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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>
56 <h2><a name="order" id="order">Order of Processing</a></h2>
58 <p>The directives provided by <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can
59 occur almost anywhere within the server configuration, and can be
60 limited in scope by enclosing them in <a href="../sections.html">configuration sections</a>.</p>
62 <p>Order of processing is important and is affected both by the
63 order in the configuration file and by placement in <a href="../sections.html#mergin">configuration sections</a>. These
64 two directives have a different effect if reversed:</p>
66 <pre class="prettyprint lang-config">RequestHeader append MirrorID "mirror 12"
67 RequestHeader unset MirrorID</pre>
70 <p>This way round, the <code>MirrorID</code> header is not set. If
71 reversed, the MirrorID header is set to "mirror 12".</p>
72 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
74 <h2><a name="early" id="early">Early and Late Processing</a></h2>
75 <p><code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can be applied either early or late
76 in the request. The normal mode is late, when <em>Request</em> Headers are
77 set immediately before running the content generator and <em>Response</em>
78 Headers just as the response is sent down the wire. Always use
79 Late mode in an operational server.</p>
81 <p>Early mode is designed as a test/debugging aid for developers.
82 Directives defined using the <code>early</code> keyword are set
83 right at the beginning of processing the request. This means
84 they can be used to simulate different requests and set up test
85 cases, but it also means that headers may be changed at any time
86 by other modules before generating a Response.</p>
88 <p>Because early directives are processed before the request path's
89 configuration is traversed, early headers can only be set in a
90 main server or virtual host context. Early directives cannot depend
91 on a request path, so they will fail in contexts such as
92 <code class="directive"><a href="../mod/core.html#directory"><Directory></a></code> or
93 <code class="directive"><a href="../mod/core.html#location"><Location></a></code>.</p>
94 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
96 <h2><a name="examples" id="examples">Examples</a></h2>
100 Copy all request headers that begin with "TS" to the
103 <pre class="prettyprint lang-config">Header echo ^TS</pre>
108 Add a header, <code>MyHeader</code>, to the response including a
109 timestamp for when the request was received and how long it
110 took to begin serving the request. This header can be used by
111 the client to intuit load on the server or in isolating
112 bottlenecks between the client and the server.
114 <pre class="prettyprint lang-config">Header set MyHeader "%D %t"</pre>
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 <pre class="prettyprint lang-config">Header set MyHeader "Hello Joe. It took %D microseconds for Apache to serve this request."</pre>
130 <p>results in this header being added to the response:</p>
132 <div class="example"><p><code>
133 MyHeader: Hello Joe. It took D=3775428 microseconds for Apache
134 to serve this request.
139 Conditionally send <code>MyHeader</code> on the response if and
140 only if header <code>MyRequestHeader</code> is present on the request.
141 This is useful for constructing headers in response to some client
142 stimulus. Note that this example requires the services of the
143 <code class="module"><a href="../mod/mod_setenvif.html">mod_setenvif</a></code> module.
145 <pre class="prettyprint lang-config">SetEnvIf MyRequestHeader myvalue HAVE_MyRequestHeader
146 Header set MyHeader "%D %t mytext" env=HAVE_MyRequestHeader</pre>
149 <p>If the header <code>MyRequestHeader: myvalue</code> is present on
150 the HTTP request, the response will contain the following header:</p>
152 <div class="example"><p><code>
153 MyHeader: D=3775428 t=991424704447256 mytext
158 Enable DAV to work with Apache running HTTP through SSL hardware
159 (<a href="http://svn.haxx.se/users/archive-2006-03/0549.shtml">problem
160 description</a>) by replacing <var>https:</var> with
161 <var>http:</var> in the <var>Destination</var> header:
163 <pre class="prettyprint lang-config">RequestHeader edit Destination ^https: http: early</pre>
168 Set the same header value under multiple nonexclusive conditions,
169 but do not duplicate the value in the final header.
