TCP modules we might want:

• TCP state machine
  • API:
    • pass in packet header and needed args, such as buffer space available
    • returns action to take, such as: drop, ack, reset, retransmit
• congestion control (vegas, reno, cubic, bbr)
• retransmission (fast retrans, retrans timeout)
• acknowledgement (selective, quick, delayed acks)

Plan for migrating network code:

1. fix qdisc bug
2. enable rust sockets in the network interface
3. finish moving majority of TCP syscall handling to rust
4. figure out how to support rust status listeners in the TCP socket
5. figure out how to deal with sendto/recvfrom syscall handlers for TCP
6. rewrite UDP sockets in rust
7. rewrite network interface and qdisc, and remove CompatSocket objects (Convert network interface and queuing to rust #3480)
8. begin rust TCP implementation

Design sketch for trait-based packet states:

https://play.rust-lang.org/?version=stable&mode=debug&edition=2021&gist=02d0eae5a60980fac0424df83e1cb0ee

mod with_traits {
    struct PacketStateA { }
    struct PacketStateB { }
    
    trait PacketState {
        fn receive(self: Box<Self>) -> Box<dyn PacketState>;
    }
    impl PacketState for PacketStateA {
        fn receive(self: Box<Self>) -> Box<dyn PacketState> {
            Box::new(PacketStateB{})
        }
    }
    impl PacketState for PacketStateB {
        fn receive(self: Box<Self>) -> Box<dyn PacketState> {
            self
        }
    }
    pub fn receive(opt: &mut Option<Box<dyn PacketState>>) {
        let s = opt.take().unwrap();
        *opt = Some(s.receive());
    }
}