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<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/quickreference.html">Directives</a> | <a href="http://wiki.apache.org/httpd/FAQ">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p>
<p class="apache">Apache HTTP Server Version 2.5</p>
-<img alt="" src="../images/feather.gif" /></div>
+<img alt="" src="../images/feather.png" /></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/">Documentation</a> > <a href="../">Version 2.5</a> > <a href="./">Modules</a></div>
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>
+<div id="quickview"><h3>Topics</h3>
<ul id="topics">
<li><img alt="" src="../images/down.gif" /> <a href="#order">Order of Processing</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#early">Early and Late Processing</a></li>
<li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
-</ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
+</ul><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>Bugfix checklist</h3><ul class="seealso"><li><a href="https://www.apache.org/dist/httpd/CHANGES_2.4">httpd changelog</a></li><li><a href="https://bz.apache.org/bugzilla/buglist.cgi?bug_status=__open__&list_id=144532&product=Apache%20httpd-2&query_format=specific&order=changeddate%20DESC%2Cpriority%2Cbug_severity&component=mod_headers">Known issues</a></li><li><a href="https://bz.apache.org/bugzilla/enter_bug.cgi?product=Apache%20httpd-2&component=mod_headers">Report a bug</a></li></ul><h3>See also</h3>
+<ul class="seealso">
+<li><a href="#comments_section">Comments</a></li></ul></div>
+<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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
+ limited in scope by enclosing them in <a href="../sections.html">configuration sections</a>.</p>
+
+ <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 directives have a different effect if reversed:</p>
+
+ <pre class="prettyprint lang-config">RequestHeader append MirrorID "mirror 12"
+RequestHeader unset MirrorID</pre>
+
+
+ <p>This way round, the <code>MirrorID</code> 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><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 <em>Request</em> Headers are
+ set immediately before running the content generator and <em>Response</em>
+ Headers just as the response is sent down the wire. Always use
+ Late mode in an operational server.</p>
+
+ <p>Early mode is designed as a test/debugging aid for developers.
+ 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 class="directive"><a href="../mod/core.html#directory"><Directory></a></code> or
+ <code class="directive"><a href="../mod/core.html#location"><Location></a></code>.</p>
+</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
+<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:
+
+ <pre class="prettyprint lang-config">Header echo ^TS</pre>
+
+ </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.
+
+ <pre class="prettyprint lang-config">Header set MyHeader "%D %t"</pre>
+
+
+ <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
+
+ <pre class="prettyprint lang-config">Header set MyHeader "Hello Joe. It took %D microseconds for Apache to serve this request."</pre>
+
+
+ <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 <code>MyRequestHeader</code> 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
+ <code class="module"><a href="../mod/mod_setenvif.html">mod_setenvif</a></code> module.
+
+ <pre class="prettyprint lang-config">SetEnvIf MyRequestHeader myvalue HAVE_MyRequestHeader
+Header set MyHeader "%D %t mytext" env=HAVE_MyRequestHeader</pre>
+
+
+ <p>If the header <code>MyRequestHeader: myvalue</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>
+
+ <li>
+ Enable DAV to work with Apache running HTTP through SSL hardware
+ (<a href="http://svn.haxx.se/users/archive-2006-03/0549.shtml">problem
+ description</a>) by replacing <var>https:</var> with
+ <var>http:</var> in the <var>Destination</var> header:
+
+ <pre class="prettyprint lang-config">RequestHeader edit Destination ^https: http: early</pre>
+
+ </li>
+
+ <li>
+ Set the same header value under multiple nonexclusive conditions,
+ but do not duplicate the value in the final header.