170 If all of the following conditions applied to a request (i.e.,
171 if the <code>CGI</code>, <code>NO_CACHE</code> and
172 <code>NO_STORE</code> environment variables all existed for the
175 <pre class="prettyprint lang-config">Header merge Cache-Control no-cache env=CGI
176 Header merge Cache-Control no-cache env=NO_CACHE
177 Header merge Cache-Control no-store env=NO_STORE</pre>
180 <p>then the response would contain the following header:</p>
182 <div class="example"><p><code>
183 Cache-Control: no-cache, no-store
186 <p>If <code>append</code> was used instead of <code>merge</code>,
187 then the response would contain the following header:</p>
189 <div class="example"><p><code>
190 Cache-Control: no-cache, no-cache, no-store
194 Set a test cookie if and only if the client didn't send us a cookie
195 <pre class="prettyprint lang-config">Header set Set-Cookie testcookie "expr=-z %{req:Cookie}"</pre>
199 Append a Caching header for responses with a HTTP status code of 200
200 <pre class="prettyprint lang-config">Header append Cache-Control s-maxage=600 "expr=%{REQUEST_STATUS} == 200"</pre>
206 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
207 <div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2>
208 <table class="directive">
209 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP response headers</td></tr>
210 <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
211 <var>header</var> [[expr=]<var>value</var> [<var>replacement</var>]
212 [early|env=[!]<var>varname</var>|expr=<var>expression</var>]]
214 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
215 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
216 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
217 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
218 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
219 available in 2.4.10 and later</td></tr>
221 <p>This directive can replace, merge or remove HTTP response
222 headers. The header is modified just after the content handler
223 and output filters are run, allowing outgoing headers to be
226 <p> The optional <var>condition</var> argument determines which internal
227 table of responses headers this directive will operate against. Despite the
228 name, the default value of <code>onsuccess</code> does <em>not</em> limit
229 an <var>action</var> to responses with a 2xx status code. Headers set under
230 this condition are still used when, for example, a request is <em>successfully</em>
231 proxied or generated by CGI, even when they have generated a failing status code.</p>
233 <p>When your action is a function of an existing header, you may need to specify
234 a condition of <code>always</code>, depending on which internal table the
235 original header was set in. The table that corresponds to <code>always</code> is
236 used for locally generated error responses as well as successful responses.
237 Note also that repeating this directive with both conditions makes sense in
238 some scenarios because <code>always</code> is not a superset of
239 <code>onsuccess</code> with respect to existing headers:</p>
242 <li> You're adding a header to a locally generated non-success (non-2xx) response, such
243 as a redirect, in which case only the table corresponding to
244 <code>always</code> is used in the ultimate response.</li>
245 <li> You're modifying or removing a header generated by a CGI script,
246 in which case the CGI scripts are in the table corresponding to
247 <code>always</code> and not in the default table.</li>
248 <li> You're modifying or removing a header generated by some piece of
249 the server but that header is not being found by the default
250 <code>onsuccess</code> condition.</li>
253 <p>Separately from the <var>condition</var> parameter described above, you
254 can limit an action based on HTTP status codes for e.g. proxied or CGI
255 requests. See the example that uses %{REQUEST_STATUS} in the section above.</p>
257 <p>The action it performs is determined by the first
258 argument (second argument if a <var>condition</var> is specified).
259 This can be one of the following values:</p>
262 <dt><code>add</code></dt>
263 <dd>The response header is added to the existing set of headers,
264 even if this header already exists. This can result in two
265 (or more) headers having the same name. This can lead to
266 unforeseen consequences, and in general <code>set</code>,
267 <code>append</code> or <code>merge</code> should be used instead.</dd>
269 <dt><code>append</code></dt>
270 <dd>The response header is appended to any existing header of
271 the same name. When a new value is merged onto an existing
272 header it is separated from the existing header with a comma.
