Python idlk

This is a proof-of-concept implementation of a lock filename generator for idlk files used by a well known desktop publishing suite.

Usage

    from idlk import idlk

    lockname = idlk(u'My Layout File.INDD')
    # lockname == u'~my layout file~q7e)nv.idlk'

    lockname = idlk(u'My Text.icml')
    # lockname == u'~my text~7h5m7u.idlk'

Technical details

The names of the lockfiles are derived from a given file name with the following steps:

1. Apply NFC unicode normalization.
2. Convert the complete filename to lower case.
3. Switch to Mac Roman encoding.
4. Generate a 32bit hash value over the whole file name and encode it using a custom base41 encoding scheme.
5. Remove extension from the prepared file name, shorten it further to 18 characters if necessary.
6. Generate the idlk file name using the following pattern: ~shortened-lowercase-basename[1..18]~hash[6].idlk

Note: Even though the hash-function is rather primitive, there is no way of directly deriving the original document name for a given idlk name.

Hash function

The hash function is a very simple shift-add function. The only tricky/weird thing is a final modulo with the magic number 0xFFFEECED.

Base41 encoding

Base41 produces a case insensitive string containing digits 0-9, characters a-z and the 5 additional characters -, _, (, ) and $.

Caveats

The algorithm has been deduced after observing the behavior of the original software. It currently only works with file names which are completely mappable to the Mac Roman encoding.

License

All code and documentation is released under the MIT license.