Issue #8969: On Windows, use mbcs codec in strict mode to encode and decode

filenames and enable os.fsencode().

Doc/library/os.rst

@@ -159,10 +159,10 @@ process and user.
 .. function:: fsencode(value)
 
    Encode *value* to bytes for use in the file system, environment variables or
-   the command line. Uses :func:`sys.getfilesystemencoding` and
+   the command line. Use :func:`sys.getfilesystemencoding` and
-   ``'surrogateescape'`` error handler for strings and returns bytes unchanged.
+   ``'surrogateescape'`` error handler for strings and return bytes unchanged.
-
+   On Windows, use ``'strict'`` error handler for strings if the file system
-   Availability: Unix.
+   encoding is ``'mbcs'`` (which is the default encoding).
 
    .. versionadded:: 3.2
 

Lib/os.py

@@ -533,14 +533,17 @@ if supports_bytes_environ:
         return environb.get(key, default)
     __all__.append("getenvb")
 
-if name != 'nt':
+def fsencode(value):
-    def fsencode(value):
     """Encode value for use in the file system, environment variables
     or the command line."""
     if isinstance(value, bytes):
         return value
     elif isinstance(value, str):
-            return value.encode(sys.getfilesystemencoding(), 'surrogateescape')
+        encoding = sys.getfilesystemencoding()
+        if encoding == 'mbcs':
+            return value.encode(encoding)
+        else:
+            return value.encode(encoding, 'surrogateescape')
     else:
         raise TypeError("expect bytes or str, not %s" % type(value).__name__)
 

Lib/test/test_ssl.py

@@ -33,16 +33,15 @@ else:
 HOST = support.HOST
 
 data_file = lambda name: os.path.join(os.path.dirname(__file__), name)
-fsencode = lambda name: name.encode(sys.getfilesystemencoding(), "surrogateescape")
 
 CERTFILE = data_file("keycert.pem")
-BYTES_CERTFILE = fsencode(CERTFILE)
+BYTES_CERTFILE = os.fsencode(CERTFILE)
 ONLYCERT = data_file("ssl_cert.pem")
 ONLYKEY = data_file("ssl_key.pem")
-BYTES_ONLYCERT = fsencode(ONLYCERT)
+BYTES_ONLYCERT = os.fsencode(ONLYCERT)
-BYTES_ONLYKEY = fsencode(ONLYKEY)
+BYTES_ONLYKEY = os.fsencode(ONLYKEY)
 CAPATH = data_file("capath")
-BYTES_CAPATH = fsencode(CAPATH)
+BYTES_CAPATH = os.fsencode(CAPATH)
 
 SVN_PYTHON_ORG_ROOT_CERT = data_file("https_svn_python_org_root.pem")
 

Misc/NEWS

@@ -12,6 +12,9 @@ What's New in Python 3.2 Alpha 1?
 Core and Builtins
 -----------------
 
+- Issue #8969: On Windows, use mbcs codec in strict mode to encode and decode
+  filenames and enable os.fsencode().
+
 - Issue #8941: decoding big endian UTF-32 data in UCS-2 builds could crash
   the interpreter with characters outside the Basic Multilingual Plane
   (higher than 0x10000).

Objects/unicodeobject.c

@@ -1478,11 +1478,17 @@ PyObject *PyUnicode_AsEncodedObject(PyObject *unicode,
 
 PyObject *PyUnicode_EncodeFSDefault(PyObject *unicode)
 {
-    if (Py_FileSystemDefaultEncoding)
+    if (Py_FileSystemDefaultEncoding) {
+#if defined(MS_WINDOWS) && defined(HAVE_USABLE_WCHAR_T)
+        if (strcmp(Py_FileSystemDefaultEncoding, "mbcs") == 0)
+            return PyUnicode_EncodeMBCS(PyUnicode_AS_UNICODE(unicode),
+                                        PyUnicode_GET_SIZE(unicode),
+                                        NULL);
+#endif
         return PyUnicode_AsEncodedString(unicode,
                                          Py_FileSystemDefaultEncoding,
                                          "surrogateescape");
-    else
+    } else
         return PyUnicode_EncodeUTF8(PyUnicode_AS_UNICODE(unicode),
                                      PyUnicode_GET_SIZE(unicode),
                                      "surrogateescape");
@@ -1639,7 +1645,7 @@ PyUnicode_DecodeFSDefaultAndSize(const char *s, Py_ssize_t size)
     if (Py_FileSystemDefaultEncoding) {
 #if defined(MS_WINDOWS) && defined(HAVE_USABLE_WCHAR_T)
         if (strcmp(Py_FileSystemDefaultEncoding, "mbcs") == 0) {
-            return PyUnicode_DecodeMBCS(s, size, "surrogateescape");
+            return PyUnicode_DecodeMBCS(s, size, NULL);
         }
 #elif defined(__APPLE__)
         if (strcmp(Py_FileSystemDefaultEncoding, "utf-8") == 0) {