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<?xml version="1.0"?> | |
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd"> | |
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?> | |
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<modulesynopsis metafile="mod_headers.xml.meta"> | |
<name>mod_headers</name> | |
<description>Customization of HTTP request and response | |
headers</description> | |
<status>Extension</status> | |
<sourcefile>mod_headers.c</sourcefile> | |
<identifier>headers_module</identifier> | |
<summary> | |
<p>This module provides directives to control and modify HTTP | |
request and response headers. Headers can be merged, replaced | |
or removed.</p> | |
</summary> | |
<section id="order"><title>Order of Processing</title> | |
<p>The directives provided by <module>mod_headers</module> can | |
occur almost anywhere within the server configuration, and can be | |
limited in scope by enclosing them in <a | |
href="../sections.html">configuration sections</a>.</p> | |
<p>Order of processing is important and is affected both by the | |
order in the configuration file and by placement in <a | |
href="../sections.html#mergin">configuration sections</a>. These | |
two headers have a different effect if reversed:</p> | |
<example> | |
RequestHeader append MirrorID "mirror 12"<br /> | |
RequestHeader unset MirrorID | |
</example> | |
<p>This way round, the <code>MirrorID</code> header is not set. If | |
reversed, the MirrorID header is set to "mirror 12".</p> | |
</section> | |
<section id="early"><title>Early and Late Processing</title> | |
<p><module>mod_headers</module> can be applied either early or late | |
in the request. The normal mode is late, when Request Headers are | |
set immediately before running the content generator and Response | |
Headers just as the response is sent down the wire. Always use | |
Late mode in an operational server.</p> | |
<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><Directory></code> or <code><Location></code>.</p> | |
</section> | |
<section id="examples"><title>Examples</title> | |
<ol> | |
<li> | |
Copy all request headers that begin with "TS" to the | |
response headers: | |
<example> | |
Header echo ^TS | |
</example> | |
</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. | |
<example> | |
Header set MyHeader "%D %t" | |
</example> | |
<p>results in this header being added to the response:</p> | |
<example> | |
MyHeader: D=3775428 t=991424704447256 | |
</example> | |
</li> | |
<li> | |
Say hello to Joe | |
<example> | |
Header set MyHeader "Hello Joe. It took %D microseconds \<br /> | |
for Apache to serve this request." | |
</example> | |
<p>results in this header being added to the response:</p> | |
<example> | |
MyHeader: Hello Joe. It took D=3775428 microseconds for Apache | |
to serve this request. | |
</example> | |
</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 | |
<module>mod_setenvif</module> module. | |
<example> | |
SetEnvIf MyRequestHeader myvalue HAVE_MyRequestHeader<br /> | |
Header set MyHeader "%D %t mytext" env=HAVE_MyRequestHeader | |
</example> | |
<p>If the header <code>MyRequestHeader: myvalue</code> is present on | |
the HTTP request, the response will contain the following header:</p> | |
<example> | |
MyHeader: D=3775428 t=991424704447256 mytext | |
</example> | |
</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: | |
<example> | |
RequestHeader edit Destination ^https: http: early | |
</example> | |
</li> | |
<li> | |
Set the same header value under multiple non-exclusive 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): | |
<example> | |
Header merge Cache-Control no-cache env=CGI<br /> | |
Header merge Cache-Control no-cache env=NO_CACHE<br /> | |
Header merge Cache-Control no-store env=NO_STORE | |
</example> | |
<p>then the response would contain the following header:</p> | |
<example> | |
Cache-Control: no-cache, no-store | |
</example> | |
<p>If <code>append</code> was used instead of <code>merge</code>, | |
then the response would contain the following header:</p> | |
<example> | |
Cache-Control: no-cache, no-cache, no-store | |
</example> | |
</li> | |
</ol> | |
</section> | |
<directivesynopsis> | |
<name>RequestHeader</name> | |
<description>Configure HTTP request headers</description> | |
<syntax>RequestHeader add|append|edit|merge|set|unset <var>header</var> | |
[<var>value</var>] [<var>replacement</var>] [early|env=[!]<var>variable</var>]</syntax> | |
<contextlist><context>server config</context><context>virtual host</context> | |
<context>directory</context><context>.htaccess</context></contextlist> | |
<override>FileInfo</override> | |
<usage> | |
<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> | |
<dd>If this request header exists, its value is transformed according | |
to a <glossary ref="regex">regular expression</glossary> | |
search-and-replace. The <var>value</var> argument is a <glossary | |
ref="regex">regular expression</glossary>, and the <var>replacement</var> | |
is a replacement string, which may contain backreferences.</dd> | |
</dl> | |
