Cache-Control headers repeated; valid or not? (Nginx)

Question

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

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

<

Answer 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".