Prevent Wordpress from sending Cache-control http header

Question

Prevent Wordpress from sending Cache-control http header

pixeline

2014年11月1日 18:39

My site sits on a server that uses Varnish as a (powerful) caching engine. Unfortunately, it seems wordpress is busting the Varnish cache by sending a cache-control http header. If I curl -I domain.com I get:

HTTP/1.1 200 OK
Server: Apache/2.4.10
X-Powered-By: PHP/5.4.4-14+deb7u14
Expires: Thu, 19 Nov 1981 08:52:00 GMT
Cache-Control: no-store, no-cache, must-revalidate, post-check=0, pre-check=0
Pragma: no-cache
Set-Cookie: PHPSESSID=e00738aoughg407ljm270kj0l6; path=/
Content-Type: text/html; charset=UTF-8
Accept-Ranges: bytes
Date: Fri, 31 Oct 2014 21:44:16 GMT
Connection: keep-alive
Via: 1.1 varnish
Age: 0

I have other wordpress sites hosted on this server, which work correctly with the Varnish server, so I'm pretty sure the problem is caused by this specific installation. Here is what I tried:

disable all plugins. Empty Varnish cache, then curl -I: same result.
looked through all my theme files. Nothing suspicious.

Do you have any other idea as to what may cause the problem?

Topic varnish http cache Wordpress

Category Web

pixeline · Accepted Answer · 2014年11月1日 18:39

Thanks to @chrisguitarguy's answer, you can control the http headers sent by Wordpress via the "send_headers" hook. Here is the function I added to my theme's functions.php file, and that solved the issue with the Varnish server.

function varnish_safe_http_headers() {
    header( 'X-UA-Compatible: IE=edge,chrome=1' );
    session_cache_limiter('');
    header("Cache-Control: public, s-maxage=120");
  if( !session_id() )
  {
    session_start();
  }
}
add_action( 'send_headers', 'varnish_safe_http_headers' );

chrisguitarguy · Accepted Answer · 2014年10月31日 22:38

You can hook into wp_headers and remove the cache control headers. WordPress generally doesn't send Cache-Control except for admin area or ajax requests, however.

add_filter('wp_headers', 'wpse167128_nocache');
function wpse167128_nocache($headers)
{
    unset($headers['Cache-Control']);
    return $headers;
}

Prevent Wordpress from sending Cache-control http header

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