+ If all of the following conditions applied to a request (i.e.,
+ if the <code>CGI</code>, <code>NO_CACHE</code> and
+ <code>NO_STORE</code> environment variables all existed for the
+ request):
+
+ <pre class="prettyprint lang-config">Header merge Cache-Control no-cache env=CGI
+Header merge Cache-Control no-cache env=NO_CACHE
+Header merge Cache-Control no-store env=NO_STORE</pre>
+
+
+ <p>then the response would contain the following header:</p>
+
+ <div class="example"><p><code>
+ Cache-Control: no-cache, no-store
+ </code></p></div>
+
+ <p>If <code>append</code> was used instead of <code>merge</code>,
+ then the response would contain the following header:</p>
+
+ <div class="example"><p><code>
+ Cache-Control: no-cache, no-cache, no-store
+ </code></p></div>
+ </li>
+ <li>
+ Set a test cookie if and only if the client didn't send us a cookie
+ <pre class="prettyprint lang-config">Header set Set-Cookie testcookie "expr=-z %{req:Cookie}"</pre>
+
+ </li>
+ <li>
+ Append a Caching header for responses with a HTTP status code of 200
+ <pre class="prettyprint lang-config">Header append Cache-Control s-maxage=600 "expr=%{REQUEST_STATUS} == 200"</pre>
+
+ </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#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
-<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
+<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
available in 2.4.10 and later</td></tr>
</table>
<p>This directive can replace, merge or remove HTTP response
<p> The optional <var>condition</var> argument determines which internal
table of responses headers this directive will operate against. Despite the
- name, the default value of <code>onsuccess</code> does <em>not</em> limit
+ name, the default value of <code>onsuccess</code> does <em>not</em> limit
an <var>action</var> to responses with a 2xx status code. Headers set under
this condition are still used when, for example, a request is <em>successfully</em>
proxied or generated by CGI, even when they have generated a failing status code.</p>
<p>When your action is a function of an existing header, you may need to specify
a condition of <code>always</code>, depending on which internal table the
original header was set in. The table that corresponds to <code>always</code> is
- used for locally generated error responses as well as successful responses.
+ used for locally generated error responses as well as successful responses.
Note also that repeating this directive with both conditions makes sense in
some scenarios because <code>always</code> is not a superset of
<code>onsuccess</code> with respect to existing headers:</p>
<code>onsuccess</code> condition.</li>
</ul>
- <p>Separately from the <var>condition</var> parameter described above, you
- can limit an action based on HTTP status codes for e.g. proxied or CGI
+ <p>Separately from the <var>condition</var> parameter described above, you
+ can limit an action based on HTTP status codes for e.g. proxied or CGI
requests. See the example that uses %{REQUEST_STATUS} in the section above.</p>
<p>The action it performs is determined by the first
<dt><code>setifempty</code></dt>
<dd>The request header is set, but only if there is no previous header
- with this name.<br />
- Available in 2.4.7 and later.</dd>
+ with this name.
+ <div class="note">
+ The Content-Type header is a special use case since there might be
+ the chance that its value have been determined but the header is not part
+ of the response when <code>setifempty</code> is evaluated.
+ It is safer to use <code>set</code> for this use case like in the
+ following example:
+ <pre class="prettyprint lang-config">Header set Content-Type "text/plain" "expr=-z %{CONTENT_TYPE}"</pre>
+
+ </div></dd>
<dt><code>unset</code></dt>
<dd>The response header of this name is removed, if it exists.
<code>add</code> a <var>value</var> is specified as the next argument.
If <var>value</var>
contains spaces, it should be surrounded by double quotes.
- <var>value</var> may be a character string, a string containing
- <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> specific format specifiers (and character
+ <var>value</var> may be a character string, a string containing
+ <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> specific format specifiers (and character
literals), or an <a href="../expr.html">ap_expr</a> expression prefixed
with <em>expr=</em></p>
-
+
<p> The following format specifiers are supported in <var>value</var>:</p>
<table class="bordered"><tr class="header"><th>Format</th><th>Description</th></tr>
<em>boolean</em> expressions such as <If>:</p>
<ul>
<li>The starting point of the grammar is 'string' rather than 'expr'.</li>
- <li>Function calls use the %{funcname:arg} syntax rather than
+ <li>Function calls use the %{funcname:arg} syntax rather than
funcname(arg).</li>
<li>Multi-argument functions are not currently accessible from this
starting point</li>
- <li>Quote the entire parameter, such as
+ <li>Quote the entire parameter, such as
<pre class="prettyprint lang-config">Header set foo-checksum "expr=%{md5:foo}"</pre>
</li>
-
+
</ul>
</div>
<dt><code>expr=<var>expression</var></code></dt>
<dd>The directive is applied if and only if <var>expression</var>
evaluates to true. Details of expression syntax and evaluation are
- documented in the <a href="../expr.html">ap_expr</a> documentation.</dd>
+ documented in the <a href="../expr.html">ap_expr</a> documentation.
