libxml_set_external_entity_loader

Changes the default external entity loader

&reftitle.description; `bool` `libxml_set_external_entity_loader` ``callable``null```resolver_function`

Changes the default external entity loader. This can be used to suppress the expansion of arbitrary external entities to avoid XXE attacks, even when `LIBXML_NOENT` has been set for the respective operation, and is usually preferable over calling `libxml_disable_entity_loader`.

&reftitle.parameters;

`resolver_function`

- A `callable` with the following signature: ``resource``string``null````resolver`` ``string``null```public_id` `string` `system_id` `array` `context`

  `public_id`

- The public ID.

`system_id`

- The system ID.

`context`

- An array with the four elements `"directory"`, `"intSubName"`, `"extSubURI"` and `"extSubSystem"`.

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.
&reftitle.returnvalues;

&return.success;

&reftitle.examples;

### `libxml_set_external_entity_loader` example

    <?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());
    ?>

&example.outputs;

    string(10) "-//FOO/BAR"
    string(25) "http://example.com/foobar"
    array(4) {
        ["directory"]    => NULL
        ["intSubName"]   => NULL
        ["extSubURI"]    => NULL
        ["extSubSystem"] => NULL
    }
    bool(true)

&reftitle.seealso;

- `libxml_disable_entity_loader`
- `libxml_get_external_entity_loader`