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| <p class="apache">Apache HTTP Server Version 2.5</p> | |
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| <div id="preamble"><h1>Apache Module mod_headers</h1> | |
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| <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#Status">Status:</a></th><td>Extension</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#SourceFile">Source File:</a></th><td>mod_headers.c</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>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><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></div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="section"> | |
| <h2 id="order">Order of Processing <a title="Permanent link" href="#order" class="permalink">¶</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#merging">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 id="early">Early and Late Processing <a title="Permanent link" href="#early" class="permalink">¶</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 id="examples">Examples <a title="Permanent link" href="#examples" class="permalink">¶</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 id="header"><span id="Header">Header</span> Directive <a title="Permanent link" href="#header" class="permalink">¶</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>] add|append|echo|edit|edit*|merge|set|setifempty|unset|note | |
| <var>header</var> [[expr=]<var>value</var> [<var>replacement</var>] | |
| [early|env=[!]<var>varname</var>|expr=<var>expression</var>]] | |
| </code></td></tr> | |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> | |
| <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 | |
| available in 2.4.10 and later</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> argument determines which internal | |
| table of responses headers this directive will operate against: | |
| <code>onsuccess</code> (default, can be omitted) or <code>always</code>. | |
| Guidance on when to specify <code>always</code> is provided relative to each | |
| action below. </p> | |
| <div class="warning"><h3>Warning</h3> | |
| <p>Carefully read the difference between <code>always</code> | |
| and <code>onsuccess</code> for each action listed below as the | |
| behavior can be unintuitive and is a frequent source of confusion. | |
| Where the guidance suggest repeating the conditions, it is safe to try | |
| each experimentally and use the one you find effective to match the | |
| pre-existing header.</p> | |
| </div> | |
| <dl> | |
| <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 <code>set</code>, | |
| <code>append</code> or <code>merge</code> should be used instead. | |
| <br><br><p>Choosing a <var>condition</var>: Specify a condition of <code>always</code> if you want the header to | |
| be included in non-2xx response (such as redirects or errors)</p> | |
| </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. | |
| Note that the <code>Set-Cookie</code> header is an exception: | |
| <a href="https://www.rfc-editor.org/rfc/rfc6265">RFC 6265</a> requires multiple <code>Set-Cookie</code> headers | |
| rather than combining values with commas. Use <code>add</code> | |
| instead of <code>append</code> for <code>Set-Cookie</code>. | |
| <br><br><p>Choosing a <var>condition</var>: If the existing header to be appended to was added by this module, you must match the condition | |
| parameter that was originally used. Otherwise, you must determine by trial | |
| and error whether <code>always</code> should be specified because you can't | |
| reliably know which internal table the existing value is present in.</p> | |
| </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 | |
| <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>. | |
| <var>value</var> must be omitted. | |
| <br><br><p>Choosing a <var>condition</var>: Specify a condition of <code>always</code> if you want the header to | |
| be included in non-2xx response (such as redirects or errors).</p> | |
| </dd> | |
| <dt><code>edit</code></dt> | |
| <dt><code>edit*</code></dt> | |
| <dd>If this response header exists, its value is transformed according | |
| to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a> | |
| search-and-replace. The <var>value</var> argument is a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>, and the <var>replacement</var> | |
| is a replacement string, which may contain backreferences or format specifiers. | |
| The <code>edit</code> form will match and replace exactly once | |
| in a header value, whereas the <code>edit*</code> form will replace | |
| <em>every</em> instance of the search pattern if it appears more | |
| than once. | |
| <br><br><p>Choosing a <var>condition</var>: Depending on the origins of the header to be edited, | |
| you may have to repeat your edit/edit* directive with both <code>always</code> and | |
| <code>onsuccess</code>. Alternatively, determine by experimentation | |
| whether a condition of <code>always</code> is necessary.</p> | |
| </dd> | |
| <dt><code>merge</code></dt> | |
