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Developing the Server-side Layer of an Email Application in AJAX

Here you have it. Welcome to the concluding part of the series “Take AJAX to your email inbox.” In three parts, this series shows in a friendly format how to develop a simple web-based POP3 client which uses AJAX as the driving technology for fetching and displaying email messages on a web document.

Author Info:

By: Alejandro Gervasio

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April 12, 2006

TABLE OF CONTENTS:

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head>
<title>AJAX-BASED POP3 CLIENT</title>
<meta http-equiv="Content-Type" content="text/html; charset=iso-
8859-1" />
<script language="javascript">
var index=0;
function sendHttpRequest(url,callbackFunc,respXml){
    var xmlobj=null;
    try{
        xmlobj=new XMLHttpRequest();
    }
    catch(e){
        try{
            xmlobj=new ActiveXObject("Microsoft.XMLHTTP");
        }
        catch(e){
            alert('AJAX isn't supported by your browser!');
            return false;
        }
   }
   xmlobj.onreadystatechange=function(){
        if(xmlobj.readyState==4){
            if(xmlobj.status==200){
                respXml?eval
(callbackFunc+'(xmlobj.responseXML)'):eval
(callbackFunc+'(xmlobj.responseText)');
            }
        }
   }
   // open socket connection
   xmlobj.open('POST',url,true);
   // send http header
   xmlobj.setRequestHeader('Content-Type','application/x-www-
form-urlencoded; charset=UTF-8');
   // get form values and send http request
   xmlobj.send(getFormValues(document.getElementsByTagName
('form')[0]));
}
// get form values
function getFormValues(fobj){
    var str='';
    for(var i=0;i< fobj.elements.length;i++){
        str+=fobj.elements[i].name+'='+ escape(fobj.elements
[i].value)+'&';
    }
    str=str.substr(0,(str.length-1));
    return str;
}
// fetch messages from POP3 server
function fetchMessages(messages){
    // build messages array
    var messages=messages.split('||||');
    var mdiv=document.getElementById('mailcontainer');
    if(!mdiv){return};
    // display mail server response
    mdiv.innerHTML=messages[0];
    // get 'previous' button
    var prev=document.getElementsByTagName('form')[1].elements
['prev'];
    if(!prev){return};
    // get 'next' button
    var next=document.getElementsByTagName('form')[1].elements
['next'];
    if(!next){return};
    // get 'clear' button
    var clear=document.getElementsByTagName('form')[1].elements
['clear'];
    if(!clear){return};
    // move messages pointer back
    prev.onclick=function(){
        index--;
        if(index<0){index=0};
        mdiv.innerHTML=messages[index];
    }
    // move messages pointer forward
    next.onclick=function(){
        index++;
        if(index==messages.length){index=messages.length-1};
        mdiv.innerHTML=messages[index];
    }
    // clear mail container
    clear.onclick=function(){mdiv.innerHTML=''};
}
// initialize user panel
function initializeUserPanel(){
    // get 'connect' button
    var sendbtn=document.getElementsByTagName('form')[0].elements['connect'];
    // send http request when button is clicked on
    sendbtn.onclick=function(){
        // send request & fetch messages from POP3 server
        sendHttpRequest('http://pop_processor.php','fetchMessages');
        // display 'Retrieving...' message
        var mdiv=document.getElementById('mailcontainer');
        if(!mdiv){return};
        mdiv.innerHTML='Retrieving messages from the server...';
    }
}
// initialize user panel when page is loaded
window.onload=function(){
    // check if browser is DOM compatible
    if(document.createElement&&document.getElementById&&document.
getElementsByTagName){
        // initialize user panel
        initializeUserPanel();
    }
}
</script>
<style type="text/css">
body {
            margin: 10px 0 0 0;
}
#userinfo {
            width: 700px;
            height: 22px;
            padding: 2px 5px 2px 5px;
            border-top: 2px solid #000;
            border-left: 2px solid #000;
            border-right: 2px solid #000;
            background: #9cf;
            margin-left: auto;
            margin-right: auto;
            font: bold 11px Verdana, Arial, Helvetica, sans-
serif;
            color: #000;
}
#mailcontainer {
            width: 700px;
            height: 520px;
            padding: 2px 5px 2px 5px;
            border: 2px solid #000;
            background: #eee;
            margin-left: auto;
            margin-right: auto;
            font: 12px normal Arial, Helvetica, sans-serif;
            color: #000;
            overflow: auto;
}
#navbar {
            width: 700px;
            height: 22px;
            padding: 2px 5px 2px 5px;
            border-left: 2px solid #000;
            border-right: 2px solid #000;
            border-bottom: 2px solid #000;
            background: #9cf;
            margin-left: auto;
            margin-right: auto;
}
form {
            display: inline;
}
.inputbox {
            width: 150px;
            border: 1px solid #000;
            background: #eee;
}
.formbutton {
            width: 70px;
            height: 20px;
            font: bold 11px Verdana, Arial, Helvetica, sans-
serif;
            color: #000;
}
</style>
</head>
<body>
<div id="userinfo">
<form>
HOST <input name="host" type="text" class="inputbox" title="Enter
mail hostname" />
USER <input name="user" type="text" class="inputbox" title="Enter
username" />
PASSWORD <input name="pass" type="password" class="inputbox"
title="Enter password" />
<input name="connect" type="button" value="Connect"
class="formbutton" />
</form>
</div>
<div id="mailcontainer">
</div>
<div id="navbar">
<form>
<input name="prev" type="button" value="<&lt Prev"
class="formbutton" title="Previous message" />
<input name="next" type="button" value="Next >>"
class="formbutton" title="Next message" />
<input name="clear" type="button" value="Clear"
class="formbutton" title="Clear all messages" />
</form>
</div>
</body>
</html>

