PHP判断设备访问来源

/**
 * 判断用户请求设备是否是移动设备
 * @return bool
 */
function ismobile() {

    //如果有http_x_wap_profile则一定是移动设备
    if (isset($_server['http_x_wap_profile'])) {
        return true;
    }

    //如果via信息含有wap则一定是移动设备,部分服务商会屏蔽该信息
    if (isset($_server['http_via']) && stristr($_server['http_via'], 'wap')) {
        return true;
    }

    //野蛮方法,判断手机发送的客户端标志,兼容性有待提高
    if (isset($_server['http_user_agent'])) {

        $clientkeywords = ['nokia','sony','ericsson','mot','samsung','htc','sgh','lg','sharp','sie-','philips','panasonic','alcatel','lenovo','iphone','ipod','blackberry','meizu','android','netfront','symbian','ucweb','windowsce','palm','operamini','operamobi','openwave','nexusone','cldc','midp','wap','mobile'];

        //从http_user_agent中查找手机浏览器的关键字
        if (preg_match("/(".implode('|', $clientkeywords).")/i", strtolower($_server['http_user_agent']))) {
            return true;
        }
    }

    //协议法,因为有可能不准确,放到最后判断
    if (isset($_server['http_accept'])) {
        //如果只支持wml并且不支持html那一定是移动设备
        //如果支持wml和html但是wml在html之前则是移动设备
        if ((strpos($_server['http_accept'], 'vnd.wap.wml') !== false) && (strpos($_server['http_accept'], 'text/html') === false || (strpos($_server['http_accept'], 'vnd.wap.wml') < strpos($_server['http_accept'], 'text/html')))) {
            return true;
        }
    }

    return false;
}