#!/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 or as permitted by the MIT license deed below.

Copyright (c) 2012 Jose Fonseca (jfonseca@zefonseca.com)

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.



    
    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";
}