Detector for animated GIF image (perl5)

detect-animated-gif.pl

#!/usr/bin/env perl
# Detector for animated GIF image (perl5)
# Based on http://d.hatena.ne.jp/namanamanamana/20090415/1239729068 Thanks.
use strict;
use warnings;
use LWP::UserAgent;

# Fetch a GIF image
my $ua = LWP::UserAgent->new();
my $res = $ua->get('http://example.com/foo-animation.gif');
print "Fetch status = " . $res->status_line . "\n";

# Check the file
my $fh;
open($fh, '<', $res->content_ref); # Or you can also read a file from local with the open method.
if (is_anim_gif_file($fh)) {
	print "This is an animated GIF image.\n";
} else {
	print "This is not an animated GIF image.\n";
}
close($fh);

exit;

sub is_anim_gif_file {
	my $fh = shift;

	my ($frame_num, $c) = (0, undef);

	read($fh, $c, 4);
	$c = undef;

	# Check a GIF89 identifier
	read($fh, $c, 1);
	if (unpack("H*", $c) ne "39") {
		return 0;
	}
	$c = undef;

	# Read frames
	while (!eof $fh) {

		# Read until start point of extended block
		do {
			$c = undef;
			read($fh, $c, 1);
		} while (unpack("H*", $c) ne "21" && !eof $fh);

		if (eof $fh) {
			last;
		}

		# Read the Graphic Control Extension
		$c = undef;
		read($fh, $c, 2);
		my $ext = unpack("H*", $c);
		if ($ext eq "f904") {
			$frame_num++; # Increment a number of frames
		}

	}

	if ($frame_num <= 1){
		return 0;
	}

	return 1; # Animated GIF
}