From f91c0ec37e5e495c7303dcbf1ba24066ec60e914 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Tom=C3=A1s=20Gr=C3=BCner?=
 <47506558+MegaRedHand@users.noreply.github.com>
Date: Wed, 29 Nov 2023 08:02:15 -0300
Subject: [PATCH] fix: was mixing max size instead of length in hash
 calculation (#469)

---
 native/ssz_nif/src/utils/helpers.rs | 14 +++++++-------
 test/unit/ssz_test.exs              |  9 ++++++++-
 2 files changed, 15 insertions(+), 8 deletions(-)

diff --git a/native/ssz_nif/src/utils/helpers.rs b/native/ssz_nif/src/utils/helpers.rs
index 481c4b801..24fd300ae 100644
--- a/native/ssz_nif/src/utils/helpers.rs
+++ b/native/ssz_nif/src/utils/helpers.rs
@@ -78,8 +78,9 @@ where
     Elx: Decoder<'a>,
     Ssz: TreeHash + FromElx<Elx>,
 {
+    let list_size = list.len();
     let root = hash_vector_tree_root::<'a, Elx, Ssz>((list, max_size))?;
-    let bytes = tree_hash::mix_in_length(&Hash256::from(root), max_size).0;
+    let bytes = tree_hash::mix_in_length(&Hash256::from(root), list_size).0;
     Ok(bytes)
 }
 
@@ -95,16 +96,15 @@ where
     Ok(vec_tree_hash_root(&x, max_size))
 }
 
-/// A helper function providing common functionality between the `TreeHash` implementations for
-/// `FixedVector` and `VariableList`.
-pub fn vec_tree_hash_root<T>(vec: &[T], size: usize) -> [u8; 32]
+/// Taken from `ssz_types` and modified to take `max_size` as dynamic parameter.
+pub fn vec_tree_hash_root<T>(vec: &[T], max_size: usize) -> [u8; 32]
 where
     T: TreeHash,
 {
     let root = match T::tree_hash_type() {
         TreeHashType::Basic => {
-            let mut hasher: MerkleHasher = MerkleHasher::with_leaves(
-                (size + T::tree_hash_packing_factor() - 1) / T::tree_hash_packing_factor(),
+            let mut hasher = MerkleHasher::with_leaves(
+                (max_size + T::tree_hash_packing_factor() - 1) / T::tree_hash_packing_factor(),
             );
 
             for item in vec {
@@ -118,7 +118,7 @@ where
                 .expect("ssz_types variable vec should not have a remaining buffer")
         }
         TreeHashType::Container | TreeHashType::List | TreeHashType::Vector => {
-            let mut hasher = MerkleHasher::with_leaves(size);
+            let mut hasher = MerkleHasher::with_leaves(max_size);
 
             for item in vec {
                 hasher
diff --git a/test/unit/ssz_test.exs b/test/unit/ssz_test.exs
index 846ddd09c..3ae214b2d 100644
--- a/test/unit/ssz_test.exs
+++ b/test/unit/ssz_test.exs
@@ -171,10 +171,17 @@ defmodule Unit.SSZTests do
         Enum.join(deserialized)
       ])
 
+    assert serialized ==
+             Base.decode16!(
+               "0C000000140000001F000000617366617366617331383431383238303139327A6439673861733066373061307366"
+             )
+
     assert {:ok, ^serialized} = Ssz.to_ssz_typed(deserialized, SszTypes.Transaction)
     assert {:ok, ^deserialized} = Ssz.list_from_ssz(serialized, SszTypes.Transaction)
 
-    assert {:ok, _hash} =
+    hash = Base.decode16!("D5ACD42F851C9AE241B55AB79B23D7EC613E01BB6404B4A49D8CF214DBA26CF2")
+
+    assert {:ok, ^hash} =
              Ssz.hash_list_tree_root_typed(deserialized, 1_048_576, SszTypes.Transaction)
   end