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| <modulesynopsis metafile="mod_headers.xml.meta"> |
| |
| <name>mod_headers</name> |
| <description>Customization of HTTP request and response |
| headers</description> |
| <status>Extension</status> |
| <sourcefile>mod_headers.c</sourcefile> |
| <identifier>headers_module</identifier> |
| <compatibility><directive module="mod_headers">RequestHeader</directive> |
| is available only in Apache 2.0</compatibility> |
| |
| <summary> |
| <p>This module provides directives to control and modify HTTP |
| request and response headers. Headers can be merged, replaced |
| or removed.</p> |
| </summary> |
| |
| <section id="order"><title>Order of Processing</title> |
| |
| <p>The directives provided by <module>mod_headers</module> can |
| occur almost anywhere within the server configuration, and can be |
| limited in scope by enclosing them in <a |
| href="../sections.html">configuration sections</a>.</p> |
| |
| <p>Order of processing is important and is affected both by the |
| order in the configuration file and by placement in <a |
| href="../sections.html#mergin">configuration sections</a>. These |
| two headers have a different effect if reversed:</p> |
| |
| <example> |
| RequestHeader append MirrorID "mirror 12"<br /> |
| RequestHeader unset MirrorID |
| </example> |
| |
| <p>This way round, the <code>MirrorID</code> header is not set. If |
| reversed, the MirrorID header is set to "mirror 12".</p> |
| </section> |
| |
| <section id="early"><title>Early and Late Processing</title> |
| <p><module>mod_headers</module> can be applied either early or late |
| in the request. The normal mode is late, when Request Headers are |
| set immediately before running the content generator and Response |
| Headers just as the response is sent down the wire. Always use |
| Late mode in an operational server.</p> |
| |
| <p>Early mode is designed as a test/debugging aid for developers. |
| Directives defined using the <code>early</code> keyword are set |
| right at the beginning of processing the request. This means |
| they can be used to simulate different requests and set up test |
| cases, but it also means that headers may be changed at any time |
| by other modules before generating a Response.</p> |
| |
| <p>Because early directives are processed before the request path's |
| configuration is traversed, early headers can only be set in a |
| main server or virtual host context. Early directives cannot depend |
| on a request path, so they will fail in contexts such as |
| <code><Directory></code> or <code><Location></code>.</p> |
| </section> |
| |
| <section id="examples"><title>Examples</title> |
| |
| <ol> |
| <li> |
| Copy all request headers that begin with "TS" to the |
| response headers: |
| |
| <example> |
| Header echo ^TS |
| </example> |
| </li> |
| |
| <li> |
| Add a header, <code>MyHeader</code>, to the response including a |
| timestamp for when the request was received and how long it |
| took to begin serving the request. This header can be used by |
| the client to intuit load on the server or in isolating |
| bottlenecks between the client and the server. |
| |
| <example> |
| Header add MyHeader "%D %t" |
| </example> |
| |
| <p>results in this header being added to the response:</p> |
| |
| <example> |
| MyHeader: D=3775428 t=991424704447256 |
| </example> |
| </li> |
| |
| <li> |
| Say hello to Joe |
| |
| <example> |
| Header add MyHeader "Hello Joe. It took %D microseconds \<br /> |
| for Apache to serve this request." |
| </example> |
| |
| <p>results in this header being added to the response:</p> |
| |
| <example> |
| MyHeader: Hello Joe. It took D=3775428 microseconds for Apache |
| to serve this request. |
| </example> |
| </li> |
| |
| <li> |
| Conditionally send <code>MyHeader</code> on the response if and |
| only if header "MyRequestHeader" is present on the request. This |
| is useful for constructing headers in response to some client |
| stimulus. Note that this example requires the services of the |
| <module>mod_setenvif</module> module. |
| |
| <example> |
| SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br /> |
| Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader<br /> |
| </example> |
| |
| <p>If the header <code>MyRequestHeader: value</code> is present on |
| the HTTP request, the response will contain the following header:</p> |
| |
| <example> |
| MyHeader: D=3775428 t=991424704447256 mytext |
| </example> |
| </li> |
| </ol> |
| </section> |
| |
| <directivesynopsis> |
| <name>RequestHeader</name> |
