Question

I’m looking for an HTML or XML parser that lets one access the offset/position of the current element in the input string or file.

For example if walking through this string:

<div>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit</p>
    <p>sed do eiusmod tempor incididunt ut labore et dolore magna aliqua.</p>
</div>

I’m looking for a way to get the starting position (including whitespace) of each <p> tag, here: 7 and 72.

It’d be great if a PHP parser supported that natively (I’ve looked at DOM, XMLReader, and other libraries mentionned in this SO question but haven’t found a way to do it), but otherwise any language/framework would be fine.

Note: Related to this question, but less localized.

Answer 1

Maybe you could use Generic XML parser class (also on github).
According to the author’s description:

• Parses arbitrary XML input and builds an array with the structure of all tag and data elements.
• It can validate and extract data from a whole XML document with just a single call. It supports validationg common tag value data types and can perform custom validations using a subclass.
• Optionally, keeps track of the positions of each element to allow the determination of the exact location of elements that may be contextually in error.
• Supports parsed file cache to minimize the overhead of parsing the same file repeatdly.
• Optimized parsing of simplified XML (SML) formats ignoring the tag attributes.
• Validate and extract data from a whole XML document with single function call

I’ve tested it with this code:

<?php

require('xml_parser.php');

$file_name = 'test.xml';
$error = XMLParseFile($parser, $file_name, 1, $file_name.'.cache');

foreach ($parser->structure as $key => $val) {
    if (is_array($val) && isset($val['Tag']) && !strcasecmp($val['Tag'], 'p')) {
        print_r($parser->positions[$key]);
    }
}

?>

The test.xml file contains your sample HTML snippet.
By running the script from the command line I get this output:

Array
(
    [Line] => 2
    [Column] => 7
    [Byte] => 12
)
Array
(
    [Line] => 3
    [Column] => 7
    [Byte] => 80
)

So, the Byte field is probably what you’re looking for.
For a better understanding of how it works, have also a look at its source code.