And below is the source code that corresponds to the "pop_processor.php" file:

<?php
class POP3Processor{
    // declare data members
    private $output='';
    private $fp;
    // constructor
    public function __construct($host,$user,$password){
        if(!$this->fp=fsockopen($host,110,$errno,$errstr,30)){
            throw new Exception('Failed to connect to POP3 server
'.$errstr.$errno);
        }
        stream_set_timeout($this->fp,2);
        $this->output.=fgets($this->fp,128).'<br />';
        fputs($this->fp,"USER $usern");// send USER command
        $this->output.=fgets($this->fp,128).'<br />';
        fputs($this->fp,"PASS $passwordn");// send PASS command
        $this->output.=fgets($this->fp,128).'<br />';
        $this->output.='||||';// send delimiter string
    }
    // fetch email messages
    public function fetch(){
        fputs($this->fp,"STATn");// send STAT command
        $ret=fgets($this->fp,128).'<br />';
        if(substr($ret,0,5)!='-ERR '){
            $messages=intval(substr($ret,4,1));
            for($i=1;$i<=$messages;$i++){
                fputs($this->fp,"RETR $in"); // send RETR
command
                $this->output.=stream_get_contents($this-
>fp).'<br /><br />';// fetch email messages
                $this->output.='||||';// send delimiter string
            }
        }
        $this->output=substr($this->output,0,strlen($this-
>output)-4);
        return $ret.$this->output;
    }
    // close mail server connection
    public function close(){
        fputs($this->fp,"QUITn");
        fclose($this->fp);
    }
}
try{
    // clean up POST data
    array_map('trim',$_POST);
    // instantiate POP3 processor object
    $popProc=new POP3Processor($_POST['host'],$_POST
['user'],$_POST['pass']);
    // fetch messages from mail server
    echo $popProc->fetch();
    // close mail server connection
    $popProc->close();
}
catch(Exception $e){
    echo $e->getMessage();
    exit();
}
?>

That's all the source code you need to copy and paste, in order to use the web-based POP3 client. I hope you enjoy the experience!

To wrap up

As I said before, we're done now. Over this three-part series I've demonstrated another possible implementation of AJAX, by creating a web-based POP3 client application, handy for retrieving and displaying email messages on a web document. Of course, the program is just a starting point for developing more complex projects, but you should have a clear idea of how to get started using AJAX for building desktop-like applications. Want to know more about web programming? Fine, see you in the next tutorial!

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