=encoding utf-8

=head1 NAME

ngx_http_headers_module - Module ngx_http_headers_module




=head1



The C<ngx_http_headers_module> module allows adding
the C<Expires> and C<Cache-Control> header
fields, and arbitrary fields, to a response header.




=head1 Example Configuration




    
    expires    24h;
    expires    modified +24h;
    expires    @24h;
    expires    0;
    expires    -1;
    expires    epoch;
    expires    $expires;
    add_header Cache-Control private;






=head1 Directives

=head2 add_header


B<syntax:> add_header I<
I<C<name>> I<C<value>>
[C<always>]>



B<context:> I<http>


B<context:> I<server>


B<context:> I<location>


B<context:> I<if in location>





Adds the specified field to a response header provided that
the response code equals 200, 201, 204, 206, 301, 302, 303, 304, or 307.
A value can contain variables.





There could be several C<add_header> directives.
These directives are inherited from the previous level if and
only if there are no
C<add_header>
directives defined on the current level.





If the C<always> parameter is specified (1.7.5),
the header field will be added regardless of the response code.







=head2 expires


B<syntax:> expires I<[C<modified>] I<C<time>>>


B<syntax:> expires I<
    C<epoch> E<verbar>
    C<max> E<verbar>
    C<off>>


B<default:> I<off>


B<context:> I<http>


B<context:> I<server>


B<context:> I<location>


B<context:> I<if in location>





Enables or disables adding or modifying the C<Expires>
and C<Cache-Control> response header fields provided that
the response code equals 200, 201, 204, 206, 301, 302, 303, 304, or 307.
A parameter can be a positive or negative
L<time|syntax>.





A time in the C<Expires> field is computed as a sum of the
current time and I<C<time>> specified in the directive.
If the C<modified> parameter is used (0.7.0, 0.6.32)
then time is computed as a sum of the file’s modification time and
I<C<time>> specified in the directive.





In addition, it is possible to specify a time of the day using
the “C<@>” prefix (0.7.9, 0.6.34):

    
    expires @15h30m;







The C<epoch> parameter corresponds to the absolute time
“C<Thu, 01 Jan 1970 00:00:01 GMT>”.
The contents of the C<Cache-Control> field depends
on the sign of the specified time:

=over




=item *

time is negative — C<Cache-Control: no-cache>.



=item *

time is positive or zero —
C<Cache-Control: max-age=I<C<t>>>,
where I<C<t>> is a time specified in the directive, in seconds.



=back







The C<max> parameter sets C<Expires>
to the value “C<Thu, 31 Dec 2037 23:55:55 GMT>”,
and C<Cache-Control> to 10 years.





The C<off> parameter disables adding or modifying the
C<Expires> and C<Cache-Control> response
header fields.





The last parameter value can contain variables (1.7.9):

    
    map $sent_http_content_type $expires {
        default         off;
        application/pdf 42d;
        ~image/         max;
    }
    
    expires $expires;