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305 lines
11 KiB
HTML
305 lines
11 KiB
HTML
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<meta name="generator" content="HTML Tidy, see www.w3.org" />
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<title>Apache module mod_headers</title>
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</head>
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<!--#include virtual="header.html" -->
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<h1 align="CENTER">Module mod_headers</h1>
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<p>This module provides for the customization of HTTP request
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and response headers.</p>
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<p><a href="module-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="module-dict.html#SourceFile"
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rel="Help"><strong>Source File:</strong></a>
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mod_headers.c<br />
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<a href="module-dict.html#ModuleIdentifier"
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rel="Help"><strong>Module Identifier:</strong></a>
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headers_module<br />
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<a href="module-dict.html#Compatibility"
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rel="Help"><strong>Compatibility:</strong></a> Available in
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Apache 1.2 and later. RequestHeader appeared in Apache 2.0.</p>
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<h2>Summary</h2>
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This module provides directives to control and modify HTTP
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request and response headers. Headers can be merged, replaced
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or removed.
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<h2>Directives</h2>
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<ul>
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<li><a href="#requestheader">RequestHeader</a></li>
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<li><a href="#header">Header</a></li>
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</ul>
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<h2>Order of Processing</h2>
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<p>The directives provided by mod_header can occur almost
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anywhere within the server configuration. They are valid in the
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main server config and virtual host sections, inside
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<Directory>, <Location> and <Files> sections,
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and within .htaccess files.</p>
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<p>The directives are processed in the following order:</p>
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<ol>
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<li>main server</li>
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<li>virtual host</li>
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<li><Directory> sections and .htaccess</li>
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<li><Location></li>
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<li><Files></li>
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</ol>
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<p>Order is important. These two headers have a different
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effect if reversed:</p>
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<blockquote>
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<code>RequestHeader append MirrorID "mirror 12"<br />
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RequestHeader unset MirrorID</code>
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</blockquote>
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<p>This way round, the MirrorID header is not set. If reversed,
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the MirrorID header is set to "mirror 12".</p>
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<h2>Examples</h2>
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<ol>
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<li>Copy all request headers that begin with "TS" to the
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response headers:</li>
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<li style="list-style: none">
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<pre>
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Header echo ^TS*
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</pre>
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</li>
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<li>Add a header, MyHeader, to the response including a
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timestamp for when the request was received and how long it
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took to begin serving the request. This header can be used by
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the client to intuit load on the server or in isolating
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bottlenecks between the client and the server.</li>
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<li style="list-style: none">
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<pre>
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Header add MyHeader "%D %t"
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</pre>
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results in this header being added to the response:
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<pre>
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MyHeader: D=3775428 t=991424704447256
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</pre>
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</li>
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<li>Say hello to Joe</li>
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<li style="list-style: none">
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<pre>
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Header add MyHeader "Hello Joe. It took %D microseconds for Apache to serve this request."
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</pre>
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results in this header being added to the response:
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<pre>
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MyHeader: Hello Joe. It took D=3775428 microseconds for Apache to serve this request.
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</pre>
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</li>
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<li>Conditionally send MyHeader on the response if and only
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if header "MyRequestHeader" is present on the request. This
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is useful for constructing headers in response to some client
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stimulus. Note that this example requires the services of the
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mod_setenvif module.</li>
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<li style="list-style: none">
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<pre>
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SetEnvIf MyRequestHeader value HAVE_MyRequestHeader<br />
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Header add MyHeader "%D %t mytext" env=HAVE_MyRequestHeader
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</pre>
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If the header "MyRequestHeader: value" is present on the
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HTTP request, the response will contain the following
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header:
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<pre>
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MyHeader: D=3775428 t=991424704447256 mytext
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</pre>
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</li>
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</ol>
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<hr />
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<h2><a id="requestheader"
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name="requestheader">RequestHeader</a> directive</h2>
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> RequestHeader
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set|append|add <em>header</em> <em>value</em><br />
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> RequestHeader unset
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<em>header</em><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config, virtual
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host, access.conf, .htaccess<br />
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<a href="directive-dict.html#Override"
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rel="Help"><strong>Override:</strong></a> FileInfo<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_header
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<p>This directive can replace, merge or remove HTTP request
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headers. The header is modified just before the content handler
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is run, allowing incoming headers to be modified. The action it
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performs is determined by the first argument. This can be one
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of the following values:</p>
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<ul>
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<li><strong>set</strong><br />
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The request header is set, replacing any previous header
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with this name</li>
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<li><strong>append</strong><br />
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The request header is appended to any existing header of the
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same name. When a new value is merged onto an existing header
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it is separated from the existing header with a comma. This
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is the HTTP standard way of giving a header multiple
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values.</li>
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<li><strong>add</strong><br />
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The request header is added to the existing set of headers,
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even if this header already exists. This can result in two
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(or more) headers having the same name. This can lead to
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unforeseen consequences, and in general "append" should be
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used instead.</li>
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<li><strong>unset</strong><br />
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The request header of this name is removed, if it exists. If
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there are multiple headers of the same name, all will be
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removed.</li>
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</ul>
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<p>This argument is followed by a header name, which can
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include the final colon, but it is not required. Case is
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ignored. For <code>add</code>, <code>append</code> and
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<code>set</code> a value is given as the third argument. If
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this value contains spaces, it should be surrounded by double
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quotes. For unset, no value should be given.</p>
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<p>The <code>RequestHeader</code> directive is processed just
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before the request is run by its handler in the fixup phase.
