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--><title>mod_headers - Apache HTTP Server</title><link href="/style/css/manual.css" rel="stylesheet" media="all" type="text/css" title="Main stylesheet" /><link href="/style/css/manual-loose-100pc.css" rel="alternate stylesheet" media="all" type="text/css" title="No Sidebar - Default font size" /><link href="/style/css/manual-print.css" rel="stylesheet" media="print" type="text/css" /><link href="/images/favicon.ico" rel="shortcut icon" /></head><body><div id="page-header"><p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="/faq/">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p><p class="apache">Apache HTTP Server Version 2.0</p><img alt="" src="/images/feather.gif" /></div><div class="up"><a href="./"><img title="<-" alt="<-" src="/images/left.gif" /></a></div><div id="path"><a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs-project/">Documentation</a> > <a href="../">Version 2.0</a> > <a href="./">Modules</a></div><div id="page-content"><div id="preamble"><h1>Apache Module mod_headers</h1><table class="module"><tr><th><a href="module-dict.html#Description">Description:
</a></th><td>Customization of HTTP request
</a></th><td>Extension</td></tr><tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:
</a></th><td>RequestHeader is available only in Apache 2.0</td></tr></table><h3>Summary</h3>
<p>This module provides directives to control and modify HTTP
request and response headers. Headers can be merged, replaced
or removed.</p>
</div><div id="quickview"><h3 class="directives">Directives</h3><ul id="toc"><li><img alt="" src="/images/down.gif" /> <a href="#header">Header</a></li><li><img alt="" src="/images/down.gif" /> <a href="#requestheader">RequestHeader</a></li></ul><h3>Topics</h3><ul id="topics"><li><img alt="" src="/images/down.gif" /> Order of Processing</li><li><img alt="" src="/images/down.gif" /> Example</li></ul></div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="section"><h2>Order of Processing</h2>
<p>The directives provided by mod_header can occur almost
anywhere within the server configuration. They are valid in the
main server config and virtual host sections, inside
<Directory>, <Location> and <Files> sections,
and within .htaccess files.</p>
<p>The directives are processed in the following order:</p>
<ol>
<li>main server</li>
<li>virtual host</li>
<li><Directory> sections and .htaccess</li>
<li><Location></li>
<li><Files></li>
</ol>
<p>Order is important. These two headers have a different
effect if reversed:</p>
<div class="example"><p><code>
RequestHeader append MirrorID "mirror 12"<br />
RequestHeader unset MirrorID
</code></p></div>
<p>This way round, the MirrorID header is not set. If reversed,
the MirrorID header is set to "mirror 12".</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="section"><h2>Example</h2>
<ol>
<li>Copy all request headers that begin with "TS" to the
response headers:
<div class="example"><p><code>
Header echo ^TS*
</code></p></div></li>
<li>Add a header, MyHeader, to the response including a
timestamp for when the request was received and how long it
took to begin serving the request. This header can be used by
the client to intuit load on the server or in isolating
bottlenecks between the client and the server.
<div class="example"><p><code>
Header add MyHeader "%D %t"
</code></p></div>
results in this header being added to the response:
<div class="example"><p><code>
MyHeader: D=3775428 t=991424704447256
</code></p></div>
</li>
<li>Say hello to Joe
<div class="example"><p><code>
Header add MyHeader "Hello Joe. It took %D microseconds for Apache to serve this request."
</code></p></div>
results in this header being added to the response:
<div class="example"><p><code>
MyHeader: Hello Joe. It took D=3775428 microseconds for Apache to serve this request.
</code></p></div>
</li>
<li>Conditionally send MyHeader on the response if and only
if header "MyRequestHeader" is present on the request. This
is useful for constructing headers in response to some client
stimulus. Note that this example requires the services of the
mod_setenvif module.
<div class="example"><p><code>
SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader
</code></p></div>
If the header "MyRequestHeader: value" is present on the
HTTP request, the response will contain the following
header:
<div class="example"><p><code>
MyHeader: D=3775428 t=991424704447256 mytext
</code></p></div>
</li>
</ol>
</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2><table class="directive"><tr><th><a href="directive-dict.html#Description">Description:
</a></th><td>Configure HTTP response headers</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
</a></th><td>Header set|append|add|unset|echo <em>header</em>
</a></th><td>server config, virtual host, directory, .htaccess</td></tr><tr><th><a href="directive-dict.html#Override">Override:
</a></th><td>mod_headers</td></tr></table>
<p>This directive can replace, merge or remove HTTP response
headers. The header is modified just after the content handler
and output filters are run, allowing outgoing headers to be
modified. The action it performs is determined by the first
argument. This can be one of the following values:</p>
<ul>
<li><strong>set</strong><br />
The response header is set, replacing any previous header
with this name. The <em>value</em> may be a format
string.</li>
<li><strong>append</strong><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>
<li><strong>add</strong><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
unforeseen consequences, and in general "append" should be
used instead.</li>
<li><strong>unset</strong><br />
The response header of this name is removed, if it exists.
