PHP：计算服务器和客户端之间的时差

Question

I am building a chat for my website and I want to calculate the time difference between the server and the client. I am using the following code to get the time difference and put it in a hidden input field. But it doesn't work.

<script type = "text/javascript">
var time = new Date().getTime()/1000;
$.post('timediff.php',{time:time},function(response){
    alert(response);
});
</script>

And in my timediff.php file I have the following code:

<?php
if(isset($_POST['time'])){
    $client_time = $_POST['time'];
    $server_time = time();
    $time_diff = $server_time - $client_time;
    echo $time_diff;
}
?>

I tested this on another computer which has the same time setting as the server but the result that I am getting is larger. Am I doing anything wrong? Is there any better way to do this? Thanks in advance.

Answer 1

Are you accounting for the latency between the client and the server? Even if they are one and the same, if it takes > 1 ms to process the response, you will get a non-zero difference.

EDIT: Try getTimezoneOffset() (JavaScript, returns minutes) and DateTime::getOffset() (PHP, returns seconds). It's possible getTime() and time() are returning time-zone-dependent values. If you haven't set the timezone in your PHP script, that could also be a factor.

You might also try this in your PHP:

echo $client_time."
".$server_time;

It could be useful to see what time JS and PHP are each reporting; it may be very different from the system time for any number of reasons.