Jaslabs: High performance Software

by Justin Silverton

While working on an AJAX project over the weekend, I ran into the following issue: (through a GET request), every time I tried to call a certain function, It was returning the same data (which was supposed to be different each time)

I first tried the following (which should disable browser caching):

(in PHP)

header( “Expires: Mon, 26 Jul 1997 05:00:00 GMT” );
header( “Last-Modified: ” . gmdate( “D, d M Y H:i:s” ) . ” GMT” );
header( “Cache-Control: no-cache, must-revalidate” );
header( “Pragma: no-cache” );

The data still did not change.

I finally came to the following solutions:

1) use a POST request. When using with xmlhttprequest, it is slightly more complicated.

2) add a unique identifier to the end of my GET url.

I choose #2. A unique Identifier can be created using the current data+time. Here is a simple way to generate this (in Javascript):

var date = new Date();
var timestamp = date.getTime();

createXMLHttpRequest();
xmlHttp.onreadystatechange = handleMessages;
xmlHttp.open(”GET”,”script.php?time=”+timestamp,true);
xmlHttp.send(null);

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by Justin Silverton

Zlib compression has been built into php since version 3 and it can be used to compress the output of your php applications (which can significantly decrease the amount of bandwidth of a page), but what you can also do is compress any file accessible from your webserver.

The code

The following are two functions: compress and uncompress, which can compress and uncompress a specified file.

function uncompress($srcName, $dstName) {
$string = implode(”", gzfile($srcName));
$fp = fopen($dstName, “w”);
fwrite($fp, $string, strlen($string));
fclose($fp);
}

function compress($srcName, $dstName)
{
$fp = fopen($srcName, “r”);
$data = fread ($fp, filesize($srcName));
fclose($fp);

$zp = gzopen($dstName, “w9″);
gzwrite($zp, $data);
gzclose($zp);
}

compress(”test.php”,”test.gz”);
uncompress(”test.gz”,”test2.php”);

Source code can be downloaded here

Description of related zlib functions

gzclose — Close an open gz-file pointer

gzcompress — Compress a string

gzencode — Create a gzip compressed string

gzeof — Test for end-of-file on a gz-file pointer

gzfile — Read entire gz-file into an array

gzgetc — Get character from gz-file pointer

gzgets — Get line from file pointer

gzgetss — Get line from gz-file pointer and strip HTML tags

gzinflate — Inflate a deflated string

gzopen — Open gz-file

gzpassthru — Output all remaining data on a gz-file pointer

More information on zlib related functions can be found here

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Introduction 

This is a simple yet useful tutorial on how to write an image gallery script in PHP.  It could be used for anything from banner rotation to just a couple of images that you would like to display in rotation on your website.  It requires no external libraries, works with php 4.0.3 and above, and will allow you to display all the images in a specifiied directory.

The Code

The code consists of a simple class with two main functions: GetAllFiles() and DisplayImages(). GetAllFiles() retrieves all the images within a specified directory and DisplayImages randomly displays them.

//set your directory here and remember to include the trailing slash
//the script will automatically pull images out of the specified directory and display them
define(”IMAGE_DIRECTORY”, “images/”);

class jrotate {

var $Imagelist = array();         //this stores all of the images that were found in your directory
var $ImageExtList = array();      //this will store the image extensions

function GetAllFiles() {

// Open a known directory, and proceed to read its contents
if (is_dir(IMAGE_DIRECTORY)) {
   if ($dh = opendir(IMAGE_DIRECTORY)) {
       while (($file = readdir($dh)) !== false) {
        //check to see if it is a file
        if (filetype(IMAGE_DIRECTORY.$file) == “file”) {
              //get the files extension and make sure it is one of our supported image types
              $current_ext = substr($file,strlen($file)-3,strlen($file));
              if ($current_ext == “jpg” || $current_ext == “gif” || $current_ext == “png”) {
                 //push the filename  and extension onto our arrays
                 array_push($this->Imagelist,IMAGE_DIRECTORY.$file);
                 array_push($this->ImageExtList,$current_ext);
              }
          }
       }
       closedir($dh);
   }
 } 
}

function DisplayImage() {
 
 //get the total number of images
 $imagecount = count($this->Imagelist);
 //randomly generate the next image that we will display
 $nextimage = rand(0,$imagecount-1);
 
 //determine the image type and return the proper header information
 switch($this->ImageExtList) {
 case ‘png’:
   header(”Content-type: image/png”);
 break;
 case ‘gif’:
   header(”Content-type: image/gif”);
 break;
 case ‘jpg’:
      header(”Content-type: image/jpeg”);
 break;
}

 //read image into string and output it
 $contents = file_get_contents($this->Imagelist[$nextimage]);
 echo $contents;
}

} //end class

//create a new instance of the jrotate class
$imagerotator = new jrotate;

//display random image
$imagerotator->GetAllFiles();
$imagerotator->DisplayImage();
//$test = array();

 Download

To download the entire script explained here and an example of usage, please go Here

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