bpo-34384: Fix os.readlink() on Windows (GH-8740)

os.readlink() now accepts path-like and bytes objects on Windows.
Previously, support for path-like and bytes objects was only
implemented on Unix.

This commit also merges Unix and Windows implementations of
os.readlink() in one function and adds basic unit tests to increase
test coverage of the function.

Doc/library/os.rst

@@ -2014,8 +2014,10 @@ features:
       The *dir_fd* argument.
 
    .. versionchanged:: 3.6
-      Accepts a :term:`path-like object`.
+      Accepts a :term:`path-like object` on Unix.
 
+   .. versionchanged:: 3.8
+      Accepts a :term:`path-like object` and a bytes object on Windows.
 
 .. function:: remove(path, *, dir_fd=None)
 

Lib/test/test_os.py

@@ -2039,6 +2039,53 @@ class Win32ListdirTests(unittest.TestCase):
                 [os.fsencode(path) for path in self.created_paths])
 
 
+@unittest.skipUnless(hasattr(os, 'readlink'), 'needs os.readlink()')
+class ReadlinkTests(unittest.TestCase):
+    filelink = 'readlinktest'
+    filelink_target = os.path.abspath(__file__)
+    filelinkb = os.fsencode(filelink)
+    filelinkb_target = os.fsencode(filelink_target)
+
+    def setUp(self):
+        self.assertTrue(os.path.exists(self.filelink_target))
+        self.assertTrue(os.path.exists(self.filelinkb_target))
+        self.assertFalse(os.path.exists(self.filelink))
+        self.assertFalse(os.path.exists(self.filelinkb))
+
+    def test_not_symlink(self):
+        filelink_target = FakePath(self.filelink_target)
+        self.assertRaises(OSError, os.readlink, self.filelink_target)
+        self.assertRaises(OSError, os.readlink, filelink_target)
+
+    def test_missing_link(self):
+        self.assertRaises(FileNotFoundError, os.readlink, 'missing-link')
+        self.assertRaises(FileNotFoundError, os.readlink,
+                          FakePath('missing-link'))
+
+    @support.skip_unless_symlink
+    def test_pathlike(self):
+        os.symlink(self.filelink_target, self.filelink)
+        self.addCleanup(support.unlink, self.filelink)
+        filelink = FakePath(self.filelink)
+        self.assertEqual(os.readlink(filelink), self.filelink_target)
+
+    @support.skip_unless_symlink
+    def test_pathlike_bytes(self):
+        os.symlink(self.filelinkb_target, self.filelinkb)
+        self.addCleanup(support.unlink, self.filelinkb)
+        path = os.readlink(FakePath(self.filelinkb))
+        self.assertEqual(path, self.filelinkb_target)
+        self.assertIsInstance(path, bytes)
+
+    @support.skip_unless_symlink
+    def test_bytes(self):
+        os.symlink(self.filelinkb_target, self.filelinkb)
+        self.addCleanup(support.unlink, self.filelinkb)
+        path = os.readlink(self.filelinkb)
+        self.assertEqual(path, self.filelinkb_target)
+        self.assertIsInstance(path, bytes)
+
+
 @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
 @support.skip_unless_symlink
 class Win32SymlinkTests(unittest.TestCase):

Misc/NEWS.d/next/Library/2018-08-12-08-43-21.bpo-34384.yjofCv.rst

@@ -0,0 +1,2 @@
+:func:`os.readlink` now accepts :term:`path-like <path-like object>` and
+:class:`bytes` objects on Windows.

Modules/posixmodule.c

@@ -7414,18 +7414,24 @@ If dir_fd is not None, it should be a file descriptor open to a directory,\n\
   and path should be relative; path will then be relative to that directory.\n\
 dir_fd may not be implemented on your platform.\n\
   If it is unavailable, using it will raise a NotImplementedError.");
-#endif
 
-#ifdef HAVE_READLINK
-
-/* AC 3.5: merge win32 and not together */
 static PyObject *
 posix_readlink(PyObject *self, PyObject *args, PyObject *kwargs)
 {
     path_t path;
     int dir_fd = DEFAULT_DIR_FD;
+#if defined(HAVE_READLINK)
     char buffer[MAXPATHLEN+1];
     ssize_t length;
+#elif defined(MS_WINDOWS)
+    DWORD n_bytes_returned;
+    DWORD io_result;
+    HANDLE reparse_point_handle;
+
+    char target_buffer[_Py_MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
+    _Py_REPARSE_DATA_BUFFER *rdb = (_Py_REPARSE_DATA_BUFFER *)target_buffer;
+    const wchar_t *print_name;
+#endif
     PyObject *return_value = NULL;
     static char *keywords[] = {"path", "dir_fd", NULL};
 
@@ -7436,6 +7442,7 @@ posix_readlink(PyObject *self, PyObject *args, PyObject *kwargs)
                           READLINKAT_DIR_FD_CONVERTER, &dir_fd))
         return NULL;
 
