Fixed SystemError when decoding bad data for Fractional

docs/versionhistory.rst

@@ -5,6 +5,10 @@ Version history
 
 This library adheres to `Semantic Versioning <http://semver.org/>`_.
 
+**UNRELEASED**
+
+- Fixed ``SystemError`` when decoding a ``Fractional`` with a bad number of arguments
+
 **5.5.1** (2023-11-02)
 
 - Fixed ``CBORSimpleValue`` allowing the use of reserved values (24 to 31) which resulted in

source/decoder.c

@@ -1367,16 +1367,14 @@ CBORDecoder_decode_rational(CBORDecoderObject *self)
     // NOTE: see semantic type 4
     tuple = decode(self, DECODE_IMMUTABLE | DECODE_UNSHARED);
     if (tuple) {
-        if (PyTuple_CheckExact(tuple) && PyTuple_GET_SIZE(tuple) == 2) {
-            ret = PyObject_CallFunctionObjArgs(
-                    _CBOR2_Fraction,
-                    PyTuple_GET_ITEM(tuple, 0),
-                    PyTuple_GET_ITEM(tuple, 1),
-                    NULL);
+        if (PyTuple_CheckExact(tuple)) {
+            ret = PyObject_Call(_CBOR2_Fraction, tuple, NULL);
+            if (ret) {
+                set_shareable(self, ret);
+            }
         }
         Py_DECREF(tuple);
     }
-    set_shareable(self, ret);
     return ret;
 }
 

tests/test_decoder.py

@@ -809,3 +809,18 @@ def test_decimal_payload_unpacking(impl, data, expected):
     with pytest.raises(impl.CBORDecodeValueError) as exc_info:
         impl.loads(unhexlify(data))
     assert exc_info.value.args[0] == f"Incorrect tag {expected} payload"
+
+
+@pytest.mark.parametrize(
+    "payload, exception, pattern",
+    [
+        pytest.param(
+            b"\xd8\x1e\x84\xff\xff\xff\xff",
+            TypeError,
+            r"__new__\(\) takes from 1 to 3 positional arguments but 5 were given",
+        )
+    ],
+)
+def test_invalid_data(impl, payload, exception, pattern) -> None:
+    with pytest.raises(exception, match=pattern):
+        impl.loads(b"\xd8\x1e\x84\xff\xff\xff\xff")