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    DOMNode::C14N

    (PHP 5 >= 5.2.0, PHP 7, PHP 8)

    DOMNode::C14N — Canonicalize nodes to a string

    Description

    public DOMNode::C14N(
        bool $exclusive = false,
        bool $withComments = false,
        ?array $xpath = null,
        ?array $nsPrefixes = null
    ): string|false

    Canonicalize nodes to a string

    Parameters

    exclusive

    Enable exclusive parsing of only the nodes matched by the provided xpath or namespace prefixes.

    withComments

    Retain comments in output.

    xpath

    An array of XPaths to filter the nodes by. Each entry in this array is an associative array with:

    • A required query key containing the XPath expression as a string.
    • An optional namespaces key containing an array that maps namespace prefixes (keys) to namespace URIs (values).

    nsPrefixes

    An array of namespace prefixes to filter the nodes by.

    Return Values

    Returns canonicalized nodes as a string or false on failure

    Examples

    Example #1 Example with XPath query

    This example demonstrates advanced usage canonicalizing and filtering the nodes by an XPath query.

    <?php

    $dom     = new DOMDocument();
    $dom->loadXML(<<<XML
    <root xmlns:food="urn:food">
    <!-- redundant namespace declaration will be canonicalized -->
    <food:fruit xmlns:food="urn:food">Apple</food:fruit>
    <food:fruit>Orange</food:fruit>
    <food:fruit>Pear</food:fruit>
    <!-- vegetables here -->
    <food:vegetable>Lettuce</food:vegetable>
    </root>
    XML);

    echo     $dom->C14N(true, false, [
    "query" => ".//f:fruit|.//f:fruit/text()",
    "namespaces" => ["f" => "urn:food"],
    ]);
    ?>

    The above example will output:

    <food:fruit>Apple</food:fruit><food:fruit>Orange</food:fruit><food:fruit>Pear</food:fruit>

    See Also

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    User Contributed Notes 3 notes

    up
    21
    Rijk
    11 years ago
    When working with (malformed) HTML, you're probably better off using DOMDocument's saveHTML() method instead. C14N() will attempt to make your HTML valid XML, for example by converting <br> to <br></br>.

    So instead of:
    $html = $Node->C14N();

    Use:
    $html = $Node->ownerDocument->saveHTML( $Node );
    up
    16
    jorda at edpsciences dot org
    9 years ago
    C14N() returns an empty string if the node is not included in the document tree:
    <?php
    $d     = new DOMDocument('1.0');
    $d->loadXML('<foo></foo>');
    $n = $d->createElement('bar');
    var_dump($n->C14N());
    $d->documentElement->appendChild($n);
    var_dump($n->C14N());
    ?>
    output:
    string(0) ""
    string(11) "<bar></bar>"
    up
    3
    lordbaco
    8 years ago
    [edit by nielsdos: This has been fixed starting in PHP 8.4]

    Good to know:

    << Due to a known issue in XML canonicalization in PHP, processing large metadata files in SimpleSAMLphp takes a big amount of resources, with that amount growing approximately by the square of the number of entities in the metadata set >>
    https://simplesamlphp.org/metaprocessing

    << The C14N() function appears to have a runtime that is O(N^2) (or possibly worse?) depending on input size, which means that it becomes very slow as the input grows. For example, an input with around 196000 nodes takes about 290 seconds, while an input with 486000 nodes takes 2200 seconds. >>
    https://bugs.php.net/bug.php?id=53655

    We had the same issue with a 4.1 MB XML (105k lines). The sample code of ticket #53655 takes 1h36 minute to canonicalize it!
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