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  21 <div id="page-content">
  22 <div id="preamble"><h1>Apache Module mod_headers</h1>
  23 <div class="toplang">
  24 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English">&nbsp;en&nbsp;</a> |
  25 <a href="../ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
  26 <a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
  27 </div>
  28 <table class="module"><tr><th><a href="module-dict.html#Description">Description:</a></th><td>Customization of HTTP request and response
  29 headers</td></tr>
  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></table>
  33 <h3>Summary</h3>
  34
  35     <p>This module provides directives to control and modify HTTP
  36     request and response headers. Headers can be merged, replaced
  37     or removed.</p>
  38 </div>
  39 <div id="quickview"><h3 class="directives">Directives</h3>
  40 <ul id="toc">
  41 <li><img alt="" src="../images/down.gif" /> <a href="#header">Header</a></li>
  42 <li><img alt="" src="../images/down.gif" /> <a href="#requestheader">RequestHeader</a></li>
  43 </ul>
  44 <h3>Topics</h3>
  45 <ul id="topics">
  46 <li><img alt="" src="../images/down.gif" /> <a href="#order">Order of Processing</a></li>
  47 <li><img alt="" src="../images/down.gif" /> <a href="#early">Early and Late Processing</a></li>
  48 <li><img alt="" src="../images/down.gif" /> <a href="#examples">Examples</a></li>
  49 </ul></div>
  50 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  51 <div class="section">
  52 <h2><a name="order" id="order">Order of Processing</a></h2>
  53
  54     <p>The directives provided by <code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can
  55     occur almost anywhere within the server configuration, and can be
  56     limited in scope by enclosing them in <a href="../sections.html">configuration sections</a>.</p>
  57
  58     <p>Order of processing is important and is affected both by the
  59     order in the configuration file and by placement in <a href="../sections.html#mergin">configuration sections</a>. These
  60     two headers have a different effect if reversed:</p>
  61
  62     <div class="example"><p><code>
  63       RequestHeader append MirrorID "mirror 12"<br />
  64       RequestHeader unset MirrorID
  65     </code></p></div>
  66
  67     <p>This way round, the <code>MirrorID</code> header is not set. If
  68     reversed, the MirrorID header is set to "mirror 12".</p>
  69 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  70 <div class="section">
  71 <h2><a name="early" id="early">Early and Late Processing</a></h2>
  72     <p><code class="module"><a href="../mod/mod_headers.html">mod_headers</a></code> can be applied either early or late
  73     in the request.  The normal mode is late, when Request Headers are
  74     set immediately before running the content generator and Response
  75     Headers just as the response is sent down the wire.  Always use
  76     Late mode in an operational server.</p>
  77
  78     <p>Early mode is designed as a test/debugging aid for developers.
  79     Directives defined using the <code>early</code> keyword are set
  80     right at the beginning of processing the request.  This means
  81     they can be used to simulate different requests and set up test
  82     cases, but it also means that headers may be changed at any time
  83     by other modules before generating a Response.</p>
  84
  85     <p>Because early directives are processed before the request path's
  86     configuration is traversed, early headers can only be set in a
  87     main server or virtual host context.  Early directives cannot depend
  88     on a request path, so they will fail in contexts such as
  89     <code>&lt;Directory&gt;</code> or <code>&lt;Location&gt;</code>.</p>
  90 </div><div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
  91 <div class="section">
  92 <h2><a name="examples" id="examples">Examples</a></h2>
  93
  94     <ol>
  95       <li>
  96         Copy all request headers that begin with "TS" to the
  97         response headers:
  98
  99         <div class="example"><p><code>
 100           Header echo ^TS
 101         </code></p></div>
 102       </li>
 103
 104       <li>
 105         Add a header, <code>MyHeader</code>, to the response including a
 106         timestamp for when the request was received and how long it
 107         took to begin serving the request. This header can be used by
 108         the client to intuit load on the server or in isolating
 109         bottlenecks between the client and the server.
 110
 111         <div class="example"><p><code>
 112           Header set MyHeader "%D %t"
 113         </code></p></div>
 114
 115         <p>results in this header being added to the response:</p>
 116
 117         <div class="example"><p><code>
 118           MyHeader: D=3775428 t=991424704447256
 119         </code></p></div>
 120       </li>
 121
 122       <li>
 123         Say hello to Joe
 124
 125         <div class="example"><p><code>
 126           Header set MyHeader "Hello Joe. It took %D microseconds \<br />
 127           for Apache to serve this request."
 128         </code></p></div>
 129
 130         <p>results in this header being added to the response:</p>
 131
 132         <div class="example"><p><code>
 133           MyHeader: Hello Joe. It took D=3775428 microseconds for Apache
 134           to serve this request.
 135         </code></p></div>
 136       </li>
 137
 138       <li>
 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.