+#if defined(HAVE_READLINK)
     Py_BEGIN_ALLOW_THREADS
 #ifdef HAVE_READLINKAT
     if (dir_fd != DEFAULT_DIR_FD)
@@ -7455,45 +7462,11 @@ posix_readlink(PyObject *self, PyObject *args, PyObject *kwargs)
         return_value = PyUnicode_DecodeFSDefaultAndSize(buffer, length);
     else
         return_value = PyBytes_FromStringAndSize(buffer, length);
-exit:
-    path_cleanup(&path);
-    return return_value;
-}
-
-#endif /* HAVE_READLINK */
-
-#if !defined(HAVE_READLINK) && defined(MS_WINDOWS)
-
-static PyObject *
-win_readlink(PyObject *self, PyObject *args, PyObject *kwargs)
-{
-    const wchar_t *path;
-    DWORD n_bytes_returned;
-    DWORD io_result;
-    PyObject *po, *result;
-    int dir_fd;
-    HANDLE reparse_point_handle;
-
-    char target_buffer[_Py_MAXIMUM_REPARSE_DATA_BUFFER_SIZE];
-    _Py_REPARSE_DATA_BUFFER *rdb = (_Py_REPARSE_DATA_BUFFER *)target_buffer;
-    const wchar_t *print_name;
-
-    static char *keywords[] = {"path", "dir_fd", NULL};
-
-    if (!PyArg_ParseTupleAndKeywords(args, kwargs, "U|$O&:readlink", keywords,
-                          &po,
-                          dir_fd_unavailable, &dir_fd
-                          ))
-        return NULL;
-
-    path = _PyUnicode_AsUnicode(po);
-    if (path == NULL)
-        return NULL;
-
+#elif defined(MS_WINDOWS)
     /* First get a handle to the reparse point */
     Py_BEGIN_ALLOW_THREADS
     reparse_point_handle = CreateFileW(
-        path,
+        path.wide,
         0,
         0,
         0,
@@ -7502,8 +7475,10 @@ win_readlink(PyObject *self, PyObject *args, PyObject *kwargs)
         0);
     Py_END_ALLOW_THREADS
 
-    if (reparse_point_handle==INVALID_HANDLE_VALUE)
-        return win32_error_object("readlink", po);
+    if (reparse_point_handle == INVALID_HANDLE_VALUE) {
+        return_value = path_error(&path);
+        goto exit;
+    }
 
     Py_BEGIN_ALLOW_THREADS
     /* New call DeviceIoControl to read the reparse point */
@@ -7518,26 +7493,31 @@ win_readlink(PyObject *self, PyObject *args, PyObject *kwargs)
     CloseHandle(reparse_point_handle);
     Py_END_ALLOW_THREADS
 
-    if (io_result==0)
-        return win32_error_object("readlink", po);
+    if (io_result == 0) {
+        return_value = path_error(&path);
+        goto exit;
+    }
 
     if (rdb->ReparseTag != IO_REPARSE_TAG_SYMLINK)
     {
         PyErr_SetString(PyExc_ValueError,
                 "not a symbolic link");
-        return NULL;
+        goto exit;
     }
     print_name = (wchar_t *)((char*)rdb->SymbolicLinkReparseBuffer.PathBuffer +
                  rdb->SymbolicLinkReparseBuffer.PrintNameOffset);
 
-    result = PyUnicode_FromWideChar(print_name,
-                    rdb->SymbolicLinkReparseBuffer.PrintNameLength / sizeof(wchar_t));
-    return result;
+    return_value = PyUnicode_FromWideChar(print_name,
+                          rdb->SymbolicLinkReparseBuffer.PrintNameLength / sizeof(wchar_t));
+    if (path.narrow) {
+        Py_SETREF(return_value, PyUnicode_EncodeFSDefault(return_value));
+    }
+#endif
+exit:
+    path_cleanup(&path);
+    return return_value;
 }
-
-#endif /* !defined(HAVE_READLINK) && defined(MS_WINDOWS) */
-
-
+#endif /* defined(HAVE_READLINK) || defined(MS_WINDOWS) */
 
 #ifdef HAVE_SYMLINK
 
@@ -12950,16 +12930,11 @@ static PyMethodDef posix_methods[] = {
     OS_GETPRIORITY_METHODDEF
     OS_SETPRIORITY_METHODDEF
     OS_POSIX_SPAWN_METHODDEF
-#ifdef HAVE_READLINK
+#if defined(HAVE_READLINK) || defined(MS_WINDOWS)
     {"readlink",        (PyCFunction)posix_readlink,
                         METH_VARARGS | METH_KEYWORDS,
                         readlink__doc__},
-#endif /* HAVE_READLINK */
-#if !defined(HAVE_READLINK) && defined(MS_WINDOWS)
-    {"readlink",        (PyCFunction)win_readlink,
-                        METH_VARARGS | METH_KEYWORDS,
-                        readlink__doc__},
-#endif /* !defined(HAVE_READLINK) && defined(MS_WINDOWS) */
+#endif /* defined(HAVE_READLINK) || defined(MS_WINDOWS) */
     OS_RENAME_METHODDEF
     OS_REPLACE_METHODDEF
     OS_RMDIR_METHODDEF