<SYSTEM_TASK:>
Solve the following problem using Python, implementing the functions described below, one line at a time
<END_TASK>
<USER_TASK:>
Description:
 def faasport(func: Faasport) -> Faasport: """Decorator that registers the user's faasport function."""

    global user_faasport

    if user_faasport is not None:
        raise RuntimeError('Multiple definitions of faasport.')

    user_faasport = func
    return func