How to retrieve comments from within an XML Document in PHP

Question

I want to extract all comments below a specific node within an XML document, using PHP. I have tried both the SimpleXML and DOMDocument methods, but I keep getting blank outputs. Is there a way to retrieve comments from within a document without having to resort to Regex?

Answer 1

SimpleXML cannot handle comments, but the DOM extension can. Here's how you can extract all the comments. You just have to adapt the XPath expression to target the node you want.

$doc = new DOMDocument;
$doc->loadXML(
    '<doc>
        <node><!-- First node --></node>
        <node><!-- Second node --></node>
    </doc>'
);

$xpath = new DOMXPath($doc);

foreach ($xpath->query('//comment()') as $comment)
{
    var_dump($comment->textContent);
}

Answer 2

Do you have access to an XPath API ? XPath allows you to find comments using (e.g.)

//comment()

Answer 3

If you are using a SAX event driven-parser, the parser should have an event for comments. For example, when using Expat you would implement a handler and set it using:

void XMLCALL
XML_SetCommentHandler(XML_Parser p,
                      XML_CommentHandler cmnt);

Answer 4

Use XMLReader. Comments can be easily detected/found, they are xml elements of type COMMENT. For details see PHP documentation: The XMLReader class

Code example:

$reader = new XMLReader();
$reader->open('filename.xml');
while ($reader->read()){
    if ($reader->nodeType == XMLReader::COMMENT) {
        $comments[] = $reader->readOuterXml();
    }
}

And in array $comments you will have all comments found in XML file.