| <dd>The response header is appended to any existing header of | |
| the same name, unless the value to be appended already appears in the | |
| header's comma-delimited list of values. 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. | |
| Values are compared in a case sensitive manner, and after | |
| all format specifiers have been processed. Values in double quotes | |
| are considered different from otherwise identical unquoted values. | |
| <br><br><p>Choosing a <var>condition</var>: If the target header to be merged was added by this module, you must match the condition | |
| parameter that was originally used. Otherwise, you must determine by experimentation | |
| whether a condition of <code>always</code> is necessary.</p> | |
| </dd> | |
| <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. | |
| <br><br><p>Choosing a <var>condition</var>: If the target header to be replaced was added by this module, you must match the condition | |
| parameter that was originally used. Otherwise, you must determine by experimentation | |
| whether a condition <code>always</code> is necessary.</p> | |
| </dd> | |
| <dt><code>setifempty</code></dt> | |
| <dd>The request header is set, but only if there is no previous header | |
| with this name. | |
| <br><br><p>Choosing a <var>condition</var>: If the target header to conditionally set was added by this module, you must match the condition | |
| parameter that was originally used. Otherwise, you must determine by experimentation | |
| whether a condition of <code>always</code> is necessary.</p> | |
| <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. | |
| If there are multiple headers of the same name, all will be | |
| removed. <var>value</var> must be omitted. | |
| <br><br><p>Choosing a <var>condition</var>: Repeat this directive with both <code>always</code> and | |
| <code>onsuccess</code> to be certain the header is unset, or determine by experimentation | |
| whether a condition of <code>always</code> is necessary..</p> | |
| </dd> | |
| <dt><code>note</code></dt> | |
| <dd>The value of the named response <var>header</var> is copied into an | |
| internal note whose name is given by <var>value</var>. This is useful | |
| if a header sent by a CGI or proxied resource is configured to be unset | |
| but should also be logged.<br> | |
| Available in 2.4.7 and later. | |
| <br><br><p>Choosing a <var>condition</var>: If the target header was added by this module, you must match the condition | |
| parameter that was originally used. Otherwise, you must determine by experimentation | |
| whether a condition of <code>always</code> is necessary..</p> | |
| </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>merge</code>, | |
| <code>add</code>, <code>unset</code> and <code>edit</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>set</code>, <code>append</code>, <code>merge</code> and | |
| <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 | |
| 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> | |
| <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>. | |
| The value is measured in microseconds.</td></tr> | |
| <tr class="odd"><td><code>%l</code></td> | |
| <td>The current load averages of the actual server itself. It is | |
| designed to expose the values obtained by <code>getloadavg()</code> | |
| and this represents the current load average, the 5 minute average, and | |
| the 15 minute average. The value is preceded by <code>l=</code> with each | |
| average separated by <code>/</code>.<br> | |
| Available in 2.4.4 and later. | |
| </td></tr> | |
| <tr><td><code>%i</code></td> | |
| <td>The current idle percentage of httpd (0 to 100) based on available | |
| processes and threads. The value is preceded by <code>i=</code>.<br> | |
| Available in 2.4.4 and later. | |
| </td></tr> | |
| <tr class="odd"><td><code>%b</code></td> | |
| <td>The current busy percentage of httpd (0 to 100) based on available | |
| processes and threads. The value is preceded by <code>b=</code>.<br> | |
| Available in 2.4.4 and later. | |
| </td></tr> | |
| <tr><td><code>%{VARNAME}e</code></td> | |
| <td>The contents of the <a href="../env.html">environment | |
| variable</a> <code>VARNAME</code>.</td></tr> | |
| <tr class="odd"><td><code>%{VARNAME}s</code></td> | |
| <td>The contents of the <a href="mod_ssl.html#envvars">SSL environment | |
| variable</a> <code>VARNAME</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> | |
| <div class="note"><h3>Note on expression values</h3> | |
| <p> When the value parameter uses the <a href="../expr.html">ap_expr</a> | |
| parser, some expression syntax will differ from examples that evaluate | |
| <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 | |
| funcname(arg).</li> | |
| <li>Multi-argument functions are not currently accessible from this | |
| starting point</li> | |
| <li>Quote the entire parameter, such as | |
| <pre class="prettyprint lang-config">Header set foo-checksum "expr=%{md5:foo}"</pre> | |
| </li> | |
| </ul> | |
| </div> | |
| <p>For <code>edit</code> there is both a <var>value</var> argument | |
