Avoid global umask for setting file mode.

[ryan-clancy]

This PR updates the method for setting the permissions on cache_path after calling shutil.move. The call to shutil.move may not preserve permissions if the source and destination are on different filesystems. Reading and resetting umask can cause race conditions, so directly read what permissions were set for the temp_file instead.

This fixes #7536.

[lhoestq]

this doesn't necessarily return the user's umask no ?

we need the user's umask since some people use datasets with shared disks and use group permissions (see #2157 #5799)

[ryan-clancy]

When looking more at the history of this code, I am not sure the umask block below is needed at all anymore and could just be deleted.

datasets/src/datasets/utils/file_utils.py

Lines 582 to 626 in f5f6c7e

	with FileLock(lock_path):
	if resume_download:
	incomplete_path = cache_path + ".incomplete"
	@contextmanager
	def _resumable_file_manager():
	with open(incomplete_path, "a+b") as f:
	yield f
	temp_file_manager = _resumable_file_manager
	if os.path.exists(incomplete_path):
	resume_size = os.stat(incomplete_path).st_size
	else:
	resume_size = 0
	else:
	temp_file_manager = partial(tempfile.NamedTemporaryFile, dir=cache_dir, delete=False)
	resume_size = 0
	# Download to temporary file, then copy to cache dir once finished.
	# Otherwise you get corrupt cache entries if the download gets interrupted.
	with temp_file_manager() as temp_file:
	logger.info(f"{url} not found in cache or force_download set to True, downloading to {temp_file.name}")
	# GET file object
	if scheme == "ftp":
	ftp_get(url, temp_file)
	elif scheme not in ("http", "https"):
	fsspec_get(url, temp_file, storage_options=storage_options, desc=download_desc)
	else:
	http_get(
	url,
	temp_file,
	proxies=proxies,
	resume_size=resume_size,
	headers=headers,
	cookies=cookies,
	max_retries=max_retries,
	desc=download_desc,
	)
	logger.info(f"storing {url} in cache at {cache_path}")
	shutil.move(temp_file.name, cache_path)
	umask = os.umask(0o666)
	os.umask(umask)
	os.chmod(cache_path, 0o666 & ~umask)

is the code just after the umask was added and NamedTemporaryFile was used to create the files. NamedTemporaryFile always set 600 permissions and didn't respect umask so umask code was added to fix the permissions.

d536e37 removed the NamedTemporaryFile and moved to open(), which respects the umask.

We should just be able to remove this temp_file_mode + updated chmod lines and then remove:

umask = os.umask(0o666)
os.umask(umask)
os.chmod(cache_path, 0o666 & ~umask)

Thoughts?