Implement basic vec tree hash cache

eth2/utils/ssz/src/cached_tree_hash/impls.rs

@@ -1,7 +1,9 @@
 use super::*;
-use crate::ssz_encode;
+use crate::{ssz_encode, Encodable};
 
 impl CachedTreeHash for u64 {
+    type Item = Self;
+
     fn build_cache_bytes(&self) -> Vec<u8> {
         merkleize(ssz_encode(self))
     }
@@ -10,10 +12,6 @@ impl CachedTreeHash for u64 {
         8
     }
 
-    fn max_num_leaves(&self) -> usize {
-        1
-    }
-
     fn cached_hash_tree_root(
         &self,
         other: &Self,
@@ -28,3 +26,65 @@ impl CachedTreeHash for u64 {
         Some(chunk + 1)
     }
 }
+
+impl<T> CachedTreeHash for Vec<T>
+where
+    T: CachedTreeHash + Encodable,
+{
+    type Item = Self;
+
+    fn build_cache_bytes(&self) -> Vec<u8> {
+        let num_packed_bytes = self.num_bytes();
+        let num_leaves = num_sanitized_leaves(num_packed_bytes);
+
+        let mut packed = Vec::with_capacity(num_leaves * HASHSIZE);
+
+        for item in self {
+            packed.append(&mut ssz_encode(item));
+        }
+
+        let packed = sanitise_bytes(packed);
+
+        merkleize(packed)
+    }
+
+    fn num_bytes(&self) -> usize {
+        self.iter().fold(0, |acc, item| acc + item.num_bytes())
+    }
+
+    fn cached_hash_tree_root(
+        &self,
+        other: &Self::Item,
+        cache: &mut TreeHashCache,
+        chunk: usize,
+    ) -> Option<usize> {
+        let num_packed_bytes = self.num_bytes();
+        let num_leaves = num_sanitized_leaves(num_packed_bytes);
+
+        if num_leaves != num_sanitized_leaves(other.num_bytes()) {
+            panic!("Need to handle a change in leaf count");
+        }
+
+        let mut packed = Vec::with_capacity(num_leaves * HASHSIZE);
+
+        // TODO: try and avoid fully encoding the whole list
+        for item in self {
+            packed.append(&mut ssz_encode(item));
+        }
+
+        let packed = sanitise_bytes(packed);
+
+        let num_nodes = num_nodes(num_leaves);
+        let num_internal_nodes = num_nodes - num_leaves;
+
+        {
+            let mut chunk = chunk + num_internal_nodes;
+            for new_chunk_bytes in packed.chunks(HASHSIZE) {
+                cache.maybe_update_chunk(chunk, new_chunk_bytes)?;
+                chunk += 1;
+            }
+        }
+
+        Some(chunk + num_nodes)
+    }
+}