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PR: 38819 git-svn-id: https://svn.apache.org/repos/asf/httpd/httpd/trunk@561458 13f79535-47bb-0310-9956-ffa450edef68
374 lines
16 KiB
XML
374 lines
16 KiB
XML
<?xml version="1.0"?>
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<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
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<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
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<!-- $LastChangedRevision$ -->
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<!--
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Licensed to the Apache Software Foundation (ASF) under one or more
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contributor license agreements. See the NOTICE file distributed with
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this work for additional information regarding copyright ownership.
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The ASF licenses this file to You under the Apache License, Version 2.0
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(the "License"); you may not use this file except in compliance with
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the License. You may obtain a copy of the License at
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http://www.apache.org/licenses/LICENSE-2.0
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Unless required by applicable law or agreed to in writing, software
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distributed under the License is distributed on an "AS IS" BASIS,
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WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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See the License for the specific language governing permissions and
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limitations under the License.
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-->
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<modulesynopsis metafile="mod_headers.xml.meta">
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<name>mod_headers</name>
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<description>Customization of HTTP request and response
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headers</description>
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<status>Extension</status>
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<sourcefile>mod_headers.c</sourcefile>
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<identifier>headers_module</identifier>
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<summary>
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<p>This module provides directives to control and modify HTTP
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request and response headers. Headers can be merged, replaced
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or removed.</p>
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</summary>
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<section id="order"><title>Order of Processing</title>
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<p>The directives provided by <module>mod_headers</module> can
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occur almost anywhere within the server configuration, and can be
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limited in scope by enclosing them in <a
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href="../sections.html">configuration sections</a>.</p>
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<p>Order of processing is important and is affected both by the
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order in the configuration file and by placement in <a
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href="../sections.html#mergin">configuration sections</a>. These
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two headers have a different effect if reversed:</p>
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<example>
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RequestHeader append MirrorID "mirror 12"<br />
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RequestHeader unset MirrorID
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</example>
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<p>This way round, the <code>MirrorID</code> header is not set. If
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reversed, the MirrorID header is set to "mirror 12".</p>
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</section>
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<section id="early"><title>Early and Late Processing</title>
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<p><module>mod_headers</module> can be applied either early or late
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in the request. The normal mode is late, when Request Headers are
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set immediately before running the content generator and Response
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Headers just as the response is sent down the wire. Always use
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Late mode in an operational server.</p>
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<p>Early mode is designed as a test/debugging aid for developers.
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Directives defined using the <code>early</code> keyword are set
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right at the beginning of processing the request. This means
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they can be used to simulate different requests and set up test
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cases, but it also means that headers may be changed at any time
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by other modules before generating a Response.</p>
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<p>Because early directives are processed before the request path's
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configuration is traversed, early headers can only be set in a
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main server or virtual host context. Early directives cannot depend
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on a request path, so they will fail in contexts such as
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<code><Directory></code> or <code><Location></code>.</p>
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</section>
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<section id="examples"><title>Examples</title>
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<ol>
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<li>
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Copy all request headers that begin with "TS" to the
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response headers:
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<example>
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Header echo ^TS
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</example>
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</li>
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<li>
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Add a header, <code>MyHeader</code>, to the response including a
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timestamp for when the request was received and how long it
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took to begin serving the request. This header can be used by
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the client to intuit load on the server or in isolating
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bottlenecks between the client and the server.
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<example>
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Header add MyHeader "%D %t"
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</example>
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<p>results in this header being added to the response:</p>
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<example>
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MyHeader: D=3775428 t=991424704447256
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</example>
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</li>
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<li>
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Say hello to Joe
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<example>
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Header add MyHeader "Hello Joe. It took %D microseconds \<br />
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for Apache to serve this request."
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</example>
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<p>results in this header being added to the response:</p>
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<example>
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MyHeader: Hello Joe. It took D=3775428 microseconds for Apache
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to serve this request.
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</example>
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</li>
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<li>
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Conditionally send <code>MyHeader</code> on the response if and
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only if header "MyRequestHeader" is present on the request. This
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is useful for constructing headers in response to some client
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stimulus. Note that this example requires the services of the
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<module>mod_setenvif</module> module.
