Building an AJAX Chat Application

Requires Prado versions 3.1a or later.

This tutorial introduces the Prado web application framework's ActiveRecord and Active Controls to build a Chat web application. It is assumed that you are familiar with PHP and you have access to a web server that is able to serve PHP5 scripts. This basic chat application will utilize the following ideas/components in Prado.

  • Building a custom User Manager class.
  • Authenticating and adding a new user to the database.
  • Using ActiveRecord to interact with the database.
  • Using Active Controls and callbacks to implement the user interface.
  • Separating application logic and application flow.

In this tutorial you will build an AJAX Chat web application that allows multiple users to communicate through their web browser. The application consists of two pages: a login page that asks the user to enter their nickname and the main application chat page. You can try the application locally or at Prado website. The main application chat page is shown bellow.

Download, Install and Create a New Application

The download and installation steps are similar to those in the Currency converter tutorial. To create the application, we run from the command line the following. See the Command Line Tool for more details.

php prado/framework/prado-cli.php -c chat

The above command creates the necessary directory structure and minimal files (including "index.php" and "Home.page") to run a Prado web application. Now you can point your browser's URL to the web server to serve up the index.php script in the chat directory. You should see the message "Welcome to Prado!"

Authentication and Authorization

The first task for this application is to ensure that each user of the chat application is assigned with a unique (chosen by the user) username. To achieve this, we can secure the main chat application page to deny access to anonymous users. First, let us create the Login page with the following code. We save the Login.php and Login.page in the chat/protected/pages/ directory (there should be a Home.page file created by the command line tool).

<?php
class Login extends TPage
{
}
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8" />
    <title>Prado Chat Demo Login</title>
</head>
<body>
<com:TForm>
    <h1 class="login">Prado Chat Demo Login</h1>
    <fieldset class="login">
        <legend>Please enter your name:</legend>
        <div class="username">
            <com:TLabel ForControl="username" Text="Username:" />
            <com:TTextBox ID="username" MaxLength="20" />
            <com:TRequiredFieldValidator
                ControlToValidate="username"
                Display="Dynamic"
                ErrorMessage="Please provide a username." />
        </div>
        <div class="login-button">
            <com:TButton Text="Login" />
        </div>
</com:TForm>
</body>
</html>

The login page contains a TForm, a TTextBox, a TRequiredFieldValidator and a TButton. The resulting page looks like the following (after applying some a style sheet). If you click on the Login button without entering any text in the username textbox, an error message is displayed. This is due to the TRequiredFieldValidator requiring the user to enter some text in the textbox before proceeding.

Securing the Home page

Now we wish that if the user is trying to access the main application page, Home.page, before they have logged in, the user is presented with the Login.page first. We add a chat/protected/application.xml configuration file to import some classes that we shall use later.

<?xml version="1.0" encoding="utf-8"?>
<application id="Chat" Mode="Debug">
  <paths>
    <using namespace="System.Data.*" />
    <using namespace="System.Data.ActiveRecord.*" />
    <using namespace="System.Security.*" />
    <using namespace="System.Web.UI.ActiveControls.*" />
  </paths>
</application>
Next, we add a chat/protected/pages/config.xml configuration file to secure the pages directory.
<?xml version="1.0" encoding="utf-8"?>
<configuration>
  <modules>
    <module id="users" class="TUserManager" />
    <module id="auth" class="TAuthManager" UserManager="users" LoginPage="Login" />
  </modules>
  <authorization>
    <allow pages="Login" users="?" />
    <allow roles="normal" />
    <deny users="*" />
  </authorization>
</configuration>
We setup the authentication using the default classes as explained in the authentication/authorization quickstart. In the authorization definition, we allow anonymous users to access the Login page (anonymous users is specified by the ? question mark). We allow any users with role equal to "normal" (to be defined later) to access all the pages, that is, the Login and Home pages. Lastly, we deny all users without any roles to access any page. The authorization rules are executed on first match basis.