| <description>Configure HTTP request headers</description> |
| <syntax>RequestHeader set|append|add|unset <var>header</var> |
| [<var>value</var>] [early|env=[!]<var>variable</var>]</syntax> |
| <contextlist><context>server config</context><context>virtual host</context> |
| <context>directory</context><context>.htaccess</context></contextlist> |
| <override>FileInfo</override> |
| |
| <usage> |
| <p>This directive can replace, merge or remove HTTP request |
| headers. The header is modified just before the content handler |
| is run, allowing incoming headers to be modified. The action it |
| performs is determined by the first argument. This can be one |
| of the following values:</p> |
| |
| <dl> |
| <dt><code>set</code></dt> |
| <dd>The request header is set, replacing any previous header |
| with this name</dd> |
| |
| <dt><code>append</code></dt> |
| <dd>The request header is appended to any existing header of the |
| same name. When a new value is merged onto an existing header |
| it is separated from the existing header with a comma. This |
| is the HTTP standard way of giving a header multiple |
| values.</dd> |
| |
| <dt><code>add</code></dt> |
| <dd>The request header is added to the existing set of headers, |
| even if this header already exists. This can result in two |
| (or more) headers having the same name. This can lead to |
| unforeseen consequences, and in general <code>append</code> should be |
| used instead.</dd> |
| |
| <dt><code>unset</code></dt> |
| <dd>The request header of this name is removed, if it exists. If |
| there are multiple headers of the same name, all will be removed. |
| <var>value</var> must be omitted.</dd> |
| </dl> |
| |
| <p>This argument is followed by a header name, which can |
| include the final colon, but it is not required. Case is |
| ignored. For <code>add</code>, <code>append</code> and |
| <code>set</code> a <var>value</var> is given as the third argument. If |
| <var>value</var> contains spaces, it should be surrounded by double |
| quotes. For unset, no <var>value</var> should be given. |
| <var>value</var> may be a character string, a string containing format |
| specifiers or a combination of both. The supported format specifiers |
| are the same as for the <directive module="mod_headers">Header</directive>, |
| please have a look there for details.</p> |
| |
| <p>The <directive>RequestHeader</directive> directive may be followed by |
| an additional argument, which may be used to specify conditions under |
| which the action will be taken, or may be the keyword <code>early</code> |
| to specify <a href="#early">early processing</a>. If the |
| <a href="../env.html">environment |
| variable</a> specified in the <code>env=<var>...</var></code> argument |
| exists (or if the environment variable does not exist and |
| <code>env=!<var>...</var></code> is specified) then the action specified |
| by the <directive>RequestHeader</directive> directive will take effect. |
| Otherwise, the directive will have no effect on the request.</p> |
| |
| <p>Except in <a href="#early">early</a> mode, the |
| <directive>RequestHeader</directive> directive is processed |
| just before the request is run by its handler in the fixup phase. |
| This should allow headers generated by the browser, or by Apache |
| input filters to be overridden or modified.</p> |
| </usage> |
| </directivesynopsis> |
| |
| <directivesynopsis> |
| <name>Header</name> |
| <description>Configure HTTP response headers</description> |
| <syntax>Header [<var>condition</var>] set|append|add|unset|echo |
| <var>header</var> [<var>value</var>] [early|env=[!]<var>variable</var>]</syntax> |
| <contextlist><context>server config</context><context>virtual host</context> |
| <context>directory</context><context>.htaccess</context></contextlist> |
| <override>FileInfo</override> |
| |
| <usage> |
| <p>This directive can replace, merge or remove HTTP response |
| headers. The header is modified just after the content handler |
| and output filters are run, allowing outgoing headers to be |
| modified.</p> |
| |
| <p>The optional <var>condition</var> can be either <code>onsuccess</code> |
| or <code>always</code>. It determines, which internal header table should be |
| operated on. <code>onsuccess</code> stands for <code>2<var>xx</var></code> |
| status codes and <code>always</code> for all status codes (including |
| <code>2<var>xx</var></code>). Especially if you want to unset headers |
| set by certain modules, you should try out, which table is affected.</p> |
| |
| <p>The action it performs is determined by the second |
