Timezone diff between server and client?

Question

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Scenario:

Servers systems are all over the world.
Web page on the client machine is requesting data.

Issue:

How to know the time zone offset between any server and any client machine?

Work:

JavaScript

var DocumentTime = new Date();
function GetTimeZoneOffset()
	{
		var nTime = DocumentTime.getTime();
		var sUrl = xxxPhpUrl + '?TimeZoneOffSet=' + nTime;
		if(window.XMLHttpRequest)
		{
			var xhr = new XMLHttpRequest();
			xhr.open("GET", sUrl, true);
			xhr.onreadystatechange = function()
			{
				if (xhr.readyState == 4)
				{}
			}
			xhr.timeout = 30000;
			xhr.ontimeout = TimeOut;
			xhr.send(null);
		}
		nNow = null;
		nTime = null;
		sUrl = null;
	}

<body  önload="GetTimeZoneOffset()"

PHP::

PHP

if (isset($_GET['TimeZoneOffSet']))
{
	$ClientTime = $_GET['TimeZoneOffSet'];
	$ServerTime = time();
	$ServerTime = $ServerTime*1000;
	$Diff = $ServerTime - $ClientTime;
	echo $Diff;
	echo " Server ";
	echo $ServerTime;
	echo " and client ";
	echo $ClientTime;
}

Webpage Posts a timestamp to the php on the server (using get date function) and php should take the timestamp and give difference between the webpage timestamp and its local timestamp.

Output:
The difference is hardly 70000 microseconds. even though the server timezone is in PST and client is in EST. Is this correct?

How do i achieve this?

Posted 24-Jun-14 10:24am

amarasat

Updated 24-Jun-14 10:54am

v2

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Sergey Alexandrovich Kryukov · Answer 1 · 2014-06-24T11:34:00

Calculating the time difference between two location is not a good thing. In particular, it may change, because in different location there can be a different policy about summer saving time (who needs it anyway? such an archaic pointless trick…) which can change with time.

I would advise the following approach: do all the programming, on all severs and all clients, in UTC time: http://en.wikipedia.org/wiki/UTC[^].

This manual page explains how to use it in PHP: http://www.php.net//manual/en/function.time.php[^].

…and this one — in Javascript: https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Date/UTC[^].

And only in one point, in the client-side script, only in showing time in UI, convert UTC time to local. This way, you never need to know the timezone of the server, its summer saving time, anything; you will only need to convert universal UTC time to the client host local time. Having correct local time on the host is a purely local concern, so you won't need any coordination between hosts (everything is already coordinated by UTC :-)), won't need any redundant knowledge in time setting on any of them.

—SA