bpo-29248: Fix os.readlink() on Windows (GH-5577)

The PrintNameOffset field of the reparse data buffer
was treated as a number of characters instead of bytes.

(cherry picked from commit 3c34aad4e7a95913ec7db8e5e948a8fc69047bf7)

Co-authored-by: SSE4 <tomskside@gmail.com>

1 files changed, 15 insertions, 0 deletions

diff --git a/Lib/test/test_os.py b/Lib/test/test_os.py
index b65ccb7..033e544 100644
--- a/Lib/test/test_os.py
+++ b/Lib/test/test_os.py
@@ -2171,6 +2171,21 @@ class Win32SymlinkTests(unittest.TestCase):
         finally:
             os.chdir(orig_dir)
 
+    @unittest.skipUnless(os.path.lexists(r'C:\Users\All Users')
+                            and os.path.exists(r'C:\ProgramData'),
+                            'Test directories not found')
+    def test_29248(self):
+        # os.symlink() calls CreateSymbolicLink, which creates
+        # the reparse data buffer with the print name stored
+        # first, so the offset is always 0. CreateSymbolicLink
+        # stores the "PrintName" DOS path (e.g. "C:\") first,
+        # with an offset of 0, followed by the "SubstituteName"
+        # NT path (e.g. "\??\C:\"). The "All Users" link, on
+        # the other hand, seems to have been created manually
+        # with an inverted order.
+        target = os.readlink(r'C:\Users\All Users')
+        self.assertTrue(os.path.samefile(target, r'C:\ProgramData'))
+
 
 @unittest.skipUnless(sys.platform == "win32", "Win32 specific tests")
 class Win32JunctionTests(unittest.TestCase):