[issue37609] support "UNC" device paths in ntpath.splitdrive

[Steve Dower]

Steve Dower  added the comment:

If you can build this on top of nt._path_splitroot then it could save a decent 
amount of work, though at the same time I think it's worthwhile having a pure 
Python implementation which is cross-platform.

Haven't looked at the PR yet (or Eryk's implementation recently), but at the 
very least it would be nice to have tests that verify consistency with 
nt._path_splitroot. That way at least we'll discover if the native version 
changes.

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Eryk Sun]

Change by Eryk Sun :


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Removed message: https://bugs.python.org/msg390391

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Barney Gale]

Change by Barney Gale :


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pull_request: https://github.com/python/cpython/pull/31702

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Barney Gale]

Barney Gale  added the comment:

I'd like to pick this up, as it would allow us to remove a duplicate 
implementation in pathlib with its own shortcomings.

If using native functionality if difficult to get right, could I put @eryksun's 
splitdrive.py implementation up for review?

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Steve Dower]

Change by Steve Dower :


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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Steve Dower]

Change by Steve Dower :


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pull_request: https://github.com/python/cpython/pull/25261

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Eryk Sun]

Eryk Sun  added the comment:

> I've got a fairly simple implementation for this using the (new) 
> nt._path_splitroot native method

It's for the best to let the system path API handle this, especially if doing 
so gets this issue resolved, as well as others like it and those that depend on 
it. I'm a bit disappointed, however, that PathCchSkipRoot() doesn't handle some 
of the cases that I handled in splitdrive.py. 

PathCchSkipRoot() doesn't support the "Global" link in device paths. 
Fortunately this case is uncommon. In practice "Global" is only needed when a 
DOS device name has to be created globally, e.g. "\\.\Global\SomeGlobalDevice".

PathCchSkipRoot() splits "\\.\UNC\server\share" as "\\.\UNC\" and 
"server\share", but that's okay since no one uses "\\.\UNC". 

PathCchSkipRoot() restricts the "\\?\" prefix to drive names, volume GUID 
names, and the "UNC" device -- such as "\\?\X:", 
"\\?\Volume{12345678-1234-1234-1234-123456789ABC}", and "\\?\UNC\server\share". 
Other device names such as the "PIPE" device have to use the "\\.\" prefix. 
Rarely, a device path may need "\\?\" if it's a long path or needs to bypass 
normalization. I wanted splitdrive() to remain neutral for such cases, but that 
will have to be sacrificed.

PathCchSkipRoot() doesn't ignore repeated slashes in the drive part of a UNC 
"\\server\share" or "\\?\UNC\server\share" path, even though GetFullPathNameW() 
collapses all but the initial two slashes. (More than two initial slashes is 
invalid.) For example, the system normalizes "//localhost///C$" as 
"\\localhost\C$:

>>> os.chdir('//localhost///C$/Temp')
>>> print(os.getcwd())
\\localhost\C$\Temp

PathCchSkipRoot() also allows just a UNC server to count as a root, e.g. 
"\\server" or "\\?\UNC\server", though a valid UNC path requires a share name. 
Without a share, FindFirstFileW(L"//server/*", _data) will fail to parse 
the directory name correctly and try to open "//server/*", which is an invalid 
name. If splitdrive() requires a valid drive name, it should not return 
"//server" or "//server/" as a drive name.

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Steve Dower]

Steve Dower  added the comment:

Once issue43105 is merged, I've got a fairly simple implementation for this 
using the (new) nt._path_splitroot native method, as well as improved tests 
that cover both the native and emulated calculations.

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assignee:  -> steve.dower
versions: +Python 3.10 -Python 3.8, Python 3.9

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Eryk Sun]

Change by Eryk Sun :


Removed file: https://bugs.python.org/file48607/splitdrive.py

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Eryk Sun]

Eryk Sun  added the comment:

I'm attaching a rewrite of splitdrive() from msg352355. This version uses an 
internal _next() function to get the indices of the next path component, 
ignoring repeated separators. It also flattens the nested structure of the 
previous implementation by adding multiple return statements.

