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16 <p class="apache">Apache HTTP Server Version 2.3</p>
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20 <a href="http://www.apache.org/">Apache</a> > <a href="http://httpd.apache.org/">HTTP Server</a> > <a href="http://httpd.apache.org/docs/">Documentation</a> > <a href="../">Version 2.3</a> > <a href="./">Modules</a></div>
21 <div id="page-content">
22 <div id="preamble"><h1>Apache Module mod_headers</h1>
24 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English"> en </a> |
25 <a href="../ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
26 <a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
28 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Customization of HTTP request and response
30 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
31 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>headers_module</td></tr>
32 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_headers.c</td></tr>
33 <tr><th><a href="module-dict.html#Compatibility">Compatibility:</a></th><td><code class="directive"><a href="#requestheader">RequestHeader</a></code>
34 is available only in Apache 2.0</td></tr></table>
37 <p>This module provides directives to control and modify HTTP
38 request and response headers. Headers can be merged, replaced
41 <div id="quickview"><h3 class="directives">Directives</h3>
43 <li><img alt="" src="../images/down.gif" /> <a href="#header">Header</a></li>
44 <li><img alt="" src="../images/down.gif" /> <a href="#requestheader">RequestHeader</a></li>
48 <li><img alt="" src="../images/down.gif" /> <a href="#order">Order of Processing</a></li>
49 <li><img alt="" src="../images/down.gif" /> <a href="#early">Early and Late Processing</a></li>
50 <li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
52 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
54 <h2><a name="order" id="order">Order of Processing</a></h2>
56 <p>The directives provided by <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can
57 occur almost anywhere within the server configuration, and can be
58 limited in scope by enclosing them in <a href="../sections.html">configuration sections</a>.</p>
60 <p>Order of processing is important and is affected both by the
61 order in the configuration file and by placement in <a href="../sections.html#mergin">configuration sections</a>. These
62 two headers have a different effect if reversed:</p>
64 <div class="example"><p><code>
65 RequestHeader append MirrorID "mirror 12"<br />
66 RequestHeader unset MirrorID
69 <p>This way round, the <code>MirrorID</code> header is not set. If
70 reversed, the MirrorID header is set to "mirror 12".</p>
71 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
73 <h2><a name="early" id="early">Early and Late Processing</a></h2>
74 <p><code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can be applied either early or late
75 in the request. The normal mode is late, when Request Headers are
76 set immediately before running the content generator and Response
77 Headers just as the response is sent down the wire. Always use
78 Late mode in an operational server.</p>
80 <p>Early mode is designed as a test/debugging aid for developers.
81 Directives defined using the <code>early</code> keyword are set
82 right at the beginning of processing the request. This means
83 they can be used to simulate different requests and set up test
84 cases, but it also means that headers may be changed at any time
85 by other modules before generating a Response.</p>
87 <p>Because early directives are processed before the request path's
88 configuration is traversed, early headers can only be set in a
89 main server or virtual host context. Early directives cannot depend
90 on a request path, so they will fail in contexts such as
91 <code><Directory></code> or <code><Location></code>.</p>
92 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
94 <h2><a name="examples" id="examples">Examples</a></h2>
98 Copy all request headers that begin with "TS" to the
101 <div class="example"><p><code>
107 Add a header, <code>MyHeader</code>, to the response including a
108 timestamp for when the request was received and how long it
109 took to begin serving the request. This header can be used by
110 the client to intuit load on the server or in isolating
111 bottlenecks between the client and the server.
113 <div class="example"><p><code>
114 Header add MyHeader "%D %t"
117 <p>results in this header being added to the response:</p>
119 <div class="example"><p><code>
120 MyHeader: D=3775428 t=991424704447256
127 <div class="example"><p><code>
128 Header add MyHeader "Hello Joe. It took %D microseconds \<br />
129 for Apache to serve this request."
132 <p>results in this header being added to the response:</p>
134 <div class="example"><p><code>
135 MyHeader: Hello Joe. It took D=3775428 microseconds for Apache
136 to serve this request.
141 Conditionally send <code>MyHeader</code> on the response if and
142 only if header "MyRequestHeader" is present on the request. This
143 is useful for constructing headers in response to some client
144 stimulus. Note that this example requires the services of the
145 <code class="module"><a href="../mod/mod_setenvif.html">mod_setenvif</a></code> module.
