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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="../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>
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>
-<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>
+<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 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></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>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>
+ two directives have a different effect if reversed:</p>
+
+ <pre class="prettyprint lang-config">RequestHeader append MirrorID "mirror 12"
+RequestHeader unset MirrorID</pre>
- <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
+ 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>
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>
+ <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>
Copy all request headers that begin with "TS" to the
response headers:
- <div class="example"><p><code>
- Header echo ^TS
- </code></p></div>
+ <pre class="prettyprint lang-config">Header echo ^TS</pre>
+
</li>
<li>
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>
+ <pre class="prettyprint lang-config">Header set MyHeader "%D %t"</pre>
+
<p>results in this header being added to the response:</p>
<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>
+ <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>
<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
+ 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>
- SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
- Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader<br />
- </code></p></div>
+ MyHeader: D=3775428 t=991424704447256 mytext
+ </code></p></div>
+ </li>
- <p>If the header <code>MyRequestHeader: value</code> is present on
- the HTTP request, the response will contain the following header:</p>
+ <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>
- <div class="example"><p><code>
- MyHeader: D=3775428 t=991424704447256 mytext
- </code></p></div>
</li>
+
</ol>
</div>
<div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
<div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2>
<table class="directive">
<tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP response headers</td></tr>
-<tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><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#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> 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>
+ <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
+ 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.
+ 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>
+
+ <ul>
+ <li> You're adding a header to a locally generated non-success (non-2xx) response, such
+ as a redirect, in which case only the table corresponding to
+ <code>always</code> is used in the ultimate response.</li>
+ <li> You're modifying or removing a header generated by a CGI script,
+ in which case the CGI scripts are in the table corresponding to
+ <code>always</code> and not in the default table.</li>
+ <li> You're modifying or removing a header generated by some piece of
+ the server but that header is not being found by the default
+ <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
+ requests. See the example that uses %{REQUEST_STATUS} in the section above.</p>
+
+ <p>The action it performs is determined by the first
+ argument (second argument if a <var>condition</var> is specified).
+ 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>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.</dd>
<dt><code>append</code></dt>
<dd>The response header is appended to any existing header of
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>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.</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.</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.</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.</dd>
+
+ <dt><code>setifempty</code></dt>
+ <dd>The request header is set, but only if there is no previous header
+ 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.
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 regular expression.
- <var>value</var> must be omitted.</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.</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 regular expression.</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>
+ 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>
<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>
+ 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>FOOBAR</code>.</td></tr>
-<tr><td><code>%{FOOBAR}s</code></td>
+ 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>
FOOBAR</code>, if <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> is enabled.</td></tr>
+ 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>
+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
- <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">Header</code> directive
- will take effect. Otherwise, the directive will have no effect
- on the request.</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. These means that it is
- possible to set and/or override most headers, except for those headers
- added by the header filter.</p>
+ 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><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#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 or remove HTTP request
+ <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>set</code></dt>
- <dd>The request header is set, replacing any previous header
- with this name</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>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
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>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
<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
+ 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 unset, no <var>value</var> should be given.
+ 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.</p>
+ 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 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>
+ 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
</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 1995-2005 The Apache Software Foundation or its licensors, as applicable.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
-<p class="menu"><a href="../mod/">Modules</a> | <a href="../mod/directives.html">Directives</a> | <a href="../faq/">FAQ</a> | <a href="../glossary.html">Glossary</a> | <a href="../sitemap.html">Sitemap</a></p></div>
+</div><div class="top"><a href="#page-header"><img src="../images/up.gif" alt="top" /></a></div><div class="section"><h2><a id="comments_section" name="comments_section">Comments</a></h2><div class="warning"><strong>Notice:</strong><br />This is not a Q&A section. Comments placed here should be pointed towards suggestions on improving the documentation or server, and may be removed again by our moderators if they are either implemented or considered invalid/off-topic. Questions on how to manage the Apache HTTP Server should be directed at either our IRC channel, #httpd, on Freenode, or sent to our <a href="http://httpd.apache.org/lists.html">mailing lists</a>.</div>
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