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Added file: https://bugs.python.org/file49541/splitdrive.py

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Eryk Sun]

Eryk Sun  added the comment:

Please consult the attached file "splitdrive.py". I redesigned splitdrive() to 
support "UNC" and "GLOBAL" junctions in device paths. I relaxed the design to 
allow repeated separators everywhere except for the UNC root. IIRC, Windows has 
supported this since XP. For example:

>>> print(nt._getfullpathname('//server///share'))
\\server\share
>>> print(nt._getfullpathname(r'\\server\\\share'))
\\server\share

There are also a couple of minor behavior changes in the new implementation.

The old implementation would split "//server/" as ('//server/', ''). Since 
there's no share, this should not count as a drive. The new implementation 
splits it as ('', '//server/'). Similarly it splits '//?/UNC/server/' as ('', 
'//?/UNC/server/'). 

The old implementation also allowed any character as a drive 'letter'. For 
example, it would split '/:/spam' as ('/:', '/spam'). The new implementation 
ensures that the drive letter in a DOS drive is alphabetic.

I also extended test_splitdrive to use a list of test cases in order to avoid 
having to define each case twice. It calls tester() a second time for each 
case, with slash and backslash swapped.

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Added file: https://bugs.python.org/file48607/splitdrive.py

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Steve Dower]

Steve Dower  added the comment:

For clarity, given Eryk's examples above, both "\\?\UNC\" and "//?/UNC/" are 
okay (as are any combination of forward and backslashes in the prefix, as 
normalization will be applied for any except the "\\?\" version). "UNC" is also 
case-insensitive.

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Ngalim Siregar]

Ngalim Siregar  added the comment:

I was unsure about implementation in the patch, do you have UNC format 
specification?

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Ngalim Siregar]

Change by Ngalim Siregar :


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keywords: +patch
pull_requests: +14632
stage: needs patch -> patch review
pull_request: https://github.com/python/cpython/pull/14841

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Serhiy Storchaka]

Serhiy Storchaka  added the comment:

Do you want to create a PR Eryk?

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[issue37609] support "UNC" device paths in ntpath.splitdrive

[Eryk Sun]

New submission from Eryk Sun :

Windows Python includes UNC shares such as "//server/spam" in its definition of 
a drive. This is natural because Windows supports setting a UNC path as the 
working directory and handles the share component as the working drive when 
resolving rooted paths such as "/eggs". For the sake of generality when working 
with \\?\ extended paths, Python should expand its definition of a UNC drive to 
include "UNC" device paths.

A practical example is calling glob.glob with a "//?/UNC" device path.

>>> import os, sys, glob
>>> sys.addaudithook(lambda s,a: print('#', a[0]) if s == 'glob.glob' else 
None)

regular UNC path:

>>> glob.glob('//localhost/C$/Sys*')
# //localhost/C$/Sys*
['//localhost/C$/System Volume Information']

"UNC" device path:

>>> glob.glob('//?/UNC/localhost/C$/Sys*')
# //?/UNC/localhost/C$/Sys*
# //?/UNC/localhost/C$
# //?/UNC/localhost
# //?/UNC/
[]

Since the magic character "?" is in the path (IMO, the drive should be excluded 
from this check, but that's a separate issue), the internal function 
glob._iglob calls itself recursively until it reaches the base case of dirname 
== pathname, where dirname is from os.path.split(pathname). The problem here is 
that ntpath.split doesn't stop at the proper base case of 
"//?/UNC/localhost/C$". This is due to ntpath.splitdrive. For example:

>>> os.path.splitdrive('//?/UNC/localhost/C$/Sys*')
('//?/UNC', '/localhost/C$/Sys*')

>>> os.path.splitdrive('//./UNC/localhost/C$/Sys*')
('//./UNC', '/localhost/C$/Sys*')

The results should be "//?/UNC/localhost/C$" and "//./UNC/localhost/C$". 

In other cases, returning a device as the drive is fine, if not exactly 
meaningful (e.g. "//./NUL"). I don't think this needs to change.

--
components: Library (Lib), Windows
messages: 348055
nosy: eryksun, paul.moore, steve.dower, tim.golden, zach.ware
priority: normal
severity: normal
stage: needs patch
status: open
title: support "UNC" device paths in ntpath.splitdrive
type: behavior
versions: Python 3.8, Python 3.9

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