Bug in convert_os_errors

[isaacHuh]

pyfilesystem2/fs/error_tools.py

Line 87 in 2d0ffc3

if getattr(exc_value, "args", None) == 32: # pragma: no cover

This compares a tuple to int and is always false.

[dargueta]

PR: #491

[lurch]

@isaacHuh In #491 we're trying to figure out what this code is supposed to be doing... do you have a reliable way of triggering this exception? 🙂

[isaacHuh]

@isaacHuh In #491 we're trying to figure out what this code is supposed to be doing... do you have a reliable way of triggering this exception? 🙂

@lurch So I would do this to test:

from fs.error_tools import convert_os_errors
import errno


with convert_os_errors("test", "path"):
    o = OSError(32)
    o.errno = errno.EACCES
    raise o

should be resource locked error but I just found I get this:

fs.errors.FileExpected: path 'path' should be a file

https://github.com/PyFilesystem/pyfilesystem2/blob/master/fs/error_tools.py#L63

this line prevents the correct error raising since it remaps FILE_ERRORS[13] and errno.EACCES is 13 so _errno == errno.EACCES is always false.

[lurch]

@isaacHuh I meant a way to provoke this from actual pyfilesystem code, not provoking it by manually constructing an "artificial OSError" that we may or may not ever actually see in the real world 😉

[isaacHuh]

@lurch

from fs.osfs import OSFS
import os
import win32file
import win32con
import pywintypes
from fs.error_tools import convert_os_errors

f = OSFS('./')
path = "test_file.story"
f.create(path)
sys_path = f.getsyspath(path)

fd = os.open(sys_path, os.O_RDWR)

win32file.LockFileEx(
    win32file._get_osfhandle(fd),
    (win32con.LOCKFILE_FAIL_IMMEDIATELY | win32con.LOCKFILE_EXCLUSIVE_LOCK),
    0, -0x10000, pywintypes.OVERLAPPED())

# do this in a new process or something:
new_content = b'123456'
with convert_os_errors("test", sys_path):
    os.write(fd, new_content)


win32file.UnlockFileEx(win32file._get_osfhandle(fd), 0, -0x10000, pywintypes.OVERLAPPED())
os.close(fd)

haven't gotten this working but something like this and you could try creating another process that interacts with the file while there is a lock on it. Or you could use an application like storyline 360 that holds a lock on a file to test and have that file open while you run a script that attempts to write to it. Both should work but haven't tried it myself.

idk if thats what you were looking for

[lurch]

idk if thats what you were looking for

Yes, that's more along the lines of what I meant with "do you have a reliable way of triggering this exception?" 👍

haven't gotten this working

Ahh, that's a shame. As I suggested in #491 "I guess there's a possibility that this code may not even be needed now, given the changes to both Windows and Python over the past 12 years?" 🤷‍♂️ 🤷‍♂️

[isaacHuh]

@lurch oh ok I see. This code does get hit when a process is attempting to read or write to a file that another process has a lock on it tho. I've seen storyline 360 causing this to get hit because that application holds a lock on a file the entire time it has the file open while most other applications don't, so any other process attempting to read from the file throws would throw a resource locked error.

I played with it a bit after work and this raises the exception. just run file 1 and run file 2 while file 1 is sleep. Again I get fs.errors.FileExpected when it should be resource locked when I run this because of the bug but this is it:

file 1:

from fs.error_tools import convert_os_errors
from multiprocessing import Process
import time

f = OSFS('./')
path = "test_file.story"
f.create(path)
sys_path = f.getsyspath(path)

fd = os.open(sys_path, os.O_RDWR)

win32file.LockFileEx(
    win32file._get_osfhandle(fd),
    (win32con.LOCKFILE_FAIL_IMMEDIATELY | win32con.LOCKFILE_EXCLUSIVE_LOCK),
    0, -0x10000, pywintypes.OVERLAPPED())

time.sleep(30)

win32file.UnlockFileEx(win32file._get_osfhandle(fd), 0, -0x10000, pywintypes.OVERLAPPED())
os.close(fd)

file 2:

from fs.error_tools import convert_os_errors
import os

path = "test_file.story"
sys_path = path

fd = os.open(sys_path, os.O_RDWR)

new_content = b'123456'
with convert_os_errors("test", sys_path):
    os.write(fd, new_content)