swimtracker-app/data_processing/SwimTrackerWebsocketConnection.js

import ReconnectingWebSocket from 'reconnecting-websocket';

const OpCodes = {
    // from device to frontend
    INITIAL_INFO: 1,
    SESSION_STARTED: 2,
    SESSION_STOPPED: 3,
    SESSION_NEW_DATA: 4,
    ANSWER_USER_LIST : 5,
    ANSWER_SESSION_LIST : 6,
  
    // from frontend to device
    START_SESSION: 7,
    STOP_SESSION: 8,
    TARE: 9,
    QUERY_USER_LIST: 10,
    QUERY_SESSION_LIST: 11
};

export default class SwimTrackerWebsocketConnection {
    constructor(swimTrackerHost, onData, onStarted, onStopped, onConnect, onDisconnect) {
        this.swimTrackerHost = swimTrackerHost;

        this.onData = onData;
        this.onStarted = onStarted;
        this.onStopped = onStopped;
        this.onConnect = onConnect;
        this.onDisconnect = onDisconnect;

        const wsOptions = {
            maxReconnectionDelay: 4000
        };
        this.ws = new ReconnectingWebSocket(`ws://${swimTrackerHost}:81`, [], wsOptions);
        this.ws.onmessage = this._onMessage;
        this.ws.onopen = this.onConnect;
        this.ws.onclose = this.onDisconnect;
        this.ws.onerror = this._onError;
        this.ws.binaryType = 'arraybuffer';
    }

    sendStartCommand() {
        const data = new Uint8Array(1);
        data[0] = OpCodes.START_SESSION;
        this.ws.send(data);
    }

    sendStopCommand() {
        const data = new Uint8Array(1);
        data[0] = OpCodes.STOP_SESSION;
        this.ws.send(data);
    }

    sendTareCommand() {
        const data = new Uint8Array(1);
        data[0] = OpCodes.TARE;
        this.ws.send(data);
    }

    _onMessage = (e) => {
        const dv = new DataView(e.data);
        const opCode = dv.getInt8(0);

        if (opCode === OpCodes.INITIAL_INFO) {
            const headerSize = 6;
            const running = Boolean(dv.getInt8(1));
            const sessionId = dv.getUint32(2);
            if (running && e.data.byteLength > headerSize) {
                const data = new Uint16Array(e.data.slice(headerSize));
                this.onStarted(sessionId);
                this.onData(data);
            } else
                this.onStopped();
        } else if (opCode === OpCodes.SESSION_STARTED) {
            const sessionId = dv.getUint32(1);
            this.onStarted(sessionId);
        } else if (opCode === OpCodes.SESSION_STOPPED) {
            this.onStopped();
        } else if (opCode === OpCodes.SESSION_NEW_DATA) {
            const data = new Uint16Array(e.data.slice(1));
            this.onData(data);
        }
    }

    _onError = (ev) => {
        console.log("Websocket error", ev);
    }
};