From 7e2495e5cbff855e2b5bc5d15f28f53aa544d5fa Mon Sep 17 00:00:00 2001
From: Matt Corallo <git@bluematt.me>
Date: Sun, 29 Aug 2021 05:40:28 +0000
Subject: [PATCH] Add support for deserializing the new SCID alias in
 funding_locked

---
 lightning/src/ln/channel.rs |  4 ++++
 lightning/src/ln/msgs.rs    | 10 ++++++++--
 lightning/src/util/ser.rs   | 14 +++++++++++++-
 3 files changed, 25 insertions(+), 3 deletions(-)

diff --git a/lightning/src/ln/channel.rs b/lightning/src/ln/channel.rs
index 2357c68f1..60e162d5a 100644
--- a/lightning/src/ln/channel.rs
+++ b/lightning/src/ln/channel.rs
@@ -3361,6 +3361,7 @@ impl<Signer: Sign> Channel<Signer> {
 			Some(msgs::FundingLocked {
 				channel_id: self.channel_id(),
 				next_per_commitment_point,
+				short_channel_id_alias: None,
 			})
 		} else { None };
 
@@ -3582,6 +3583,7 @@ impl<Signer: Sign> Channel<Signer> {
 				funding_locked: Some(msgs::FundingLocked {
 					channel_id: self.channel_id(),
 					next_per_commitment_point,
+					short_channel_id_alias: None,
 				}),
 				raa: None, commitment_update: None, mon_update: None,
 				order: RAACommitmentOrder::CommitmentFirst,
@@ -3617,6 +3619,7 @@ impl<Signer: Sign> Channel<Signer> {
 			Some(msgs::FundingLocked {
 				channel_id: self.channel_id(),
 				next_per_commitment_point,
+				short_channel_id_alias: None,
 			})
 		} else { None };
 
@@ -4351,6 +4354,7 @@ impl<Signer: Sign> Channel<Signer> {
 					return Some(msgs::FundingLocked {
 						channel_id: self.channel_id,
 						next_per_commitment_point,
+						short_channel_id_alias: None,
 					});
 				}
 			} else {
diff --git a/lightning/src/ln/msgs.rs b/lightning/src/ln/msgs.rs
index 39c00105f..c1f1bb545 100644
--- a/lightning/src/ln/msgs.rs
+++ b/lightning/src/ln/msgs.rs
@@ -40,7 +40,7 @@ use io_extras::read_to_end;
 
 use util::events::MessageSendEventsProvider;
 use util::logger;
-use util::ser::{Readable, Writeable, Writer, FixedLengthReader, HighZeroBytesDroppedVarInt};
+use util::ser::{U48, Readable, Writeable, Writer, FixedLengthReader, HighZeroBytesDroppedVarInt};
 
 use ln::{PaymentPreimage, PaymentHash, PaymentSecret};
 
@@ -218,6 +218,9 @@ pub struct FundingLocked {
 	pub channel_id: [u8; 32],
 	/// The per-commitment point of the second commitment transaction
 	pub next_per_commitment_point: PublicKey,
+	/// If set, provides a short_channel_id alias for this channel. The sender will accept payments
+	/// which are to be forwarded over this channel ID alias and forward them to us.
+	pub short_channel_id_alias: Option<U48>,
 }
 
 /// A shutdown message to be sent or received from a peer
@@ -1121,7 +1124,9 @@ impl_writeable_msg!(FundingSigned, {
 impl_writeable_msg!(FundingLocked, {
 	channel_id,
 	next_per_commitment_point,
-}, {});
+}, {
+	(1, short_channel_id_alias, option),
+});
 
 impl Writeable for Init {
 	fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
@@ -2190,6 +2195,7 @@ mod tests {
 		let funding_locked = msgs::FundingLocked {
 			channel_id: [2; 32],
 			next_per_commitment_point: pubkey_1,
+			short_channel_id_alias: None,
 		};
 		let encoded_value = funding_locked.encode();
 		let target_value = hex::decode("0202020202020202020202020202020202020202020202020202020202020202031b84c5567b126440995d3ed5aaba0565d71e1834604819ff9c17f5e9d5dd078f").unwrap();
diff --git a/lightning/src/util/ser.rs b/lightning/src/util/ser.rs
index 6a52e5e1c..d10d1d332 100644
--- a/lightning/src/util/ser.rs
+++ b/lightning/src/util/ser.rs
@@ -277,7 +277,19 @@ impl<T: MaybeReadable> Readable for VecReadWrapper<T> {
 	}
 }
 
-pub(crate) struct U48(pub u64);
+#[derive(Clone, Copy, Debug, PartialEq, Eq)]
+/// A 48-bit unsigned integer. This is used in lightning largely to represent the "short channel
+/// ID" values.
+pub struct U48(pub(crate) u64);
+impl U48 {
+	/// Construts a new U48 from a u64, checking that it is in range or returning `Err(())`
+	#[inline]
+	pub fn from_u64(src: u64) -> Result<Self, ()> {
+		if src < (1 << 48) - 1 { Ok(Self(src)) } else { Err(()) }
+	}
+	/// Gets the current value as a u64
+	pub fn as_u64(&self) -> u64 { self.0 }
+}
 impl Writeable for U48 {
 	#[inline]
 	fn write<W: Writer>(&self, writer: &mut W) -> Result<(), io::Error> {
-- 
2.39.5