Test async receive

In the previous commit we completed support for async receive from an
always-online sender to an often-offline receiver, minus support for acting as
the async receiver's always-online channel counterparty.

Author: valentinewallace

lightning/src/blinded_path/payment.rs

@@ -12,6 +12,7 @@
 use bitcoin::hashes::hmac::Hmac;
 use bitcoin::hashes::sha256::Hash as Sha256;
 use bitcoin::secp256k1::{self, PublicKey, Secp256k1, SecretKey};
+use bitcoin::secp256k1::ecdh::SharedSecret;
 
 use crate::blinded_path::{BlindedHop, BlindedPath, IntroductionNode, NodeIdLookUp};
 use crate::blinded_path::utils;
@@ -170,15 +171,8 @@ impl BlindedPaymentPath {
 		NL::Target: NodeIdLookUp,
 		T: secp256k1::Signing + secp256k1::Verification,
 	{
-		let control_tlvs_ss = node_signer.ecdh(Recipient::Node, &self.inner_path.blinding_point, None)?;
-		let rho = onion_utils::gen_rho_from_shared_secret(&control_tlvs_ss.secret_bytes());
-		let encrypted_control_tlvs = &self.inner_path.blinded_hops.get(0).ok_or(())?.encrypted_payload;
-		let mut s = Cursor::new(encrypted_control_tlvs);
-		let mut reader = FixedLengthReader::new(&mut s, encrypted_control_tlvs.len() as u64);
-		match ChaChaPolyReadAdapter::read(&mut reader, rho) {
-			Ok(ChaChaPolyReadAdapter {
-				readable: BlindedPaymentTlvs::Forward(ForwardTlvs { short_channel_id, .. })
-			}) => {
+		match self.decrypt_blinded_payload::<NS>(0, node_signer) {
+			Ok((BlindedPaymentTlvs::Forward(ForwardTlvs { short_channel_id, .. }), control_tlvs_ss)) => {
 				let next_node_id = match node_id_lookup.next_node_id(short_channel_id) {
 					Some(node_id) => node_id,
 					None => return Err(()),
@@ -195,6 +189,20 @@ impl BlindedPaymentPath {
 		}
 	}
 
+	pub(crate) fn decrypt_blinded_payload<NS: Deref>(
+		&self, hop_idx: usize, node_signer: &NS
+	) -> Result<(BlindedPaymentTlvs, SharedSecret), ()> where NS::Target: NodeSigner {
+		let control_tlvs_ss = node_signer.ecdh(Recipient::Node, &self.inner_path.blinding_point, None)?;
+		let rho = onion_utils::gen_rho_from_shared_secret(&control_tlvs_ss.secret_bytes());
+		let encrypted_control_tlvs = &self.inner_path.blinded_hops.get(hop_idx).ok_or(())?.encrypted_payload;
+		let mut s = Cursor::new(encrypted_control_tlvs);
+		let mut reader = FixedLengthReader::new(&mut s, encrypted_control_tlvs.len() as u64);
+		match ChaChaPolyReadAdapter::read(&mut reader, rho) {
+			Ok(ChaChaPolyReadAdapter { readable, .. }) => Ok((readable, control_tlvs_ss)),
+			_ => Err(())
+		}
+	}
+
 	pub(crate) fn inner_blinded_path(&self) -> &BlindedPath {
 		&self.inner_path
 	}