<?xml version="1.0"?>

<!--
  Copyright (C) Igor Sysoev
  Copyright (C) Nginx, Inc.
  -->

<!DOCTYPE module SYSTEM "../../../../dtd/module.dtd">

<module name="Module ngx_http_map_module"
        link="/en/docs/http/ngx_http_map_module.html"
        lang="en"
        rev="2">

<section id="summary">

<para>
The <literal>ngx_http_map_module</literal> module creates variables
whose values depend on values of other variables.
</para>

</section>


<section id="example" name="Example Configuration">

<para>
<example>
map $http_host $name {
    hostnames;

    default       0;

    example.com   1;
    *.example.com 1;
    example.org   2;
    *.example.org 2;
    .example.net  3;
    wap.*         4;
}

map $http_user_agent $mobile {
    default       0;
    "~Opera Mini" 1;
}
</example>
</para>

</section>


<section id="directives" name="Directives">

<directive name="map">
<syntax block="yes">
    <value>string</value>
    <value>$variable</value></syntax>
<default/>
<context>http</context>

<para>
Creates a new variable whose value
depends on values of one or more of the source variables
specified in the first parameter.
<note>
Before version 0.9.0 only a single variable could be
specified in the first parameter.
</note>
</para>

<para>
<note>
Since variables are evaluated only when used, the mere existence
of even a large number of declared “<literal>map</literal>” variables
does not incur any extra costs for request processing.
</note>
</para>

<para>
Parameters inside the <literal>map</literal> block specify a mapping
between source and resulting values.
</para>

<para>
Source values are specified as strings or regular expressions (0.9.6).
</para>

<para>
A regular expression should either start from the “<literal>~</literal>”
symbol for a case-sensitive matching, or from the “<literal>~*</literal>”
symbols (1.0.4) for case-insensitive matching.
A regular expression can contain named and positional captures
that can later be used in other directives along with the
resulting variable.
</para>

<para>
If a source value matches one of the names of special parameters
described below, it should be prefixed with the “<literal>\</literal>” symbol.
</para>

<para>
The resulting value can be a string
or another variable (0.9.0).
</para>

<para>
The directive also supports three special parameters:
<list type="tag">
<tag-name><literal>default</literal> <value>value</value></tag-name>
<tag-desc>
sets the resulting value if the source value matches none
of the specified variants.
When <literal>default</literal> is not specified, the default
resulting value will be an empty string.
</tag-desc>

<tag-name><literal>hostnames</literal></tag-name>
<tag-desc>
allows to specify hostnames with a prefix or suffix mask, as source
values, for example,
<example>
*.example.com 1;
example.*     1;
</example>
The following two records
<example>
example.com   1;
*.example.com 1;
</example>
can be combined:
<example>
.example.com  1;
</example>
This parameter should be specified before the list of values.
</tag-desc>

<tag-name><literal>include</literal> <value>file</value></tag-name>
<tag-desc>
includes a file with values.
There can be several inclusions.
</tag-desc>

</list>
</para>

<para>
If the source value matches more than one of the specified variants,
e.g. both mask and regular expression match, the first matching
variant will be chosen, in the following order of precedence:
<list type="enum">

<listitem>
string value without a mask
</listitem>

<listitem>
longest string value with a prefix mask,
e.g. “<literal>*.example.com</literal>”
</listitem>

<listitem>
longest string value with a suffix mask,
e.g. “<literal>mail.*</literal>”
</listitem>

<listitem>
first matching regular expression
(in order of appearance in a configuration file)
</listitem>

<listitem>
default value
</listitem>

</list>
</para>

</directive>


<directive name="map_hash_bucket_size">
<syntax><value>size</value></syntax>
<default>32|64|128</default>
<context>http</context>

<para>
Sets the bucket size for the <link id="map"/> variables hash tables.
Default value depends on the size of the processor’s cache line.
Details of setting up hash tables are provided in a separate
<link doc="../hash.xml">document</link>.
</para>

</directive>


<directive name="map_hash_max_size">
<syntax><value>size</value></syntax>
<default>2048</default>
<context>http</context>

<para>
Sets the maximum <value>size</value> of the <link id="map"/> variables
hash tables.
Details of setting up hash tables are provided in a separate
<link doc="../hash.xml">document</link>.
</para>

</directive>

</section>

</module>