Fix Feature endianness by swapping bytes on read/write.

The spec is a bit mum on feature endianness, so I suppose it falls
under the "everything is big endian unless otherwise specified"
clause, but we were treating it as little.

diff --git a/lightning/src/ln/msgs.rs b/lightning/src/ln/msgs.rs
index cccbf83acd2a740271f8d962e67d6038c4b61f75..0610c02c1ce25c8c694e93f33c7a4b2db8f7fccd 100644 (file)
--- a/lightning/src/ln/msgs.rs
+++ b/lightning/src/ln/msgs.rs
@@ -105,6 +105,7 @@ impl FeatureContextInitNode for FeatureContextNode {}
 /// appears.
 pub struct Features<T: FeatureContext> {
        #[cfg(not(test))]
+       /// Note that, for convinience, flags is LITTLE endian (despite being big-endian on the wire)
        flags: Vec<u8>,
        // Used to test encoding of diverse msgs
        #[cfg(test)]
@@ -265,18 +266,25 @@ impl Features<FeatureContextInit> {
 impl<T: FeatureContext> Writeable for Features<T> {
        fn write<W: Writer>(&self, w: &mut W) -> Result<(), ::std::io::Error> {
                w.size_hint(self.flags.len() + 2);
-               self.flags.write(w)
+               (self.flags.len() as u16).write(w)?;
+               for f in self.flags.iter().rev() { // We have to swap the endianness back to BE for writing
+                       f.write(w)?;
+               }
+               Ok(())
        }
 }
 
 impl<R: ::std::io::Read, T: FeatureContext> Readable<R> for Features<T> {
        fn read(r: &mut R) -> Result<Self, DecodeError> {
+               let mut flags: Vec<u8> = Readable::read(r)?;
+               flags.reverse(); // Swap to big-endian
                Ok(Self {
-                       flags: Readable::read(r)?,
+                       flags,
                        mark: PhantomData,
                })
        }
 }
+
 /// An init message to be sent or received from a peer
 pub struct Init {
        pub(crate) features: InitFeatures,