Converting ICalendar to XML

By Evert on 2009-09-02 17:25:45

I've started working on a CalDAV implementation, which also requires analysis of ICalendar (rfc 2554) objects.

ICalendar objects have properties, components (such as VEVENT, VTODO) and attributes. This is awfully familiar to XML. So instead of trying to come up with a complicated parser and object structure, I decided to just convert it to XML and use PHP's simplexml.

This is my current script:


<?php



function iCalendarToXML($icalendarData) {



    // Detecting line endings

    if (strpos($icalendarData,"\r\n")) $lb = "\r\n";

    elseif (strpos($icalendarData,"\n")) $lb = "\n";

    else $lb = "\r\n";



    // Splitting up items per line

    $lines = explode($lb,$icalendarData);



    // Properties can be folded over 2 lines. In this case the second

    // line will be preceeded by a space or tab.

    $lines2 = array();

    foreach($lines as $line) {



        if ($line[0]==" " || $line[0]=="\t") {

            $lines2[count($lines2)-1].=substr($line,1);

            continue;

        }



        $lines2[]=$line;



    }



    $xml = '<?xml version="1.0"?>' . "\n";



    $spaces = 0;

    foreach($lines2 as $line) {



        $matches = array();

        // This matches PROPERTYNAME;ATTRIBUTES:VALUE

        if (preg_match('/^([^:^;]*)(?:;([^:]*))?:(.*)$/',$line,$matches)) {

            $propertyName = strtoupper($matches[1]);

            $attributes = $matches[2];

            $value = $matches[3];



            // If the line was in the format BEGIN:COMPONENT or END:COMPONENT, we need to special case it.

            if ($propertyName == 'BEGIN') {

                $xml.=str_repeat(" ",$spaces);

                $xml.='<' . strtoupper($value) . ">\n";

                $spaces+=2;

                continue;

            } elseif ($propertyName == 'END') {

                $spaces-=2;

                $xml.=str_repeat(" ",$spaces);

                $xml.='</' . strtoupper($value) . ">\n";

                continue;

            }



            $xml.=str_repeat(" ",$spaces);

            $xml.='<' . $propertyName;

            if ($attributes) {

                // There can be multiple attributes

                $attributes = explode(';',$attributes);

                foreach($attributes as $att) {

                    

                    list($attName,$attValue) = explode('=',$att,2);

                    $xml.=' ' . $attName . '="' . htmlspecialchars($attValue) . '"';



                }

            }



            $xml.='>'. htmlspecialchars($value) . '</' . $propertyName . ">\n";

          

        }



    }



    return $xml;



}



?>

This will convert:


BEGIN:VCALENDAR

VERSION:2.0

PRODID:-//Example Corp.//CalDAV Client//EN

BEGIN:VTIMEZONE

LAST-MODIFIED:20040110T032845Z

TZID:US/Eastern

BEGIN:DAYLIGHT

DTSTART:20000404T020000

RRULE:FREQ=YEARLY;BYDAY=1SU;BYMONTH=4

TZNAME:EDT

TZOFFSETFROM:-0500

TZOFFSETTO:-0400

END:DAYLIGHT

BEGIN:STANDARD

DTSTART:20001026T020000

RRULE:FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10

TZNAME:EST

TZOFFSETFROM:-0400

TZOFFSETTO:-0500

END:STANDARD

END:VTIMEZONE

BEGIN:VEVENT

DESCRIPTION:Hello Im evert

 Next line also

  Blabla

ATTENDEE;PARTSTAT=ACCEPTED;ROLE=CHAIR:mailto:cyrus@example.com

ATTENDEE;PARTSTAT=NEEDS-ACTION:mailto:lisa@example.com

DTSTAMP:20060206T001220Z

DTSTART;TZID=US/Eastern:20060104T100000

DURATION:PT1H

LAST-MODIFIED:20060206T001330Z

ORGANIZER:mailto:cyrus@example.com

SEQUENCE:1

STATUS:TENTATIVE

SUMMARY:Event #3

UID:DC6C50A017428C5216A2F1CD@example.com

X-ABC-GUID:E1CX5Dr-0007ym-Hz@example.com

END:VEVENT

END:VCALENDAR

To:


<?xml version="1.0"?>

<VCALENDAR>

  <VERSION>2.0</VERSION>

  <PRODID>-//Example Corp.//CalDAV Client//EN</PRODID>

  <VTIMEZONE>

    <LAST-MODIFIED>20040110T032845Z</LAST-MODIFIED>

    <TZID>US/Eastern</TZID>

    <DAYLIGHT>

      <DTSTART>20000404T020000</DTSTART>

      <RRULE>FREQ=YEARLY;BYDAY=1SU;BYMONTH=4</RRULE>

      <TZNAME>EDT</TZNAME>

      <TZOFFSETFROM>-0500</TZOFFSETFROM>

      <TZOFFSETTO>-0400</TZOFFSETTO>

    </DAYLIGHT>

    <STANDARD>

      <DTSTART>20001026T020000</DTSTART>

      <RRULE>FREQ=YEARLY;BYDAY=-1SU;BYMONTH=10</RRULE>

      <TZNAME>EST</TZNAME>

      <TZOFFSETFROM>-0400</TZOFFSETFROM>

      <TZOFFSETTO>-0500</TZOFFSETTO>

    </STANDARD>

  </VTIMEZONE>

  <VEVENT>

    <DESCRIPTION>Hello Im evertNext line also Blabla</DESCRIPTION>

    <ATTENDEE PARTSTAT="ACCEPTED" ROLE="CHAIR">mailto:cyrus@example.com</ATTENDEE>

    <ATTENDEE PARTSTAT="NEEDS-ACTION">mailto:lisa@example.com</ATTENDEE>

    <DTSTAMP>20060206T001220Z</DTSTAMP>

    <DTSTART TZID="US/Eastern">20060104T100000</DTSTART>

    <DURATION>PT1H</DURATION>

    <LAST-MODIFIED>20060206T001330Z</LAST-MODIFIED>

    <ORGANIZER>mailto:cyrus@example.com</ORGANIZER>

    <SEQUENCE>1</SEQUENCE>

    <STATUS>TENTATIVE</STATUS>

    <SUMMARY>Event #3</SUMMARY>

    <UID>DC6C50A017428C5216A2F1CD@example.com</UID>

    <X-ABC-GUID>E1CX5Dr-0007ym-Hz@example.com</X-ABC-GUID>

  </VEVENT>

</VCALENDAR>