Merge pull request #3144 from TheBlueMatt/2024-06-message-flags

[rust-lightning] / lightning / src / ln / msgs.rs

diff --git a/lightning/src/ln/msgs.rs b/lightning/src/ln/msgs.rs
index aa69abb712b3a0c744ff7cd7c79ad6fe0b976180..8f389d07cefc9b59cb314b58a597ac75d23aa199 100644 (file)
--- a/lightning/src/ln/msgs.rs
+++ b/lightning/src/ln/msgs.rs
@@ -1244,8 +1244,11 @@ pub struct UnsignedChannelUpdate {
        pub short_channel_id: u64,
        /// A strictly monotonic announcement counter, with gaps allowed, specific to this channel
        pub timestamp: u32,
-       /// Channel flags
-       pub flags: u8,
+       /// Flags pertaining to this message.
+       pub message_flags: u8,
+       /// Flags pertaining to the channel, including to which direction in the channel this update
+       /// applies and whether the direction is currently able to forward HTLCs.
+       pub channel_flags: u8,
        /// The number of blocks such that if:
        /// `incoming_htlc.cltv_expiry < outgoing_htlc.cltv_expiry + cltv_expiry_delta`
        /// then we need to fail the HTLC backwards. When forwarding an HTLC, `cltv_expiry_delta` determines
@@ -2896,13 +2899,13 @@ impl_writeable!(ChannelAnnouncement, {
 
 impl Writeable for UnsignedChannelUpdate {
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), io::Error> {
-               // `message_flags` used to indicate presence of `htlc_maximum_msat`, but was deprecated in the spec.
-               const MESSAGE_FLAGS: u8 = 1;
                self.chain_hash.write(w)?;
                self.short_channel_id.write(w)?;
                self.timestamp.write(w)?;
-               let all_flags = self.flags as u16 | ((MESSAGE_FLAGS as u16) << 8);
-               all_flags.write(w)?;
+               // Thw low bit of message_flags used to indicate the presence of `htlc_maximum_msat`, and
+               // now must be set
+               (self.message_flags | 1).write(w)?;
+               self.channel_flags.write(w)?;
                self.cltv_expiry_delta.write(w)?;
                self.htlc_minimum_msat.write(w)?;
                self.fee_base_msat.write(w)?;
@@ -2915,22 +2918,26 @@ impl Writeable for UnsignedChannelUpdate {
 
 impl Readable for UnsignedChannelUpdate {
        fn read<R: Read>(r: &mut R) -> Result<Self, DecodeError> {
-               Ok(Self {
+               let res = Self {
                        chain_hash: Readable::read(r)?,
                        short_channel_id: Readable::read(r)?,
                        timestamp: Readable::read(r)?,
-                       flags: {
-                               let flags: u16 = Readable::read(r)?;
-                               // Note: we ignore the `message_flags` for now, since it was deprecated by the spec.
-                               flags as u8
-                       },
+                       message_flags: Readable::read(r)?,
+                       channel_flags: Readable::read(r)?,
                        cltv_expiry_delta: Readable::read(r)?,
                        htlc_minimum_msat: Readable::read(r)?,
                        fee_base_msat: Readable::read(r)?,
                        fee_proportional_millionths: Readable::read(r)?,
                        htlc_maximum_msat: Readable::read(r)?,
                        excess_data: read_to_end(r)?,
-               })
+               };
+               if res.message_flags & 1 != 1 {
+                       // The `must_be_one` flag should be set (historically it indicated the presence of the
+                       // `htlc_maximum_msat` field, which is now required).
+                       Err(DecodeError::InvalidValue)
+               } else {
+                       Ok(res)
+               }
        }
 }
 
@@ -3526,7 +3533,8 @@ mod tests {
                        chain_hash: ChainHash::using_genesis_block(Network::Bitcoin),
                        short_channel_id: 2316138423780173,
                        timestamp: 20190119,
-                       flags: if direction { 1 } else { 0 } | if disable { 1 << 1 } else { 0 },
+                       message_flags: 1, // Only must_be_one
+                       channel_flags: if direction { 1 } else { 0 } | if disable { 1 << 1 } else { 0 },
                        cltv_expiry_delta: 144,
                        htlc_minimum_msat: 1000000,
                        htlc_maximum_msat: 131355275467161,