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<example>
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SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
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Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader<br />
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</example>
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<p>If the header <code>MyRequestHeader: value</code> is present on
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the HTTP request, the response will contain the following header:</p>
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<example>
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MyHeader: D=3775428 t=991424704447256 mytext
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</example>
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</li>
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<li>Enable DAV to work with Apache running HTTP through SSL hardware
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(<a href="http://svn.haxx.se/users/archive-2006-03/0549.shtml"
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>problem description</a>) by replacing <var>https:</var> with
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<var>http:</var> in the <var>Destination</var> header:
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<example>
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RequestHeader edit Destination ^https: http: early
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</example>
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</li>
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</ol>
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</section>
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<directivesynopsis>
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<name>RequestHeader</name>
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<description>Configure HTTP request headers</description>
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<syntax>RequestHeader set|append|add|unset|edit <var>header</var>
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[<var>value</var>] [<var>replacement</var>] [early|env=[!]<var>variable</var>]</syntax>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context><context>.htaccess</context></contextlist>
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<override>FileInfo</override>
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<usage>
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<p>This directive can replace, merge, change or remove HTTP request
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headers. The header is modified just before the content handler
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is run, allowing incoming headers to be modified. The action it
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performs is determined by the first argument. This can be one
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of the following values:</p>
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<dl>
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<dt><code>set</code></dt>
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<dd>The request header is set, replacing any previous header
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with this name</dd>
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<dt><code>append</code></dt>
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<dd>The request header is appended to any existing header of the
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same name. When a new value is merged onto an existing header
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it is separated from the existing header with a comma. This
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is the HTTP standard way of giving a header multiple
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values.</dd>
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<dt><code>add</code></dt>
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<dd>The request header is added to the existing set of headers,
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even if this header already exists. This can result in two
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(or more) headers having the same name. This can lead to
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unforeseen consequences, and in general <code>append</code> should be
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used instead.</dd>
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<dt><code>unset</code></dt>
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<dd>The request header of this name is removed, if it exists. If
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there are multiple headers of the same name, all will be removed.
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<var>value</var> must be omitted.</dd>
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<dt><code>edit</code></dt>
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<dd>If this request header exists, its value is transformed according
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to a <glossary ref="regex">regular expression</glossary>
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search-and-replace. The <var>value</var> argument is a <glossary
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ref="regex">regular expression</glossary>, and the <var>replacement</var>
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is a replacement string, which may contain backreferences.</dd>
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</dl>
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<p>This argument is followed by a header name, which can
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include the final colon, but it is not required. Case is
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ignored. For <code>add</code>, <code>append</code> and
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<code>set</code> a <var>value</var> is given as the third argument. If a
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<var>value</var> contains spaces, it should be surrounded by double
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quotes. For unset, no <var>value</var> should be given.
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<var>value</var> may be a character string, a string containing format
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specifiers or a combination of both. The supported format specifiers
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are the same as for the <directive module="mod_headers">Header</directive>,
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please have a look there for details. For <code>edit</code> both
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a <var>value</var> and a <var>replacement</var> are required, and are
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a <glossary ref="regex">regular expression</glossary> and a
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replacement string respectively.</p>
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<p>The <directive>RequestHeader</directive> directive may be followed by
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an additional argument, which may be used to specify conditions under
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which the action will be taken, or may be the keyword <code>early</code>
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to specify <a href="#early">early processing</a>. If the
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<a href="../env.html">environment
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variable</a> specified in the <code>env=<var>...</var></code> argument
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exists (or if the environment variable does not exist and
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<code>env=!<var>...</var></code> is specified) then the action specified
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by the <directive>RequestHeader</directive> directive will take effect.
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Otherwise, the directive will have no effect on the request.</p>
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<p>Except in <a href="#early">early</a> mode, the
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<directive>RequestHeader</directive> directive is processed
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just before the request is run by its handler in the fixup phase.
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This should allow headers generated by the browser, or by Apache
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input filters to be overridden or modified.</p>
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</usage>
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</directivesynopsis>
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<directivesynopsis>
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<name>Header</name>
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<description>Configure HTTP response headers</description>
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<syntax>Header [<var>condition</var>] set|append|add|unset|echo|edit
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<var>header</var> [<var>value</var>] [early|env=[!]<var>variable</var>]</syntax>
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<contextlist><context>server config</context><context>virtual host</context>
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<context>directory</context><context>.htaccess</context></contextlist>
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<override>FileInfo</override>
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<usage>
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<p>This directive can replace, merge or remove HTTP response
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headers. The header is modified just after the content handler
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and output filters are run, allowing outgoing headers to be
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modified.</p>
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<p>The optional <var>condition</var> can be either <code>onsuccess</code>
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or <code>always</code>. It determines, which internal header table should be
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operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code>
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status codes and <code>always</code> for all status codes (including
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<code>2<var>xx</var></code>). Especially if you want to unset headers
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set by certain modules, you should try out, which table is affected.</p>
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<p>The action it performs is determined by the second
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argument. This can be one of the following values:</p>
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<dl>
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<dt><code>set</code></dt>
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<dd>The response header is set, replacing any previous header
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with this name. The <var>value</var> may be a format string.</dd>
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<dt><code>append</code></dt>
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<dd>The response header is appended to any existing header of
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the same name. When a new value is merged onto an existing
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header it is separated from the existing header with a comma.
