Is it difficult to have a “wrapper” around a function so that when a function (or handler) is called, it has a particular routine run against it? For example, a web handler has a wrapper that logs a connection details, or times the length of a function runtime, or checks the credentials attached to a request from a client has the right to access a particular part of the system? Or maybe all of those things if you have a function/handler wrapped in multiple wrapper-functions?

you can write a macro to do it