 144
 145         <div class="example"><p><code>
 146           SetEnvIf MyRequestHeader myvalue HAVE_MyRequestHeader<br />
 147           Header set MyHeader "%D %t mytext" env=HAVE_MyRequestHeader
 148         </code></p></div>
 149
 150         <p>If the header <code>MyRequestHeader: myvalue</code> is present on
 151         the HTTP request, the response will contain the following header:</p>
 152
 153         <div class="example"><p><code>
 154           MyHeader: D=3775428 t=991424704447256 mytext
 155         </code></p></div>
 156       </li>
 157
 158       <li>
 159         Enable DAV to work with Apache running HTTP through SSL hardware
 160         (<a href="http://svn.haxx.se/users/archive-2006-03/0549.shtml">problem
 161         description</a>) by replacing <var>https:</var> with
 162         <var>http:</var> in the <var>Destination</var> header:
 163
 164         <div class="example"><p><code>
 165           RequestHeader edit Destination ^https: http: early
 166         </code></p></div>
 167       </li>
 168
 169       <li>
 170         Set the same header value under multiple non-exclusive conditions,
 171         but do not duplicate the value in the final header.
 172         If all of the following conditions applied to a request (i.e.,
 173         if the <code>CGI</code>, <code>NO_CACHE</code> and
 174         <code>NO_STORE</code> environment variables all existed for the
 175         request):
 176
 177         <div class="example"><p><code>
 178           Header merge Cache-Control no-cache env=CGI<br />
 179           Header merge Cache-Control no-cache env=NO_CACHE<br />
 180           Header merge Cache-Control no-store env=NO_STORE
 181         </code></p></div>
 182
 183         <p>then the response would contain the following header:</p>
 184
 185         <div class="example"><p><code>
 186           Cache-Control: no-cache, no-store
 187         </code></p></div>
 188
 189         <p>If <code>append</code> was used instead of <code>merge</code>,
 190         then the response would contain the following header:</p>
 191
 192         <div class="example"><p><code>
 193           Cache-Control: no-cache, no-cache, no-store
 194         </code></p></div>
 195       </li>
 196     </ol>
 197 </div>
 198 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 199 <div class="directive-section"><h2><a name="Header" id="Header">Header</a> <a name="header" id="header">Directive</a></h2>
 200 <table class="directive">
 201 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP response headers</td></tr>
 202 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>Header [<var>condition</var>] add|append|echo|edit|merge|set|unset
 203 <var>header</var> [<var>value</var>] [early|env=[!]<var>variable</var>]</code></td></tr>
 204 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
 205 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
 206 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
 207 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
 208 </table>
 209     <p>This directive can replace, merge or remove HTTP response
 210     headers. The header is modified just after the content handler
 211     and output filters are run, allowing outgoing headers to be
 212     modified.</p>
 213
 214     <p>The optional <var>condition</var> can be either <code>onsuccess</code>
 215     or <code>always</code>. It determines, which internal header table should be
 216     operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code>
 217     status codes and <code>always</code> for all status codes (including
 218     <code>2<var>xx</var></code>). Especially if you want to unset headers
 219     set by certain modules, you should try out, which table is affected.</p>
 220
 221     <p>The action it performs is determined by the second
 222     argument. This can be one of the following values:</p>
 223
 224     <dl>
 225     <dt><code>add</code></dt>
 226     <dd>The response header is added to the existing set of headers,
 227     even if this header already exists. This can result in two
 228     (or more) headers having the same name. This can lead to
 229     unforeseen consequences, and in general <code>set</code>,
 230     <code>append</code> or <code>merge</code> should be used instead.</dd>
 231
 232     <dt><code>append</code></dt>
 233     <dd>The response header is appended to any existing header of
 234     the same name. When a new value is merged onto an existing
 235     header it is separated from the existing header with a comma.
 236     This is the HTTP standard way of giving a header multiple values.</dd>
 237
 238     <dt><code>echo</code></dt>
 239     <dd>Request headers with this name are echoed back in the
 240     response headers. <var>header</var> may be a
 241     <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>.
 242     <var>value</var> must be omitted.</dd>
 243
 244     <dt><code>edit</code></dt>
 245     <dd>If this request header exists, its value is transformed according
 246     to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>
 247     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>
 248     is a replacement string, which may contain backreferences.</dd>
 249
 250     <dt><code>merge</code></dt>
 251     <dd>The response header is appended to any existing header of
 252     the same name, unless the value to be appended already appears in the
 253     header's comma-delimited list of values.  When a new value is merged onto
 254     an existing header it is separated from the existing header with a comma.
