<?xml version="1.0" encoding="utf-8"?>
<refentry xml:id="random-randomizer.getbytesfromstring" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>Random\Randomizer::getBytesFromString</refname>
  <refpurpose>Get random bytes from a source string</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis role="Random\\Randomizer">
   <modifier>public</modifier> <type>string</type><methodname>Random\Randomizer::getBytesFromString</methodname>
   <methodparam><type>string</type><parameter>string</parameter></methodparam>
   <methodparam><type>int</type><parameter>length</parameter></methodparam>
  </methodsynopsis>
  <para>
   Generates a string containing uniformly selected random bytes from the
   input <parameter>string</parameter> with the requested <parameter>length</parameter>.
  </para>
  <para>
   The chance for a byte to be selected is proportional to its share
   of the input <parameter>string</parameter>. If each byte occurs
   the same amount of times, each byte is equally likely to be selected.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <para>
   <variablelist>
    <varlistentry>
     <term><parameter>string</parameter></term>
     <listitem>
      <para>
       The &string; from which the returned bytes are selected.
      </para>
     </listitem>
    </varlistentry>
    <varlistentry>
     <term><parameter>length</parameter></term>
     <listitem>
      <para>
       The length of the random &string; that should be returned in bytes; must be <literal>1</literal> or greater.
      </para>
     </listitem>
    </varlistentry>
   </variablelist>
  </para>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   A &string; containing the requested number of random bytes taken from the input <parameter>string</parameter>.
  </para>
 </refsect1>

 <refsect1 role="errors">
  &reftitle.errors;
  <itemizedlist>
   <listitem>
    <simpara>
     If <parameter>string</parameter> is empty,
     a <classname>ValueError</classname> will be thrown.
    </simpara>
   </listitem>
   <listitem>
    <simpara>
     If the value of <parameter>length</parameter> is less than <literal>1</literal>,
     a <classname>ValueError</classname> will be thrown.
    </simpara>
   </listitem>
   &random.engineErrors;
  </itemizedlist>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <example>
   <title><methodname>Random\Randomizer::getBytesFromString</methodname> example</title>
   <programlisting role="php">
<![CDATA[
<?php
$randomizer = new \Random\Randomizer();

printf(
    "%s.example.com",
    $randomizer->getBytesFromString('abcdefghijklmnopqrstuvwxyz0123456789', 16)
);
?>
]]>
   </programlisting>
   &example.outputs.similar;
   <screen>
<![CDATA[
3zsw04eiubcf82jd.example.com
]]>
   </screen>
  </example>

  <example>
   <title>Generate a random code for multi-factor authentication</title>
   <programlisting role="php">
<![CDATA[
<?php
// The Secure engine is the default, but we make it explicit, because
// multi-factor codes are security sensitive.
$randomizer = new \Random\Randomizer(new \Random\Engine\Secure());

echo implode('-', str_split($randomizer->getBytesFromString('0123456789', 20), 5));
?>
]]>
   </programlisting>
   &example.outputs.similar;
   <screen>
<![CDATA[
11551-80418-27047-42075
]]>
   </screen>
  </example>

  <example>
   <title>Select from a string with a non-uniform distribution</title>
   <programlisting role="php">
<![CDATA[
<?php
$randomizer = new \Random\Randomizer();

echo $randomizer->getBytesFromString('aaaaabcdef', 20);
?>
]]>
   </programlisting>
   &example.outputs.similar;
   <screen>
<![CDATA[
fddacbeaaeaaacaaaaca
]]>
   </screen>
  </example>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <simplelist>
   <member><methodname>Random\Randomizer::getBytes</methodname></member>
  </simplelist>
 </refsect1>

</refentry>
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