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<title>mod_headers - Apache HTTP Server</title>
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<p class="apache">Apache HTTP Server Version 2.3</p>
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<a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Modules</a></div>
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<div id="preamble"><h1>Apache Module mod_headers</h1>
<div class="toplang">
<p><span>Available Languages: </span><a href="/en/mod/mod_headers.html" title="English"> en </a> |
<a href="/ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
<a href="/ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
</div>
<table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Customization of HTTP request and response
headers</td></tr>
<tr><th><a href="module-dict.html#ModuleIdentifier">Module�Identifier:</a></th><td>headers_module</td></tr>
<tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td><code class="directive"><a href="#requestheader">RequestHeader</a></code>
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">
</ul>
<h3>Topics</h3>
<ul id="topics">
</ul></div>
<div class="section">
<h2><a name="order" id="order">Order of Processing</a></h2>
<p>The directives provided by <code class="module"><a href="/mod/mod_headers.html">mod_headers</a></code> can
occur almost anywhere within the server configuration, and can be
<p>Order of processing is important and is affected both by the
order in the configuration file and by placement in <a href="/sections.html#mergin">configuration sections</a>. 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 <code>MirrorID</code> header is not set. If
reversed, the MirrorID header is set to "mirror 12".</p>
<div class="section">
<h2><a name="early" id="early">Early and Late Processing</a></h2>
<p><code class="module"><a href="/mod/mod_headers.html">mod_headers</a></code> can be applied either early or late
in the request. The normal mode is late, when Request Headers are
set immediately before running the content generator and Response
Headers just as the response is sent down the wire. Always use
Late mode in an operational server.</p>
Directives defined using the <code>early</code> keyword are set
right at the beginning of processing the request. This means
they can be used to simulate different requests and set up test
cases, but it also means that headers may be changed at any time
by other modules before generating a Response.</p>
<p>Because early directives are processed before the request path's
configuration is traversed, early headers can only be set in a
main server or virtual host context. Early directives cannot depend
on a request path, so they will fail in contexts such as
<code><Directory></code> or <code><Location></code>.</p>
<div class="section">
<h2><a name="examples" id="examples">Examples</a></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, <code>MyHeader</code>, 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>
<p>results in this header being added to the response:</p>
<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 \<br />
for Apache to serve this request."
</code></p></div>
<p>results in this header being added to the response:</p>
<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 <code>MyHeader</code> 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
<div class="example"><p><code>
SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader<br />
</code></p></div>
<p>If the header <code>MyRequestHeader: value</code> is present on
the HTTP request, the response will contain the following header:</p>
<div class="example"><p><code>
MyHeader: D=3775428 t=991424704447256 mytext
</code></p></div>
</li>
</ol>
</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><code>Header [<var>condition</var>] set|append|add|unset|echo
<var>header</var> [<var>value</var>] [early|env=[!]<var>variable</var>]</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</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.</p>
<p>The optional <var>condition</var> can be either <code>onsuccess</code>
or <code>always</code>. It determines, which internal header table should be
operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code>
status codes and <code>always</code> for all status codes (including
<code>2<var>xx</var></code>). Especially if you want to unset headers
set by certain modules, you should try out, which table is affected.</p>
<p>The action it performs is determined by the second
argument. This can be one of the following values:</p>
<dl>
<dt><code>set</code></dt>
<dd>The response header is set, replacing any previous header
with this name. The <var>value</var> may be a format string.</dd>
<dt><code>append</code></dt>
<dd>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.</dd>
<dt><code>add</code></dt>
<dd>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.</dd>
<dt><code>unset</code></dt>
<dd>The response header of this name is removed, if it exists.
