schallaven / pwexplode

implementation of the PKWARE Data Compression Library format (imploding) for byte streams

pwexplode library

Simple implementation of the PKWARE Data Compression Library format (imploding) for byte streams in Python 3 licensed under GPL-3.0.

Implementation

This library is mostly based on the description of Ben Rudiak- Gould in the comp.compression group and zlib's blast.c.

It should be noted that there is a small mistake in Ben's example. He uses 00 04 82 24 25 c7 80 7f as example, which should decompress to AIAIAIAIAIAIA. However, testing this with my implementation failed. When I created it with the official pkware ziptool (see tests in pwexplode), the sequence turned out to be actually 00 04 82 24 25 8f 80 7f (notice the difference at byte 6). This will successfully decompress to AIAIAIAIAIAIA.

Instead of pure dictionaries, this package uses functions to provide the data of the tables necessary to decompress streams. This approach makes functions 'read-only' and can provide error feedback. However, it creates minimal overhead and slightly longer runtimes. In order to reduce the extra time a little bit, all tables are 'complete', i.e. each entry just needs to be extracted but not calculated. The difference is minimal and practical non-existant when accessing a function one time only; but these functions can be called hundred or thousand times per stream.

Usage

Import pwexplode in your Python 3 programs and call the explode(...) function. Note that input and output are byte strings!

import pwexplode
...
# Decompress input byte string 
inputdata = b'\x01\x04\x02\x6F\x5A\x08\xB6\x67\xE8\x86\x6A\xA9\x8A\x6D\x28'
            b'\x5E\x56\x6D\xCD\x5B\x5B\x6C\x47\x73\x18\xB6\x8A\x17\xF0\x0F'
...
outputdata = pwexplode.explode(inputdata) 
...
# prints b'I like consistent user interfaces.'
print(outputdata)

Calling pwexplode directly will run some tests:

$ ./pwexplode.py

Contributors

• KOLANICH
• sourcekris