date / time conversion from user's local time to UTC on website

Question

I'm currently adding an out of office like system to a website, where users will be able to mark their out of office dates and times such that they can provide another users's information to use as a backup while they are out.

The problem I have, is converting the users's local time to UTC. I've seen other posts that address this issue by supplying UTC to the user, and having the client (js) convert the time to and from local time. I do, however, have access to a propriety system I can use to convert the date server-side based on the user's time-zone preference.

My question is this: Should I use the server side conversion, which would allow a user's home local time to be supplied (say, their US time, regardless of where they are logged in), or should I use the client side conversion?

Does anyone have any experience with this? What are some of the less obvious advantages / disadvantages of each method?

Answer 1

Storing everything in UTC is a very good idea and I recommend that you stick to it.

There are few approaches you can use. I assume that you would have User's profiles. You may decide to give users an ability to pick the time zone they prefer and display everything using this information. As well as treat all user input appropriately (convert on server side, assuming the time zone is preferred one).

Another way to handle it, is to actually take User's time zone offset via Date.getTimeZoneOffset() and send it out to your server somehow (i.e. via hidden form field or Ajax). When you know that, showing everything in User's time would be piece of cake. In this case you might want to convert date/time on the client and send it out as UTC (or use hidden form field with time zone offset).

In both cases you handle database date conversion on server side. This is the best approach from my experience. I would like to point out, that apart from just converting time zones, you probably should think about displaying date/time in correct format (i.e. depending on AcceptLanguage header value).