273 This is the HTTP standard way of giving a header multiple values.</dd>
275 <dt><code>echo</code></dt>
276 <dd>Request headers with this name are echoed back in the
277 response headers. <var>header</var> may be a
278 <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>.
279 <var>value</var> must be omitted.</dd>
281 <dt><code>edit</code></dt>
282 <dt><code>edit*</code></dt>
283 <dd>If this response header exists, its value is transformed according
284 to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>
285 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>
286 is a replacement string, which may contain backreferences or format specifiers.
287 The <code>edit</code> form will match and replace exactly once
288 in a header value, whereas the <code>edit*</code> form will replace
289 <em>every</em> instance of the search pattern if it appears more
292 <dt><code>merge</code></dt>
293 <dd>The response header is appended to any existing header of
294 the same name, unless the value to be appended already appears in the
295 header's comma-delimited list of values. When a new value is merged onto
296 an existing header it is separated from the existing header with a comma.
297 This is the HTTP standard way of giving a header multiple values.
298 Values are compared in a case sensitive manner, and after
299 all format specifiers have been processed. Values in double quotes
300 are considered different from otherwise identical unquoted values.</dd>
302 <dt><code>set</code></dt>
303 <dd>The response header is set, replacing any previous header
304 with this name. The <var>value</var> may be a format string.</dd>
306 <dt><code>setifempty</code></dt>
307 <dd>The request header is set, but only if there is no previous header
308 with this name.<br />
309 Available in 2.4.7 and later.</dd>
311 <dt><code>unset</code></dt>
312 <dd>The response header of this name is removed, if it exists.
313 If there are multiple headers of the same name, all will be
314 removed. <var>value</var> must be omitted.</dd>
316 <dt><code>note</code></dt>
317 <dd>The value of the named response <var>header</var> is copied into an
318 internal note whose name is given by <var>value</var>. This is useful
319 if a header sent by a CGI or proxied resource is configured to be unset
320 but should also be logged.<br />
321 Available in 2.4.7 and later.</dd>
325 <p>This argument is followed by a <var>header</var> name, which
326 can include the final colon, but it is not required. Case is
327 ignored for <code>set</code>, <code>append</code>, <code>merge</code>,
328 <code>add</code>, <code>unset</code> and <code>edit</code>.
329 The <var>header</var> name for <code>echo</code>
330 is case sensitive and may be a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular
333 <p>For <code>set</code>, <code>append</code>, <code>merge</code> and
334 <code>add</code> a <var>value</var> is specified as the next argument.
336 contains spaces, it should be surrounded by double quotes.
337 <var>value</var> may be a character string, a string containing
338 <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> specific format specifiers (and character
339 literals), or an <a href="../expr.html">ap_expr</a> expression prefixed
340 with <em>expr=</em></p>
342 <p> The following format specifiers are supported in <var>value</var>:</p>
344 <table class="bordered"><tr class="header"><th>Format</th><th>Description</th></tr>
345 <tr><td><code>%%</code></td>
346 <td>The percent sign</td></tr>
347 <tr class="odd"><td><code>%t</code></td>
348 <td>The time the request was received in Universal Coordinated Time
349 since the epoch (Jan. 1, 1970) measured in microseconds. The value
350 is preceded by <code>t=</code>.</td></tr>
351 <tr><td><code>%D</code></td>
352 <td>The time from when the request was received to the time the
353 headers are sent on the wire. This is a measure of the duration
354 of the request. The value is preceded by <code>D=</code>.
