Indeed, it seems there is nothing to check if a market is open/closed.

I'm currently relying on getting the book (bid/ask).

A closed market will have:

1. Bid/ask readings to be 0 (one or both of them).
2. Bid will equal ask (more common).

By validating the book, you can get a grasp of what is being traded out there.
Obviously, it is not bulletproof, as a market can have a circuit breaker on.

Also note that requesting historical data is not enough, as a market can be open for trading, but without any trades traded so far (zero volume).