Class SaveFile

src/borg/platform/base.py:222–272

Update file contents atomically. Must be used as a context manager (defining the scope of the transaction). On a journaling filesystem the file contents are always updated atomically and won't become corrupted, even on power failures or crashes (for caveats see SyncFile).

class SaveFile:
    """
    Update file contents atomically.

    Must be used as a context manager (defining the scope of the transaction).

    On a journaling filesystem the file contents are always updated
    atomically and won't become corrupted, even on power failures or
    crashes (for caveats see SyncFile).

    SaveFile can safely be used in parallel (e.g., by multiple processes) to write
    to the same target path. Whatever writer finishes last (executes the os.replace
    last) "wins" and has successfully written its content to the target path.
    Internally used temporary files are created in the target directory and are
    named <BASENAME>-<RANDOMCHARS>.tmp and cleaned up in normal and error conditions.
    """

    def __init__(self, path, binary=False):
        self.binary = binary
        self.path = path
        path_obj = Path(path)
        self.dir = str(path_obj.parent)
        self.tmp_prefix = path_obj.name + "-"
        self.tmp_fd = None  # OS-level fd
        self.tmp_fname = None  # full path/filename corresponding to self.tmp_fd
        self.f = None  # Python file-like SyncFile

    def __enter__(self):
        from .. import platform
        from ..helpers.fs import mkstemp_mode

        self.tmp_fd, self.tmp_fname = mkstemp_mode(prefix=self.tmp_prefix, suffix=".tmp", dir=self.dir, mode=0o666)
        self.f = platform.SyncFile(self.tmp_fname, fd=self.tmp_fd, binary=self.binary)
        return self.f

    def __exit__(self, exc_type, exc_val, exc_tb):
        from .. import platform

        self.f.close()  # this indirectly also closes self.tmp_fd
        self.tmp_fd = None
        if exc_type is not None:
            safe_unlink(self.tmp_fname)  # with-body has failed, clean up tmp file
            return  # continue processing the exception normally

        try:
            os.replace(self.tmp_fname, self.path)  # POSIX: atomic rename
        except OSError:
            safe_unlink(self.tmp_fname)  # rename has failed, clean up tmp file
            raise
        finally:
            platform.sync_dir(self.dir)


def swidth(s):