Fix duplicated map keys check in decode_dag_cbor (#16)

pytests/test_dag_cbor.py

@@ -26,6 +26,14 @@ def _dag_cbor_roundtrip(benchmark, data) -> None:
     assert obj == decoded, f'{obj} != {decoded}'
 
 
+def test_dag_cbor_decode_duplicate_keys() -> 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)
+
+
 @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

@@ -79,17 +79,21 @@ 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 {
-                // FIXME (MarshalX): we should raise on duplicate keys?
                 let key = decode_dag_cbor_to_pyobject(py, r, deep + 1)?;
                 let value = decode_dag_cbor_to_pyobject(py, r, deep + 1)?;
+
+                if dict.get_item(&key)?.is_some() {
+                    return Err(anyhow::anyhow!("Duplicate keys are not allowed"));
+                }
+
                 dict.set_item(key, value).unwrap();
             }
             dict.into()
         }
         MajorKind::Tag => {
             let value = decode::read_uint(r, major)?;
             if value != 42 {
-                return Err(anyhow::anyhow!("non-42 tags are not supported"));
+                return Err(anyhow::anyhow!("Non-42 tags are not supported"));
             }
 
             decode::read_link(r)?.to_string().to_object(py)
@@ -100,7 +104,7 @@ fn decode_dag_cbor_to_pyobject<R: Read + Seek>(py: Python, r: &mut R, deep: usiz
             cbor::NULL => py.None(),
             cbor::F32 => (decode::read_f32(r)? as f64).to_object(py),
             cbor::F64 => decode::read_f64(r)?.to_object(py),
-            _ => return Err(anyhow::anyhow!(format!("unsupported major type"))),
+            _ => return Err(anyhow::anyhow!(format!("Unsupported major type"))),
         },
     };
     Ok(py_object)