If you now try to access the Home page by pointing your browser to the index.php you will be redirected to the Login page.

Active Record for chat_users table

The TUserManager class only provides a read-only list of users. We need to be able to add or login new users dynamically. So we need to create our own user manager class. First, we shall setup a database with a chat_users table and create an ActiveRecord that can work with the chat_users table with ease. For the demo, we use sqlite as our database for ease of distributing the demo. The demo can be extended to use other databases such as MySQL or Postgres SQL easily. We define the chat_users table as follows.

CREATE TABLE chat_users
(
	username VARCHAR(20) NOT NULL PRIMARY KEY,
	last_activity INTEGER NOT NULL DEFAULT "0"
);
Next we define the corresponding ChatUserRecord class and save it as chat/protected/App_Code/ChatUserRecord.php (you need to create the App_Code directory as well). We also save the sqlite database file as App_Code/chat.db.
class ChatUserRecord extends TActiveRecord
{
    const TABLE='chat_users';

    public $username;
    public $last_activity;

    public static function finder($className=__CLASS__)
    {
        return parent::finder($className);
    }
}
Before using the ChatUserRecord class we to configure a default database connection for ActiveRecord to function. In the chat/protected/application.xml we import classes from the App_Code directory and add an ActiveRecord configuration module.
<?xml version="1.0" encoding="utf-8"?>
<application id="Chat" Mode="Debug">
  <paths>
    <using namespace="Application.App_Code.*" />
    <using namespace="System.Data.*" />
    <using namespace="System.Data.ActiveRecord.*" />
    <using namespace="System.Security.*" />
    <using namespace="System.Web.UI.ActiveControls.*" />
  </paths>
  <modules>
    <module class="TActiveRecordConfig" EnableCache="true"
        Database.ConnectionString="sqlite:protected/App_Code/chat.db" />
  </modules>
</application>

Custom User Manager class

To implement a custom user manager module class we just need to extends the TModule class and implement the IUserManager interface. The getGuestName(), getUser() and validateUser() methods are required by the IUserManager interface. We save the custom user manager class as App_Code/ChatUserManager.php.

class ChatUserManager extends TModule implements IUserManager
{
    public function getGuestName()
    {
        return 'Guest';
    }

    public function getUser($username=null)
    {
        $user=new TUser($this);
        $user->setIsGuest(true);
        if($username !== null && $this->usernameExists($username))
        {
            $user->setIsGuest(false);
            $user->setName($username);
            $user->setRoles(array('normal'));
        }
        return $user;
    }

    public function addNewUser($username)
    {
        $user = new ChatUserRecord();
        $user->username = $username;
        $user->save();
    }

    public function usernameExists($username)
    {
        $finder = ChatUserRecord::finder();
        $record = $finder->findByUsername($username);
        return $record instanceof ChatUserRecord;
    }

    public function validateUser($username,$password)
    {
        return $this->usernameExists($username);
    }
}

The getGuestName() method simply returns the name for a guest user and is not used in our application. The getUser() method returns a TUser object if the username exists in the database, the TUser object is set with role of "normal" that corresponds to the <authorization> rules defined in our config.xml file.

The addNewUser() and usernameExists() method uses the ActiveRecord corresponding to the chat_users table to add a new user and to check if a username already exists, respectively.

The next thing to do is change the config.xml configuration to use our new custom user manager class. We simply change the <module> configuration with id="users".

<module id="users" class="ChatUserManager" />

Authentication

To perform authentication, we just want the user to enter a unique username. We add a TCustomValidator for validate the uniqueness of the username and add an OnClick event handler for the login button.

<com:TCustomValidator
    ControlToValidate="username"
    Display="Dynamic"
    OnServerValidate="checkUsername"
    ErrorMessage="The username is already taken." />

...

