最近一直关注COMET推 技术 ，现在已经应用很普遍了 比如renren，新浪微博，都用到了COMET技术 大部分使用java实现的，下面是用PHP实现的原理 原理：利用htmlfile这个ActiveX，往页面上放一个iframe，设置它的src为请求的地址。 1.我们需要一个持久链接的HTTP请求 2.需要一个加载javascript的html页面 这个脚本会做一个无限循环，将返回服务器的时间，只要客户端连接。
<?php header("Cache-Control: no-cache, must-revalidate"); header("Expires: Mon, 26 Jul 1997 05:00:00 GMT"); flush(); ?><!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.1//EN" "http://www.w3.org/TR/xhtml11/DTD/xhtml11.dtd"> <html xmlns="http://www.w3.org/1999/xhtml"> <head> <title>Comet php backend</title> <meta http-equiv="Content-Type" content="text/html; charset=utf-8" /> </head> <body> <script type="text/javascript"> // KHTML browser don't share javascripts between iframes var is_khtml = navigator.appName.match("Konqueror") || navigator.appVersion.match("KHTML"); if (is_khtml) { var prototypejs = document.createElement('script'); prototypejs.setAttribute('type','text/javascript'); prototypejs.setAttribute('src','prototype.js'); var head = document.getElementsByTagName('head'); head[0].appendChild(prototypejs); } // load the comet object var comet = window.parent.comet; </script> <?php while(1) { echo '<script type="text/javascript">'; echo 'comet.printServerTime('.time().');'; echo '</script>'; flush(); // used to send the echoed data to the client sleep(1); // a little break to unload the server CPU } ?> </body> </html>
创建客户端脚本
var comet = { connection : false, iframediv : false, initialize: function() { if (navigator.appVersion.indexOf("MSIE") != -1) { // For IE browsers comet.connection = new ActiveXObject("htmlfile"); comet.connection.open(); comet.connection.write("<html>"); comet.connection.write("<script>document.domain = '"+document.domain+"'"); comet.connection.write("</html>"); comet.connection.close(); comet.iframediv = comet.connection.createElement("div"); comet.connection.appendChild(comet.iframediv); comet.connection.parentWindow.comet = comet; comet.iframediv.innerHTML = "<iframe id='comet_iframe' src='./backend.php'></iframe>"; } else if (navigator.appVersion.indexOf("KHTML") != -1) { // for KHTML browsers comet.connection = document.createElement('iframe'); comet.connection.setAttribute('id', 'comet_iframe'); comet.connection.setAttribute('src', './backend.php'); with (comet.connection.style) { position = "absolute"; left = top = "-100px"; height = width = "1px"; visibility = "hidden"; } document.body.appendChild(comet.connection); } else { // For other browser (Firefox...) comet.connection = document.createElement('iframe'); comet.connection.setAttribute('id', 'comet_iframe'); with (comet.connection.style) { left = top = "-100px"; height = width = "1px"; visibility = "hidden"; display = 'none'; } comet.iframediv = document.createElement('iframe'); comet.iframediv.setAttribute('src', './backend.php'); comet.connection.appendChild(comet.iframediv); document.body.appendChild(comet.connection); } }, // this function will be called from backend.php printServerTime: function (time) { $('content').innerHTML = time; }, onUnload: function() { if (comet.connection) { comet.connection = false; // release the iframe to prevent problems with IE when reloading the page } } } Event.observe(window, "load", comet.initialize); Event.observe(window, "unload", comet.onUnload);