result<(R, Option<([u8; 32], N)>), OnionDecodeErr> {
 	decode_next_hop(shared_secret, hop_data, hmac_bytes, None, read_args)
 }

lightning/src/onion_message/mod.rs

@@ -28,6 +28,7 @@ mod functional_tests;
 
 // Re-export structs so they can be imported with just the `onion_message::` module prefix.
 pub use self::messenger::{CustomOnionMessageHandler, DefaultMessageRouter, Destination, MessageRouter, OnionMessageContents, OnionMessagePath, OnionMessenger, PeeledOnion, PendingOnionMessage, SendError};
+pub use self::messenger::{create_onion_message, peel_onion_message};
 #[cfg(not(c_bindings))]
 pub use self::messenger::{SimpleArcOnionMessenger, SimpleRefOnionMessenger};
 pub use self::offers::{OffersMessage, OffersMessageHandler};