cfbwrite
Write a complete MS-CFB v3 (Microsoft Compound File Binary) container from Python — including streams that changed size.
olefile reads Compound Files well and can replace a stream only with data of
exactly the same length. That is enough to rearrange existing content and not
enough to add any, so anything that grows a stream needs the container
rebuilt. This library rebuilds it.
from cfbwrite import rebuild
rebuild(src="original.rdb", dst="updated.rdb", replacements={
("Relays", "QPC1_TR1", "SET_D1.TXT"): new_bytes, # any size
})
Two properties it is built around, because it came from a tool that writes protection-relay settings files:
- It verifies its own output. The result is reopened and every stream compared against the source before it is handed over. A bug in the writer surfaces as a failed write, never as a silently corrupt file.
- It writes atomically. The container is built in a temporary file beside
the destination and only then
os.replaced into place, so a failure leaves the destination exactly as it was.
Extracted from PAC CT.
Licence
AGPL-3.0-or-later — see LICENSE.
Install
pip install cfbwrite
Requires Python 3.10+ and olefile.
Why it exists
It was pacct/parsers/ole_rebuild.py inside
PAC CT, a commissioning toolkit
for protective relays. Those relays keep their settings in .rdb files, which
are Compound Files, and editing a DNP3 point map there routinely grows a
stream. Nothing in the module knows any of that — it is the container format
and nothing else — so it lives here instead.
1 maintainer
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