Add base code

.env.development

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+PORT=3002

.eslintignore

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+dist
+node_modules

.eslintrc.json

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+{
+    "extends": "@jitsi/eslint-config"
+}

.gitignore

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+.DS_Store
+dist
+node_modules

babel.config.json

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+{}

package.json

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+{
+    "name": "excalidraw-backend",
+    "version": "1.0.0",
+    "main": "src/index.js",
+    "description": "Excalidraw backend",
+    "repository": {
+        "type": "git",
+        "url": "https://github.com/jitsi/excalidraw-backend"
+    },
+    "private": true,
+    "engines": {
+        "node": ">=14.0.0",
+        "npm": ">=7.0.0"
+    },
+    "dependencies": {
+        "@babel/core": "7.16.0",
+        "@babel/eslint-parser": "7.16.0",
+        "@babel/plugin-proposal-export-default-from": "7.16.0",
+        "@babel/preset-env": "7.16.0",
+        "@babel/runtime": "7.16.0",
+        "@excalidraw/eslint-config": "1.0.1",
+        "@excalidraw/prettier-config": "1.0.2",
+        "@jitsi/eslint-config": "^4.1.0",
+        "@types/debug": "4.1.5",
+        "@types/express": "4.17.11",
+        "@types/node": "14.14.31",
+        "@types/socket.io": "2.1.4",
+        "@typescript-eslint/eslint-plugin": "5.30.5",
+        "@typescript-eslint/parser": "5.30.4",
+        "babel-loader": "8.2.3",
+        "babel-plugin-optional-require": "0.3.1",
+        "circular-dependency-plugin": "5.2.0",
+        "clean-css-cli": "4.3.0",
+        "copy-webpack-plugin": "^9.0.0",
+        "cross-env": "^7.0.3",
+        "css-loader": "3.6.0",
+        "debug": "4.3.1",
+        "dotenv": "^10.0.0",
+        "eslint": "8.1.0",
+        "eslint-plugin-import": "2.25.2",
+        "eslint-plugin-jsdoc": "37.0.3",
+        "express": "4.17.1",
+        "socket.io": "^2.5.0",
+        "ts-node-dev": "^1.1.8",
+        "typescript": "4.2.3"
+    },
+    "license": "MIT",
+    "scripts": {
+        "build": "tsc",
+        "start": "tsc && node dist/index.js",
+        "start:dev": "cross-env NODE_ENV=development ts-node-dev --respawn --transpile-only src/index.ts"
+    }
+}

src/index.ts

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+import debug from "debug";
+import express from "express";
+import http from "http";
+import socketIO from "socket.io";
+
+const serverDebug = debug("server");
+const ioDebug = debug("io");
+const socketDebug = debug("socket");
+
+require("dotenv").config(
+  process.env.NODE_ENV !== "development"
+    ? { path: ".env.production" }
+    : { path: ".env.development" },
+);
+
+const app = express();
+const port = process.env.PORT || 80; // default port to listen
+
+app.use(express.static("public"));
+
+app.get("/", (req, res) => {
+  res.send("Excalidraw backend is up :)");
+});
+
+const server = http.createServer(app);
+
+server.listen(port, () => {
+  serverDebug(`listening on port: ${port}`);
+});
+
+const io = socketIO(server, {
+  handlePreflightRequest: (req, res) => {
+    const headers = {
+      "Access-Control-Allow-Headers": "Content-Type, Authorization",
+      "Access-Control-Allow-Origin":
+        (req.header && req.header.origin) || "https://meet.jit.si",
+      "Access-Control-Allow-Credentials": true,
+    };
+    res.writeHead(200, headers);
+    res.end();
+  },
+});
+
+io.on("connection", (socket) => {
+  ioDebug("connection established!");
+  io.to(`${socket.id}`).emit("init-room");
+  socket.on("join-room", (roomID) => {
+    socketDebug(`${socket.id} has joined ${roomID}`);
+    socket.join(roomID);
+    if (io.sockets.adapter.rooms[roomID].length <= 1) {
+      io.to(`${socket.id}`).emit("first-in-room");
+    } else {
+      socket.broadcast.to(roomID).emit("new-user", socket.id);
+    }
+    io.in(roomID).emit(
+      "room-user-change",
+      Object.keys(io.sockets.adapter.rooms[roomID].sockets),
+    );
+  });
+
+  socket.on(
+    "server-broadcast",
+    (roomID: string, encryptedData: ArrayBuffer, iv: Uint8Array) => {
+      socketDebug(`${socket.id} sends update to ${roomID}`);
+      socket.broadcast.to(roomID).emit("client-broadcast", encryptedData, iv);
+    },
+  );
+
+  socket.on(
+    "server-volatile-broadcast",
+    (roomID: string, encryptedData: ArrayBuffer, iv: Uint8Array) => {
+      socketDebug(`${socket.id} sends volatile update to ${roomID}`);
+      socket.volatile.broadcast
+        .to(roomID)
+        .emit("client-broadcast", encryptedData, iv);
+    },
+  );
+
+  socket.on("disconnecting", () => {
+    const rooms = io.sockets.adapter.rooms;
+    for (const roomID in socket.rooms) {
+      const clients = Object.keys(rooms[roomID].sockets).filter(
+        (id) => id !== socket.id,
+      );
+      if (clients.length > 0) {
+        socket.broadcast.to(roomID).emit("room-user-change", clients);
+      }
+    }
+  });
+
+  socket.on("disconnect", () => {
+    socket.removeAllListeners();
+  });
+});

tsconfig.json

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+{
+    "compilerOptions": {
+        "allowSyntheticDefaultImports": true,
+        "target": "es5",
+        "lib": ["dom", "dom.iterable", "esnext"],
+        "allowJs": true,
+        "skipLibCheck": true,
+        "esModuleInterop": true,
+        "strict": true,
+        "moduleResolution": "Node",
+        "forceConsistentCasingInFileNames": true,
+        "resolveJsonModule": true,
+        "isolatedModules": true,
+        "outDir": "dist"
+    }
+  }
+