docs: add example with capped collection and TTL index

examples/capped-example/index.js

@@ -0,0 +1,79 @@
+import { MongoClient } from "mongodb";
+import { Server } from "socket.io";
+import { createAdapter } from "@socket.io/mongo-adapter";
+import { io } from "socket.io-client";
+
+async function initMongoCollection() {
+  const DB = "mydb";
+  const COLLECTION = "socket.io-adapter-events-capped";
+
+  const mongoClient = new MongoClient(
+    "mongodb://localhost:27017/?replicaSet=rs0&directConnection=true"
+  );
+
+  await mongoClient.connect();
+
+  try {
+    await mongoClient.db(DB).createCollection(COLLECTION, {
+      capped: true,
+      size: 1e6,
+    });
+  } catch (e) {
+    // collection already exists
+  }
+
+  return mongoClient.db(DB).collection(COLLECTION);
+}
+
+function initServer(mongoCollection) {
+  const io = new Server({
+    connectionStateRecovery: {},
+  });
+
+  io.adapter(createAdapter(mongoCollection));
+
+  return io;
+}
+
+function initClient(port) {
+  const socket = io(`http://localhost:${port}`);
+
+  socket.on("connect", () => {
+    console.log(`[${port}] connected (recovered? ${socket.recovered})`);
+  });
+
+  socket.on("ping", () => {
+    console.log(`[${port}] got ping`);
+  });
+
+  socket.on("disconnect", (reason) => {
+    console.log(`[${port}] disconnected due to ${reason}`);
+  });
+
+  return socket;
+}
+
+const mongoCollection = await initMongoCollection();
+
+const io1 = initServer(mongoCollection);
+const io2 = initServer(mongoCollection);
+const io3 = initServer(mongoCollection);
+
+io1.listen(3000);
+io2.listen(3001);
+io3.listen(3002);
+
+initClient(3000);
+initClient(3001);
+initClient(3002);
+
+setInterval(() => {
+  io1.emit("ping");
+}, 2000);
+
+// uncomment to test connection state recovery
+// setTimeout(() => {
+//   io2.close(() => {
+//     io2.listen(3001);
+//   });
+// }, 3000);