#!/usr/bin/perl -w

=begin

    cws2fws v 0.0.1 - Flash format 6+ decompressor
    Jose Melo de Assis Fonseca / JMAF
    http://zefonseca.com/
    2008-04-26
    
    Usage: cws2fws <COMPRESSED_SWF_FILE.swf>
    
    Will output a FWS uncompressed Flash file in same format and version
    to "COMPRESSED_SWF_FILE.fws.swf"
    
    This is free software which you can use, modify and redistribute in the same terms as Perl itself.
    
    Observing the SWF file format:
    - the first 3 bytes are a signature indicating file type
    - compressed files which SWF::Search currently cannot open always are CWS
    - files it opens fine are always FWS (SWF backwards?)
    - the next byte seems to match the version from output of the `file example.swf` command
    - according to http://the-labs.com/MacromediaFlash/SWF-Spec/SWFfileformat.html the next
      4 bytes indicate the total file length. it is a little endian 32 bit integer.
      the url above mentions the file format is always "FWS", which is no longer true for
      versions 6 and above of the SWF file format.
    
    So how do we decompress the file? Seems to be simpler than I imagined.
    
    1) read the 3 first bytes, compare to CWS, if not equal then exit
    2) read the rest of the header. unless you need version or file length just leave version . length concatenated. we won't need them.
    3) decompress everything from byte 9 to EOF
    4) concatenate "FWS", the 5 header bytes and the decompressed stream
    
    
=cut

use Compress::Zlib qw{uncompress};

my $zlib_data;
my $header;
my $type_sig;
my $unc;
my $file_prefix;
my $outfile;

usage() unless(defined($ARGV[0]));

if ( $ARGV[0] !~ m{^(.+?)\.swf}i) {
    usage();
}
$file_prefix = $1;

open(FIL, $ARGV[0]) or die "Fatal: Could not open source SWF file $ARGV[0]\n";
read(FIL, $type_sig, 3, 0);

# is case sensitive, bytes must match ASCII 0x43 0x57 0x53 ("CWS" )
if ($type_sig eq 'FWS') {
    die "Flash file is not compressed(CWS) or header is invalid.\n";
}

# reads last bytes of header
read(FIL, $header, 5, 0);

# filehandle pointer now at 8 bytes offset
# the rest of the file is zlib compressed data
while (<FIL>) {
    $zlib_data .= $_;
}
close(FIL);

=begin
i observed that the CWS file length(bytes 5 to 8, little endian 32 bit integer) does not match that of the compressed
data. by decompressing and checking again i see that the length header field
refers to the zlib uncompressed stream + 8 bytes (header length). therefore
to finish our decompression all we have to do is substitute the first 3
byte signature for FWS and concatenate the rest of the header. works a dandy.
- JMAF
=cut
$unc = uncompress($zlib_data);
$outfile = $file_prefix . ".fws.swf";
open(ZIL, ">$outfile") or die "Fatal: Could not open target SWF file $outfile\n";
print ZIL "FWS" . $header . $unc;
close(ZIL);

sub usage {
    die "Usage: cws2fws COMPRESSED_SWF_FILE\n";
}