036-4kyu-A Simplistic TCP Finite State Machine (FSM).py

def traverse_TCP_states(events):
    state = "CLOSED"  # initial state, always
    AUTOM = {("CLOSED","APP_PASSIVE_OPEN"):"LISTEN",
             ("CLOSED","APP_ACTIVE_OPEN"):"SYN_SENT",
             ("LISTEN","RCV_SYN"):"SYN_RCVD",
             ("LISTEN","APP_SEND"):"SYN_SENT",
             ("LISTEN","APP_CLOSE"):"CLOSED",
             ("SYN_RCVD","APP_CLOSE"):"FIN_WAIT_1",
             ("SYN_RCVD","RCV_ACK"):"ESTABLISHED",
             ("SYN_SENT","RCV_SYN"):"SYN_RCVD",
             ("SYN_SENT","RCV_SYN_ACK"):"ESTABLISHED",
             ("SYN_SENT","APP_CLOSE"):"CLOSED",
             ("ESTABLISHED","APP_CLOSE"):"FIN_WAIT_1",
             ("ESTABLISHED","RCV_FIN"):"CLOSE_WAIT",
             ("FIN_WAIT_1","RCV_FIN"):"CLOSING",
             ("FIN_WAIT_1","RCV_FIN_ACK"):"TIME_WAIT",
             ("FIN_WAIT_1","RCV_ACK"):"FIN_WAIT_2",
             ("CLOSING","RCV_ACK"):"TIME_WAIT",
             ("FIN_WAIT_2","RCV_FIN"):"TIME_WAIT",
             ("TIME_WAIT","APP_TIMEOUT"):"CLOSED",
             ("CLOSE_WAIT","APP_CLOSE"):"LAST_ACK",
             ("LAST_ACK","RCV_ACK"):"CLOSED"}
    for event in events:
        if (state,event) in AUTOM:
            state = AUTOM[state,event]
        else:
            return "ERROR"
    return state