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24 <div id="page-content">
25 <div id="preamble"><h1>Apache Module mod_headers</h1>
27 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English"> en </a> |
28 <a href="../fr/mod/mod_headers.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
29 <a href="../ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
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32 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Customization of HTTP request and response
34 <tr><th><a href="module-dict.html#Status">Status:</a></th><td>Extension</td></tr>
35 <tr><th><a href="module-dict.html#ModuleIdentifier">Module Identifier:</a></th><td>headers_module</td></tr>
36 <tr><th><a href="module-dict.html#SourceFile">Source File:</a></th><td>mod_headers.c</td></tr></table>
39 <p>This module provides directives to control and modify HTTP
40 request and response headers. Headers can be merged, replaced
43 <div id="quickview"><h3 class="directives">Directives</h3>
45 <li><img alt="" src="../images/down.gif" /> <a href="#header">Header</a></li>
46 <li><img alt="" src="../images/down.gif" /> <a href="#requestheader">RequestHeader</a></li>
50 <li><img alt="" src="../images/down.gif" /> <a href="#order">Order of Processing</a></li>
51 <li><img alt="" src="../images/down.gif" /> <a href="#early">Early and Late Processing</a></li>
52 <li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
53 </ul><ul class="seealso"><li><a href="#comments_section">Comments</a></li></ul></div>
54 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
55 <div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2>
56 <table class="directive">
57 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP response headers</td></tr>
58 <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
59 <var>header</var> [[expr=]<var>value</var> [<var>replacement</var>]
60 [early|env=[!]<var>varname</var>|expr=<var>expression</var>]]
62 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
63 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
64 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
65 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
66 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
67 available in 2.4.10 and later</td></tr>
69 <p>This directive can replace, merge or remove HTTP response
70 headers. The header is modified just after the content handler
71 and output filters are run, allowing outgoing headers to be
74 <p> The optional <var>condition</var> argument determines which internal
75 table of responses headers this directive will operate against. Despite the
76 name, the default value of <code>onsuccess</code> does <em>not</em> limit
77 an <var>action</var> to responses with a 2xx status code. Headers set under
78 this condition are still used when, for example, a request is <em>successfully</em>
79 proxied or generated by CGI, even when they have generated a failing status code.</p>
81 <p>When your action is a function of an existing header, you may need to specify
82 a condition of <code>always</code>, depending on which internal table the
83 original header was set in. The table that corresponds to <code>always</code> is
84 used for locally generated error responses as well as successful responses.
85 Note also that repeating this directive with both conditions makes sense in
86 some scenarios because <code>always</code> is not a superset of
87 <code>onsuccess</code> with respect to existing headers:</p>
90 <li> You're adding a header to a locally generated non-success (non-2xx) response, such
91 as a redirect, in which case only the table corresponding to
92 <code>always</code> is used in the ultimate response.</li>
93 <li> You're modifying or removing a header generated by a CGI script,
94 in which case the CGI scripts are in the table corresponding to
95 <code>always</code> and not in the default table.</li>
96 <li> You're modifying or removing a header generated by some piece of
97 the server but that header is not being found by the default
98 <code>onsuccess</code> condition.</li>
101 <p>Separately from the <var>condition</var> parameter described above, you
102 can limit an action based on HTTP status codes for e.g. proxied or CGI
103 requests. See the example that uses %{REQUEST_STATUS} in the section above.</p>
105 <p>The action it performs is determined by the first
106 argument (second argument if a <var>condition</var> is specified).
107 This can be one of the following values:</p>
110 <dt><code>add</code></dt>
111 <dd>The response header is added to the existing set of headers,
112 even if this header already exists. This can result in two
113 (or more) headers having the same name. This can lead to
114 unforeseen consequences, and in general <code>set</code>,
115 <code>append</code> or <code>merge</code> should be used instead.</dd>
117 <dt><code>append</code></dt>
118 <dd>The response header is appended to any existing header of
119 the same name. When a new value is merged onto an existing
120 header it is separated from the existing header with a comma.
121 This is the HTTP standard way of giving a header multiple values.</dd>
123 <dt><code>echo</code></dt>
124 <dd>Request headers with this name are echoed back in the
125 response headers. <var>header</var> may be a
126 <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>.
