Runtime type safety for Erlang/otp behaviours

Callback-oriented Erlang/OTP behaviours such as the gen_server library are susceptible to malformed requests and ill-typed messages, causing server processes to crash unless a defensive programming style is used. We contribute an alternative approach in the form of a fully automatic hybrid analysis of callback modules using a notion of type safety based upon a sub-typing relation for Erlang. A combination of compile-time type inference, automatic code injection, and modifications to the request dispatch code of gen_server are used to demonstrate how generic server processes can be protected from client-side type errors.