355 The value is measured in microseconds.</td></tr>
356 <tr class="odd"><td><code>%l</code></td>
357 <td>The current load averages of the actual server itself. It is
358 designed to expose the values obtained by <code>getloadavg()</code>
359 and this represents the current load average, the 5 minute average, and
360 the 15 minute average. The value is preceded by <code>l=</code> with each
361 average separated by <code>/</code>.<br />
362 Available in 2.4.4 and later.
364 <tr><td><code>%i</code></td>
365 <td>The current idle percentage of httpd (0 to 100) based on available
366 processes and threads. The value is preceded by <code>i=</code>.<br />
367 Available in 2.4.4 and later.
369 <tr class="odd"><td><code>%b</code></td>
370 <td>The current busy percentage of httpd (0 to 100) based on available
371 processes and threads. The value is preceded by <code>b=</code>.<br />
372 Available in 2.4.4 and later.
374 <tr><td><code>%{VARNAME}e</code></td>
375 <td>The contents of the <a href="../env.html">environment
376 variable</a> <code>VARNAME</code>.</td></tr>
377 <tr class="odd"><td><code>%{VARNAME}s</code></td>
378 <td>The contents of the <a href="mod_ssl.html#envvars">SSL environment
379 variable</a> <code>VARNAME</code>, if <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> is enabled.</td></tr>
382 <div class="note"><h3>Note</h3>
383 <p>The <code>%s</code> format specifier is only available in
384 Apache 2.1 and later; it can be used instead of <code>%e</code>
385 to avoid the overhead of enabling <code>SSLOptions
386 +StdEnvVars</code>. If <code>SSLOptions +StdEnvVars</code> must
387 be enabled anyway for some other reason, <code>%e</code> will be
388 more efficient than <code>%s</code>.</p>
391 <p>For <code>edit</code> there is both a <var>value</var> argument
392 which is a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>,
393 and an additional <var>replacement</var> string. As of version 2.4.7
394 the replacement string may also contain format specifiers.</p>
396 <p>The <code class="directive">Header</code> directive may be followed by
397 an additional argument, which may be any of:</p>
399 <dt><code>early</code></dt>
400 <dd>Specifies <a href="#early">early processing</a>.</dd>
401 <dt><code>env=[!]<var>varname</var></code></dt>
402 <dd>The directive is applied if and only if the <a href="../env.html">environment variable</a> <code>varname</code> exists.
403 A <code>!</code> in front of <code>varname</code> reverses the test,
404 so the directive applies only if <code>varname</code> is unset.</dd>
405 <dt><code>expr=<var>expression</var></code></dt>
406 <dd>The directive is applied if and only if <var>expression</var>
407 evaluates to true. Details of expression syntax and evaluation are
408 documented in the <a href="../expr.html">ap_expr</a> documentation.</dd>
411 <p>Except in <a href="#early">early</a> mode, the
412 <code class="directive">Header</code> directives are processed just
413 before the response is sent to the network. This means that it is
414 possible to set and/or override most headers, except for some headers
415 added by the HTTP header filter. Prior to 2.2.12, it was not possible
416 to change the Content-Type header with this directive.</p>
420 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
421 <div class="directive-section"><h2><a name="RequestHeader" id="RequestHeader">RequestHeader</a> <a name="requestheader" id="requestheader">Directive</a></h2>
422 <table class="directive">
423 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP request headers</td></tr>
424 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RequestHeader add|append|edit|edit*|merge|set|setifempty|unset
425 <var>header</var> [[expr=]<var>value</var> [<var>replacement</var>]
426 [early|env=[!]<var>varname</var>|expr=<var>expression</var>]]
428 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
429 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
430 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
431 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
432 <tr><th><a href="directive-dict.html#Compatibility">Compatibility:</a></th><td>SetIfEmpty available in 2.4.7 and later, expr=value
433 available in 2.4.10 and later</td></tr>
435 <p>This directive can replace, merge, change or remove HTTP request
436 headers. The header is modified just before the content handler
437 is run, allowing incoming headers to be modified. The action it
438 performs is determined by the first argument. This can be one
439 of the following values:</p>
443 <dt><code>add</code></dt>
444 <dd>The request header is added to the existing set of headers,
445 even if this header already exists. This can result in two
446 (or more) headers having the same name. This can lead to
447 unforeseen consequences, and in general <code>set</code>,
448 <code>append</code> or <code>merge</code> should be used instead.</dd>
450 <dt><code>append</code></dt>
451 <dd>The request header is appended to any existing header of the
452 same name. When a new value is merged onto an existing header
453 it is separated from the existing header with a comma. This
454 is the HTTP standard way of giving a header multiple
457 <dt><code>edit</code></dt>
458 <dt><code>edit*</code></dt>
459 <dd>If this request header exists, its value is transformed according
460 to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>
461 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>
462 is a replacement string, which may contain backreferences or format specifiers.