<com:TButton Text="Login" OnClick="createNewUser" />
In the Login.php file, we add the following 2 methods.
function checkUsername($sender, $param)
{
    $manager = $this->Application->Modules['users'];
    if($manager->usernameExists($this->username->Text))
        $param->IsValid = false;
}

function createNewUser($sender, $param)
{
    if($this->Page->IsValid)
    {
        $manager = $this->Application->Modules['users'];
        $manager->addNewUser($this->username->Text);

        //do manual login
        $user = $manager->getUser($this->username->Text);
        $auth = $this->Application->Modules['auth'];
        $auth->updateSessionUser($user);
        $this->Application->User = $user;

        $url = $this->Service->constructUrl($this->Service->DefaultPage);
        $this->Response->redirect($url);
    }
}
The checkUserName() method uses the ChatUserManager class (recall that in the config.xml configuration we set the ID of the custom user manager class as "users") to validate the username is not taken.

In the createNewUser method, when the validation passes (that is, when the user name is not taken) we add a new user. Afterward we perform a manual login process:

  • First we obtain a TUser instance from our custom user manager class using the $manager->getUser(...) method.
  • Using the TAuthManager we set/update the user object in the current session data.
  • Then we set/update the Application's user instance with our new user object.

Finally, we redirect the client to the default Home page.

Default Values for ActiveRecord

If you try to perform a login now, you will receive an error message like "Property 'ChatUserRecord::$last_activity' must not be null as defined by column 'last_activity' in table 'chat_users'.". This means that the $last_activity property value was null when we tried to insert a new record. We need to either define a default value in the corresponding column in the table and allow null values or set the default value in the ChatUserRecord class. We shall demonstrate the later by altering the ChatUserRecord with the addition of a set getter/setter methods for the last_activity property.

private $_last_activity;

public function getLast_Activity()
{
    if($this->_last_activity === null)
        $this->_last_activity = time();
    return $this->_last_activity;
}

public function setLast_Activity($value)
{
    $this->_last_activity = $value;
}
Notice that we renamed $last_activity to $_last_activity (note the underscore after the dollar sign).

Main Chat Application

Now we are ready to build the main chat application. We use a simple layout that consist of one panel holding the chat messages, one panel to hold the users list, a textarea for the user to enter the text message and a button to send the message.

<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="utf-8" />
    <title>Prado Chat Demo</title>
<style>
.messages
{
    width: 500px;
    height: 300px;
    float: left;
    border: 1px solid ButtonFace;
    overflow: auto;
}
.user-list
{
    margin-left: 2px;
    float: left;
    width: 180px;
    height: 300px;
    border: 1px solid ButtonFace;
    overflow: auto;
    font-size: 0.85em;
}
.message-input
{
    float: left;
}

.message-input textarea
{
    margin-top: 3px;
    padding: 0.4em 0.2em;
    width: 493px;
    font-family: Verdana, Geneva, Arial, Helvetica, sans-serif;
    font-size: 0.85em;
    height: 40px;
}
.send-button
{
    margin: 0.5em;
}
</style>
</head>
<body>
<com:TForm>
<h1>Prado Chat Demo</h1>
<div id="messages" class="messages">
    <com:TPlaceHolder ID="messageList" />
</div>
<div id="users" class="user-list">
    <com:TPlaceHolder ID="userList" />
</div>
<div class="message-input">
    <com:TActiveTextBox ID="userinput"
        Columns="40" Rows="2" TextMode="MultiLine" />
    <com:TActiveButton ID="sendButton" CssClass="send-button"
        Text="Send" />
</div>
</com:TForm>
</body>
</html>
We added two Active Control components: a TActiveTextBox and a TActiveButton. We also added a TJavascriptLogger that will be very useful for understanding how the Active Controls work.

Exploring the Active Controls

We should have some fun before we proceeding with setting up the chat buffering. We want to see how we can update the current page when we receive a message. First, we add an OnClick event handler for the Send button.

