Marge fixes to test_harness, add serdehex crate

eth2/utils/ssz/src/impl_decode.rs

@@ -24,11 +24,30 @@ macro_rules! impl_decodable_for_uint {
     };
 }
 
+macro_rules! impl_decodable_for_u8_array {
+    ($len: expr) => {
+        impl Decodable for [u8; $len] {
+            fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
+                if index + $len > bytes.len() {
+                    Err(DecodeError::TooShort)
+                } else {
+                    let mut array: [u8; $len] = [0; $len];
+                    array.copy_from_slice(&bytes[index..index + $len]);
+
+                    Ok((array, index + $len))
+                }
+            }
+        }
+    };
+}
+
 impl_decodable_for_uint!(u16, 16);
 impl_decodable_for_uint!(u32, 32);
 impl_decodable_for_uint!(u64, 64);
 impl_decodable_for_uint!(usize, 64);
 
+impl_decodable_for_u8_array!(4);
+
 impl Decodable for u8 {
     fn ssz_decode(bytes: &[u8], index: usize) -> Result<(Self, usize), DecodeError> {
         if index >= bytes.len() {
@@ -246,4 +265,12 @@ mod tests {
         let result: Result<(bool, usize), DecodeError> = decode_ssz(&ssz, 0);
         assert_eq!(result, Err(DecodeError::Invalid));
     }
+
+    #[test]
+    fn test_decode_u8_array() {
+        let ssz = vec![0, 1, 2, 3];
+        let (result, index): ([u8; 4], usize) = decode_ssz(&ssz, 0).unwrap();
+        assert_eq!(index, 4);
+        assert_eq!(result, [0, 1, 2, 3]);
+    }
 }