127 <var>value</var> must be omitted.</dd>
129 <dt><code>edit</code></dt>
130 <dt><code>edit*</code></dt>
131 <dd>If this response header exists, its value is transformed according
132 to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>
133 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>
134 is a replacement string, which may contain backreferences or format specifiers.
135 The <code>edit</code> form will match and replace exactly once
136 in a header value, whereas the <code>edit*</code> form will replace
137 <em>every</em> instance of the search pattern if it appears more
140 <dt><code>merge</code></dt>
141 <dd>The response header is appended to any existing header of
142 the same name, unless the value to be appended already appears in the
143 header's comma-delimited list of values. When a new value is merged onto
144 an existing header it is separated from the existing header with a comma.
145 This is the HTTP standard way of giving a header multiple values.
146 Values are compared in a case sensitive manner, and after
147 all format specifiers have been processed. Values in double quotes
148 are considered different from otherwise identical unquoted values.</dd>
150 <dt><code>set</code></dt>
151 <dd>The response header is set, replacing any previous header
152 with this name. The <var>value</var> may be a format string.</dd>
154 <dt><code>setifempty</code></dt>
155 <dd>The request header is set, but only if there is no previous header
156 with this name.<br />
157 Available in 2.4.7 and later.</dd>
159 <dt><code>unset</code></dt>
160 <dd>The response header of this name is removed, if it exists.
161 If there are multiple headers of the same name, all will be
162 removed. <var>value</var> must be omitted.</dd>
164 <dt><code>note</code></dt>
165 <dd>The value of the named response <var>header</var> is copied into an
166 internal note whose name is given by <var>value</var>. This is useful
167 if a header sent by a CGI or proxied resource is configured to be unset
168 but should also be logged.<br />
169 Available in 2.4.7 and later.</dd>
173 <p>This argument is followed by a <var>header</var> name, which
174 can include the final colon, but it is not required. Case is
175 ignored for <code>set</code>, <code>append</code>, <code>merge</code>,
176 <code>add</code>, <code>unset</code> and <code>edit</code>.
177 The <var>header</var> name for <code>echo</code>
178 is case sensitive and may be a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular
181 <p>For <code>set</code>, <code>append</code>, <code>merge</code> and
182 <code>add</code> a <var>value</var> is specified as the next argument.
184 contains spaces, it should be surrounded by double quotes.
185 <var>value</var> may be a character string, a string containing
186 <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> specific format specifiers (and character
187 literals), or an <a href="../expr.html">ap_expr</a> expression prefixed
188 with <em>expr=</em></p>
190 <p> The following format specifiers are supported in <var>value</var>:</p>
192 <table class="bordered"><tr class="header"><th>Format</th><th>Description</th></tr>
193 <tr><td><code>%%</code></td>
194 <td>The percent sign</td></tr>
195 <tr class="odd"><td><code>%t</code></td>
196 <td>The time the request was received in Universal Coordinated Time
197 since the epoch (Jan. 1, 1970) measured in microseconds. The value
198 is preceded by <code>t=</code>.</td></tr>
199 <tr><td><code>%D</code></td>
200 <td>The time from when the request was received to the time the
201 headers are sent on the wire. This is a measure of the duration
202 of the request. The value is preceded by <code>D=</code>.
