Expo UDP Module

Overview

The Expo UDP Module is a custom module for Expo applications that facilitates UDP communication. This module allows you to create both UDP servers and clients within your Expo app, enabling bidirectional communication over UDP.

GitHub Repository

Features

• Initialize and manage UDP servers and clients.
• Send and receive messages over UDP.
• Handle server and client disconnections and errors.
• Listen for incoming messages and errors.

Installation

To use the Expo UDP Module, follow these steps:

expo install expo-udp

Usage

Importing the Module

import { initServer, initClient, addServerMessageListener, addServerErrorListener, addServerDisconnectListener, addClientMessageListener, addClientErrorListener } from 'expo-udp';

Initializing a UDP Server

To initialize a UDP server, use the initServer function:

const server = await initServer(port, ip);

• port: The port number on which the server will listen.
• ip: The IP address on which the server will listen.

Sending Messages from the Server

To send a message from the server to a client, use the sendServerMessage method:

await server.sendServerMessage(clientIp, clientPort, message);

• clientIp: The IP address of the client.
• clientPort: The port number of the client.
• message: The message to send.

Stopping the Server

To stop the server, use the stop method:

await server.stop();

Listening for Server Events

You can listen for various server events such as incoming messages, errors, and disconnections:

const serverMessageSub = addServerMessageListener((event) => {
  console.log(`Server received: ${event.message} from ${event.fromIp}:${event.fromPort}`);
});

const serverErrorSub = addServerErrorListener((event) => {
  console.error(`Server error: ${event.error}`);
});

const serverDisconnectSub = addServerDisconnectListener((event) => {
  console.log(`Server disconnected: ${event.message}`);
});

Initializing a UDP Client

To initialize a UDP client, use the initClient function:

const client = await initClient(serverIp, serverPort);

• serverIp: The IP address of the server.
• serverPort: The port number of the server.

Sending Messages from the Client

To send a message from the client to the server, use the sendMessage method:

await client.sendMessage(serverIp, serverPort, message);

• serverIp: The IP address of the server.
• serverPort: The port number of the server.
• message: The message to send.

Stopping the Client

To stop the client, use the stop method:

await client.stop();

Listening for Client Events

You can listen for various client events such as incoming messages and errors:

const clientMessageSub = addClientMessageListener((event) => {
  console.log(`Client received: ${event.message} from ${event.fromIp}:${event.fromPort}`);
});

const clientErrorSub = addClientErrorListener((event) => {
  console.error(`Client error: ${event.error}`);
});

EAS Build Considerations

Why EAS Build is Required?

The Expo UDP module contains native code, which means it does not work in Expo Go. Instead, you must use a development build created with EAS.

Building for Development (Local & Cloud)

Option 1: EAS Build (Cloud Build)

Run this command to build an Expo Development Build in the cloud:

eas build --profile development --platform android

After the build completes, install the APK or IPA on your device. Then, launch your app and select "Switch to development build" in Expo.

Option 2: EAS Build (Local Build)

If you want to build locally instead of using the cloud, run:

eas build --local --profile development --platform android

This will generate an APK locally, which you can install and test.

Running the App Without EAS Build?

If you try to run the module in Expo Go, you will see the error:

(NOBRIDGE) ERROR  Error: Cannot find native module 'ExpoUdp'

This happens because Expo Go does not support native modules. Always use an EAS development build to test the UDP module.

Example Node.js UDP Server and Client

UDP Server (Node.js)

const dgram = require('dgram');
const server = dgram.createSocket('udp4');

server.on('error', (err) => {
  console.error(`Server error:\n${err.stack}`);
  server.close();
});

server.on('message', (msg, rinfo) => {
  console.log(`Server received: ${msg} from ${rinfo.address}:${rinfo.port}`);
  server.send('Message received', rinfo.port, rinfo.address);
});

server.on('listening', () => {
  const address = server.address();
  console.log(`Server listening ${address.address}:${address.port}`);
});

server.bind(12345, '127.0.0.1');

UDP Client (Node.js)

const dgram = require('dgram');
const client = dgram.createSocket('udp4');

client.on('message', (msg, rinfo) => {
  console.log(`Client received: ${msg} from ${rinfo.address}:${rinfo.port}`);
});

const message = Buffer.from('Hello, Server!');
client.send(message, 0, message.length, 12345, '127.0.0.1', (err) => {
  if (err) {
    console.error(`Client error: ${err}`);
  } else {
    console.log('Message sent');
  }
  client.close();
});

Testing with the Expo Module App

1. Start the Node.js UDP Server on your local machine.
2. Run the Expo Module App on your device or emulator with an EAS development build.
3. Configure the app to connect to the Node.js server's IP and port.
4. Send and receive messages between the Expo app and the Node.js server to verify the communication.

Contributing

Contributions are welcome! Please open an issue or submit a pull request.

License

This module is licensed under the MIT License.