curl -i and curl -I returning different results

问题

My understanding was that curl -i and curl -I would return virtually the same results except that curl -i would return the standard output along with the header and curl -I would only return the header -- the header of both being the same. We've been doing some gzip and un-gzipped testing with Varnish and stumbled upon the oddity that curl -i shows X-Cache: HIT but curl -I returns X-Cache: MISS! How this is possible, I am unsure and that is precisely my question in this post.

Here are some more details that may or may not make a difference:

The URL is usually SSL enforced (https) but both HTTP and HTTPS have been tested to receive same results
The results are consistent
Is Varnish Running site says "Yes! Sort of"

回答1:

curl sends different HTTP requests to the server (or Varnish in this case) when you use the -I option. Normally, curl will send a GET request, but when you specify -I, it sends HEAD instead (essentially telling the server to just send the header, not the actual content). I'm not particularly familiar with Varnish, but it appears to normally cache both GET and HEAD requests -- but in your case it might be configured to do something different, or the backend server may be triggering a difference... In any case, I'm pretty sure it's GET vs. HEAD that's making the cache respond differently with -i vs. -I.