203 The value is measured in microseconds.</td></tr>
204 <tr class="odd"><td><code>%l</code></td>
205 <td>The current load averages of the actual server itself. It is
206 designed to expose the values obtained by <code>getloadavg()</code>
207 and this represents the current load average, the 5 minute average, and
208 the 15 minute average. The value is preceded by <code>l=</code> with each
209 average separated by <code>/</code>.<br />
210 Available in 2.4.4 and later.
212 <tr><td><code>%i</code></td>
213 <td>The current idle percentage of httpd (0 to 100) based on available
214 processes and threads. The value is preceded by <code>i=</code>.<br />
215 Available in 2.4.4 and later.
217 <tr class="odd"><td><code>%b</code></td>
218 <td>The current busy percentage of httpd (0 to 100) based on available
219 processes and threads. The value is preceded by <code>b=</code>.<br />
220 Available in 2.4.4 and later.
222 <tr><td><code>%{VARNAME}e</code></td>
223 <td>The contents of the <a href="../env.html">environment
224 variable</a> <code>VARNAME</code>.</td></tr>
225 <tr class="odd"><td><code>%{VARNAME}s</code></td>
226 <td>The contents of the <a href="mod_ssl.html#envvars">SSL environment
227 variable</a> <code>VARNAME</code>, if <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> is enabled.</td></tr>
230 <div class="note"><h3>Note</h3>
231 <p>The <code>%s</code> format specifier is only available in
232 Apache 2.1 and later; it can be used instead of <code>%e</code>
233 to avoid the overhead of enabling <code>SSLOptions
234 +StdEnvVars</code>. If <code>SSLOptions +StdEnvVars</code> must
235 be enabled anyway for some other reason, <code>%e</code> will be
236 more efficient than <code>%s</code>.</p>
239 <div class="note"><h3>Note on expression values</h3>
240 <p> When the value parameter uses the <a href="../expr.html">ap_expr</a>
241 parser, some expression syntax will differ from examples that evaluate
242 <em>boolean</em> expressions such as <If>:</p>
244 <li>The starting point of the grammar is 'string' rather than 'expr'.</li>
245 <li>Function calls use the %{funcname:arg} syntax rather than
247 <li>Multi-argument functions are not currently accessible from this
249 <li>Quote the entire parameter, such as
250 <pre class="prettyprint lang-config">Header set foo-checksum "expr=%{md5:foo}"</pre>
257 <p>For <code>edit</code> there is both a <var>value</var> argument
258 which is a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>,
259 and an additional <var>replacement</var> string. As of version 2.4.7
260 the replacement string may also contain format specifiers.</p>
262 <p>The <code class="directive">Header</code> directive may be followed by
263 an additional argument, which may be any of:</p>
265 <dt><code>early</code></dt>
266 <dd>Specifies <a href="#early">early processing</a>.</dd>
267 <dt><code>env=[!]<var>varname</var></code></dt>
268 <dd>The directive is applied if and only if the <a href="../env.html">environment variable</a> <code>varname</code> exists.
269 A <code>!</code> in front of <code>varname</code> reverses the test,
270 so the directive applies only if <code>varname</code> is unset.</dd>
271 <dt><code>expr=<var>expression</var></code></dt>
272 <dd>The directive is applied if and only if <var>expression</var>
273 evaluates to true. Details of expression syntax and evaluation are
274 documented in the <a href="../expr.html">ap_expr</a> documentation.</dd>
277 <p>Except in <a href="#early">early</a> mode, the
278 <code class="directive">Header</code> directives are processed just
279 before the response is sent to the network. This means that it is
280 possible to set and/or override most headers, except for some headers
281 added by the HTTP header filter. Prior to 2.2.12, it was not possible
282 to change the Content-Type header with this directive.</p>
286 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
287 <div class="directive-section"><h2><a name="RequestHeader" id="RequestHeader">RequestHeader</a> <a name="requestheader" id="requestheader">Directive</a></h2>
288 <table class="directive">
289 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP request headers</td></tr>
290 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RequestHeader add|append|edit|edit*|merge|set|setifempty|unset
291 <var>header</var> [[expr=]<var>value</var> [<var>replacement</var>]
292 [early|env=[!]<var>varname</var>|expr=<var>expression</var>]]
294 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
295 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
296 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
297 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
298 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
299 available in 2.4.10 and later</td></tr>
301 <p>This directive can replace, merge, change or remove HTTP request
302 headers. The header is modified just before the content handler
303 is run, allowing incoming headers to be modified. The action it
304 performs is determined by the first argument. This can be one
305 of the following values:</p>
309 <dt><code>add</code></dt>
310 <dd>The request header is added to the existing set of headers,
311 even if this header already exists. This can result in two
312 (or more) headers having the same name. This can lead to
313 unforeseen consequences, and in general <code>set</code>,
314 <code>append</code> or <code>merge</code> should be used instead.</dd>
316 <dt><code>append</code></dt>
317 <dd>The request header is appended to any existing header of the
318 same name. When a new value is merged onto an existing header
319 it is separated from the existing header with a comma. This
320 is the HTTP standard way of giving a header multiple
323 <dt><code>edit</code></dt>
324 <dt><code>edit*</code></dt>
325 <dd>If this request header exists, its value is transformed according
326 to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>
327 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>
328 is a replacement string, which may contain backreferences or format specifiers.
