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A Simplistic TCP Finite State Machine (FSM) - Javascript Solution
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| /* | |
| The "transition table" from the instructions: | |
| 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 | |
| */ | |
| // this isn't really code it's just the instructions above but represented as an object | |
| const data = { | |
| CLOSED: { APP_PASSIVE_OPEN: "LISTEN", APP_ACTIVE_OPEN: "SYN_SENT" }, | |
| LISTEN: { RCV_SYN: "SYN_RCVD", APP_SEND: "SYN_SENT", APP_CLOSE: "CLOSED" }, | |
| SYN_RCVD: { | |
| APP_CLOSE: "FIN_WAIT_1", | |
| RCV_ACK: "ESTABLISHED", | |
| }, | |
| SYN_SENT: { | |
| RCV_SYN: "SYN_RCVD", | |
| RCV_SYN_ACK: "ESTABLISHED", | |
| APP_CLOSE: "CLOSED", | |
| }, | |
| ESTABLISHED: { APP_CLOSE: "FIN_WAIT_1", RCV_FIN: "CLOSE_WAIT" }, | |
| FIN_WAIT_1: { | |
| RCV_FIN: "CLOSING", | |
| RCV_FIN_ACK: "TIME_WAIT", | |
| 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" }, | |
| } | |
| function traverseTCPStates(eventList) { | |
| let state = "CLOSED" | |
| for (event of eventList) { | |
| let transitions = data[state] | |
| if (transitions == undefined) { | |
| return "ERROR" | |
| } | |
| state = transitions[event] | |
| if (state === undefined) { | |
| return "ERROR" | |
| } | |
| } | |
| return state | |
| } |
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You can actually write
traverseTCPStatesone line:But it's kinda hard to read because
reduce&?.are kinda advanced.