docs/manual/mod/mod_substitute.xml

<?xml version="1.0"?>
<!DOCTYPE modulesynopsis SYSTEM "../style/modulesynopsis.dtd">
<?xml-stylesheet type="text/xsl" href="../style/manual.en.xsl"?>
<!-- $LastChangedRevision$ -->

<!--
 Licensed to the Apache Software Foundation (ASF) under one or more
 contributor license agreements.  See the NOTICE file distributed with
 this work for additional information regarding copyright ownership.
 The ASF licenses this file to You under the Apache License, Version 2.0
 (the "License"); you may not use this file except in compliance with
 the License.  You may obtain a copy of the License at

     http://www.apache.org/licenses/LICENSE-2.0

 Unless required by applicable law or agreed to in writing, software
 distributed under the License is distributed on an "AS IS" BASIS,
 WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 See the License for the specific language governing permissions and
 limitations under the License.
-->

<modulesynopsis metafile="mod_substitute.xml.meta">

<name>mod_substitute</name>
<description>Perform search and replace operations on response bodies</description>
<status>Extension</status>
<sourcefile>mod_substitute.c</sourcefile>
<identifier>substitute_module</identifier>

<summary>
    <p><module>mod_substitute</module> provides a mechanism to perform
    both regular expression and fixed string substitutions on
    response bodies.</p>
</summary>

<directivesynopsis>
<name>Substitute</name>
<description>Pattern to filter the response content</description>
<syntax>Substitute <var>s/pattern/substitution/[infq]</var></syntax>
<contextlist><context>directory</context>
<context>.htaccess</context></contextlist>
<override>FileInfo</override>

<usage>
    <p>The <directive>Substitute</directive> directive specifies a
    search and replace pattern to apply to the response body.</p>

    <p>The meaning of the pattern can be modified by using any
    combination of these flags:</p>

    <dl>
        <dt><code>i</code></dt>
        <dd>Perform a case-insensitive match.</dd>
        <dt><code>n</code></dt>
        <dd>By default the pattern is treated as a regular expression.
        Using the <code>n</code> flag forces the pattern to be treated
        as a fixed string.</dd>
        <dt><code>f</code></dt>
        <dd>The <code>f</code> flag causes <code>mod_substitute</code> to flatten the
        result of a substitution allowing for later substitutions to
        take place on the boundary of this one. This is the default.</dd>
        <dt><code>q</code></dt>
        <dd>The <code>q</code> flag causes <code>mod_substitute</code> to not
        flatten the buckets after each substitution. This can
        result in much faster response and a decrease in memory
        utilization, but should only be used if there is no possibility
        that the result of one substitution will ever match a pattern
        or regex of a subsequent one.</dd>
    </dl>

    <example><title>Example</title>
    <highlight language="config">
&lt;Location "/"&gt;
    AddOutputFilterByType SUBSTITUTE text/html
    Substitute "s/foo/bar/ni"
&lt;/Location&gt;
        </highlight>
    </example>

    <p>If either the pattern or the substitution contain a slash
    character then an alternative delimiter should be used:</p>

    <example><title>Example of using an alternate delimiter</title>
    <highlight language="config">
&lt;Location "/"&gt;
    AddOutputFilterByType SUBSTITUTE text/html
    Substitute "s|&lt;BR */?&gt;|&lt;br /&gt;|i"
&lt;/Location&gt;
        </highlight>
    </example>

    <p>Backreferences can be used in the comparison and in the substitution,
    when regular expressions are used, as illustrated in the following example: </p>
    <example><title>Example of using backreferences and captures</title>
    <highlight language="config">
&lt;Location "/"&gt;
    AddOutputFilterByType SUBSTITUTE text/html
    # "foo=k,bar=k" -> "foo/bar=k"
    Substitute "s|foo=(\w+),bar=\1|foo/bar=$1"
&lt;/Location&gt;
    </highlight>
    </example>

    <p>A common use scenario for <code>mod_substitute</code> is the
    situation in which a front-end server proxies requests to a back-end
    server which returns HTML with hard-coded embedded URLs that refer
    to the back-end server. These URLs don't work for the end-user,
    since the back-end server is unreachable.</p>

    <p>In this case, <code>mod_substitute</code> can be used to rewrite
    those URLs into something that will work from the front end:</p>

    <example><title>Rewriting URLs embedded in proxied content</title>
    <highlight language="config">
ProxyPass        "/blog/" "http://internal.blog.example.com"
ProxyPassReverse "/blog/" "http://internal.blog.example.com/"

Substitute "s|http://internal.blog.example.com/|http://www.example.com/blog/|i"
    </highlight>
    </example>

    <p><directive module="mod_proxy">ProxyPassReverse</directive>
    modifies any <code>Location</code> (redirect) headers that are sent
    by the back-end server, and, in this example,
    <directive>Substitute</directive> takes care of the rest of the problem by
    fixing up the HTML response as well.</p>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>SubstituteMaxLineLength</name>
<description>Set the maximum line size</description>
<syntax>SubstituteMaxLineLength <var>bytes</var>(b|B|k|K|m|M|g|G)</syntax>
<default>SubstituteMaxLineLength 1m</default>
<contextlist><context>directory</context>
<context>.htaccess</context></contextlist>
<override>FileInfo</override>
<compatibility>Available in httpd 2.4.11 and later</compatibility>

<usage>
    <p>The maximum line size handled by <module>mod_substitute</module>
    is limited to restrict memory use. The limit can be configured
    using <directive>SubstituteMaxLineLength</directive>.
    The value can be given as the number of bytes and can be suffixed
    with a single letter <code>b</code>, <code>B</code>, <code>k</code>,
    <code>K</code>, <code>m</code>, <code>M</code>, <code>g</code>,
    <code>G</code> to provide the size in bytes, kilobytes, megabytes
    or gigabytes respectively.</p>

    <example><title>Example</title>
    <highlight language="config">
&lt;Location "/"&gt;
    AddOutputFilterByType SUBSTITUTE text/html
    SubstituteMaxLineLength 10m
    Substitute "s/foo/bar/ni"
&lt;/Location&gt;
        </highlight>
    </example>

</usage>
</directivesynopsis>

<directivesynopsis>
<name>SubstituteInheritBefore</name>
<description>Change the merge order of inherited patterns</description>
<syntax>SubstituteInheritBefore on|off</syntax>
<default>SubstituteInheritBefore on</default>
<contextlist><context>directory</context>
<context>.htaccess</context></contextlist>
<override>FileInfo</override>
<compatibility>Available in httpd 2.4.17 and later</compatibility>

<usage>
    <p>Whether to apply the inherited <directive module="mod_substitute">Substitute</directive>
    patterns first (<code>on</code>), or after the ones of the current
    context (<code>off</code>).
    The latter was the default in versions 2.4 and earlier, but changed
    starting with 2.5, hence <directive>SubstituteInheritBefore</directive>
    set to <code>off</code> allows to restore the legacy behaviour.
    <directive>SubstituteInheritBefore</directive> is itself inherited,
    hence contexts that inherit it (those that don't specify their own
    <directive>SubstituteInheritBefore</directive> value) will apply the
    closest defined merge order.</p>
</usage>
</directivesynopsis>

</modulesynopsis>