Fix non-string map keys check in decode_dag_cbor

pytests/test_dag_cbor.py

@@ -26,14 +26,22 @@ def _dag_cbor_roundtrip(benchmark, data) -> None:
     assert obj == decoded, f'{obj} != {decoded}'
 
 
-def test_dag_cbor_decode_duplicate_keys() -> None:
+def test_dag_cbor_decode_duplicate_keys_error() -> None:
     with pytest.raises(ValueError) as exc_info:
         # {"abc": 1, "abc": 2}
         libipld.decode_dag_cbor(bytes.fromhex('a263616263016361626302'))
 
     assert 'Duplicate keys are not allowed' in str(exc_info.value)
 
 
+def test_dag_cbor_decode_non_string_key_error() -> None:
+    with pytest.raises(ValueError) as exc_info:
+        # {1:2}
+        libipld.decode_dag_cbor(bytes.fromhex('A10102'))
+
+    assert 'Map keys must be strings' in str(exc_info.value)
+
+
 @pytest.mark.parametrize('data', load_data_fixtures(_ROUNDTRIP_DATA_DIR), ids=lambda data: data[0])
 def test_dag_cbor_encode(benchmark, data) -> None:
     _dag_cbor_encode(benchmark, data)

src/lib.rs

@@ -79,7 +79,15 @@ fn decode_dag_cbor_to_pyobject<R: Read + Seek>(py: Python, r: &mut R, deep: usiz
             let len = decode_len(decode::read_uint(r, major)?)?;
             let dict = PyDict::new(py);
             for _ in 0..len {
-                let key = decode_dag_cbor_to_pyobject(py, r, deep + 1)?;
+                // DAG-CBOR keys are always strings
+                let key_major = decode::read_major(r)?;
+                if key_major.kind() != MajorKind::TextString {
+                    return Err(anyhow::anyhow!("Map keys must be strings"));
+                }
+
+                let key_len = decode::read_uint(r, key_major)?;
+                let key = decode::read_str(r, key_len)?.to_object(py);
+
                 let value = decode_dag_cbor_to_pyobject(py, r, deep + 1)?;
 
                 if dict.get_item(&key)?.is_some() {