Fixed SystemError from non-tuple input value when decoding Fraction

cbor2/_decoder.py

@@ -629,10 +629,16 @@ def decode_rational(self) -> Fraction:
         # Semantic tag 30
         from fractions import Fraction
 
+        inputval = self._decode(immutable=True, unshared=True)
         try:
-            value = Fraction(*self._decode())
+            value = Fraction(*inputval)
         except (TypeError, ZeroDivisionError) as exc:
-            raise CBORDecodeValueError("error decoding rational value") from exc
+            if not isinstance(inputval, tuple):
+                raise CBORDecodeValueError(
+                    "error decoding rational: input value was not a tuple"
+                ) from None
+
+            raise CBORDecodeValueError("error decoding rational") from exc
 
         return self.set_shareable(value)
 

docs/versionhistory.rst

@@ -12,7 +12,7 @@ This library adheres to `Semantic Versioning <http://semver.org/>`_.
 - Made the C extension mandatory when the environment variable ``CBOR2_BUILD_C_EXTENSION`` is set
   to ``1``.
 - Fixed ``SystemError`` in the C extension when decoding a ``Fractional`` with a bad
-  number of arguments
+  number of arguments or a non-tuple value
 - Fixed ``SystemError`` in the C extension when the decoder object hook raises an
   exception
 - Fixed a segmentation fault when decoding invalid unicode data

source/decoder.c

@@ -1655,7 +1655,12 @@ CBORDecoder_decode_rational(CBORDecoderObject *self)
                 PyErr_GivenExceptionMatches(PyErr_Occurred(), PyExc_TypeError)
                 || PyErr_GivenExceptionMatches(PyErr_Occurred(), PyExc_ZeroDivisionError)
             ))
-                raise_from(_CBOR2_CBORDecodeValueError, "error decoding rational value");
+                raise_from(_CBOR2_CBORDecodeValueError, "error decoding rational");
+        } else {
+            PyErr_SetString(
+                _CBOR2_CBORDecodeValueError,
+                "error decoding rational: input value was not a tuple"
+            );
         }
         Py_DECREF(tuple);
     }

tests/test_decoder.py

@@ -537,6 +537,13 @@ def test_rational(impl):
     assert decoded == Fraction(2, 5)
 
 
+def test_rational_invalid_iterable(impl):
+    with pytest.raises(
+        impl.CBORDecodeValueError, match="error decoding rational: input value was not a tuple"
+    ):
+        impl.loads(unhexlify("d81e01"))
+
+
 def test_rational_zero_denominator(impl):
     with pytest.raises(impl.CBORDecodeValueError, match="error decoding rational") as exc:
         impl.loads(unhexlify("d81e820100"))