147 <div class="example"><p><code>
148 SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
149 Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader<br />
152 <p>If the header <code>MyRequestHeader: value</code> is present on
153 the HTTP request, the response will contain the following header:</p>
155 <div class="example"><p><code>
156 MyHeader: D=3775428 t=991424704447256 mytext
161 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
162 <div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2>
163 <table class="directive">
164 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP response headers</td></tr>
165 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>Header [<var>condition</var>] set|append|add|unset|echo
166 <var>header</var> [<var>value</var>] [early|env=[!]<var>variable</var>]</code></td></tr>
167 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
168 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
169 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
170 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
172 <p>This directive can replace, merge or remove HTTP response
173 headers. The header is modified just after the content handler
174 and output filters are run, allowing outgoing headers to be
177 <p>The optional <var>condition</var> can be either <code>onsuccess</code>
178 or <code>always</code>. It determines, which internal header table should be
179 operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code>
180 status codes and <code>always</code> for all status codes (including
181 <code>2<var>xx</var></code>). Especially if you want to unset headers
182 set by certain modules, you should try out, which table is affected.</p>
184 <p>The action it performs is determined by the second
185 argument. This can be one of the following values:</p>
188 <dt><code>set</code></dt>
189 <dd>The response header is set, replacing any previous header
190 with this name. The <var>value</var> may be a format string.</dd>
192 <dt><code>append</code></dt>
193 <dd>The response header is appended to any existing header of
194 the same name. When a new value is merged onto an existing
195 header it is separated from the existing header with a comma.
196 This is the HTTP standard way of giving a header multiple values.</dd>
198 <dt><code>add</code></dt>
199 <dd>The response header is added to the existing set of headers,
200 even if this header already exists. This can result in two
201 (or more) headers having the same name. This can lead to
202 unforeseen consequences, and in general "append" should be
205 <dt><code>unset</code></dt>
206 <dd>The response header of this name is removed, if it exists.
207 If there are multiple headers of the same name, all will be
208 removed. <var>value</var> must be omitted.</dd>
210 <dt><code>echo</code></dt>
211 <dd>Request headers with this name are echoed back in the
212 response headers. <var>header</var> may be a
213 <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>.
214 <var>value</var> must be omitted.</dd>
217 <p>This argument is followed by a <var>header</var> name, which
218 can include the final colon, but it is not required. Case is
219 ignored for <code>set</code>, <code>append</code>, <code>add</code>
220 and <code>unset</code>. The <var>header</var> name for <code>echo</code>
221 is case sensitive and may be a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular
224 <p>For <code>add</code>, <code>append</code> and <code>set</code> a
225 <var>value</var> is specified as the third argument. If <var>value</var>
226 contains spaces, it should be surrounded by doublequotes.
227 <var>value</var> may be a character string, a string containing format
228 specifiers or a combination of both. The following format specifiers
229 are supported in <var>value</var>:</p>
231 <table class="bordered"><tr class="header"><th>Format</th><th>Description</th></tr>
232 <tr><td><code>%%</code></td>
233 <td>The percent sign</td></tr>
234 <tr class="odd"><td><code>%t</code></td>
235 <td>The time the request was received in Universal Coordinated Time
236 since the epoch (Jan. 1, 1970) measured in microseconds. The value
237 is preceded by <code>t=</code>.</td></tr>
238 <tr><td><code>%D</code></td>
239 <td>The time from when the request was received to the time the
240 headers are sent on the wire. This is a measure of the duration
241 of the request. The value is preceded by <code>D=</code>.</td></tr>
242 <tr class="odd"><td><code>%{FOOBAR}e</code></td>
243 <td>The contents of the <a href="../env.html">environment
244 variable</a> <code>FOOBAR</code>.</td></tr>
245 <tr><td><code>%{FOOBAR}s</code></td>
246 <td>The contents of the <a href="mod_ssl.html#envvars">SSL environment
247 variable</a> <code>FOOBAR</code>, if <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> is enabled.</td></tr>
250 <div class="note"><h3>Note</h3>
251 <p>The <code>%s</code> format specifier is only available in
252 Apache 2.1 and later; it can be used instead of <code>%e</code>
253 to avoid the overhead of enabling <code>SSLOptions
254 +StdEnvVars</code>. If <code>SSLOptions +StdEnvVars</code> must
255 be enabled anyway for some other reason, <code>%e</code> will be
