使用PHP+ajax打造聊天室应用

<meta content="text/html; charset=UTF-8" http-equiv="Content-Type">
<title>Comet Test</title>
<script type="text/javascript" src="http://lib.sinaapp.com/js/jquery/1.7.2/jquery.min.js"></script>
<script type="text/javascript">
(function($){
    function handleResponse(response){
    $('#content').append('<div>' + response['msg'] + '</div>');
    }
 
    var timestamp = 0;
    var url = './chat_backend.php';
    var noerror = true;
    var ajax;
 
    function connect() {
        ajax = $.ajax(url, {
            type: 'get',
            data: { 'timestamp' : timestamp },
            success: function(transport) {
                eval('var response = '+transport);
                timestamp = response['timestamp'];
                handleResponse(response);
                noerror = true;
            },
            complete: function(transport) {
                (!noerror) && setTimeout(function(){ connect() }, 5000) || connect();
                noerror = false;
            }
        });
    }
 
    function doRequest(request) {
        $.ajax(url, {
            type: 'get',
            data: { 'msg' : request }
        });
    }
 
    $('#cometForm').live('submit', function(){
        doRequest($('#word').val());
        $('#word').val('');
        return false;
    });
 
    $(document).ready(function(){
        connect();
    });
})(jQuery);
</script>
<div ></div>
<div style="margin: 5px 0;">
<form action="javascript:void(0);" >
<input >
<input name="submit" type="submit" value="Send">
 
</form></div>

 <?php
  
 $filename  = dirname(__FILE__).'/data.txt';
  
 // 消息都储存在这个文件中
 $msg = isset($_GET['msg']) ? $_GET['msg'] : '';
  
 if ($msg != ''){
     file_put_contents($filename,$msg);
     die();
 }
  
 // 不停的循环，直到储存消息的文件被修改
 $lastmodif    = isset($_GET['timestamp']) ? $_GET['timestamp'] : 0;
 $currentmodif = filemtime($filename);
 while ($currentmodif <= $lastmodif){ // 如果数据文件已经被修改
     usleep(100000); // 100ms暂停 缓解CPU压力
     clearstatcache(); //清除缓存信息
     $currentmodif = filemtime($filename);
 }
  
 // 返回json数组
 $response = array();
 $response['msg']       = file_get_contents($filename);
 $response['timestamp'] = $currentmodif;
 echo json_encode($response);
 flush();
  
 ?>