从Javascript运行PHP文件以检查在线用户：表示未登录的用户是

Question

I am writing just a simple admin panel but want to enable users who are logged in to see other logged in users. To do this, I have a sessions MySQL table which contains the active sessions (logged in users) and a PHP file which essentially will update the timestamp of each active user every few seconds using JavaScript on all pages (so it will only update if active and will delete sessions that are greater than 30 seconds ago). Here is the code for that:

Javascript:

<script type="text/javascript">
function track() {
var url = "tracking.php?username=<?PHP echo $_SESSION['username']; ?>";
xmlReq=new XMLHttpRequest();
xmlReq.open("GET",url,true);
xmlReq.send();
}
setInterval(function(){track();}, 3000);
</script>

PHP: So the url would be tracking.php?username=john.doe

<?PHP
$username=$_GET['username'];
if($username){
$result = mysql_query("SELECT * FROM sessions WHERE username='$username'");

if(mysql_fetch_array($result) !== false){
mysql_query("UPDATE sessions SET time=now() WHERE username='$username'");
} else {
mysql_query("INSERT INTO `sessions` (`username`, `time`) VALUES ('$username',now())") or die (mysql_error());
}
mysql_query("DELETE FROM sessions WHERE time < (now() - 30);");
}
?>

This works fine and the session table updates every 3 seconds. The problem is when I come to display which users are currently logged in. I have a check.php file which contains the following:

<?PHP
$username=$_GET['username'];
$result=mysql_query("SELECT * FROM sessions WHERE username = '$username'");
$num=mysql_num_rows($result);
if($num>0){
echo "Online";
} else {
echo "Offline";
}
?>

And the Javascript function:

<script type="text/javascript">
function checklogin(username) {
var element = "status";
newusername = username.substring(0, username.indexOf('.'));
newelement = element + newusername;
$.ajax({
url: ‘check.php?username='+username,
type: "GET",
dataType: "html",
success: function(data)
{
if(data === "Online")
{
document.getElementById(newelement).innerHTML='<div class="online"></div>';
}
}
});
}
</script>

Which would change the div of the user:

<?PHP
$sql=mysql_query("SELECT * FROM tbl_admin_users order by id ASC");
$num=mysql_num_rows($sql);
$i=0;
while($num>$i){
$id=mysql_result($sql,$i,"id");
$username=mysql_result($sql,$i,"username");
$first_name=mysql_result($sql,$i,"firstname");
$last_name=mysql_result($sql,$i,"lastname");
$jobtitle=mysql_result($sql,$i,"jobtitle");
$email=mysql_result($sql,$i,"email");
$phone=mysql_result($sql,$i,"phone_office");
$spanar=explode(".",$username);
$spanid=$spanar[0];
?>

<tr>
<td class="center" width="40px">
<script type="text/javascript">
setInterval(function(){checklogin('<?PHP echo $username; ?>');}, <?PHP echo rand(2000,4000); ?>);
</script>
<span id="status<?PHP echo $spanid?>"></span>
</td>

Now everything seems to be working fine apart from over time other users who are not active and are not in the session table are being displayed as online. For the life of me I am unable to see where the problem is. Is it with the javascript or the PHP checking the DB?

Could the file be running on the server in the background once run and it picks up the previous running of the check.php which was online and moving it onto the other user? Do I need to close the file after retrieving the online/offline? I have tried to ensure that the time the file is run is randomised so as not to run at the same time.

Any help would be appreciated.

Answer 1

Seems like your Javascripts are getting cached responses. disable caching on the PHP files.

Use headers in you php:

<?php
header("Cache-Control: no-cache, must-revalidate"); // HTTP/1.1
header("Expires: Sat, 26 Jul 1997 05:00:00 GMT"); // Date in the past
?>