<com:TActiveButton ID="sendButton" CssClass="send-button"
	Text="Send" OnClick="processMessage"/>
And the corresponding event handler method in the Home.php class (we need to create this new file too).
class Home extends TPage
{
    function processMessage($sender, $param)
    {
        echo $this->userinput->Text;
    }
}
If you now type something in the main application textbox and click the send button you should see whatever you have typed echoed in the TJavascriptLogger console.

To append or add some content to the message list panel, we need to use some methods in the TCallbackClientScript class which is available through the CallbackClient property of the current TPage object. For example, we do can do

function processMessage($sender, $param)
{
    $this->CallbackClient->appendContent("messages", $this->userinput->Text);
}
This is one way to update some part of the existing page during a callback (AJAX style events) and will be the primary way we will use to implement the chat application.

Active Record for chat_buffer table

To send a message to all the connected users we need to buffer or store the message for each user. We can use the database to buffer the messages. The chat_buffer table is defined as follows.

CREATE TABLE chat_buffer
(
	id INTEGER PRIMARY KEY,
	for_user VARCHAR(20) NOT NULL,
	from_user VARCHAR(20) NOT NULL,
	message TEXT NOT NULL,
	created_on INTEGER NOT NULL DEFAULT "0"
);
The corresponding ChatBufferRecord class is saved as App_Code/ChatBufferRecord.php.
class ChatBufferRecord extends TActiveRecord
{
	const TABLE='chat_buffer';

    public $id;
    public $for_user;
    public $from_user;
    public $message;
    private $_created_on;

    public function getCreated_On()
    {
        if($this->_created_on === null)
            $this->_created_on = time();
        return $this->_created_on;
    }

    public function setCreated_On($value)
    {
        $this->_created_on = $value;
    }

    public static function finder($className=__CLASS__)
    {
        return parent::finder($className);
    }
}

Chat Application Logic

We finally arrive at the guts of the chat application logic. First, we need to save a received message into the chat buffer for all the current users. We add this logic in the ChatBufferRecord class.

public function saveMessage()
{
    foreach(ChatUserRecord::finder()->findAll() as $user)
    {
        $message = new self;
        $message->for_user = $user->username;
        $message->from_user = $this->from_user;
        $message->message = $this->message;
        $message->save();
        if($user->username == $this->from_user)
        {
            $user->last_activity = time(); //update the last activity;
            $user->save();
        }
    }
}
We first find all the current users using the ChatUserRecord finder methods. Then we duplicate the message and save it into the database. In addition, we update the message sender's last activity timestamp. The above piece of code demonstrates the simplicity and succinctness of using ActiveRecords for simple database designs.

The next piece of the logic is to retrieve the users' messages from the buffer. We simply load all the messages for a particular username and format that message appropriately (remember to escape the output to prevent Cross-Site Scripting attacks). After we load the messages, we delete those loaded messages and any older messages that may have been left in the buffer.

public function getUserMessages($user)
{
    $content = '';
    foreach($this->findAll('for_user = ?', $user) as $message)
        $content .= $this->formatMessage($message);
    $this->deleteAll('for_user = ? OR created_on < ?',
                          $user, time() - 300); //5 min inactivity
    return $content;
}

protected function formatMessage($message)
{
    $user = htmlspecialchars($message->from_user);
    $content = htmlspecialchars($message->message);
    return "<div class=\"message\"><strong>{$user}:</strong>"
                  ." <span>{$content}</span></div>";
}
To retrieve a list of current users (formatted), we add this logic to the ChatUserRecord class. We delete any users that may have been inactive for awhile.
public function getUserList()
{
    $this->deleteAll('last_activity < ?', time()-300); //5 min inactivity
    $content = '<ul>';
    foreach($this->findAll() as $user)
        $content .= '<li>'.htmlspecialchars($user->username).'</li>';
    $content .= '</ul>';
    return $content;
}
Note: For simplicity we formatted the messages in these Active Record classes. For large applications, these message formatting tasks should be done using Prado components (e.g. using a TRepeater in the template or a custom component).

