check that tree is non-empty for root generation

olivmath · Dec 27, 2023 · eb8e9d8 · eb8e9d8
1 parent 638f3fc
commit eb8e9d8
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diff --git a/merkly/mtree.py b/merkly/mtree.py
@@ -80,6 +80,9 @@ def concat_nodes(left: Node, right: Node) -> Node:
         return reduce(concat_nodes, full_proof).data == self.root
 
     def make_root(self, leaves: List[bytes]) -> bytes:
+        if len(leaves) == 0:
+            raise ValueError("Cannot get root of an empty tree")
+
         while len(leaves) > 1:
             next_level = []
             for i in range(0, len(leaves) - 1, 2):

diff --git a/test/errors/test_errors.py b/test/errors/test_errors.py
@@ -25,3 +25,13 @@ def invalid_hash_function(data):
             ["a", "b", "c", "d"],
             invalid_hash_function,
         )
+
+
+def test_empty_tree_root():
+    mtree = MerkleTree(['a', 'b', 'c', 'd'])
+    mtree.leaves = []
+
+    with raises(ValueError) as error:
+        mtree.root
+
+    assert str(error.value) == 'Cannot get root of an empty tree'