[Tutorials] Add example server

tutorial-server/app.js

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+/*global require,process,console*/
+
+var CONFIG = {
+    port: 8081,
+    dictionary: "dictionary.json",
+    interval: 1000
+};
+
+(function () {
+    "use strict";
+
+    var WebSocketServer = require('ws').Server,
+        fs = require('fs'),
+        wss = new WebSocketServer({ port: CONFIG.port }),
+        dictionary = JSON.parse(fs.readFileSync(CONFIG.dictionary, "utf8")),
+        spacecraft = {
+            "prop.fuel": 77,
+            "prop.thrusters": "OFF",
+            "comms.recd": 0,
+            "comms.sent": 0,
+            "pwr.temp": 245,
+            "pwr.c": 8.15,
+            "pwr.v": 30
+        },
+        histories = {},
+        listeners = [];
+
+    function updateSpacecraft() {
+        spacecraft["prop.fuel"] = Math.max(
+            0,
+            spacecraft["prop.fuel"] -
+            (spacecraft["prop.thrusters"] === "ON" ? 0.5 : 0)
+        );
+        spacecraft["pwr.temp"] = spacecraft["pwr.temp"] * 0.985
+        + Math.random() * 0.25 + Math.sin(Date.now());
+        spacecraft["pwr.c"] = spacecraft["pwr.c"] * 0.985;
+        spacecraft["pwr.v"] = 30 + Math.pow(Math.random(), 3);
+    }
+
+    function generateTelemetry() {
+        var timestamp = Date.now(), sent = 0;
+        Object.keys(spacecraft).forEach(function (id) {
+            var state = { timestamp: timestamp, value: spacecraft[id] };
+            histories[id] = histories[id] || []; // Initialize
+            histories[id].push(state);
+            spacecraft["comms.sent"] += JSON.stringify(state).length;
+        });
+        listeners.forEach(function (listener) {
+            listener();
+        });
+    }
+
+    function update() {
+        updateSpacecraft();
+        generateTelemetry();
+    }
+
+    function handleConnection(ws) {
+        var subscriptions = {}, // Active subscriptions for this connection
+            handlers = {        // Handlers for specific requests
+                dictionary: function () {
+                    ws.send(JSON.stringify({
+                        type: "dictionary",
+                        value: dictionary
+                    }));
+                },
+                subscribe: function (id) {
+                    subscriptions[id] = true;
+                },
+                unsubscribe: function (id) {
+                    delete subscriptions[id];
+                },
+                history: function (id) {
+                    ws.send(JSON.stringify({
+                        type: "history",
+                        id: id,
+                        value: histories[id]
+                    }));
+                }
+            };
+
+        function notifySubscribers() {
+            Object.keys(subscriptions).forEach(function (id) {
+                var history = histories[id];
+                if (history) {
+                    ws.send(JSON.stringify({
+                        type: "data",
+                        id: id,
+                        value: history[history.length - 1]
+                    }));
+                }
+            });
+        }
+
+        // Listen for requests
+        ws.on('message', function (message) {
+            var parts = message.split(' '),
+                handler = handlers[parts[0]];
+            if (handler) {
+                handler.apply(handlers, parts.slice(1));
+            }
+        });
+
+        // Stop sending telemetry updates for this connection when closed
+        ws.on('close', function () {
+            listeners = listeners.filter(function (listener) {
+                return listener !== notifySubscribers;
+            });
+        });
+
+        // Notify subscribers when telemetry is updated
+        listeners.push(notifySubscribers);
+    }
+
+    update();
+    setInterval(update, CONFIG.interval);
+
+    wss.on('connection', handleConnection);
+
+    console.log("Example spacecraft running on port ");
+    console.log("Press Enter to toggle thruster state.");
+    process.stdin.on('data', function (data) {
+        spacecraft['prop.thrusters'] =
+            (spacecraft['prop.thrusters'] === "OFF") ? "ON" : "OFF";
+        console.log("Thrusters " + spacecraft["prop.thrusters"]);
+    });
+}());

tutorial-server/dictionary.json

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+{
+    "name": "Example Spacecraft",
+    "identifier": "sc",
+    "subsystems": [
+        {
+            "name": "Propulsion",
+            "identifier": "prop",
+            "measurements": [
+                {
+                    "name": "Fuel",
+                    "identifier": "prop.fuel",
+                    "units": "kilograms",
+                    "type": "float"
+                },
+                {
+                    "name": "Thrusters",
+                    "identifier": "prop.thrusters",
+                    "units": "None",
+                    "type": "string"
+                }
+            ]
+        },
+        {
+            "name": "Communications",
+            "identifier": "comms",
+            "measurements": [
+                {
+                    "name": "Received",
+                    "identifier": "comms.recd",
+                    "units": "bytes",
+                    "type": "integer"
+                },
+                {
+                    "name": "Sent",
+                    "identifier": "comms.sent",
+                    "units": "bytes",
+                    "type": "integer"
+                }
+            ]
+        },
+        {
+            "name": "Power",
+            "identifier": "pwr",
+            "measurements": [
+                {
+                    "name": "Generator Temperature",
+                    "identifier": "pwr.temp",
+                    "units": "\u0080C",
+                    "type": "float"
+                },
+                {
+                    "name": "Generator Current",
+                    "identifier": "pwr.c",
+                    "units": "A",
+                    "type": "float"
+                },
+                {
+                    "name": "Generator Voltage",
+                    "identifier": "pwr.v",
+                    "units": "V",
+                    "type": "float"
+                }
+            ]
+        }
+    ]
+}