329 The <code>edit</code> form will match and replace exactly once
330 in a header value, whereas the <code>edit*</code> form will replace
331 <em>every</em> instance of the search pattern if it appears more
334 <dt><code>merge</code></dt>
335 <dd>The request header is appended to any existing header of
336 the same name, unless the value to be appended already appears in the
337 existing header's comma-delimited list of values. When a new value is
338 merged onto an existing header it is separated from the existing header
339 with a comma. This is the HTTP standard way of giving a header multiple
340 values. Values are compared in a case sensitive manner, and after
341 all format specifiers have been processed. Values in double quotes
342 are considered different from otherwise identical unquoted values.</dd>
344 <dt><code>set</code></dt>
345 <dd>The request header is set, replacing any previous header
348 <dt><code>setifempty</code></dt>
349 <dd>The request header is set, but only if there is no previous header
350 with this name.<br />
351 Available in 2.4.7 and later.</dd>
353 <dt><code>unset</code></dt>
354 <dd>The request header of this name is removed, if it exists. If
355 there are multiple headers of the same name, all will be removed.
356 <var>value</var> must be omitted.</dd>
359 <p>This argument is followed by a header name, which can
360 include the final colon, but it is not required. Case is
361 ignored. For <code>set</code>, <code>append</code>, <code>merge</code> and
362 <code>add</code> a <var>value</var> is given as the third argument. If a
363 <var>value</var> contains spaces, it should be surrounded by double
364 quotes. For <code>unset</code>, no <var>value</var> should be given.
365 <var>value</var> may be a character string, a string containing format
366 specifiers or a combination of both. The supported format specifiers
367 are the same as for the <code class="directive"><a href="#header">Header</a></code>,
368 please have a look there for details. For <code>edit</code> both
369 a <var>value</var> and a <var>replacement</var> are required, and are
370 a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a> and a
371 replacement string respectively.</p>
373 <p>The <code class="directive">RequestHeader</code> directive may be followed by
374 an additional argument, which may be any of:</p>
376 <dt><code>early</code></dt>
377 <dd>Specifies <a href="#early">early processing</a>.</dd>
378 <dt><code>env=[!]<var>varname</var></code></dt>
379 <dd>The directive is applied if and only if the <a href="../env.html">environment variable</a> <code>varname</code> exists.
380 A <code>!</code> in front of <code>varname</code> reverses the test,
381 so the directive applies only if <code>varname</code> is unset.</dd>
382 <dt><code>expr=<var>expression</var></code></dt>
383 <dd>The directive is applied if and only if <var>expression</var>
384 evaluates to true. Details of expression syntax and evaluation are
385 documented in the <a href="../expr.html">ap_expr</a> documentation.</dd>
388 <p>Except in <a href="#early">early</a> mode, the
389 <code class="directive">RequestHeader</code> directive is processed
390 just before the request is run by its handler in the fixup phase.
391 This should allow headers generated by the browser, or by Apache
392 input filters to be overridden or modified.</p>
395 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
396 <div class="section">
397 <h2><a name="order" id="order">Order of Processing</a></h2>
399 <p>The directives provided by <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can
400 occur almost anywhere within the server configuration, and can be
401 limited in scope by enclosing them in <a href="../sections.html">configuration sections</a>.</p>
403 <p>Order of processing is important and is affected both by the
404 order in the configuration file and by placement in <a href="../sections.html#mergin">configuration sections</a>. These
405 two directives have a different effect if reversed:</p>
407 <pre class="prettyprint lang-config">RequestHeader append MirrorID "mirror 12"
408 RequestHeader unset MirrorID</pre>
411 <p>This way round, the <code>MirrorID</code> header is not set. If
412 reversed, the MirrorID header is set to "mirror 12".</p>
413 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
414 <div class="section">
415 <h2><a name="early" id="early">Early and Late Processing</a></h2>
416 <p><code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can be applied either early or late
417 in the request. The normal mode is late, when <em>Request</em> Headers are
418 set immediately before running the content generator and <em>Response</em>
419 Headers just as the response is sent down the wire. Always use
420 Late mode in an operational server.</p>
422 <p>Early mode is designed as a test/debugging aid for developers.