Putting It Together

Now comes to put the application flow together. In the Home.php we update the Send buttons OnClick event handler to use the application logic we just implemented.

function processMessage($sender, $param)
{
    if(strlen($this->userinput->Text) > 0)
    {
        $record = new ChatBufferRecord();
        $record->message = $this->userinput->Text;
        $record->from_user = $this->Application->User->Name;
        $record->saveMessage();

        $this->userinput->Text = '';
        $messages = $record->getUserMessages($this->Application->User->Name);
        $this->CallbackClient->appendContent("messages", $messages);
        $this->CallbackClient->focus($this->userinput);
    }
}
We simply save the message to the chat buffer and then ask for all the messages for the current user and update the client side message list using a callback response (AJAX style).

At this point the application is actually already functional, just not very user friendly. If you open two different browsers, you should be able to communicate between the two users whenever the Send button is clicked.

The next part is perhaps the more tricker and fiddly than the other tasks. We need to improve the user experience. First, we want a list of current users as well. So we add the following method to Home.php, we can call this method when ever some callback event is raised, e.g. when the Send button is clicked.

protected function refreshUserList()
{
    $lastUpdate = $this->getViewState('userList','');
    $users = ChatUserRecord::finder()->getUserList();
    if($lastUpdate != $users)
    {
        $this->CallbackClient->update('users', $users);
        $this->setViewstate('userList', $users);
    }
}

Actually, we want to periodically update the messages and user list as new users join in and new message may arrive from other users. So we need to refresh the message list as well.

function processMessage($sender, $param)
{
    ...
    $this->refreshUserList();
    $this->refreshMessageList();
    ...
}

protected function refreshMessageList()
{
    //refresh the message list
    $finder = ChatBufferRecord::finder();
    $content = $finder->getUserMessages($this->Application->User->Name);
    if(strlen($content) > 0)
    {
        $anchor = (string)time();
        $content .= "<a href=\"#\" id=\"{$anchor}\"> </a>";
        $this->CallbackClient->appendContent("messages", $content);
        $this->CallbackClient->focus($anchor);
    }
}
The anchor using time() as ID for a focus point is so that when the message list on the client side gets very long, the focus method will scroll the message list to the latest message (well, it works in most browsers).

Next, we need to redirect the user back to the login page if the user has been inactive for some time, say about 5 mins, we can add this check to any stage of the page life-cycle. Lets add it to the onLoad() stage.

public function onLoad($param)
{
    $username = $this->Application->User->Name;
    if(!$this->Application->Modules['users']->usernameExists($username))
    {
        $auth = $this->Application->Modules['auth'];
        $auth->logout();

        //redirect to login page.
        $this->Response->Redirect($this->Service->ConstructUrl($auth->LoginPage));
    }
}

Improving User Experience

The last few details are to periodically check for new messages and refresh the user list. We can accomplish this by polling the server using a TTimeTriggeredCallback control. We add a TTimeTriggeredCallback to the Home.page and call the refresh handler method defined in Home.php. We set the polling interval to 2 seconds.

<com:TTimeTriggeredCallback OnCallback="refresh"
	Interval="2" StartTimerOnLoad="true" />
function refresh($sender, $param)
{
    $this->refreshUserList();
    $this->refreshMessageList();
}

The final piece requires us to use some javascript. We want that when the user type some text in the textarea and press the Enter key, we want it to send the message without clicking on the Send button. We add to the Home.page some javascript.

<com:TClientScript>
Event.observe($("<%= $this->userinput->ClientID %>"), "keypress", function(ev)
{
    if(Event.keyCode(ev) == Event.KEY_RETURN)
    {
        if(Event.element(ev).value.length > 0)
            new Prado.Callback("<%= $this->sendButton->UniqueID %>");
        Event.stop(ev);
    }
});
</com:TClientScript>
Details regarding the javascript can be explored in the Introduction to Javascript section of the quickstart.

This completes the tutorial on making a basic chat web application using the Prado framework. Hope you have enjoyed it.