Perl Zlib last block

Kroning has asked for the wisdom of the Perl Monks concerning the following question:

Hi!

I have some packet from app that looks like "ec bd ... 00 00 ff ff" which I am trying to decode.

From what I have found, it looks like "00 00 ff ff" is a Z_SYNC_FLUSH of deflate (zlib).

I tried to reproduce it on Compress::Raw::Zlib, Compress::Zlib and some others. But the ending pattern was "00 ff 00 ff". Am I missing something?

#!/usr/local/bin/perl

use Compress::Zlib ;

my $x = deflateInit() or die "Cannot create a deflation stream\n" ;
($output, $status) = $x->deflate('text') ;

($output, $status) = $x->flush(Z_SYNC_FLUSH) ;

$output =~ s/(.)/sprintf '%04x', ord $1/seg;
print "output=$output\n";
[download]

output=002a004900ad0028000100000000000000ff00ff00000000000000ff00ff

Comment on Perl Zlib last block Download Code

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Re: Perl Zlib last block by choroba (Cardinal) on Oct 26, 2020 at 11:39 UTC
To get `ffff`, don't ask for 4 nibbles, but 2: `$output =~ s/(.)/sprintf '%02x', ord $1/seg; # ^` [download] You can also use `$output = unpack 'H', $output;` [download] instead of the s/// with /e. It should be faster. `map{substr$_->[0],$_->[1]\|\|0,1}[\\|\|{},3],[[]],[ref qr-1,-,-1],[{}],[sub{}^*ARGV,3]`	[reply] [d/l] [select]

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