Now, its time to move one step further. Better, faster and a stronger solution for your corporate squid server. ImageMagick library is a nice library, but it remains slow if you have reckless users. We will keep on manipulating images, yes, but in a much faster way. Just keep on reading.

First lets install GD library for PHP5;

sudo apt-get install php5-gd

Yes, you should have a running web server available for this to work. Now lets setup our Squid and squidGuard against facebook. First add these lines to the end of your squid.conf file;

redirect_program /usr/bin/squidGuard -c /etc/squid/squidGuard.conf
redirect_children 5

Now make sure your squidGuard.conf file looks something like this;

#
# CONFIG FILE FOR SQUIDGUARD
#

dbhome /home/squidguard/
logdir /var/log/squid/

src everyone {
        ip      192.168.1.0/255.255.255.0
}

dest facebook {
 expressionlist  facebook
 redirect        http://192.168.1.1/joker.php?url=%u
 log /var/log/squid/joker.log
}

acl {
  everyone within workhours {
    pass !facebook all
  } else {
    pass all
  }

  default {
    pass none
  }
}

Now let’s create the file that catches the URL regex. I placed it in /home/squidguard this time, since I backup my whole /home directory everyday. It does not get lost between setups.

.*facebook\.com.*(\.jpg|\.gif|\.png)
.*fbcdn\.net.*(\.jpg|\.gif|\.png)

Let’s create our image manipulation script in our web root. You should name it to joker.php or whatever you want, just keep it in sync with your squidGuard.conf file.

<?php
/*
joker.php

This is where we keep our tmp files.
You can set it to /tmp also.
*/
$path = "/var/www/joker";
if (!is_dir($path)) {
   mkdir($path,0755);
}

// Parse the URL line delivered from Squid.
$u = explode(" ",trim($_GET["url"]));
if (count($u) > 0) {
   $url = $u[0];
} else {
   $url = $u;
}

// Temporary file name.
$temp = md5(time().microtime().$url);

$ff = fopen($url, "r");
$contents = stream_get_contents($ff);
fclose($ff);

$fz = fopen($path."/".$temp,"w");
fwrite($fz, $contents);
fclose($fz);

$file = $path."/".$temp;

// U shall not touch below this line.
// ------------------------------- //
// Yeah, that line above this. //
switch (substr($url,-4)) {
   case ".jpg":
      $source = imagecreatefromjpeg($file);
      $header = "image/jpeg";
   break;
   case ".png":
      $source = imagecreatefrompng($file);
      $header = "image/png";
   break;
   case ".gif":
      $source = imagecreatefromgif($file);
      $header = "image/gif";
   break;
}

list($width, $height) = getimagesize($file);
$bwimage= imagecreate($width, $height);

for ($c = 0; $c < 256; $c++) {
   $palette[$c] = imagecolorallocate($bwimage,$c,$c,$c);
}

function yiq($r, $g, $b) {
   $gray = ($r + $g + $b) / 3;
   if ($gray > 0x7F) {
      return 0xFF;
   } else {
      return 0x00;
   }
   return (($r*0.299)+($g*0.587)+($b*0.114));
}

/*
Reads the original colors pixel by pixel
*/
for ($y = 0; $y < $height; $y++) {
   for ($x = 0; $x < $width; $x++) {
      $rgb = imagecolorat($source, $x, $y);
      $r = ($rgb >> 16) & 0xFF;
      $g = ($rgb >> 8) & 0xFF;
      $b = $rgb & 0xFF;

      /*
      This is where we actually use yiq to modify our rbg values,
      and then convert them to our grayscale palette
      */
      $gs = yiq($r, $g, $b);
      imagesetpixel($bwimage, $x, $y, $palette[$gs]);
   }
}

/*
Outputs a jpg image, but you can change this to png or gif if that
is what you are working with
*/
header("Content-type: ".$header);
imagejpeg($bwimage);
?>

Let’s restart our Squid;

sudo /etc/init.d/squid restart

Everything should be working fine right now, good luck now you facebook lovers!