When is it okay to check if a file exists?

Question

File systems are volatile. This means that you can\'t trust the result of one operation to still be valid for the next one, even if it\'s the next line of code. You can\'t

Answer 1

A variety of apps include built-in web servers. It's common for them to generate self-signed SSL certificates the first time they start up. A straightforward way to implement this would be to check whether the cert exists on startup, and create it if not.

In theory, it could exist for the check, and not exist later. In that case, we'd get an error when we try to listen, but that can be handled quite easily and is not a big deal.

It's also possible that it doesn't exist for the check, and exists later. In that case, it either gets overwritten with a new cert, or writing the new cert fails, depending on your policy. The first is a little annoying, in terms of the cert change causing some alarm, but also not really critical, especially if you do a bit of logging to indicate what is going on.

And, in practice, both cases are extraordinarily unlikely to ever come up.