docs(examples): 4th and final part of the "private messaging" example

See also: https://socket.io/get-started/private-messaging-part-4/

examples/private-messaging/server/cluster.js

@@ -0,0 +1,31 @@
+const cluster = require("cluster");
+const http = require("http");
+const { setupMaster } = require("@socket.io/sticky");
+
+const WORKERS_COUNT = 4;
+
+if (cluster.isMaster) {
+  console.log(`Master ${process.pid} is running`);
+
+  for (let i = 0; i < WORKERS_COUNT; i++) {
+    cluster.fork();
+  }
+
+  cluster.on("exit", (worker) => {
+    console.log(`Worker ${worker.process.pid} died`);
+    cluster.fork();
+  });
+
+  const httpServer = http.createServer();
+  setupMaster(httpServer, {
+    loadBalancingMethod: "least-connection", // either "random", "round-robin" or "least-connection"
+  });
+  const PORT = process.env.PORT || 3000;
+
+  httpServer.listen(PORT, () =>
+    console.log(`server listening at http://localhost:${PORT}`)
+  );
+} else {
+  console.log(`Worker ${process.pid} started`);
+  require("./index");
+}

examples/private-messaging/server/docker-compose.yml

@@ -0,0 +1,7 @@
+version: "3"
+
+services:
+  redis:
+    image: redis:5
+    ports:
+      - "6379:6379"

examples/private-messaging/server/index.js

@@ -1,23 +1,30 @@
 const httpServer = require("http").createServer();
+const Redis = require("ioredis");
+const redisClient = new Redis();
 const io = require("socket.io")(httpServer, {
   cors: {
     origin: "http://localhost:8080",
   },
+  adapter: require("socket.io-redis")({
+    pubClient: redisClient,
+    subClient: redisClient.duplicate(),
+  }),
 });
 
+const { setupWorker } = require("@socket.io/sticky");
 const crypto = require("crypto");
 const randomId = () => crypto.randomBytes(8).toString("hex");
 
-const { InMemorySessionStore } = require("./sessionStore");
-const sessionStore = new InMemorySessionStore();
+const { RedisSessionStore } = require("./sessionStore");
+const sessionStore = new RedisSessionStore(redisClient);
 
-const { InMemoryMessageStore } = require("./messageStore");
-const messageStore = new InMemoryMessageStore();
+const { RedisMessageStore } = require("./messageStore");
+const messageStore = new RedisMessageStore(redisClient);
 
-io.use((socket, next) => {
+io.use(async (socket, next) => {
   const sessionID = socket.handshake.auth.sessionID;
   if (sessionID) {
-    const session = sessionStore.findSession(sessionID);
+    const session = await sessionStore.findSession(sessionID);
     if (session) {
       socket.sessionID = sessionID;
       socket.userID = session.userID;
@@ -35,7 +42,7 @@ io.use((socket, next) => {
   next();
 });
 
-io.on("connection", (socket) => {
+io.on("connection", async (socket) => {
   // persist session
   sessionStore.saveSession(socket.sessionID, {
     userID: socket.userID,
@@ -54,8 +61,12 @@ io.on("connection", (socket) => {
 
   // fetch existing users
   const users = [];
+  const [messages, sessions] = await Promise.all([
+    messageStore.findMessagesForUser(socket.userID),
+    sessionStore.findAllSessions(),
+  ]);
   const messagesPerUser = new Map();
-  messageStore.findMessagesForUser(socket.userID).forEach((message) => {
+  messages.forEach((message) => {
     const { from, to } = message;
     const otherUser = socket.userID === from ? to : from;
     if (messagesPerUser.has(otherUser)) {
@@ -64,7 +75,8 @@ io.on("connection", (socket) => {
       messagesPerUser.set(otherUser, [message]);
     }
   });
-  sessionStore.findAllSessions().forEach((session) => {
+
+  sessions.forEach((session) => {
     users.push({
       userID: session.userID,
       username: session.username,
@@ -110,8 +122,4 @@ io.on("connection", (socket) => {
   });
 });
 
