This adds two new functions: `Conn::register_removal_hook()` and
`Conn::unregister_removal_hook()` for registering a hook function to be
called back during `connection_state_remove`. The benefit of using hook
callback approach is better scalability: the overhead of unrelated
protocols having to dispatch no-op `connection_state_remove` handlers is
avoided.
And switch Zeek's base scripts over to using it in place of
"connection_state_remove". The difference between the two is
that "connection_state_remove" is raised for all events while
"successful_connection_remove" excludes TCP connections that were never
established (just SYN packets). There can be performance benefits
to this change for some use-cases.
There's also a new event called ``connection_successful`` and a new
``connection`` record field named "successful" to help indicate this new
property of connections.
The KRB parser allowed for the following types/fields to be left
uninitialized, so an &optional attribute was added to reflect that:
- KRB::Error_Msg
- pvno
- msg_type
- server_time
- service_realm
- service_name
- KRB::KDC_Request
- kdc_options
- service_realm
- till
- nonce
- encryption_types
Usages have also been adapted to perform existence checks.
This makes it much easier for protocols where the mime type is known in
advance like, for example, TLS. We now do no longer have to perform deep
script-level magic.
