From: Jed Hurt <jed.hurt@...>
Date: 2007-09-08T02:00:02+09:00
Subject: Possible Zlib Bug

I posted to core as I assumed that this would be the mailing list with
the most knowledge of Ruby's Zlib library. Please forgive me if I
should have posted to the general list.
====================================================

I'm porting SWX PHP ( swxformat.org ) to Ruby. The idea is to assemble
Flash SWF files by converting data to SWF bytecode. SWF files support
compression using ZLib, and so I'm implementing compression using
Ruby's ZLib library.

As I'm porting SWX PHP to Ruby, I am able to generate a SWF file using
SWX PHP to see what I need to generate in rSWX ( my port ).

There seems to be a bug in Ruby's ZLib implementation that creates a
different header and trailer than PHP's gzcompress() (the function
used to compress in SWX PHP).

Here is the bytecode of two SWF files containing the same data (one
generated with SWX PHP and the other generated with rSWX):
http://pastie.caboo.se/95038

I've highlighted the discrepant parts of the two files (Please note
that the first 8 bits of a compressed SWF file are left uncompressed,
thus the header of the compressed section of the file starts on the
second line of the pastied result).

And, needless to say, the compressed SWF file generated with SWX PHP
works, and the one generated with rSWX does not.

I know very little about compression or Zlib so I'm quite lost at this
point. I'm hoping somebody can give me some advice on how to proceed
with debugging this issue.