 255     This is the HTTP standard way of giving a header multiple values.
 256     Values are compared in a case sensitive manner, and after
 257     all format specifiers have been processed.  Values in double quotes
 258     are considered different from otherwise identical unquoted values.</dd>
 259
 260     <dt><code>set</code></dt>
 261     <dd>The response header is set, replacing any previous header
 262     with this name. The <var>value</var> may be a format string.</dd>
 263
 264     <dt><code>unset</code></dt>
 265     <dd>The response header of this name is removed, if it exists.
 266     If there are multiple headers of the same name, all will be
 267     removed. <var>value</var> must be omitted.</dd>
 268     </dl>
 269
 270     <p>This argument is followed by a <var>header</var> name, which
 271     can include the final colon, but it is not required. Case is
 272     ignored for <code>set</code>, <code>append</code>, <code>merge</code>,
 273     <code>add</code>, <code>unset</code> and <code>edit</code>.
 274     The <var>header</var> name for <code>echo</code>
 275     is case sensitive and may be a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular
 276     expression</a>.</p>
 277
 278     <p>For <code>set</code>, <code>append</code>, <code>merge</code> and
 279     <code>add</code> a <var>value</var> is specified as the third argument.
 280     If <var>value</var>
 281     contains spaces, it should be surrounded by double quotes.
 282     <var>value</var> may be a character string, a string containing format
 283     specifiers or a combination of both. The following format specifiers
 284     are supported in <var>value</var>:</p>
 285
 286     <table class="bordered"><tr class="header"><th>Format</th><th>Description</th></tr>
 287 <tr><td><code>%%</code></td>
 288         <td>The percent sign</td></tr>
 289 <tr class="odd"><td><code>%t</code></td>
 290         <td>The time the request was received in Universal Coordinated Time
 291         since the epoch (Jan. 1, 1970) measured in microseconds. The value
 292         is preceded by <code>t=</code>.</td></tr>
 293 <tr><td><code>%D</code></td>
 294         <td>The time from when the request was received to the time the
 295         headers are sent on the wire. This is a measure of the duration
 296         of the request. The value is preceded by <code>D=</code>.</td></tr>
 297 <tr class="odd"><td><code>%{VARNAME}e</code></td>
 298         <td>The contents of the <a href="../env.html">environment
 299         variable</a> <code>VARNAME</code>.</td></tr>
 300 <tr><td><code>%{VARNAME}s</code></td>
 301         <td>The contents of the <a href="mod_ssl.html#envvars">SSL environment
 302         variable</a> <code>VARNAME</code>, if <code class="module"><a href="../mod/mod_ssl.html">mod_ssl</a></code> is enabled.</td></tr>
 303 </table>
 304
 305     <div class="note"><h3>Note</h3>
 306       <p>The <code>%s</code> format specifier is only available in
 307       Apache 2.1 and later; it can be used instead of <code>%e</code>
 308       to avoid the overhead of enabling <code>SSLOptions
 309       +StdEnvVars</code>.  If <code>SSLOptions +StdEnvVars</code> must
 310       be enabled anyway for some other reason, <code>%e</code> will be
 311       more efficient than <code>%s</code>.</p>
 312     </div>
 313
 314     <p>For <code>edit</code> there is both a <var>value</var> argument
 315     which is a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>,
 316     and an additional <var>replacement</var> string.</p>
 317
 318     <p>The <code class="directive">Header</code> directive may be followed by an
 319     an additional argument, which may be used to specify conditions under
 320     which the action will be taken, or may be the keyword <code>early</code>
 321     to specify <a href="#early">early processing</a>. If the
 322     <a href="../env.html">environment variable</a> specified in the
 323     <code>env=<var>...</var></code> argument exists (or if the environment
 324     variable does not exist and <code>env=!<var>...</var></code> is specified)
 325     then the action specified by the <code class="directive">Header</code> directive
 326     will take effect. Otherwise, the directive will have no effect
 327     on the request.</p>
 328
 329     <p>Except in <a href="#early">early</a> mode, the
 330     <code class="directive">Header</code> directives are processed just
 331     before the response is sent to the network. These means that it is
 332     possible to set and/or override most headers, except for those headers
 333     added by the header filter.</p>
 334
 335 </div>
 336 <div class="top"><a href="#page-header"><img alt="top" src="../images/up.gif" /></a></div>
 337 <div class="directive-section"><h2><a name="RequestHeader" id="RequestHeader">RequestHeader</a> <a name="requestheader" id="requestheader">Directive</a></h2>
 338 <table class="directive">
 339 <tr><th><a href="directive-dict.html#Description">Description:</a></th><td>Configure HTTP request headers</td></tr>
 340 <tr><th><a href="directive-dict.html#Syntax">Syntax:</a></th><td><code>RequestHeader add|append|edit|merge|set|unset <var>header</var>
 341 [<var>value</var>] [<var>replacement</var>] [early|env=[!]<var>variable</var>]</code></td></tr>
 342 <tr><th><a href="directive-dict.html#Context">Context:</a></th><td>server config, virtual host, directory, .htaccess</td></tr>