<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 | |
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>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> | |
<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 <directive module="mod_headers">Header</directive>, | |
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 <glossary ref="regex">regular expression</glossary> and a | |
replacement string respectively.</p> | |
<p>The <directive>RequestHeader</directive> 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 <directive>RequestHeader</directive> directive will take effect. | |
Otherwise, the directive will have no effect on the request.</p> | |
<p>Except in <a href="#early">early</a> mode, the | |
<directive>RequestHeader</directive> 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> | |
</usage> | |
</directivesynopsis> | |
<directivesynopsis> | |
<name>Header</name> | |
<description>Configure HTTP response headers</description> | |
<syntax>Header [<var>condition</var>] add|append|echo|edit|merge|set|unset | |
<var>header</var> [<var>value</var>] [early|env=[!]<var>variable</var>]</syntax> | |
<contextlist><context>server config</context><context>virtual host</context> | |
<context>directory</context><context>.htaccess</context></contextlist> | |
<override>FileInfo</override> | |
<usage> | |
<p>This directive can replace, merge or remove HTTP response | |
headers. The header is modified just after the content handler | |
and output filters are run, allowing outgoing headers to be | |
modified.</p> | |
<p>The optional <var>condition</var> can be either <code>onsuccess</code> | |
or <code>always</code>. It determines, which internal header table should be | |
operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code> | |
status codes and <code>always</code> for all status codes (including | |
<code>2<var>xx</var></code>). Especially if you want to unset headers | |
set by certain modules, you should try out, which table is affected.</p> | |
<p>The action it performs is determined by the second | |
argument. This can be one of the following values:</p> | |
<dl> | |
<dt><code>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 | |
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>echo</code></dt> | |
<dd>Request headers with this name are echoed back in the | |
response headers. <var>header</var> may be a | |
<glossary ref="regex">regular expression</glossary>. | |
<var>value</var> must be omitted.</dd> | |
<dt><code>edit</code></dt> | |
<dd>If this request header exists, its value is transformed according | |
to a <glossary ref="regex">regular expression</glossary> | |
search-and-replace. The <var>value</var> argument is a <glossary | |
ref="regex">regular expression</glossary>, and the <var>replacement</var> | |
is a replacement string, which may contain backreferences.</dd> | |
</dl> | |
<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>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> | |
<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 <glossary ref="regex">regular | |
expression</glossary>.</p> | |
<p>For <code>set</code>, <code>append</code>, <code>merge</code> and | |
<code>add</code> a <var>value</var> is specified as the third 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 format | |
specifiers or a combination of both. The following format specifiers | |
are supported in <var>value</var>:</p> | |
<table border="1" style="zebra"> | |
<columnspec><column width=".25"/><column width=".75"/></columnspec> | |
<tr><th>Format</th><th>Description</th></tr> | |
<tr><td><code>%%</code></td> | |
<td>The percent sign</td></tr> | |
<tr><td><code>%t</code></td> | |
<td>The time the request was received in Universal Coordinated Time | |
since the epoch (Jan. 1, 1970) measured in microseconds. The value | |
is preceded by <code>t=</code>.</td></tr> | |
<tr><td><code>%D</code></td> | |
<td>The time from when the request was received to the time the | |
headers are sent on the wire. This is a measure of the duration | |
of the request. The value is preceded by <code>D=</code>.</td></tr> | |
<tr><td><code>%{VARNAME}e</code></td> | |
<td>The contents of the <a href="../env.html">environment | |
variable</a> <code>VARNAME</code>.</td></tr> | |
<tr><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 <module>mod_ssl</module> is enabled.</td></tr> | |
</table> | |
<note><title>Note</title> | |
<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> | |
</note> | |
<p>For <code>edit</code> there is both a <var>value</var> argument | |
which is a <glossary ref="regex">regular expression</glossary>, | |
and an additional <var>replacement</var> string.</p> | |
<p>The <directive>Header</directive> 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 <directive>Header</directive> directive | |
will take effect. Otherwise, the directive will have no effect | |
on the request.</p> | |
<p>Except in <a href="#early">early</a> mode, the | |
<directive>Header</directive> 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> | |
</usage> | |
</directivesynopsis> | |
</modulesynopsis> | |