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Add documentation for the new headers module (mod_headers) 


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<!DOCTYPE HTML PUBLIC "-//IETF//DTD HTML 2.0//EN">

<HTML>

<HEAD>

<TITLE>Apache module mod_headers</TITLE>

</HEAD>



<BODY>

<!--#include virtual="header.html" -->

<h1>Headers Module</h1>



The optional headers module allows for the customisation of HTTP

response headers. Headers can be merged, replaced or removed. The

directives described in this document are only available if Apache is

compiled with <b>mod_headers.c</b>.



<hr>



<h2>Directive</h2>

<ul>

<li><A HREF="#header">Header</A>

</ul>



<hr>



<A name="header"><h2>Header</h2></A>

<strong>Sytnax:</strong> Header [ set | append | add ] <em>header</em> <em>value</em><br>

<strong>Sytnax:</strong> Header unset <em>header</em><br>

<strong>Context:</strong> server config, virtual host, access.conf, .htaccess<br>

<strong>Status:</strong> optional<br>

<strong>Module:</strong> mod_header<p>



This directive can replace, merge or remove HTTP response headers. The

action it performs is determined by the first argument. This can be one

of the following values:



<ul>

<li><b>set</b><br>

  The response header is set, replacing any previous header with this name



<li><b>append</b><br>

  The response header is appended to any existing header of the same

  name. When a new value is merged onto an existing header it is

  separated from the existing header with a comma. This is the HTTP standard

  way of giving a header multiple values.



<li><b>add</b><br>

  The response header is added to the existing set of headers, even if

  this header already exists. This can result in two (or more) headers

  having the same name. This can lead to unforseen consequences, and in

  general "append" should be used instead.



<li><b>unset</b><br>

  The response header of this name is removed, if it exists. If there are

  multiple headers of the same name, only the first one set will be removed.

</ul>



This argument is followed by a header name, which can include the

final colon, but it is not required. Case is ignored. For

add, append and set a value is given as the third argument. If this

value contains spaces, it should be surrounded by double quotes.

For unset, no value should be given.



<h3>Order of Processing</h3>



The Header directive can occur almost anywhere within the server

configuration. It is valid in the main server config and virtual host

sections, inside &lt;Directory&gt;, &lt;Location&gt; and &lt;Files&gt;

sections, and within .htaccess files.

<p>

The Header directives are processed in the following order:

<ol>

<li>main server

<li>virtual host

<li>&lt;Directory&gt; sections and .htaccess

<li>&lt;Location&gt;

<li>&lt;Files&gt;

</ol>



Order is important. These two headers have a different effect if reversed:

<pre>

Header append Author "John P. Doe"

Header unset Author

</pre>



This way round, the Author header is not set. If reversed, the Author

header is set to "John P. Doe".

<p>



The Header directives are processed just before the response is sent

by its handler. These means that some headers that are added just

before the response is sent cannot be unset or overridden. This

includes headers such as "Date" and "Server".

<P>



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