From: "yermej@..." <yermej@...>
Date: 2007-09-10T10:55:12+09:00
Subject: Re: Possible Zlib Bug

On Sep 9, 7:27 pm, "Jed Hurt" <jed.h...@gmail.com> wrote:
> I originally posted this message to core as I assumed that it would be
> the mailing list with
> the most knowledge of Ruby's Zlib library, but received no reply, so
> I'm posting it again here.
> ====================================================
>
> I'm porting SWX PHP ( swxformat.org ) to Ruby (http://rubyforge.org/projects/rswx). SWX is a data exchange format-a
> replacement for Flash Remoting, SOAP, et al. The idea is to assemble
> Flash SWF files by converting Ruby objects (hashes, array, strings,
> integers, etc.) 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've tried to make this post as thorough as possible so that
> someone with a greater knowledge of hex bytecode could help me fix the
> issue without much effort. If I could post anything else to make it
> easier to find the issue, please let me know and I'll be happy to do
> it.

I don't know much about zlib, but I did notice one thing in your
pastie example. This:

swx_file.slice!(0..8)

removes 9 bytes from the string. Maybe that should be:

swx_file.slice!(0,8), or
swx_file.slice!(0..7)

?

Jeremy