423 Directives defined using the <code>early</code> keyword are set
424 right at the beginning of processing the request. This means
425 they can be used to simulate different requests and set up test
426 cases, but it also means that headers may be changed at any time
427 by other modules before generating a Response.</p>
429 <p>Because early directives are processed before the request path's
430 configuration is traversed, early headers can only be set in a
431 main server or virtual host context. Early directives cannot depend
432 on a request path, so they will fail in contexts such as
433 <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> or
434 <code class="directive"><a href="../mod/core.html#location"><Location></a></code>.</p>
435 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
436 <div class="section">
437 <h2><a name="examples" id="examples">Examples</a></h2>
441 Copy all request headers that begin with "TS" to the
444 <pre class="prettyprint lang-config">Header echo ^TS</pre>
449 Add a header, <code>MyHeader</code>, to the response including a
450 timestamp for when the request was received and how long it
451 took to begin serving the request. This header can be used by
452 the client to intuit load on the server or in isolating
453 bottlenecks between the client and the server.
455 <pre class="prettyprint lang-config">Header set MyHeader "%D %t"</pre>
458 <p>results in this header being added to the response:</p>
460 <div class="example"><p><code>
461 MyHeader: D=3775428 t=991424704447256
468 <pre class="prettyprint lang-config">Header set MyHeader "Hello Joe. It took %D microseconds for Apache to serve this request."</pre>
471 <p>results in this header being added to the response:</p>
473 <div class="example"><p><code>
474 MyHeader: Hello Joe. It took D=3775428 microseconds for Apache
475 to serve this request.
480 Conditionally send <code>MyHeader</code> on the response if and
481 only if header <code>MyRequestHeader</code> is present on the request.
482 This is useful for constructing headers in response to some client
483 stimulus. Note that this example requires the services of the
484 <code class="module"><a href="../mod/mod_setenvif.html">mod_setenvif</a></code> module.
486 <pre class="prettyprint lang-config">SetEnvIf MyRequestHeader myvalue HAVE_MyRequestHeader
487 Header set MyHeader "%D %t mytext" env=HAVE_MyRequestHeader</pre>
490 <p>If the header <code>MyRequestHeader: myvalue</code> is present on
491 the HTTP request, the response will contain the following header:</p>
493 <div class="example"><p><code>
494 MyHeader: D=3775428 t=991424704447256 mytext
499 Enable DAV to work with Apache running HTTP through SSL hardware
500 (<a href="http://svn.haxx.se/users/archive-2006-03/0549.shtml">problem
501 description</a>) by replacing <var>https:</var> with
502 <var>http:</var> in the <var>Destination</var> header:
504 <pre class="prettyprint lang-config">RequestHeader edit Destination ^https: http: early</pre>
509 Set the same header value under multiple nonexclusive conditions,
510 but do not duplicate the value in the final header.
511 If all of the following conditions applied to a request (i.e.,
512 if the <code>CGI</code>, <code>NO_CACHE</code> and
513 <code>NO_STORE</code> environment variables all existed for the
516 <pre class="prettyprint lang-config">Header merge Cache-Control no-cache env=CGI
517 Header merge Cache-Control no-cache env=NO_CACHE
518 Header merge Cache-Control no-store env=NO_STORE</pre>
521 <p>then the response would contain the following header:</p>
523 <div class="example"><p><code>
524 Cache-Control: no-cache, no-store
527 <p>If <code>append</code> was used instead of <code>merge</code>,
528 then the response would contain the following header:</p>
530 <div class="example"><p><code>
531 Cache-Control: no-cache, no-cache, no-store
535 Set a test cookie if and only if the client didn't send us a cookie
536 <pre class="prettyprint lang-config">Header set Set-Cookie testcookie "expr=-z %{req:Cookie}"</pre>
540 Append a Caching header for responses with a HTTP status code of 200
541 <pre class="prettyprint lang-config">Header append Cache-Control s-maxage=600 "expr=%{REQUEST_STATUS} == 200"</pre>
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