php-doc-en/reference/libxml/functions/libxml-set-external-entity-loader.xml

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<refentry xml:id="function.libxml-set-external-entity-loader" xmlns="http://docbook.org/ns/docbook" xmlns:xlink="http://www.w3.org/1999/xlink">
 <refnamediv>
  <refname>libxml_set_external_entity_loader</refname>
  <refpurpose>Changes the default external entity loader</refpurpose>
 </refnamediv>

 <refsect1 role="description">
  &reftitle.description;
  <methodsynopsis>
   <type>bool</type><methodname>libxml_set_external_entity_loader</methodname>
   <methodparam><type class="union"><type>callable</type><type>null</type></type><parameter>resolver_function</parameter></methodparam>
  </methodsynopsis>
  <para>
   Changes the default external entity loader.
   This can be used to suppress the expansion of arbitrary external entities to avoid XXE attacks,
   even when <constant>LIBXML_NOENT</constant> has been set for the respective operation,
   and is usually preferable over calling <function>libxml_disable_entity_loader</function>.
  </para>
 </refsect1>

 <refsect1 role="parameters">
  &reftitle.parameters;
  <variablelist>
   <varlistentry>
    <term><parameter>resolver_function</parameter></term>
    <listitem>
     <para>
      A <type>callable</type> with the following signature:
      <methodsynopsis>
       <type class="union"><type>resource</type><type>string</type><type>null</type></type><methodname><replaceable>resolver</replaceable></methodname>
       <methodparam><type>string</type><parameter>public_id</parameter></methodparam>
       <methodparam><type>string</type><parameter>system_id</parameter></methodparam>
       <methodparam><type>array</type><parameter>context</parameter></methodparam>
      </methodsynopsis>
      <variablelist>
       <varlistentry>
        <term><parameter>public_id</parameter></term>
        <listitem>
         <simpara>
          The public ID.
         </simpara>
        </listitem>
       </varlistentry>
       <varlistentry>
        <term><parameter>system_id</parameter></term>
        <listitem>
         <simpara>
          The system ID.
         </simpara>
        </listitem>
       </varlistentry>
       <varlistentry>
        <term><parameter>context</parameter></term>
        <listitem>
         <simpara>
          An array with the four elements <literal>"directory"</literal>, <literal>"intSubName"</literal>,
          <literal>"extSubURI"</literal> and <literal>"extSubSystem"</literal>.
         </simpara>
        </listitem>
       </varlistentry>
      </variablelist>
      This callable should return a &resource;, a &string; from which a resource can be
      opened. If &null; is returned, the entity reference resolution will fail.
     </para>
    </listitem>
   </varlistentry>
  </variablelist>
 </refsect1>

 <refsect1 role="returnvalues">
  &reftitle.returnvalues;
  <para>
   &return.success;
  </para>
 </refsect1>

 <refsect1 role="examples">
  &reftitle.examples;
  <para>
   <example>
    <title><function>libxml_set_external_entity_loader</function> example</title>
    <programlisting role="php">
<![CDATA[
<?php
$xml = <<<XML
<!DOCTYPE foo PUBLIC "-//FOO/BAR" "http://example.com/foobar">
<foo>bar</foo>
XML;

$dtd = <<<DTD
<!ELEMENT foo (#PCDATA)>
DTD;

libxml_set_external_entity_loader(
    function ($public, $system, $context) use($dtd) {
        var_dump($public);
        var_dump($system);
        var_dump($context);
        $f = fopen("php://temp", "r+");
        fwrite($f, $dtd);
        rewind($f);
        return $f;
    }
);

$dd = new DOMDocument;
$r  = $dd->loadXML($xml);

var_dump($dd->validate());
?>
]]>
    </programlisting>
    &example.outputs;
    <screen>
<![CDATA[
string(10) "-//FOO/BAR"
string(25) "http://example.com/foobar"
array(4) {
    ["directory"]    => NULL
    ["intSubName"]   => NULL
    ["extSubURI"]    => NULL
    ["extSubSystem"] => NULL
}
bool(true)
]]>
    </screen>
   </example>
  </para>
 </refsect1>

 <refsect1 role="seealso">
  &reftitle.seealso;
  <para>
   <simplelist>
    <member><function>libxml_disable_entity_loader</function></member>
   </simplelist>
  </para>
 </refsect1>

</refentry>
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