The tz database is public domain, and they have HTTP/FTP/rsync APIs. You probably don't even need to implement this yourself, since every modern OS pulls from this already.
Thanks; that is what I was looking for. Last time I had to work in detail with timezones (with the above reqs, plus some others), that didn't exist (based on the date for the RFC).
As to having to/not having to implement this (and rely on the OS) - probably! I just know at the time I last dealt with this, every library I could find packaged their own TZ DB, and they were definitely not standard.
Which RFC? The RFC moving it to IANA in 2012? It's been in development in some way since the 80s [1], the current timezone names in it are from the 90s[2], and it was definitely already the standard timezone definitions when I started using Linux in the 00s.
Yes, moving it to IANA. Maybe the packaged DBs were 'standard', in a sense, but you couldn't just take a file from one and drop it into another; they were configured or serialized in various ways. Regardless, it meant updating a dependency when things changed; I don't know the state of historical timezone information at the OS level at that time, but I do know none of the libraries I looked at made OS calls.
The tz database is public domain, and they have HTTP/FTP/rsync APIs. You probably don't even need to implement this yourself, since every modern OS pulls from this already.