How can I use PHP to dynamically publish an ical file to be read by Google Calendar?

Question

Any Google search on PHP ical just brings up phpicalendar and how to parse or read IN ical files. I just want to write a PHP file that pulls events from my database and writes them out in ical format.

My problem is I can't find anywhere that will answer two questions:

1. What is the exact ical format, including headers, file format, footers, etc.? In other words, what does the file have to have, exactly, in order to be properly read in by Google Calendar, etc.?
2. If I build this file using a .php extension, how do I publish it as ical? Do I have to write to a new .ics file? Or will Google Calendar etc. read a .php file as ical so long as the contents are in the correct format? (Much like a style.css.php file will be read as a CSS file if the contents are actually CSS, etc.)

Any help you all can give or point me to will be greatly appreciated!!!

Answer 1

1. Exact ical format: http://www.ietf.org/rfc/rfc2445.txt
2. According to the spec, it has to end in .ics

Edit: actually I'm not sure - line 6186 gives an example in .ics naming format, but it also states you can use url parameters. I don't think it matters, so long as the MIME type is correct.

Edit: Example from wikipedia: http://en.wikipedia.org/wiki/ICalendar

BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
DTSTART:19970714T170000Z
DTEND:19970715T035959Z
SUMMARY:Bastille Day Party
END:VEVENT
END:VCALENDAR

MIME type is configured on the server.

Answer 2

This should be very simple if Google Calendar does not require the *.ics-extension (which will require some URL rewriting in the server).

$ical = "BEGIN:VCALENDAR
VERSION:2.0
PRODID:-//hacksw/handcal//NONSGML v1.0//EN
BEGIN:VEVENT
UID:" . md5(uniqid(mt_rand(), true)); . "@yourhost.test
DTSTAMP:" . gmdate('Ymd').'T'. gmdate('His') . "Z
DTSTART:19970714T170000Z
DTEND:19970715T035959Z
SUMMARY:Bastille Day Party
END:VEVENT
END:VCALENDAR";

//set correct content-type-header
header('Content-type: text/calendar; charset=utf-8');
header('Content-Disposition: inline; filename=calendar.ics');
echo $ical;
exit;

That's essentially all you need to make a client think that you're serving a iCalendar file, even though there might be some issues regarding caching, text encoding and so on. But you can start experimenting with this simple code.

Answer 3

@Jason : you can export an existing google calendar to iCal to have a good example

Do google refresh your iCal feeds ? Mine are not :/ Even when i suppress/recrete an iCal feed (from url), it doesnt update...

Answer 4

The example by Stefan Gehrig (Sep 23 '09 at 6:59) is very helpful. However, double quotation marks are missing around the file name: It should read

header('Content-Disposition: inline; filename="calendar.ics"');

otherwise there may occur problems (depending on the server configuration).