Eryk Sun <eryk...@gmail.com> added the comment:
> pathlib currently expects DOS paths only: it will strip '\\?\'
> prefix in resolve()
pathlib's unqualified conversion from the extended form to classic DOS form is
a bug. The resolved path may be invalid as a classic DOS path. It may be too
long, a DOS device name (e.g. "nul.txt"), or end with trailing spaces or dots
(e.g. "spam.").
Here's another pathlib bug with device paths:
>>> print(pathlib.Path(r'\\.\C:'))
\\.\C:\
>>> print(pathlib.Path('//./CON'))
\\.\CON\
In the first case, the input path is the "C:" volume device, but pathlib
changes it to the file-system root directory. The second case is invalid in
general, though some devices will ignore a remaining path.
As background, note that the Windows runtime library classifies paths into 6
types:
>>> ntdll = ctypes.WinDLL('ntdll')
>>> GetDosPathNameType = ntdll.RtlDetermineDosPathNameType_U
UNC Absolute
>>> GetDosPathNameType(r'\\eggs\spam')
1
Drive Absolute
>>> GetDosPathNameType(r'C:\spam')
2
Drive Relative
>>> GetDosPathNameType('C:spam')
3
Rooted
>>> GetDosPathNameType(r'\spam')
4
Relative
>>> GetDosPathNameType('spam')
5
Local Device
>>> GetDosPathNameType(r'\\.\C:\spam')
6
>>> GetDosPathNameType(r'\\?\C:\spam')
6
A local-device path is always absolute, so it's the only way to reference a
volume device by a DOS drive letter. Without the prefix, "C:" is a
drive-relative path.
If the prefix is exactly "\\\\?\\" (no forward slashes), then a local-device
path is an extended path. This path type never gets normalized in any way,
except to replace the WinAPI prefix with NTAPI "\\??\\". For all other
local-device paths, the runtime library resolves "." and ".." components,
translates forward slash to backslash, and strips trailing spaces and dots from
the final component. Unlike DOS paths, local-device paths do not reserve DOS
device names (e.g. "NUL" or "NUL:").
pathlib should never add a trailing slash to a local-device path. Also, the
is_reserved() method needs to distinguish the DOS, device ("\\\\.\\"), and
extended device ("\\\\?\\") namespaces.
> it would indeed be nice if pathlib handled [device] paths in its resolve()
I suggested handling volume GUID and device paths in _getfinalpathname, so it's
not special-cased just in pathlib (e.g. if we were to implement
ntpath.realpath). OTOH, pathlib's resolve() method should handle high-level
mitigation, such as working around bad links and permission errors in
non-strict mode.
> I erroneously stated that the length of the path could increase
> between GetFinalPathNameByHandle calls because an intermediate
> directory could be renamed
The rules for the rename operation are discussed in the documentation for
NtSetInformationFile, FileRenameInformation [1], and explained in detail in
File Systems Algorithms, 2.1.5.14.11 FileRenameInformation [2].
[1]:
https://docs.microsoft.com/en-us/windows-hardware/drivers/ddi/content/ntifs/ns-ntifs-_file_rename_information
[2]: https://msdn.microsoft.com/en-us/library/ff469527
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<https://bugs.python.org/issue33016>
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