Commit 087b34fe authored by Iustin Pop's avatar Iustin Pop
Browse files

Add a generic write file function

Currently there are a few version of "write a file safely" in the code.
This patch adds a generic function that should be able to replace all
the other versions.

The "take attributes from the target file" option, while useful, is not
implemented by this patch.

Reviewed-by: imsnah,ultrotter
parent 71eca7c3
......@@ -855,3 +855,54 @@ def GetUUID():
return f.read(128).rstrip("\n")
finally:
f.close()
def WriteFile(file_name, fn=None, data=None,
mode=None, uid=-1, gid=-1,
atime=None, mtime=None):
"""(Over)write a file atomically.
The file_name and either fn (a function taking one argument, the
file descriptor, and which should write the data to it) or data (the
contents of the file) must be passed. The other arguments are
optional and allow setting the file mode, owner and group, and the
mtime/atime of the file.
If the function doesn't raise an exception, it has succeeded and the
target file has the new contents. If the file has raised an
exception, an existing target file should be unmodified and the
temporary file should be removed.
"""
if not os.path.isabs(file_name):
raise errors.ProgrammerError("Path passed to WriteFile is not"
" absolute: '%s'" % file_name)
if [fn, data].count(None) != 1:
raise errors.ProgrammerError("fn or data required")
if [atime, mtime].count(None) == 1:
raise errors.ProgrammerError("Both atime and mtime must be either"
" set or None")
dir_name, base_name = os.path.split(file_name)
fd, new_name = tempfile.mkstemp('.new', base_name, dir_name)
# here we need to make sure we remove the temp file, if any error
# leaves it in place
try:
if uid != -1 or gid != -1:
os.chown(new_name, uid, gid)
if mode:
os.chmod(new_name, mode)
if data is not None:
os.write(fd, data)
else:
fn(fd)
os.fsync(fd)
if atime is not None and mtime is not None:
os.utime(new_name, (atime, mtime))
os.rename(new_name, file_name)
finally:
os.close(fd)
RemoveFile(new_name)
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