GH-126212: Fix removal of slashes in file URIs on Windows (#126214)

Adjust `urllib.request.pathname2url()` and `url2pathname()` so that they
don't remove slashes from Windows DOS drive paths and URLs. There was no
basis for this behaviour, and it conflicts with how UNC and POSIX paths are
handled.

Lib/nturl2path.py

@@ -24,23 +24,15 @@ def url2pathname(url):
             # convert this to \\host\path\on\remote\host
             # (notice halving of slashes at the start of the path)
             url = url[2:]
-        components = url.split('/')
         # make sure not to convert quoted slashes :-)
-        return urllib.parse.unquote('\\'.join(components))
+        return urllib.parse.unquote(url.replace('/', '\\'))
     comp = url.split('|')
     if len(comp) != 2 or comp[0][-1] not in string.ascii_letters:
         error = 'Bad URL: ' + url
         raise OSError(error)
     drive = comp[0][-1].upper()
-    components = comp[1].split('/')
-    path = drive + ':'
-    for comp in components:
-        if comp:
-            path = path + '\\' + urllib.parse.unquote(comp)
-    # Issue #11474 - handing url such as |c/|
-    if path.endswith(':') and url.endswith('/'):
-        path += '\\'
-    return path
+    tail = urllib.parse.unquote(comp[1].replace('/', '\\'))
+    return drive + ':' + tail
 
 def pathname2url(p):
     """OS-specific conversion from a file system path to a relative URL
@@ -60,17 +52,12 @@ def pathname2url(p):
             raise OSError('Bad path: ' + p)
     if not ':' in p:
         # No drive specifier, just convert slashes and quote the name
-        components = p.split('\\')
-        return urllib.parse.quote('/'.join(components))
+        return urllib.parse.quote(p.replace('\\', '/'))
     comp = p.split(':', maxsplit=2)
     if len(comp) != 2 or len(comp[0]) > 1:
         error = 'Bad path: ' + p
         raise OSError(error)
 
     drive = urllib.parse.quote(comp[0].upper())
-    components = comp[1].split('\\')
-    path = '///' + drive + ':'
-    for comp in components:
-        if comp:
-            path = path + '/' + urllib.parse.quote(comp)
-    return path
+    tail = urllib.parse.quote(comp[1].replace('\\', '/'))
+    return '///' + drive + ':' + tail

Lib/test/test_urllib.py

@@ -1526,8 +1526,10 @@ class Pathname_Tests(unittest.TestCase):
         self.assertEqual(fn('\\\\?\\C:\\dir'), '///C:/dir')
         self.assertEqual(fn('\\\\?\\unc\\server\\share\\dir'), '//server/share/dir')
         self.assertEqual(fn("C:"), '///C:')
-        self.assertEqual(fn("C:\\"), '///C:')
+        self.assertEqual(fn("C:\\"), '///C:/')
         self.assertEqual(fn('C:\\a\\b.c'), '///C:/a/b.c')
+        self.assertEqual(fn('C:\\a\\b.c\\'), '///C:/a/b.c/')
+        self.assertEqual(fn('C:\\a\\\\b.c'), '///C:/a//b.c')
         self.assertEqual(fn('C:\\a\\b%#c'), '///C:/a/b%25%23c')
         self.assertEqual(fn('C:\\a\\b\xe9'), '///C:/a/b%C3%A9')
         self.assertEqual(fn('C:\\foo\\bar\\spam.foo'), "///C:/foo/bar/spam.foo")
@@ -1563,13 +1565,15 @@ class Pathname_Tests(unittest.TestCase):
         self.assertEqual(fn("///C|"), 'C:')
         self.assertEqual(fn("///C:"), 'C:')
         self.assertEqual(fn('///C:/'), 'C:\\')
-        self.assertEqual(fn('/C|//'), 'C:\\')
+        self.assertEqual(fn('/C|//'), 'C:\\\\')
         self.assertEqual(fn('///C|/path'), 'C:\\path')
         # No DOS drive
         self.assertEqual(fn("///C/test/"), '\\\\\\C\\test\\')
         self.assertEqual(fn("////C/test/"), '\\\\C\\test\\')
         # DOS drive paths
         self.assertEqual(fn('C:/path/to/file'), 'C:\\path\\to\\file')
+        self.assertEqual(fn('C:/path/to/file/'), 'C:\\path\\to\\file\\')
+        self.assertEqual(fn('C:/path/to//file'), 'C:\\path\\to\\\\file')
         self.assertEqual(fn('C|/path/to/file'), 'C:\\path\\to\\file')
         self.assertEqual(fn('/C|/path/to/file'), 'C:\\path\\to\\file')
         self.assertEqual(fn('///C|/path/to/file'), 'C:\\path\\to\\file')
@@ -1583,6 +1587,9 @@ class Pathname_Tests(unittest.TestCase):
         # Localhost paths
         self.assertEqual(fn('//localhost/C:/path/to/file'), 'C:\\path\\to\\file')
         self.assertEqual(fn('//localhost/C|/path/to/file'), 'C:\\path\\to\\file')
+        # Percent-encoded forward slashes are preserved for backwards compatibility
+        self.assertEqual(fn('C:/foo%2fbar'), 'C:\\foo/bar')
+        self.assertEqual(fn('//server/share/foo%2fbar'), '\\\\server\\share\\foo/bar')
         # Round-tripping
         paths = ['C:',
                  r'\\\C\test\\',

Misc/NEWS.d/next/Library/2024-10-30-23-59-36.gh-issue-126212._9uYjT.rst

@@ -0,0 +1,3 @@
+Fix issue where :func:`urllib.request.pathname2url` and
+:func:`~urllib.request.url2pathname` removed slashes from Windows DOS drive
+paths and URLs.