How to code my HTTP response header for 8 hours in the future in php/

I know how to set a basic expires HTTP response header in PHP as follows...

header("Expires: Sat, 26 Jul 1997 05:00:00 GMT");

However, I want to make it a little more dynamic in that I want to, using PHP, specify an expiration time eight hours ahead of when the user accesses the content. Could someone help me开发者_开发技巧 achieve this?

Thanks in advance!

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You can use Cache-Control’s max-age instead that indicated the number of second relative to the response time:

The expiration time of an entity MAY be specified by the origin server using the Expires header (see section 14.21). Alternatively, it MAY be specified using the max-age directive in a response. When the max-age cache-control directive is present in a cached response, the response is stale if its current age is greater than the age value given (in seconds) at the time of a new request for that resource.

An example:

header('Cache-Control: max-age=28800');

Note that if both Expires and Cache-Control’s max-age are present, max-age is preferred over Expires:

If a response includes both an Expires header and a max-age directive, the max-age directive overrides the Expires header, even if the Expires header is more restrictive.

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Use strtotime to make a timestamp in the future, and gmdate to format it as a string in the GMT timezone.

define('EXPIRE_FORMAT', 'D, d M Y H:i:s T');
$expires = gmdate(EXPIRE_FORMAT, strtotime('+8 hours'));
header("Expires: $expires");