463 The <code>edit</code> form will match and replace exactly once
464 in a header value, whereas the <code>edit*</code> form will replace
465 <em>every</em> instance of the search pattern if it appears more
468 <dt><code>merge</code></dt>
469 <dd>The request header is appended to any existing header of
470 the same name, unless the value to be appended already appears in the
471 existing header's comma-delimited list of values. When a new value is
472 merged onto an existing header it is separated from the existing header
473 with a comma. This is the HTTP standard way of giving a header multiple
474 values. Values are compared in a case sensitive manner, and after
475 all format specifiers have been processed. Values in double quotes
476 are considered different from otherwise identical unquoted values.</dd>
478 <dt><code>set</code></dt>
479 <dd>The request header is set, replacing any previous header
482 <dt><code>setifempty</code></dt>
483 <dd>The request header is set, but only if there is no previous header
484 with this name.<br />
485 Available in 2.4.7 and later.</dd>
487 <dt><code>unset</code></dt>
488 <dd>The request header of this name is removed, if it exists. If
489 there are multiple headers of the same name, all will be removed.
490 <var>value</var> must be omitted.</dd>
493 <p>This argument is followed by a header name, which can
494 include the final colon, but it is not required. Case is
495 ignored. For <code>set</code>, <code>append</code>, <code>merge</code> and
496 <code>add</code> a <var>value</var> is given as the third argument. If a
497 <var>value</var> contains spaces, it should be surrounded by double
498 quotes. For <code>unset</code>, no <var>value</var> should be given.
499 <var>value</var> may be a character string, a string containing format
500 specifiers or a combination of both. The supported format specifiers
501 are the same as for the <code class="directive"><a href="#header">Header</a></code>,
502 please have a look there for details. For <code>edit</code> both
503 a <var>value</var> and a <var>replacement</var> are required, and are
504 a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a> and a
505 replacement string respectively.</p>
507 <p>The <code class="directive">RequestHeader</code> directive may be followed by
508 an additional argument, which may be any of:</p>
510 <dt><code>early</code></dt>
511 <dd>Specifies <a href="#early">early processing</a>.</dd>
512 <dt><code>env=[!]<var>varname</var></code></dt>
513 <dd>The directive is applied if and only if the <a href="../env.html">environment variable</a> <code>varname</code> exists.
514 A <code>!</code> in front of <code>varname</code> reverses the test,
515 so the directive applies only if <code>varname</code> is unset.</dd>
516 <dt><code>expr=<var>expression</var></code></dt>
517 <dd>The directive is applied if and only if <var>expression</var>
518 evaluates to true. Details of expression syntax and evaluation are
519 documented in the <a href="../expr.html">ap_expr</a> documentation.</dd>
522 <p>Except in <a href="#early">early</a> mode, the
523 <code class="directive">RequestHeader</code> directive is processed
524 just before the request is run by its handler in the fixup phase.
525 This should allow headers generated by the browser, or by Apache
526 input filters to be overridden or modified.</p>
530 <div class="bottomlang">
531 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English"> en </a> |
532 <a href="../fr/mod/mod_headers.html" hreflang="fr" rel="alternate" title="Français"> fr </a> |
533 <a href="../ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese"> ja </a> |
534 <a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean"> ko </a></p>
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