Update SSZ

- Implement generic list decoding>
- Expose `encode` mod.
- Add convenience encoding function.

beacon_chain/utils/ssz/src/impl_decode.rs

@@ -1,4 +1,5 @@
 use super::ethereum_types::H256;
+use super::decode::decode_ssz_list;
 use super::{
     DecodeError,
     Decodable,
@@ -65,6 +66,16 @@ impl Decodable for H256 {
     }
 }
 
+impl<T> Decodable for Vec<T>
+    where T: Decodable
+{
+    fn ssz_decode(bytes: &[u8], index: usize)
+        -> Result<(Self, usize), DecodeError>
+    {
+        decode_ssz_list(bytes, index)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use super::*;

beacon_chain/utils/ssz/src/lib.rs

@@ -11,8 +11,8 @@ extern crate bytes;
 extern crate ethereum_types;
 
 pub mod decode;
+pub mod encode;
 
-mod encode;
 mod impl_encode;
 mod impl_decode;
 
@@ -29,3 +29,13 @@ pub use encode::{
 
 pub const LENGTH_BYTES: usize = 4;
 pub const MAX_LIST_SIZE : usize = 1 << (4 * 8);
+
+
+/// Convenience function to SSZ encode an object supporting ssz::Encode.
+pub fn ssz_encode<T>(val: &T) -> Vec<u8>
+    where T: Encodable
+{
+    let mut ssz_stream = SszStream::new();
+    ssz_stream.append(val);
+    ssz_stream.drain()
+}