256 more efficient than <code>%s</code>.</p>
259 <p>The <code class="directive">Header</code> directive may be followed by an
260 an additional argument, which may be used to specify conditions under
261 which the action will be taken, or may be the keyword <code>early</code>
262 to specify <a href="#early">early processing</a>. If the
263 <a href="../env.html">environment variable</a> specified in the
264 <code>env=<var>...</var></code> argument exists (or if the environment
265 variable does not exist and <code>env=!<var>...</var></code> is specified)
266 then the action specified by the <code class="directive">Header</code> directive
267 will take effect. Otherwise, the directive will have no effect
270 <p>Except in <a href="#early">early</a> mode, the
271 <code class="directive">Header</code> directives are processed just
272 before the response is sent to the network. These means that it is
273 possible to set and/or override most headers, except for those headers
274 added by the header filter.</p>
277 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
278 <div class="directive-section"><h2><a name="RequestHeader" id="RequestHeader">RequestHeader</a> <a name="requestheader" id="requestheader">Directive</a></h2>
279 <table class="directive">
280 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP request headers</td></tr>
281 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RequestHeader set|append|add|unset <var>header</var>
282 [<var>value</var>] [early|env=[!]<var>variable</var>]</code></td></tr>
283 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
284 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
285 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
286 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
288 <p>This directive can replace, merge or remove HTTP request
289 headers. The header is modified just before the content handler
290 is run, allowing incoming headers to be modified. The action it
291 performs is determined by the first argument. This can be one
292 of the following values:</p>
295 <dt><code>set</code></dt>
296 <dd>The request header is set, replacing any previous header
299 <dt><code>append</code></dt>
300 <dd>The request header is appended to any existing header of the
301 same name. When a new value is merged onto an existing header
302 it is separated from the existing header with a comma. This
303 is the HTTP standard way of giving a header multiple
306 <dt><code>add</code></dt>
307 <dd>The request header is added to the existing set of headers,
308 even if this header already exists. This can result in two
309 (or more) headers having the same name. This can lead to
310 unforeseen consequences, and in general <code>append</code> should be
313 <dt><code>unset</code></dt>
314 <dd>The request header of this name is removed, if it exists. If
315 there are multiple headers of the same name, all will be removed.
316 <var>value</var> must be omitted.</dd>
319 <p>This argument is followed by a header name, which can
320 include the final colon, but it is not required. Case is
321 ignored. For <code>add</code>, <code>append</code> and
322 <code>set</code> a <var>value</var> is given as the third argument. If
323 <var>value</var> contains spaces, it should be surrounded by double
324 quotes. For unset, no <var>value</var> should be given.
325 <var>value</var> may be a character string, a string containing format
326 specifiers or a combination of both. The supported format specifiers
327 are the same as for the <code class="directive"><a href="#header">Header</a></code>,
328 please have a look there for details.</p>
330 <p>The <code class="directive">RequestHeader</code> directive may be followed by
331 an additional argument, which may be used to specify conditions under
332 which the action will be taken, or may be the keyword <code>early</code>
333 to specify <a href="#early">early processing</a>. If the
334 <a href="../env.html">environment
335 variable</a> specified in the <code>env=<var>...</var></code> argument
336 exists (or if the environment variable does not exist and
337 <code>env=!<var>...</var></code> is specified) then the action specified
338 by the <code class="directive">RequestHeader</code> directive will take effect.
339 Otherwise, the directive will have no effect on the request.</p>
341 <p>Except in <a href="#early">early</a> mode, the
342 <code class="directive">RequestHeader</code> directive is processed
343 just before the request is run by its handler in the fixup phase.
344 This should allow headers generated by the browser, or by Apache
345 input filters to be overridden or modified.</p>
349 <div class="bottomlang">
350 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English"> en </a> |
351 <a href="../ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
352 <a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
353 </div><div id="footer">
354 <p class="apache">Copyright 2006 The Apache Software Foundation.<br />Licensed under the <a href="http://www.apache.org/licenses/LICENSE-2.0">Apache License, Version 2.0</a>.</p>
355 <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>