phpday 2021 digital edition

libxml_set_external_entity_loader

(PHP 5 >= 5.4.0, PHP 7, PHP 8)

libxml_set_external_entity_loaderChanges the default external entity loader

说明

libxml_set_external_entity_loader ( callable|null $resolver_function ) : bool

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().

参数

resolver_function

A callable with the following signature:

resolver ( string $public_id , string $system_id , array $context ) : resource|string|null
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 资源(resource), a string from which a resource can be opened. If null is returned, the entity reference resolution will fail.

返回值

成功时返回 true, 或者在失败时返回 false

范例

示例 #1 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());
?>

以上例程会输出:

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

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