Parsing XFDF in PHP

This past week at work I have been working on using Adobe Acrobat to submit form data. The value of this is that the form data can be reimported into the PDF form then printed all purty-lookin’. Anyway, Acrobat allows you to submit your form data in several different formats. One, FDF, is usable in PHP provided you load this module thingy. Unfortunately, the server I want to run the PHP script on uses Irix and the module is unavailable for Irix. Poo.

I then turned to XFDF, which is essentially FDF data all XML-ified. PHP has an XML parser built in, so I don’t have to load any crazy modules to parse the data. Unfortunately, PHP’s parser is SAX-based rather than DOM-based, so it took me a rather long time to figure out how to get it working right. Anyway, here’s the PHP code that essentially takes XFDF data (declare $file as a string pointing to the location of your XFDF file) and parses it into an associative array ($values). The array is indexed by the XFDF field names. The code below is not entirely complete since I snipped it out of a larger file, but if you look at it, I think you’ll get the idea. It’s pretty simple once you figure out the way PHP does XML processing.

/* BEGIN VARIABLE DECLARATIONS */
//global variables for XML parsing
$values = array();
$field = "";
$curTag = "";

/* BEGIN XML PROCESSING */
// XML Parser element start function
function startElement($parser, $name, $attrs)
{
    global $curTag, $field;

    //track the tag we're currently in
    $curTag .= "^$name";

    if( $curTag == "^XFDF^FIELDS^FIELD" )
    {
        //save the name of the field in a global var
        $field = $attrs['NAME'];
    }
}


// XML Parser element end function
function endElement($parser, $name)
{
    global $curTag;

    // remove the tag we're ending from the "tag tracker"
    $caret_pos = [strrpos][1]($curTag,'^');
    $curTag = [substr][2]($curTag, 0, $caret_pos);
}


// XML Parser characterData function
function characterData( $parser, $data )
{
    global $curTag, $values, $field;
    $valueTag = "^XFDF^FIELDS^FIELD^VALUE";

    if( $curTag == $valueTag )
    {
        // we're in the value tag, so put the value in the array
        $values[$field] = $data;
    }
}

// Create the parser and parse the file
$xml_parser = xml_parser_create();
xml_set_element_handler($xml_parser, "startElement", "endElement");
xml_set_character_data_handler($xml_parser, "characterData");

if (!($fp = fopen($file,"r")))
{
    die ("could not open XML for input");
}

while ($data = fread($fp, 4096))
{
  if (!xml_parse($xml_parser, $data, feof($fp)))

    {
        die(sprintf("XML error: %s at line %d",
                    xml_error_string(xml_get_error_code($xml_parser)),
                    xml_get_current_line_number($xml_parser)));
    }
}

xml_parser_free($xml_parser);
flclose($fp);

/* END XML PROCESSING */