| which is a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>, | |
| and an additional <var>replacement</var> string. As of version 2.4.7 | |
| the replacement string may also contain format specifiers.</p> | |
| <p>The <code class="directive">Header</code> directive may be followed by | |
| an additional argument, which may be any of:</p> | |
| <dl> | |
| <dt><code>early</code></dt> | |
| <dd>Specifies <a href="#early">early processing</a>.</dd> | |
| <dt><code>env=[!]<var>varname</var></code></dt> | |
| <dd>The directive is applied if and only if the <a href="../env.html">environment variable</a> <code>varname</code> exists. | |
| A <code>!</code> in front of <code>varname</code> reverses the test, | |
| so the directive applies only if <code>varname</code> is unset.</dd> | |
| <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. | |
| <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 | |
| to change the Content-Type header with this directive.</p> | |
| </div> | |
| <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif"></a></div> | |
| <div class="directive-section"><h2 id="requestheader"><span id="RequestHeader">RequestHeader</span> Directive <a title="Permanent link" href="#requestheader" class="permalink">¶</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 add|append|edit|edit*|merge|set|setifempty|unset | |
| <var>header</var> [[expr=]<var>value</var> [<var>replacement</var>] | |
| [early|env=[!]<var>varname</var>|expr=<var>expression</var>]] | |
| </code></td></tr> | |
| <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr> | |
| <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 | |
| available in 2.4.10 and later</td></tr> | |
| </table> | |
| <p>This directive can replace, merge, change 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>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>set</code>, | |
| <code>append</code> or <code>merge</code> should be used instead.</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>edit</code></dt> | |
| <dt><code>edit*</code></dt> | |
| <dd>If this request header exists, its value is transformed according | |
| to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a> | |
| search-and-replace. The <var>value</var> argument is a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>, and the <var>replacement</var> | |
| is a replacement string, which may contain backreferences or format specifiers. | |
| The <code>edit</code> form will match and replace exactly once | |
| in a header value, whereas the <code>edit*</code> form will replace | |
| <em>every</em> instance of the search pattern if it appears more | |
| than once.</dd> | |
| <dt><code>merge</code></dt> | |
| <dd>The request header is appended to any existing header of | |
| the same name, unless the value to be appended already appears in the | |
| existing header's comma-delimited list of values. 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. Values are compared in a case sensitive manner, and after | |
| all format specifiers have been processed. Values in double quotes | |
| are considered different from otherwise identical unquoted values.</dd> | |
| <dt><code>set</code></dt> | |
| <dd>The request header is set, replacing any previous header | |
| with this name</dd> | |
| <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> | |
| <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>set</code>, <code>append</code>, <code>merge</code> and | |
| <code>add</code> a <var>value</var> is given as the third argument. If a | |
| <var>value</var> contains spaces, it should be surrounded by double | |
| quotes. For <code>unset</code>, 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. For <code>edit</code> both | |
| a <var>value</var> and a <var>replacement</var> are required, and are | |
| a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a> and a | |
| replacement string respectively.</p> | |
| <p>The <code class="directive">RequestHeader</code> directive may be followed by | |
| an additional argument, which may be any of:</p> | |
| <dl> | |
| <dt><code>early</code></dt> | |
| <dd>Specifies <a href="#early">early processing</a>.</dd> | |
| <dt><code>env=[!]<var>varname</var></code></dt> | |
| <dd>The directive is applied if and only if the <a href="../env.html">environment variable</a> <code>varname</code> exists. | |
| A <code>!</code> in front of <code>varname</code> reverses the test, | |
| so the directive applies only if <code>varname</code> is unset.</dd> | |
| <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> | |
| </dl> | |
| <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> | |
| <div class="bottomlang"> | |
| <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English"> en </a> | | |
| <a href="../fr/mod/mod_headers.html" hreflang="fr" rel="alternate" title="Français"> fr </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><div id="footer"> | |
| <p class="apache">Copyright 2026 The Apache Software Foundation.<br>Licensed under the <a href="https://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p> | |
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