Condition to check XML feeds

[JustBrewed]

Hello everyone, I am trying to create a condition to check if a users blog feed is working based on the URI they submit. This is what I'm working with and when the URI is not a correct feed, I get this: Warning: xml_parse() [function.xml-parse]: Unable to call handler cdataHandler() in /options.php on line 46

$uri = "http://www.example.com";

if( $fp = @fopen($uri, "r"))
{
    $parser = xml_parser_create();
    xml_set_object($parser, $this);
    xml_parser_set_option($parser, XML_OPTION_CASE_FOLDING, 1);
    xml_set_character_data_handler($parser, "cdataHandler");
    xml_set_element_handler($parser, "startElementHandler", "endElementHandler");

    while($xml = fread($fp, 4096))
    {
        if(!xml_parse($parser, $xml, feof($fp)))
        {
            $error = "XML ERROR: " . xml_error_string( xml_get_error_code($parser)) . " at line " . xml_get_current_line_number($parser);
        }
    }

    xml_parser_free($parser);

    fclose($fp);
    
    echo "a working feed!";
}
else
{
    echo "not a working feed!";
} 

How will I be able to check if a users URI is actually a real feed? Thank!

[JustBrewed]

I was told that I could probably use DOM to verify the XML structure as valid in php5. Is this true? If so, is there a reference I can check out? Thanks.