| argument. This can be one of the following values:</p> |
| |
| <dl> |
| <dt><code>set</code></dt> |
| <dd>The response header is set, replacing any previous header |
| with this name. The <var>value</var> may be a format string.</dd> |
| |
| <dt><code>append</code></dt> |
| <dd>The response header is appended to any existing header of |
| the same name. When a new value is merged onto an existing |
| header it is separated from the existing header with a comma. |
| This is the HTTP standard way of giving a header multiple values.</dd> |
| |
| <dt><code>add</code></dt> |
| <dd>The response header is added to the existing set of headers, |
| even if this header already exists. This can result in two |
| (or more) headers having the same name. This can lead to |
| unforeseen consequences, and in general "append" should be |
| used instead.</dd> |
| |
| <dt><code>unset</code></dt> |
| <dd>The response header of this name is removed, if it exists. |
| If there are multiple headers of the same name, all will be |
| removed. <var>value</var> must be omitted.</dd> |
| |
| <dt><code>echo</code></dt> |
| <dd>Request headers with this name are echoed back in the |
| response headers. <var>header</var> may be a regular expression. |
| <var>value</var> must be omitted.</dd> |
| </dl> |
| |
| <p>This argument is followed by a <var>header</var> name, which |
| can include the final colon, but it is not required. Case is |
| ignored for <code>set</code>, <code>append</code>, <code>add</code> |
| and <code>unset</code>. The <var>header</var> name for <code>echo</code> |
| is case sensitive and may be a regular expression.</p> |
| |
| <p>For <code>add</code>, <code>append</code> and <code>set</code> a |
| <var>value</var> is specified as the third argument. If <var>value</var> |
| contains spaces, it should be surrounded by doublequotes. |
| <var>value</var> may be a character string, a string containing format |
| specifiers or a combination of both. The following format specifiers |
| are supported in <var>value</var>:</p> |
| |
| <table border="1" style="zebra"> |
| <columnspec><column width=".25"/><column width=".75"/></columnspec> |
| <tr><th>Format</th><th>Description</th></tr> |
| <tr><td><code>%%</code></td> |
| <td>The percent sign</td></tr> |
| |
| <tr><td><code>%t</code></td> |
| <td>The time the request was received in Universal Coordinated Time |
| since the epoch (Jan. 1, 1970) measured in microseconds. The value |
| is preceded by <code>t=</code>.</td></tr> |
| |
| <tr><td><code>%D</code></td> |
| <td>The time from when the request was received to the time the |
| headers are sent on the wire. This is a measure of the duration |
| of the request. The value is preceded by <code>D=</code>.</td></tr> |
| |
| <tr><td><code>%{FOOBAR}e</code></td> |
| <td>The contents of the <a href="../env.html">environment |
| variable</a> <code>FOOBAR</code>.</td></tr> |
| |
| <tr><td><code>%{FOOBAR}s</code></td> |
| <td>The contents of the <a href="mod_ssl.html#envvars">SSL environment |
| variable</a> <code>FOOBAR</code>, if <module>mod_ssl</module> is enabled.</td></tr> |
| |
| </table> |
| |
| <note><title>Note</title> |
| <p>The <code>%s</code> format specifier is only available in |
| Apache 2.1 and later; it can be used instead of <code>%e</code> |
| to avoid the overhead of enabling <code>SSLOptions |
| +StdEnvVars</code>. If <code>SSLOptions +StdEnvVars</code> must |
| be enabled anyway for some other reason, <code>%e</code> will be |
| more efficient than <code>%s</code>.</p> |
| </note> |
| |
| <p>The <directive>Header</directive> directive may be followed by an |
| an additional argument, which may be used to specify conditions under |
| which the action will be taken, or may be the keyword <code>early</code> |
| to specify <a href="#early">early processing</a>. If the |
| <a href="../env.html">environment variable</a> specified in the |
| <code>env=<var>...</var></code> argument exists (or if the environment |
| variable does not exist and <code>env=!<var>...</var></code> is specified) |
| then the action specified by the <directive>Header</directive> directive |
| will take effect. Otherwise, the directive will have no effect |
| on the request.</p> |
| |
| <p>Except in <a href="#early">early</a> mode, the |
| <directive>Header</directive> directives are processed just |
| before the response is sent to the network. These means that it is |
| possible to set and/or override most headers, except for those headers |
| added by the header filter.</p> |
| </usage> |
| </directivesynopsis> |
| |
| </modulesynopsis> |
| |