 343 <tr><th><a href="directive-dict.html#Override">Override:</a></th><td>FileInfo</td></tr>
 344 <tr><th><a href="directive-dict.html#Status">Status:</a></th><td>Extension</td></tr>
 345 <tr><th><a href="directive-dict.html#Module">Module:</a></th><td>mod_headers</td></tr>
 346 </table>
 347     <p>This directive can replace, merge, change or remove HTTP request
 348     headers. The header is modified just before the content handler
 349     is run, allowing incoming headers to be modified. The action it
 350     performs is determined by the first argument. This can be one
 351     of the following values:</p>
 352
 353     <dl>
 354
 355     <dt><code>add</code></dt>
 356     <dd>The request header is added to the existing set of headers,
 357     even if this header already exists. This can result in two
 358     (or more) headers having the same name. This can lead to
 359     unforeseen consequences, and in general <code>set</code>,
 360     <code>append</code> or <code>merge</code> should be used instead.</dd>
 361
 362     <dt><code>append</code></dt>
 363     <dd>The request header is appended to any existing header of the
 364     same name. When a new value is merged onto an existing header
 365     it is separated from the existing header with a comma. This
 366     is the HTTP standard way of giving a header multiple
 367     values.</dd>
 368
 369     <dt><code>edit</code></dt>
 370     <dd>If this request header exists, its value is transformed according
 371     to a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a>
 372     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>
 373     is a replacement string, which may contain backreferences.</dd>
 374
 375     <dt><code>merge</code></dt>
 376     <dd>The response header is appended to any existing header of
 377     the same name, unless the value to be appended already appears in the
 378     existing header's comma-delimited list of values.  When a new value is
 379     merged onto an existing header it is separated from the existing header
 380     with a comma.  This is the HTTP standard way of giving a header multiple
 381     values.  Values are compared in a case sensitive manner, and after
 382     all format specifiers have been processed.  Values in double quotes
 383     are considered different from otherwise identical unquoted values.</dd>
 384
 385     <dt><code>set</code></dt>
 386     <dd>The request header is set, replacing any previous header
 387     with this name</dd>
 388
 389     <dt><code>unset</code></dt>
 390     <dd>The request header of this name is removed, if it exists. If
 391     there are multiple headers of the same name, all will be removed.
 392     <var>value</var> must be omitted.</dd>
 393     </dl>
 394
 395     <p>This argument is followed by a header name, which can
 396     include the final colon, but it is not required. Case is
 397     ignored. For <code>set</code>, <code>append</code>, <code>merge</code> and
 398     <code>add</code> a <var>value</var> is given as the third argument. If a
 399     <var>value</var> contains spaces, it should be surrounded by double
 400     quotes. For <code>unset</code>, no <var>value</var> should be given.
 401     <var>value</var> may be a character string, a string containing format
 402     specifiers or a combination of both. The supported format specifiers
 403     are the same as for the <code class="directive"><a href="#header">Header</a></code>,
 404     please have a look there for details.  For <code>edit</code> both
 405     a <var>value</var> and a <var>replacement</var> are required, and are
 406     a <a class="glossarylink" href="../glossary.html#regex" title="see glossary">regular expression</a> and a
 407     replacement string respectively.</p>
 408
 409     <p>The <code class="directive">RequestHeader</code> directive may be followed by
 410     an additional argument, which may be used to specify conditions under
 411     which the action will be taken, or may be the keyword <code>early</code>
 412     to specify <a href="#early">early processing</a>. If the
 413     <a href="../env.html">environment
 414     variable</a> specified in the <code>env=<var>...</var></code> argument
 415     exists (or if the environment variable does not exist and
 416     <code>env=!<var>...</var></code> is specified) then the action specified
 417     by the <code class="directive">RequestHeader</code> directive will take effect.
 418     Otherwise, the directive will have no effect on the request.</p>
 419
 420     <p>Except in <a href="#early">early</a> mode, the
 421     <code class="directive">RequestHeader</code> directive is processed
 422     just before the request is run by its handler in the fixup phase.
 423     This should allow headers generated by the browser, or by Apache
 424     input filters to be overridden or modified.</p>
 425
 426 </div>
 427 </div>
 428 <div class="bottomlang">
 429 <p><span>Available Languages: </span><a href="../en/mod/mod_headers.html" title="English">&nbsp;en&nbsp;</a> |
 430 <a href="../ja/mod/mod_headers.html" hreflang="ja" rel="alternate" title="Japanese">&nbsp;ja&nbsp;</a> |
 431 <a href="../ko/mod/mod_headers.html" hreflang="ko" rel="alternate" title="Korean">&nbsp;ko&nbsp;</a></p>
 432 </div><div id="footer">
 433 <p class="apache">Copyright 2009 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>
 434 <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>
 435 </body></html>