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This is the HTTP standard way of giving a header multiple values.</dd>
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<dt><code>add</code></dt>
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<dd>The response header is added to the existing set of headers,
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even if this header already exists. This can result in two
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(or more) headers having the same name. This can lead to
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unforeseen consequences, and in general "append" should be
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used instead.</dd>
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<dt><code>unset</code></dt>
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<dd>The response header of this name is removed, if it exists.
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If there are multiple headers of the same name, all will be
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removed. <var>value</var> must be omitted.</dd>
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<dt><code>echo</code></dt>
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<dd>Request headers with this name are echoed back in the
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response headers. <var>header</var> may be a
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<glossary ref="regex">regular expression</glossary>.
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<var>value</var> must be omitted.</dd>
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<dt><code>edit</code></dt>
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<dd>If this request header exists, its value is transformed according
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to a <glossary ref="regex">regular expression</glossary>
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search-and-replace. The <var>value</var> argument is a <glossary
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ref="regex">regular expression</glossary>, and the <var>replacement</var>
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is a replacement string, which may contain backreferences.</dd>
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</dl>
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<p>This argument is followed by a <var>header</var> name, which
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can include the final colon, but it is not required. Case is
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ignored for <code>set</code>, <code>append</code>, <code>add</code>
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and <code>unset</code>. The <var>header</var> name for <code>echo</code>
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is case sensitive and may be a <glossary ref="regex">regular
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expression</glossary>.</p>
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<p>For <code>add</code>, <code>append</code> and <code>set</code> a
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<var>value</var> is specified as the third argument. If <var>value</var>
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contains spaces, it should be surrounded by doublequotes.
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<var>value</var> may be a character string, a string containing format
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specifiers or a combination of both. The following format specifiers
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are supported in <var>value</var>:</p>
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<table border="1" style="zebra">
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<columnspec><column width=".25"/><column width=".75"/></columnspec>
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<tr><th>Format</th><th>Description</th></tr>
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<tr><td><code>%%</code></td>
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<td>The percent sign</td></tr>
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<tr><td><code>%t</code></td>
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<td>The time the request was received in Universal Coordinated Time
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since the epoch (Jan. 1, 1970) measured in microseconds. The value
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is preceded by <code>t=</code>.</td></tr>
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<tr><td><code>%D</code></td>
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<td>The time from when the request was received to the time the
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headers are sent on the wire. This is a measure of the duration
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of the request. The value is preceded by <code>D=</code>.</td></tr>
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<tr><td><code>%{FOOBAR}e</code></td>
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<td>The contents of the <a href="../env.html">environment
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variable</a> <code>FOOBAR</code>.</td></tr>
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<tr><td><code>%{FOOBAR}s</code></td>
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<td>The contents of the <a href="mod_ssl.html#envvars">SSL environment
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variable</a> <code>FOOBAR</code>, if <module>mod_ssl</module> is enabled.</td></tr>
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</table>
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<note><title>Note</title>
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<p>The <code>%s</code> format specifier is only available in
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Apache 2.1 and later; it can be used instead of <code>%e</code>
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to avoid the overhead of enabling <code>SSLOptions
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+StdEnvVars</code>. If <code>SSLOptions +StdEnvVars</code> must
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be enabled anyway for some other reason, <code>%e</code> will be
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more efficient than <code>%s</code>.</p>
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</note>
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<p>For <code>edit</code> there is both a <var>value</var> argument
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which is a <glossary ref="regex">regular expression</glossary>,
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and an additional <var>replacement</var> string.</p>
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<p>The <directive>Header</directive> directive may be followed by an
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an additional argument, which may be used to specify conditions under
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which the action will be taken, or may be the keyword <code>early</code>
|
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to specify <a href="#early">early processing</a>. If the
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<a href="../env.html">environment variable</a> specified in the
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<code>env=<var>...</var></code> argument exists (or if the environment
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variable does not exist and <code>env=!<var>...</var></code> is specified)
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then the action specified by the <directive>Header</directive> directive
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will take effect. Otherwise, the directive will have no effect
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on the request.</p>
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<p>Except in <a href="#early">early</a> mode, the
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<directive>Header</directive> directives are processed just
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before the response is sent to the network. These means that it is
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possible to set and/or override most headers, except for those headers
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added by the header filter.</p>
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</usage>
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</directivesynopsis>
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</modulesynopsis>
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