Google calendar API issue - daylight saving - asp.net-web-api

Question

I made an application using the Google calendar API, to evaluate events and finally also adds an event to a calendar. Now we come close to the switch to daylight saving time I have the problem: the API is shifting time for one hour.
Example:
$event = new Google_Service_Calendar_Event(array(
'summary' => 'title',
'description' => 'description',
'start' => array(
'dateTime' => '2018-04-05T12:00:00+1:00',
'timeZone' => 'Europe/Amsterdam',
),
'end' => array(
'dateTime' => '2018-04-05T15:00:00+1:00',
'timeZone' => 'Europe/Amsterdam',
)
));
$event = $cal->events->insert($room_calendar_id, $event);
When I execute this code the result is an event that runs from 13:00 till 16:00 hrs. When I use these parameters via the Google calendar API try-out function it gives the same result. But in the latter case it comes back with following JSON response:
"start": {
"dateTime": "2018-04-20T13:00:00+02:00",
"timeZone": "Europe/Amsterdam"
},
"end": {
"dateTime": "2018-04-20T16:00:00+02:00",
"timeZone": "Europe/Amsterdam"
}
So weird it shows an offset of +02:00.
I would expect the API does not change the time and offset parameters.
When I do the same for 2018-03-20 it works fine, so daylight saving should cause this issue in my opinion.
Can someone give more information on how I should add an event without considering the daylight saving influence?

Answer 1

Timezones - such as Europe/Amsterdam - have Daylight Saving effects, and you can't help avoiding them, because DST is part of the things controled by timezone definitions.
And during DST, the offset used in Amsterdam is changed from +01:00 to +02:00. So this is not weird, it's actually the expected behaviour.
What google API is doing - probably - is adjusting an invalid offset (2018-04-05T12:00:00+01:00) to a valid one (2018-04-05T13:00:00+02:00) - btw, both correspond to the same UTC instant, so the conversion is fine.
This doesn't happen in March 20th because DST haven't started yet - in 2018, it starts on March 25th.
If you're dealing with timezones, there's no way to ignore DST effects, because DST is part of the timezone definition.