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Creating a chat script with PHP and Ajax, Part 1

(Page 2 out of 4)

Creating the server

Let's start by creating the server, but first, create a new database to hold the messages of your chat script, with the following database scheme:

CREATE TABLE `message` (
  `messageid` int(5) NOT NULL AUTO_INCREMENT,
  `user` varchar(255) NOT NULL DEFAULT '',
  `message` text NOT NULL,
  `datetimestamp` int(11) NOT NULL DEFAULT '0',
  PRIMARY KEY  (`messageid`)

The first thing the server must do is check what the client wants: adding a new message or requesting latest messages? The following code does what we want:

if (!isset($_GET['action'])) {
        die('This chat server can only be used by the chat client.');

$action = $_GET['action'];
if ($action != 'get' AND $action != 'add') { $action = 'get'; }

// Do we want to get chat messages or add a new message?
if ($action == 'get') {
        // Get messages
} else {
        // Add a new message

As you can see we're going to use two different functions: send_messages() to return all the latest messages and add_message() to add a new message.

Adding a new message is quite simple, and it only requires some standard database code, like this:

function add_message() {
        global $db;

        // Everything there?
        if (!isset($_GET['user'])) {
        if (!isset($_GET['message'])) {

        $user = ss(htmlentities(strip_tags($_GET['user'])));
        $message = ss(htmlentities(strip_tags($_GET['message'])));
        $datetimestamp = time();

        // Insert message
        $db->query ("INSERT INTO message (user, message, datetimestamp) VALUES ('$user', '$message', $datetimestamp)");

        // Return any new message

The function first checks if both variables are there, and if they're not, it returns an error. The errors look a bit weird, but this format actually makes it easier for our client (you'll see why later). When everything is okay, the message is inserted into the database.

Note that the $db variable comes from a mysql class, which can be downloaded here: mysql.php.

The send_messages() function has to send the messages that have NOT yet been received by the client. To do this, the client sends the timestamp of the last received message, from which the server can automatically select the messages that haven't been received yet, like so:

function send_messages() {
        global $db;

        // Is there a latest timestamp?
        if (!isset($_GET['latest'])) {
                $latest = false;
        } else {
                $latest = intval($_GET['latest']);

        // If there isn't a latest, get the five newest messages, and return them
        if ($latest == false) {
                $messages = $db->sql_query ("SELECT user, message, datetimestamp FROM message ORDER BY datetimestamp DESC LIMIT 0,4");
        } else {
                $messages = $db->sql_query ("SELECT user, message, datetimestamp FROM message WHERE datetimestamp > $latest ORDER BY datetimestamp DESC LIMIT 0,9");

        // Any messages?
        if ($messages == false) {

        // Get newest timestamp
        $newest = $messages['0']['datetimestamp'];

        // Reverse array for correct order
        $messages = array_reverse($messages);

        // Return response
        $response = $newest;

        foreach ($messages as $message) {
                $response .= $message['user'] . '>' . $message['message'] . "\n";

        $response = trim($response);


This code first selects the right messages, and after that returns it in the right format (each message is separated by a newline, and the user and message are separated by >).

That's all the code we need for the server, and if you combine everything together, you get the following file: chatserver.php.

Let's create the client now.

« Previous: Introduction & How it works
Next: Creating the client »

19 Responses to “Creating a chat script with PHP and Ajax, Part 1”

  1. nobody Says:

    this script is shit, i’ve been trying to make it work but still “undefined error” … learn to code in register global @ off, make it work and give a .zip of your “working” chat and we will see.

  2. Dennis Pallett Says:

    I always code with auto_globals off, and my error reporting is set to E_ALL & E_STRICT. The ‘undefined error’ you’re seeing is probably a JS error, which has absolutely nothing to do with ‘globals’.

    Secondly, the script does work, and all the parts can already be downloaded, including the chatserver PHP script.

  3. Will Says:

    I like how your name is nobody, would you like to add that you know nothing? I would just to save us all some time. At the very least you could exhibit some resemblance of respect for a person providing knowledge to the community.

