René's URL Explorer Experiment

{"@context":"https://schema.org","@type":"DiscussionForumPosting","headline":"Add tests to verify the behavior of basic COM methods.","articleBody":"# Feature or enhancement\r\n\r\n### Proposal:\r\n\r\nI am one of the maintainers of [`comtypes`](https://github.com/enthought/comtypes/). `comtypes` is based on `ctypes` to implement [`IUnknown`](https://learn.microsoft.com/en-us/windows/win32/api/unknwn/nn-unknwn-iunknown) and other COM stuffs.\r\n\r\nIn the past, I reported in [gh-124520](https://github.com/python/cpython/issues/124520) that projects dependent on `ctypes` was broken due to changes in Python 3.13.\r\n\r\nI am currently researching whether there are any effective ways to proactively prevent such regressions beyond what I attempted in [gh-125783](https://github.com/python/cpython/issues/125783).\r\n\r\nI noticed that the `cpython` repository might not contain tests for basic COM methods, such as [`QueryInterface`](https://learn.microsoft.com/en-us/windows/win32/api/unknwn/nf-unknwn-iunknown-queryinterface(refiid_void)), [`AddRef`](https://learn.microsoft.com/en-us/windows/win32/api/unknwn/nf-unknwn-iunknown-addref), and [`Release`](https://learn.microsoft.com/en-us/windows/win32/api/unknwn/nf-unknwn-iunknown-release).\r\nThere are many projects besides `comtypes` that define COM interfaces and call COM methods, so I think it’s important to test them.\r\n\r\nI think that simple tests like the one below, which implements a very basic COM interface and calls its methods, might help prevent regressions.\r\n(I removed the complex parts in `comtypes`, such as defining methods, registering pointer types, and using `__del__` to call `Release` through metaclasse magic.)\r\n(I have confirmed that this test passes in a virtual environment with Python 3.11.2, which I could quickly set up.)\r\n\r\n```py\r\nimport sys\r\nimport unittest\r\n\r\n\r\ndef setUpModule():\r\n    if sys.platform != \"win32\":\r\n        raise unittest.SkipTest(\"Win32 only\")\r\n\r\n\r\nimport ctypes\r\nimport gc\r\nfrom ctypes import HRESULT, POINTER, byref\r\nfrom ctypes.wintypes import BYTE, DWORD, HGLOBAL, WORD\r\n\r\nole32 = ctypes.oledll.ole32\r\noleaut32 = ctypes.oledll.oleaut32\r\n\r\n\r\ndef CLSIDFromString(name):\r\n    guid = GUID()\r\n    ole32.CLSIDFromString(name, byref(guid))\r\n    return guid\r\n\r\n\r\nclass GUID(ctypes.Structure):\r\n    _fields_ = [\r\n        (\"Data1\", DWORD),\r\n        (\"Data2\", WORD),\r\n        (\"Data3\", WORD),\r\n        (\"Data4\", BYTE * 8),\r\n    ]\r\n\r\n\r\nPyInstanceMethod_New = ctypes.pythonapi.PyInstanceMethod_New\r\nPyInstanceMethod_New.argtypes = [ctypes.py_object]\r\nPyInstanceMethod_New.restype = ctypes.py_object\r\nPyInstanceMethod_Type = type(PyInstanceMethod_New(id))\r\n\r\n\r\nclass COM_METHOD:\r\n    def __init__(self, index, restype, *argtypes):\r\n        self.index = index\r\n        self.proto = ctypes.WINFUNCTYPE(restype, *argtypes)\r\n\r\n    def __set_name__(self, owner, name):\r\n        self.mth = PyInstanceMethod_Type(self.proto(self.index, name))\r\n\r\n    def __call__(self, *args, **kwargs):\r\n        return self.mth(*args, **kwargs)\r\n\r\n    def __get__(self, instance, owner):\r\n        if instance is None:\r\n            return self\r\n        return self.mth.