-const PORT = process.env.PORT || 3000;
-
-httpServer.listen(PORT, () =>
-  console.log(`server listening at http://localhost:${PORT}`)
-);
+setupWorker(io);

examples/private-messaging/server/messageStore.js

@@ -20,6 +20,35 @@ class InMemoryMessageStore extends MessageStore {
   }
 }
 
+const CONVERSATION_TTL = 24 * 60 * 60;
+
+class RedisMessageStore extends MessageStore {
+  constructor(redisClient) {
+    super();
+    this.redisClient = redisClient;
+  }
+
+  saveMessage(message) {
+    const value = JSON.stringify(message);
+    this.redisClient
+      .multi()
+      .rpush(`messages:${message.from}`, value)
+      .rpush(`messages:${message.to}`, value)
+      .expire(`messages:${message.from}`, CONVERSATION_TTL)
+      .expire(`messages:${message.to}`, CONVERSATION_TTL)
+      .exec();
+  }
+
+  findMessagesForUser(userID) {
+    return this.redisClient
+      .lrange(`messages:${userID}`, 0, -1)
+      .then((results) => {
+        return results.map((result) => JSON.parse(result));
+      });
+  }
+}
+
 module.exports = {
   InMemoryMessageStore,
+  RedisMessageStore,
 };

examples/private-messaging/server/package.json

@@ -4,11 +4,14 @@
   "description": "",
   "main": "index.js",
   "scripts": {
-    "start": "node index.js"
+    "start": "node cluster.js"
   },
   "author": "Damien Arrachequesne <damien.arrachequesne@gmail.com>",
   "license": "MIT",
   "dependencies": {
-    "socket.io": "^3.1.1"
+    "@socket.io/sticky": "^1.0.0",
+    "ioredis": "^4.22.0",
+    "socket.io": "^3.1.1",
+    "socket.io-redis": "^6.0.1"
   }
 }

examples/private-messaging/server/sessionStore.js

@@ -23,6 +23,67 @@ class InMemorySessionStore extends SessionStore {
   }
 }
 
+const SESSION_TTL = 24 * 60 * 60;
+const mapSession = ([userID, username, connected]) =>
+  userID ? { userID, username, connected: connected === "true" } : undefined;
+
+class RedisSessionStore extends SessionStore {
+  constructor(redisClient) {
+    super();
+    this.redisClient = redisClient;
+  }
+
+  findSession(id) {
+    return this.redisClient
+      .hmget(`session:${id}`, "userID", "username", "connected")
+      .then(mapSession);
+  }
+
+  saveSession(id, { userID, username, connected }) {
+    this.redisClient
+      .multi()
+      .hset(
+        `session:${id}`,
+        "userID",
+        userID,
+        "username",
+        username,
+        "connected",
+        connected
+      )
+      .expire(`session:${id}`, SESSION_TTL)
+      .exec();
+  }
+
+  async findAllSessions() {
+    const keys = new Set();
+    let nextIndex = 0;
+    do {
+      const [nextIndexAsStr, results] = await this.redisClient.scan(
+        nextIndex,
+        "MATCH",
+        "session:*",
+        "COUNT",
+        "100"
+      );
+      nextIndex = parseInt(nextIndexAsStr, 10);
+      results.forEach((s) => keys.add(s));
+    } while (nextIndex !== 0);
+    const commands = [];
+    keys.forEach((key) => {
+      commands.push(["hmget", key, "userID", "username", "connected"]);
+    });
+    return this.redisClient
+      .multi(commands)
+      .exec()
+      .then((results) => {
+        return results
+          .map(([err, session]) => (err ? undefined : mapSession(session)))
+          .filter((v) => !!v);
+      });
+  }
+}
 module.exports = {
-  InMemorySessionStore
+  InMemorySessionStore,
+  RedisSessionStore,
 };