+ <pre class="prettyprint lang-config"># This delays the evaluation of the condition clause compared to <If>
+Header always set CustomHeader my-value "expr=%{REQUEST_URI} =~ m#^/special_path.php$#"</pre>
+
+ </dd>
</dl>
<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. This means that it is
possible to set and/or override most headers, except for some headers
- added by the HTTP header filter. Prior to 2.2.12, it was not possible
+ added by the HTTP header filter. Prior to 2.2.12, it was not possible
to change the Content-Type header with this directive.</p>
<tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
<tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
<tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
-<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
+<tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
available in 2.4.10 and later</td></tr>
</table>
<p>This directive can replace, merge, change or remove HTTP request
input filters to be overridden or modified.</p>
</div>
-<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></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
- limited in scope by enclosing them in <a href="../sections.html">configuration sections</a>.</p>
-
- <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 directives have a different effect if reversed:</p>
-
- <pre class="prettyprint lang-config">RequestHeader append MirrorID "mirror 12"
-RequestHeader unset MirrorID</pre>
-
-
- <p>This way round, the <code>MirrorID</code> 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><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 <em>Request</em> Headers are
- set immediately before running the content generator and <em>Response</em>
- Headers just as the response is sent down the wire. Always use
- Late mode in an operational server.</p>
-
- <p>Early mode is designed as a test/debugging aid for developers.
- 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 class="directive"><a href="../mod/core.html#directory"><Directory></a></code> or
- <code class="directive"><a href="../mod/core.html#location"><Location></a></code>.</p>
-</div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
-<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:
-
- <pre class="prettyprint lang-config">Header echo ^TS</pre>
-
- </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.
-
- <pre class="prettyprint lang-config">Header set MyHeader "%D %t"</pre>
-
-
- <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
-
- <pre class="prettyprint lang-config">Header set MyHeader "Hello Joe. It took %D microseconds for Apache to serve this request."</pre>
-
-
- <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 <code>MyRequestHeader</code> 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
- <code class="module"><a href="../mod/mod_setenvif.html">mod_setenvif</a></code> module.
-
- <pre class="prettyprint lang-config">SetEnvIf MyRequestHeader myvalue HAVE_MyRequestHeader
-Header set MyHeader "%D %t mytext" env=HAVE_MyRequestHeader</pre>
-
-
- <p>If the header <code>MyRequestHeader: myvalue</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>
-
- <li>
- Enable DAV to work with Apache running HTTP through SSL hardware
- (<a href="http://svn.haxx.se/users/archive-2006-03/0549.shtml">problem
- description</a>) by replacing <var>https:</var> with
- <var>http:</var> in the <var>Destination</var> header:
-
- <pre class="prettyprint lang-config">RequestHeader edit Destination ^https: http: early</pre>
-
- </li>
-
- <li>
- Set the same header value under multiple nonexclusive conditions,
- but do not duplicate the value in the final header.
- If all of the following conditions applied to a request (i.e.,
- if the <code>CGI</code>, <code>NO_CACHE</code> and
- <code>NO_STORE</code> environment variables all existed for the
- request):
-
- <pre class="prettyprint lang-config">Header merge Cache-Control no-cache env=CGI
-Header merge Cache-Control no-cache env=NO_CACHE
-Header merge Cache-Control no-store env=NO_STORE</pre>
-
-
- <p>then the response would contain the following header:</p>
-
- <div class="example"><p><code>
- Cache-Control: no-cache, no-store
- </code></p></div>
-
- <p>If <code>append</code> was used instead of <code>merge</code>,
- then the response would contain the following header:</p>
-
- <div class="example"><p><code>
- Cache-Control: no-cache, no-cache, no-store
- </code></p></div>
- </li>
- <li>
- Set a test cookie if and only if the client didn't send us a cookie
- <pre class="prettyprint lang-config">Header set Set-Cookie testcookie "expr=-z %{req:Cookie}"</pre>
-
- </li>
- <li>
- Append a Caching header for responses with a HTTP status code of 200
- <pre class="prettyprint lang-config">Header append Cache-Control s-maxage=600 "expr=%{REQUEST_STATUS} == 200"</pre>
-
- </li>
-
- </ol>
-</div>
</div>
<div class="bottomlang">
<p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English"> en </a> |
}
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-<p class="apache">Copyright 201
5 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
+<p class="apache">Copyright 201
7 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
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