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Why is Google's home page logo served with contradictory "Expires" and "Cache-Control" headers?

Here is the logo currently used on www.google.com:

http://www.google.com/images/logos/ps_logo2.png

Here's its HTTP response:

HTTP/1.1 200 OK
Content-Type: image/png
Last-Modified: Thu, 05 Aug 2010 22:54:44 GMT
Date: Fri, 25 Mar 2011 16:41:05 GMT
Expires: Fri, 25 Mar 2011 16:41:05 GMT
Cache-Control: private, max-age=31536000
X-Content-Type-Options: nosniff
Server: sffe
Content-Length: 26209
Age: 0
Via: 1.1 localhost.localdomain

The Cache-Control header says it's good for 1 year. But Expires is the same as Date, i.e. it's stale immediately.

Why the difference?

Solution

  • Cache-Control overrides Expires on any HTTP/1.1 cache or client.

    So I assume Google wants to cache the image for HTTP/1.1 but not cache it at all for HTTP/1.0.

    I don't know why Google cares. I would think they'd want to cache the logo even for older clients.