Fix `Feature` eq + hash to ignore excess zero bytes

If we get a `Feature` object which has excess zero bytes, we
shouldn't consider it a different `Feature` from another with the
same bits set, but no excess zero bytes. Here we fix both the
`Hash` and `PartialEq` implementation for `Features` to ignore
excess zero bytes.

diff --git a/lightning/src/ln/features.rs b/lightning/src/ln/features.rs
index df5c0abf25f2a27f8d81589447435b61a15589ef..2e732b17aa8bc8a88f923942ce8e47f0f3807b82 100644 (file)
--- a/lightning/src/ln/features.rs
+++ b/lightning/src/ln/features.rs
@@ -469,12 +469,24 @@ impl<T: sealed::Context> Clone for Features<T> {
 }
 impl<T: sealed::Context> Hash for Features<T> {
        fn hash<H: Hasher>(&self, hasher: &mut H) {
-               self.flags.hash(hasher);
+               let mut nonzero_flags = &self.flags[..];
+               while nonzero_flags.last() == Some(&0) {
+                       nonzero_flags = &nonzero_flags[..nonzero_flags.len() - 1];
+               }
+               nonzero_flags.hash(hasher);
        }
 }
 impl<T: sealed::Context> PartialEq for Features<T> {
        fn eq(&self, o: &Self) -> bool {
-               self.flags.eq(&o.flags)
+               let mut o_iter = o.flags.iter();
+               let mut self_iter = self.flags.iter();
+               loop {
+                       match (o_iter.next(), self_iter.next()) {
+                               (Some(o), Some(us)) => if o != us { return false },
+                               (Some(b), None) | (None, Some(b)) => if *b != 0 { return false },
+                               (None, None) => return true,
+                       }
+               }
        }
 }
 impl<T: sealed::Context> PartialOrd for Features<T> {
@@ -1215,4 +1227,26 @@ mod tests {
                assert!(!converted_features.supports_any_optional_bits());
                assert!(converted_features.requires_static_remote_key());
        }
+
+       #[test]
+       #[cfg(feature = "std")]
+       fn test_excess_zero_bytes_ignored() {
+               // Checks that `Hash` and `PartialEq` ignore excess zero bytes, which may appear due to
+               // feature conversion or because a peer serialized their feature poorly.
+               use std::collections::hash_map::DefaultHasher;
+               use std::hash::{Hash, Hasher};
+
+               let mut zerod_features = InitFeatures::empty();
+               zerod_features.flags = vec![0];
+               let empty_features = InitFeatures::empty();
+               assert!(empty_features.flags.is_empty());
+
+               assert_eq!(zerod_features, empty_features);
+
+               let mut zerod_hash = DefaultHasher::new();
+               zerod_features.hash(&mut zerod_hash);
+               let mut empty_hash = DefaultHasher::new();
+               empty_features.hash(&mut empty_hash);
+               assert_eq!(zerod_hash.finish(), empty_hash.finish());
+       }
 }