Design of SMS interface

Feeling is mainly to test your logic in dealing with this problem.

To send short messages, the most basic thing is to realize the short message interface, and it is best to design it as an independent module.

After realizing the short message interface, we should consider the problem of sending, what conditions can be sent, and the interval and frequency of sending short messages. I even have to take an exam

How to control the interval and frequency? Consider preventing others from maliciously calling your SMS interface.

How to verify the validity of the verification code after receiving it?