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This should allow headers generated by the browser, or by
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Apache input filters to be overridden or modified.</p>
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<hr />
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<h2><a id="header" name="header">Header</a> directive</h2>
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> Header set|append|add
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<em>header</em> <em>value</em>
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<em>[env=[!]environment-variable]</em><br />
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> Header unset
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<em>header</em><br />
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<a href="directive-dict.html#Syntax"
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rel="Help"><strong>Syntax:</strong></a> Header echo
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<em>header</em><br />
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<a href="directive-dict.html#Context"
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rel="Help"><strong>Context:</strong></a> server config, virtual
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host, access.conf, .htaccess<br />
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<a href="directive-dict.html#Override"
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rel="Help"><strong>Override:</strong></a> FileInfo<br />
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<a href="directive-dict.html#Status"
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rel="Help"><strong>Status:</strong></a> Extension<br />
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<a href="directive-dict.html#Module"
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rel="Help"><strong>Module:</strong></a> mod_header
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<p>This directive can replace, merge or remove HTTP response
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headers. The header is modified just after the content handler
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and output filters are run, allowing outgoing headers to be
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modified. The action it performs is determined by the first
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argument. This can be one of the following values:</p>
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<ul>
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<li><strong>set</strong><br />
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The response header is set, replacing any previous header
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with this name. The <em>value</em> may be a format
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string.</li>
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<li><strong>append</strong><br />
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The response header is appended to any existing header of
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the same name. When a new value is merged onto an existing
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header it is separated from the existing header with a comma.
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This is the HTTP standard way of giving a header multiple
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values.</li>
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<li><strong>add</strong><br />
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The response header is added to the existing set of headers,
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even if this header already exists. This can result in two
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(or more) headers having the same name. This can lead to
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unforeseen consequences, and in general "append" should be
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used instead.</li>
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<li><strong>unset</strong><br />
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The response header of this name is removed, if it exists.
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If there are multiple headers of the same name, all will be
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removed.</li>
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<li><strong>echo</strong><br />
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Request headers with this name are echoed back in the
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response headers. <em>header</em> may be a regular
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expression.</li>
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</ul>
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<p>This argument is followed by a <em>header</em> name, which
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can include the final colon, but it is not required. Case is
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ignored for set, append, add and unset. The <em>header</em>
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name for echo is case sensitive and may be a regular
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expression.</p>
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<p>For <code>add</code>, <code>append</code> and
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<code>set</code> a <em>value</em> is specified as the third
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argument. If <em>value</em> contains spaces, it should be
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surrounded by doublequotes. <em>value</em> may be a character
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string, a string containing format specifiers or a combination
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of both. The following format specifiers are supported in
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<em>value</em>:</p>
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<table>
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<tr><td>%t: </td> <td>The time the request was received in Universal
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Coordinated Time since the epoch (Jan. 1, 1970) measured in
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microseconds. The value is preceded by "t=".</td></tr>
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<tr><td>%D: </td> <td>The time from when the request was received to
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the time the headers are sent on the wire. This is a measure of the
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duration of the request. The value is preceded by "D=".</td></tr>
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<tr><td>%{FOOBAR}e:</td> <td>The contents of the <a href="../env.html">environment
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variable</a> FOOBAR.</td></tr>
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</table>
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<p>When the <code>Header</code> directive is used with the
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<code>add</code>, <code>append</code>, or <code>set</code>
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argument, a fourth argument may be used to specify conditions
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under which the action will be taken. If the <a
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href="../env.html">environment variable</a> specified in the
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<code>env=...</code> argument exists (or if the environment
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variable does not exist and <code>env=!...</code> is specified)
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then the action specified by the <code>Header</code> directive
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will take effect. Otherwise, the directive will have no effect
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on the request.</p>
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<p>The Header directives are processed just before the response
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is sent to the network. These means that it is possible to set
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and/or override most headers, except for those headers added by
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the header filter.</p>
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<!--#include virtual="footer.html" -->
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</body>
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</html>
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