Server says "Forbidden" when creating event with timezone

[seanmills1020]

Hello,

I am new to Python, so I feel like I am making a silly mistake.

I am trying to add an event to my calendar. The following code works:

from datetime import datetime
import caldav


with caldav.DAVClient(url=CALENDAR_SERVER_URL, username=USERNAME, password=PASSWORD,
                      ssl_verify_cert=False) as client:

    calendar = client.calendar(url=USER_CALENDAR_URL)
    timestamp_start = datetime(year=2024, month=1, day=26, hour=18, minute=0, second=0)
    timestamp_end = datetime(year=2024, month=1, day=26, hour=18, minute=30, second=0)

    new_event = calendar.save_event(
        dtstart=timestamp_start,
        dtend=timestamp_end,
        summary="Sean's Comedy Debut"
    )

However, if I add a tzinfo argument, I get an error.

from datetime import datetime
from dateutil import tz
import caldav


with caldav.DAVClient(url=CALENDAR_SERVER_URL, username=USERNAME, password=PASSWORD,
                      ssl_verify_cert=False) as client:

    calendar = client.calendar(url=USER_CALENDAR_URL)
    timezone = tz.gettz("America/Los_Angeles")
    timestamp_start = datetime(year=2024, month=1, day=26, hour=18, minute=0, second=0, tzinfo=timezone)
    timestamp_end = datetime(year=2024, month=1, day=26, hour=18, minute=30, second=0, tzinfo=timezone)

    new_event = calendar.save_event(
        dtstart=timestamp_start,
        dtend=timestamp_end,
        summary="Sean's Comedy Debut"
    )

The last part of the traceback is:
caldav.lib.error.AuthorizationError: AuthorizationError at '<some_url>', reason Forbidden

Any ideas?

[tobixen]

Hmm ... what happens if you use zoneinfo.ZoneInfo('America/Los_Angeles') instead of tz.gettz("America/Los_Angeles")?

AuthorizationError is a bit misleading here, possibly the library transmits something the server deems to be invalid.

In the master branch (I'll try to find some time to make a new release soon) there is a debug hook, if you set the environment variable PYTHON_CALDAV_COMMDUMP then the library will dump some communication files under /tmp - would be useful to see if the library is shipping the timezone information correctly to the server. (Hm, actually I think I realized at some point that it's easier to just convert the time to UTC when creating events).

[seanmills1020]

Switching to ZoneInfo worked! Thank you!

Here is the updated code:

from datetime import datetime
from zoneinfo import ZoneInfo
import caldav


with caldav.DAVClient(url=CALENDAR_SERVER_URL, username=USERNAME, password=PASSWORD,
                      ssl_verify_cert=False) as client:

    calendar = client.calendar(url=USER_CALENDAR_URL)
    timezone = ZoneInfo("America/Los_Angeles")
    timestamp_start = datetime(year=2024, month=1, day=26, hour=18, minute=0, second=0, tzinfo=timezone)
    timestamp_end = datetime(year=2024, month=1, day=26, hour=18, minute=30, second=0, tzinfo=timezone)

    new_event = calendar.save_event(
        dtstart=timestamp_start,
        dtend=timestamp_end,
        summary="Sean's Comedy Debut"
    )

[tobixen]

It's a bit weird. I should probably come back and look into this at some point.

[tobixen]

This is the gist of it, if I remember correctly:

• The creation of icalendar data is left for the icalendar library.
• When the icalendar library gets a timestamp with a time zone, it will do a best effort on rewriting it as a time with a timezone identifier.
• Most servers will handle timezone identifiers from the Olson database correctly (i.e. "America/Noronha"), but it's not mandatory according to the RFC. The only universally valid way to send timestamps with a timezone is to embed the timezone data in the icalendar data itself. I currently consider it to be outside the scope for the caldav library (and I also think it's bloated). The easier way is to convert the time to UTC before sending it to the server.
• The objects from dateutil.tz does not contain the identifier, so the three-letter code may be applied instead. Which is deemed unacceptable by most servers
• Some servers will throw a 403 when the icalendar data is incorrect.

I'm not sure what is the best way to handle this ... possibly it involves embedding the timezone data into the icalendar object. That's something the icalendar library should handle, in that case.

I leave this open as an issue - it needs better handling than today in any case.

[tobixen]

I will close this issue. The correct thing to do after python 3.9 is to use zoneinfo.ZoneInfo. I've added a test case, but I haven't found any servers that does not accept that one. Probably this is handled all correct by the icalendar library. Python 3.9 has passed it's end-of-life already, and it's the minimum version that the caldav library accepts at the moment.

For backward compatibility, it would be nice to ensure dateutil.tz is also supported, but ... it's anyway out of the scope of the caldav library as such.