Fixed exceptions raised from decoder object hook causing SystemError

Fixes #201.

docs/versionhistory.rst

@@ -7,7 +7,10 @@ This library adheres to `Semantic Versioning <http://semver.org/>`_.
 
 **UNRELEASED**
 
-- Fixed ``SystemError`` when decoding a ``Fractional`` with a bad number of arguments
+- Fixed ``SystemError`` in the C extension when decoding a ``Fractional`` with a bad
+  number of arguments
+- Fixed ``SystemError`` in the C extension when the decoder object hook raises an
+  exception
 - Fixed a segmentation fault when decoding invalid unicode data
 
 **5.5.1** (2023-11-02)

source/decoder.c

@@ -939,11 +939,12 @@ decode_map(CBORDecoderObject *self, uint8_t subtype)
     }
     if (ret && self->object_hook != Py_None) {
         map = PyObject_CallFunctionObjArgs(self->object_hook, self, ret, NULL);
-        if (map) {
-            set_shareable(self, map);
-            Py_DECREF(ret);
-            ret = map;
-        }
+        if (!map)
+            return NULL;
+
+        set_shareable(self, map);
+        Py_DECREF(ret);
+        ret = map;
     }
     return ret;
 }

tests/test_decoder.py

@@ -690,6 +690,15 @@ def __init__(self, state):
     assert decoded.state == {"a": 3, "b": 5}
 
 
+def test_object_hook_exception(impl):
+    def object_hook(decoder, data):
+        raise RuntimeError("foo")
+
+    payload = unhexlify("A2616103616205")
+    with pytest.raises(RuntimeError, match="foo"):
+        impl.loads(payload, object_hook=object_hook)
+
+
 def test_load_from_file(impl, tmpdir):
     path = tmpdir.join("testdata.cbor")
     path.write_binary(b"\x82\x01\x0a")