urllib.request.url2pathname() mishandles a UNC URI variant

[barneygale]

Bug report

Bug description:

On Windows, urllib.request.url2pathname() mishandles an uncommon file URI variant encoding a UNC path. Specifically, a URI with five leading slashes should be converted to a UNC path with two leading slashes, but url2pathname() returns a path with three leading slashes. Such URIs are created by software that simply prepends file:/// to a Windows path. See RFC 8089 E.3.2, final example.

>>> from urllib.request import url2pathname
>>> url2pathname('/////server/share')
'\\\\\\server\\share'  # expected: '\\\\server\\share'

CPython versions tested on:

CPython main branch

Operating systems tested on:

Windows

Linked PRs

• GH-127078: url2pathname(): handle extra slash before UNC drive in URL path #127132
• [3.13] GH-127078: url2pathname(): handle extra slash before UNC drive in URL path (GH-127132) #127135
• [3.12] GH-127078: url2pathname(): handle extra slash before UNC drive in URL path (GH-127132) #127136

[barneygale]

I think we should wait for #126367 to be fixed before tackling this bug

[barneygale]

I think we should wait for #126367 to be fixed before tackling this bug

On second thought, it's better to solve this issue first to avoid backport conflicts.