  4. Todd Says:

    I’ve parsed through this code many times but cannot find my error. The issue is that after login the chat window re-displays the same info over and over (the last few entries), scrolling down to infinity. Any hints or suggestions would be appreciated, otherwise this tutorial was great, despite what nobody says. :-)

  5. Says:

    the problem is the mysql.php file. at the end of the file, there is a blank (whitespace) after the php end tag ?>

    this causes the chatserver to return a blank as first character. so the the timestamp is always in the past and the messages are re-displayed.

    step of my solutionfinding:
    1.) call chatserver.php and have a look what it really delivers (not in the browser, in the source.
    2.) add a header(”Content-type: text/plain”); before the response in function send_messages() before die($response);
    3.) the error shows you the position, why the header can not be sent. (mysql.php:229)

    thats all folks

  6. Sw3eT Says:

    I have the same problem of Todd, The last entrie is repeated to infinity.
    If someone can help me.

  7. Yen Says:

    the problem are found by, I have just change this :
    // We’re getting a valid response, first get the latest timestamp
    latest = response.substring(1,11);
    // Now get the messages
    var messages = response.substring(11, response.length);

    Do you notice that chat doesn’t work very well with Internet Explorer ?


  8. Mike Greubel Says:

    WOW!! Nice tutorial to explain the power of ajax. My respect to you, there should be more people like you.

    I fixed the “undefined”-bug like this (script.js @ line 97)

    // Add each message
    var chat = $(’chat’);
    for (var i=0; i “);

    if(message == ‘undefined’ || message == ‘’ || message == null) continue;
    chat.value = chat.value + ‘\n’;
    chat.value = chat.value + message[0] + ‘: ‘ + message[1];

    It fixes for me.

  9. Mike Greubel Says:

    Huh?? Your script cut my code into pieces of s…

    Ok, line 84 I add a validation of message, its inside the for(i

  10. Matthieu Says:

    I have the same problem like Yen, but i have another solution.
    I’ve seen that there is a white-space in the first position of the return of Ajax in the function “handle_response”…
    so, if i apply the function “trim” to the response, it will works, and i don’t have to change the code like Yen.
    Sorry for my english but i’m french.
    thanks a lot

  11. spadgos Says:

    yeh there are some bugs. i left it a little while and then something i typed came up in duplicate, then this came up. need some better error checking.

    HTML PUBLIC “-//W3C//DTD HTML 4.01 Transitional//EN” “”:

  12. Rock Says:

    Yeah, this is a very gud script i’ve come across. Dont care about nobody. NOBODY is a shit creature in this world. Is this script working fine with u all. I haven’t checked yet. Got impressed with this n replied right back.

  13. nickp Says:

    Thanks for the great lesson. I’m just starting to do some server administration, setting up php and mysql, and I found this a great way to A) test my installations and B) get to know basic php and mysql and the basics of AJAX techniques. Thanks a lot and I hope the second edition of this tutorial comes out soon!

  14. » Creare una chat con PHP ed Ajax Says:

    […] Tra le moltissime letture, mi ero dimenticato di far presente del primo di una serie di articoli dedicati alla creazione di una chat  utilizzando il linguaggio di programmazione PHP ed ovviamente Ajax. Be’, lo faccio ora insieme all’annuncio dell’uscita della seconda parte. […]

  15. Cypheros Says:

    Matthieu, where exactly did you invoke the trim() function. I’ve toyed with it all over the place, and either NO text shows up, or I keep getting the error…

  16. Jorge Rubiano Says:

    Very good chat, in addition the code is very easy to understand, speaks and writes in Spanish, reason why I use carácteres special in my writing, which does not accept. Felecitaciones to the developer of this application, that is very useful for the people who we are beginning in this technique of development Web (Ajax).

  17. :v:revolution - web:v:]中文[: » 用PHP和Ajax技术构建实时聊天系统(一) Says:

    […] April 26, 2006 at 4:15 am · Filed under PHP, 文献翻译 完整显示   1 2 3 4 5 原文地址 作者:Dennis Pallett 译者:!oEL […]

  18. WoOzY Says:

    lol, just finished translating part 1 into chinese and posted on my blog (of course i saved your original info. what am i, a pirate? no seriously, if you have any problem with this, i’ll stop, or i’ll continue translating your goodies :)

  19. xilin Says:

    There is a way to slove this problem:
    add this function in script.js:
    String.prototype.trim = function()
    return this.replace(/(^\s+)|\s+$/g,”");
    and then change : var response = request.responseText;
    use:var response = request.responseText.trim(); it will work;

    sorry about my english

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About the author
Dennis Pallett is the main contributor to PHPit. He owns several websites, including ASPit and Chill2Music. He is currently still studying.
Article Index
  1. Introduction & How it works
  2. Creating the server
  3. Creating the client
  4. Conclusion
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