If there are multiple headers of the same name, all will be
removed.</li>
<li><strong>echo</strong><br />
Request headers with this name are echoed back in the
response headers. <em>header</em> may be a regular
expression.</li>
</ul>
<p>This argument is followed by a <em>header</em> name, which
can include the final colon, but it is not required. Case is
ignored for set, append, add and unset. The <em>header</em>
name for echo is case sensitive and may be a regular
expression.</p>
<p>For <code>add</code>, <code>append</code> and
<code>set</code> a <em>value</em> is specified as the third
argument. If <em>value</em> contains spaces, it should be
surrounded by doublequotes. <em>value</em> may be a character
string, a string containing format specifiers or a combination
of both. The following format specifiers are supported in
<em>value</em>:</p>
<table>
<tr><td>%t: </td> <td>The time the request was received in Universal
Coordinated Time since the epoch (Jan. 1, 1970) measured in
microseconds. The value is preceded by "t=".</td></tr>
<tr><td>%D: </td> <td>The time from when the request was received to
the time the headers are sent on the wire. This is a measure of the
duration of the request. The value is preceded by "D=".</td></tr>
variable</a> FOOBAR.</td></tr>
</table>
<p>When the <code class="directive">Header</code> directive is used with the
<code>add</code>, <code>append</code>, or <code>set</code>
argument, a fourth argument may be used to specify conditions
under which the action will be taken. If the <a href="/env.html">environment variable</a> specified in the
<code>env=...</code> argument exists (or if the environment
variable does not exist and <code>env=!...</code> is specified)
then the action specified by the <code class="directive">Header</code> directive
will take effect. Otherwise, the directive will have no effect
on the request.</p>
<p>The Header directives are processed just before the response
is sent to the network. These means that it is possible to set
the header filter.</p>
</div><div class="top"><a href="#page-header"><img alt="top" src="/images/up.gif" /></a></div><div class="directive-section"><h2><a name="RequestHeader" id="RequestHeader">RequestHeader</a> <a name="requestheader" id="requestheader">Directive</a></h2><table class="directive"><tr><th><a href="directive-dict.html#Description">Description:
</a></th><td>Configure HTTP request headers</td></tr><tr><th><a href="directive-dict.html#Syntax">Syntax:
</a></th><td>RequestHeader set|append|add|unset <em>header</em>
</a></th><td>server config, virtual host, directory, .htaccess</td></tr><tr><th><a href="directive-dict.html#Override">Override:
</a></th><td>mod_headers</td></tr></table>
<p>This directive can replace, merge or remove HTTP request
headers. The header is modified just before the content handler
is run, allowing incoming headers to be modified. The action it
performs is determined by the first argument. This can be one
of the following values:</p>
<ul>
<li><strong>set</strong><br />
The request header is set, replacing any previous header
with this name</li>
<li><strong>append</strong><br />
The request 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>
<li><strong>add</strong><br />
The request 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
unforeseen consequences, and in general "append" should be
used instead.</li>
<li><strong>unset</strong><br />
The request header of this name is removed, if it exists. If
there are multiple headers of the same name, all will be
removed.</li>
</ul>
<p>This argument is followed by a header name, which can
include the final colon, but it is not required. Case is
ignored. For <code>add</code>, <code>append</code> and
<code>set</code> a <em>value</em> is given as the third argument. If
<em>value</em> contains spaces, it should be surrounded by double
quotes. For unset, no <em>value</em> should be given.</p>
<p>The <code class="directive">RequestHeader</code> directive is processed
just before the request is run by its handler in the fixup phase.
This should allow headers generated by the browser, or by Apache
input filters to be overridden or modified.</p>
</div></div><div id="footer"><p class="apache">Maintained by the <a href="http://httpd.apache.org/docs-project/">Apache HTTP Server Documentation Project</a></p><p class="menu"><a href="/mod/">Modules</a> | <a href="/mod/directives.html">Directives</a> | <a href="/faq/">FAQ</a> | <a href="/glossary.html">Glossary</a> | <a href="/sitemap.html">Sitemap</a></p></div></body></html>