Cache-Control headers repeated; valid or not? (Ngi

问题:

I've got a resource in my Nginx that is configured like this:

location ~ foo\.js$ {
    add_header Cache-Control public;
    expires 1d;
}

If I open this with Firebug and look at the headers it shows this:

Cache-Control   max-age=86400, public

The site is using HTTPS so I want to make sure I get it right because apparently browsers don't cache it unless it's max-age>0 AND public. See this

But what happens with my Nginx when I use curl -Ik https://... is that it says:

...
Expires: Sat, 22 Jan 2011 18:23:36 GMT
Cache-Control: max-age=86400
Cache-Control: public
...

It repeats the Cache-Control header! Clearly Firebug doesn't mind. But is it right?

Is there a perhaps a better way to set Expires and Cache-Control (with public) in one just two lines?

回答1:

Yes, it's valid and equivalent to use multiple Cache-Control headers.

From the HTTP 1.1 spec:

Multiple message-header fields with the same field-name MAY be present in a message if and only if the entire field-value for that header field is defined as a comma-separated list [i.e., #(values)]. It MUST be possible to combine the multiple header fields into one "field-name: field-value" pair, without changing the semantics of the message, by appending each subsequent field-value to the first, each separated by a comma.

It's easy to verify that this provision applies to the Cache-Control header because of how it's defined:

Cache-Control = "Cache-Control" ":" 1#cache-directive

To understand how to interpret the line above, see the spec's notational conventions. The 1# means "a comma-separated list of one or more".

回答2:

I was having the same problem on different configuration. What worked for me is to change the order of two lines that set headers and place header setting just after "server" opening bracket. This will set headers to all objects perhaps but maybe will work in you "if" statement too:

server {
   expires     31d;
   add_header  Cache-Control public;

   server_name example.com
   ...
}

It seems that add_header sends header before expires directive to have time to change it.