__get__(instance)\r\n\r\n\r\nclass IUnknown(ctypes.c_void_p):\r\n    IID = CLSIDFromString(\"{00000000-0000-0000-C000-000000000046}\")\r\n    QueryInterface = COM_METHOD(0, HRESULT, POINTER(GUID), POINTER(ctypes.c_void_p))\r\n    AddRef = COM_METHOD(1, ctypes.c_long)\r\n    Release = COM_METHOD(2, ctypes.c_long)\r\n\r\n\r\nclass ICreateTypeLib(IUnknown):\r\n    IID = CLSIDFromString(\"{00020406-0000-0000-C000-000000000046}\")\r\n    # `CreateTypeInfo` and more methods should be implemented\r\n\r\n\r\nclass ICreateTypeLib2(ICreateTypeLib):\r\n    IID = CLSIDFromString(\"{0002040F-0000-0000-C000-000000000046}\")\r\n    # `DeleteTypeInfo` and more methods should be implemented\r\n\r\n\r\nclass ISequentialStream(IUnknown):\r\n    IID = CLSIDFromString(\"{0C733A30-2A1C-11CE-ADE5-00AA0044773D}\")\r\n    # `Read` and `Write` methods should be implemented\r\n\r\n\r\nclass IStream(ISequentialStream):\r\n    IID = CLSIDFromString(\"{0000000C-0000-0000-C000-000000000046}\")\r\n    # `Seek` and more methods should be implemented\r\n\r\n\r\nCreateTypeLib2 = oleaut32.CreateTypeLib2\r\nCreateTypeLib2.argtypes = (ctypes.c_int, ctypes.c_wchar_p, POINTER(ICreateTypeLib2))\r\n\r\nCreateStreamOnHGlobal = ole32.CreateStreamOnHGlobal\r\nCreateStreamOnHGlobal.argtypes = (HGLOBAL, ctypes.c_bool, POINTER(IStream))\r\n\r\n\r\nCOINIT_APARTMENTTHREADED = 0x2\r\nS_OK = 0\r\nE_NOINTERFACE = -2147467262\r\n\r\n\r\nclass Test(unittest.TestCase):\r\n    def setUp(self):\r\n        ole32.CoInitializeEx(None, COINIT_APARTMENTTHREADED)\r\n\r\n    def tearDown(self):\r\n        ole32.CoUninitialize()\r\n        gc.collect()\r\n\r\n    def test_create_typelib_2(self):\r\n        pctlib = ICreateTypeLib2()\r\n        hr = CreateTypeLib2(0, \"sample.tlb\", pctlib)\r\n        self.assertEqual(S_OK, hr)\r\n\r\n        self.assertEqual(2, pctlib.AddRef())\r\n        self.assertEqual(3, pctlib.AddRef())\r\n\r\n        self.assertEqual(2, pctlib.Release())\r\n        self.assertEqual(1, pctlib.Release())\r\n        self.assertEqual(0, pctlib.Release())\r\n\r\n    def test_stream(self):\r\n        pstm = IStream()\r\n        hr = CreateStreamOnHGlobal(None, True, pstm)\r\n        self.assertEqual(S_OK, hr)\r\n\r\n        self.assertEqual(2, pstm.AddRef())\r\n        self.assertEqual(3, pstm.AddRef())\r\n\r\n        self.assertEqual(2, pstm.Release())\r\n        self.assertEqual(1, pstm.Release())\r\n        self.assertEqual(0, pstm.Release())\r\n\r\n    def test_query_interface(self):\r\n        pctlib2 = ICreateTypeLib2()\r\n        CreateTypeLib2(0, \"sample.tlb\", pctlib2)\r\n\r\n        pctlib = ICreateTypeLib()\r\n        hr1 = pctlib2.QueryInterface(byref(ICreateTypeLib.IID), byref(pctlib))\r\n        self.assertEqual(S_OK, hr1)\r\n        self.assertEqual(1, pctlib.Release())\r\n\r\n        punk = IUnknown()\r\n        hr2 = pctlib.QueryInterface(byref(IUnknown.IID), byref(punk))\r\n        self.assertEqual(S_OK, hr2)\r\n        self.assertEqual(1, punk.Release())\r\n\r\n        pstm = IStream()\r\n        with self.assertRaises(WindowsError) as e:  # Why not `COMError`?\r\n            punk.QueryInterface(byref(IStream.IID), byref(pstm))\r\n        self.assertEqual(E_NOINTERFACE, e.exception.winerror)\r\n\r\n        self.assertEqual(0, punk.Release())\r\n```\r\n\r\n- I am not sure why a `WindowsError` is raised instead of a `COMError` when `QueryInterface` fails.\r\n- Perhaps an interface with even fewer methods should be used in the test.\r\n- At this stage, I think creating custom COM type libraries and interfaces might be excessive.\r\n\r\nI welcome any feedback.\r\n\r\n\r\n\r\n### Has this already been discussed elsewhere?\r\n\r\nNo response given\r\n\r\n### Links to previous discussion of this feature:\r\n\r\n_No response_\n\n\u003c!-- gh-linked-prs --\u003e\n### Linked PRs\n* gh-126610\n* gh-127159\n* gh-127160\n\u003c!-- /gh-linked-prs --\u003e\n","author":{"url":"https://github.com/junkmd","@type":"Person","name":"junkmd"},"datePublished":"2024-11-04T08:13:18.000Z","interactionStatistic":{"@type":"InteractionCounter","interactionType":"https://schema.org/CommentAction","userInteractionCount":2},"url":"https://github.com/126384/cpython/issues/126384"}