From: Jed Hurt <jed.hurt@...>
Date: 2007-09-10T11:22:35+09:00
Subject: Re: Possible Zlib Bug

It was a bonehead error. String#slice!(0..8) consumes the first 9
bytes of the string. String#slice!(0..7) fixed it. Sorry for the
noise.

On 9/7/07, Jed Hurt <jed.hurt@gmail.com> wrote:
> 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.
>