If there are multiple headers of the same name, all will be
removed. <var>value</var> must be omitted.</dd>
<dt><code>echo</code></dt>
<dd>Request headers with this name are echoed back in the
response headers. <var>header</var> may be a
<var>value</var> must be omitted.</dd>
</dl>
<p>This argument is followed by a <var>header</var> name, which
can include the final colon, but it is not required. Case is
ignored for <code>set</code>, <code>append</code>, <code>add</code>
and <code>unset</code>. The <var>header</var> name for <code>echo</code>
is case sensitive and may be a <a class="glossarylink" href="/glossary.html#regex" title="see glossary">regular
expression</a>.</p>
<p>For <code>add</code>, <code>append</code> and <code>set</code> a
<var>value</var> is specified as the third argument. If <var>value</var>
contains spaces, it should be surrounded by doublequotes.
<var>value</var> may be a character string, a string containing format
specifiers or a combination of both. The following format specifiers
are supported in <var>value</var>:</p>
<table class="bordered"><tr class="header"><th>Format</th><th>Description</th></tr>
<tr><td><code>%%</code></td>
<td>The percent sign</td></tr>
<tr class="odd"><td><code>%t</code></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 <code>t=</code>.</td></tr>
<tr><td><code>%D</code></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 <code>D=</code>.</td></tr>
<tr class="odd"><td><code>%{FOOBAR}e</code></td>
variable</a> <code>FOOBAR</code>.</td></tr>
<tr><td><code>%{FOOBAR}s</code></td>
variable</a> <code>FOOBAR</code>, if <code class="module"><a href="/mod/mod_ssl.html">mod_ssl</a></code> is enabled.</td></tr>
</table>
<div class="note"><h3>Note</h3>
<p>The <code>%s</code> format specifier is only available in
Apache 2.1 and later; it can be used instead of <code>%e</code>
to avoid the overhead of enabling <code>SSLOptions
+StdEnvVars</code>. If <code>SSLOptions +StdEnvVars</code> must
be enabled anyway for some other reason, <code>%e</code> will be
more efficient than <code>%s</code>.</p>
</div>
<p>The <code class="directive">Header</code> directive may be followed by an
an additional argument, which may be used to specify conditions under
which the action will be taken, or may be the keyword <code>early</code>
to specify <a href="#early">early processing</a>. If the
<code>env=<var>...</var></code> argument exists (or if the environment
variable does not exist and <code>env=!<var>...</var></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>Except in <a href="#early">early</a> mode, the
<code class="directive">Header</code> directives are processed just
before the response is sent to the network. These means that it is
added by the header filter.</p>
</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><code>RequestHeader set|append|add|unset <var>header</var>
[<var>value</var>] [early|env=[!]<var>variable</var>]</code></td></tr>
<tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</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>
<dl>
<dt><code>set</code></dt>
<dd>The request header is set, replacing any previous header
with this name</dd>
<dt><code>append</code></dt>
<dd>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.</dd>
<dt><code>add</code></dt>
<dd>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 <code>append</code> should be
used instead.</dd>
<dt><code>unset</code></dt>
<dd>The request header of this name is removed, if it exists. If
there are multiple headers of the same name, all will be removed.
<var>value</var> must be omitted.</dd>
</dl>
<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 <var>value</var> is given as the third argument. If
<var>value</var> contains spaces, it should be surrounded by double
quotes. For unset, no <var>value</var> should be given.
<var>value</var> may be a character string, a string containing format
specifiers or a combination of both. The supported format specifiers
are the same as for the <code class="directive"><a href="#header">Header</a></code>,
please have a look there for details.</p>
<p>The <code class="directive">RequestHeader</code> directive may be followed by
an additional argument, which may be used to specify conditions under
which the action will be taken, or may be the keyword <code>early</code>
to specify <a href="#early">early processing</a>. If the
<a href="/env.html">environment
variable</a> specified in the <code>env=<var>...</var></code> argument
exists (or if the environment variable does not exist and
<code>env=!<var>...</var></code> is specified) then the action specified
by the <code class="directive">RequestHeader</code> directive will take effect.
Otherwise, the directive will have no effect on the request.</p>
<p>Except in <a href="#early">early</a> mode, 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>
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<p><span>Available Languages: </span><a href="/en/mod/mod_headers.html" title="English"> en </a> |
<a href="/ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
<a href="/ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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