How does Open Office compress its files?

I'm trying to create an Open Office spreadsheet programmatically but for some reason simply compressing a folder with all the necessary files makes Open Office flag the file as corrupted.

How did I get to this? I started by creating a normal spreadsheet in Open Office with some values in it. After saving I change the extension to .zip and make a copy of the folder. I then compress the second folder using command line zip and change the file extension to .ods. When trying to open the resulting file I get an error from Open Office saying the file is corrupt.

Does Open Office use a special compression algorithm? Doing a "file test.ods" shows it as a compressed zip, so what does Open Office add during the compression routine to make it work?

zip openoffice.org opendocument

Edit Report

Section 17 Of the OASIS OpenOffice Specification defines how OpenDocument Packages need to be packaged.

Section 17.4 MIME Type Stream reads like this:

If a MIME type for a document that makes use of packages is existing, then the package SHOULD contain a stream called "mimetype". This stream SHOULD be first stream of the package's zip file, it MUST NOT be compressed, and it MUST NOT use an 'extra field' in its header (see [ZIP])..

The purpose is to allow packaged files to be identified through 'magic number' mechanisms, such as Unix's file/magic utility. If a ZIP file contains a stream at the beginning of the file that is uncompressed, and has no extra data in the header, then the stream name and the stream content can be found at fixed positions. More specifically, one will find:

a string 'PK' at position 0 of all zip files

a string 'mimetype' at position 30 of all such package files

the mimetype itself at position 38 of such a package.

answered 2011-02-10T13:19:40.570

How does Open Office compress its files?

1 Answer

Your Answer