How to Build Your Own Real-Time Chat App
Real-time chat has become a common feature in many modern web and mobile applications. From basic customer support to massive multiplayer gaming, the ability to instantly communicate between client and server opens up a range of possibilities for interactive experiences.
In this guide, we‘ll break down what goes into building your own real-time chat application from scratch. While the exact tools you choose may differ, the core architecture and concepts can be applied across many languages and frameworks. Let‘s dive in!
What is a real-time chat app?
At a high level, a real-time chat app consists of a front-end client interface that allows users to send and receive messages, and a back-end server that handles distributing those messages to the appropriate recipients. The key to "real-time" communication is maintaining an open connection between the clients and server so that data can be transmitted as soon as it‘s available, without needing to refresh the page or poll the server for updates.
Traditionally, HTTP web traffic operates on a request-response model – the client sends a request, the server handles the request and sends back a response, and the connection is closed. This works fine for static pages, but real-time data requires a more persistent connection.
Technologies like WebSockets, server-sent events (SSE), and long-polling allow for full-duplex (two-way) communication between client and server over a single, long-lived connection. The server can push data to the client instantly without the client needing to request it. In a chat app, this means new messages can appear almost instantly from the user‘s perspective.
Architecture of a real-time chat app
While there are many possible approaches, a typical real-time chat app consists of the following components:
-
Client application – the user interface that allows sending and receiving of messages. This is often a web app built with HTML/CSS/JavaScript, but could also be a native mobile or desktop app.
-
WebSocket server – a server that accepts WebSocket connections from clients and routes messages between them. The WebSocket protocol provides a full-duplex communication channel over a single TCP connection.
-
Message broker – responsible for distributing messages to the appropriate recipients, handling real-time pub/sub messaging. Redis is a popular choice due to its high performance and built-in pub/sub capabilities.
-
Database – for storing persistent data like user info, message history, group info, etc. This could be a relational database like PostgreSQL or a NoSQL database like MongoDB.
Here‘s a simplified diagram of how the components interact:
+-------------+ +---------------+
| | | |
| Client |<---------->| WebSocket |
| | WebSocket | Server |
+-------------+ +-------+-------+
|
+-------v------+
| |
| Message |
| Broker |
| |
+-------+------+
|
+-------v-------+
| |
| Database |
| |
+---------------+The client establishes a WebSocket connection with the server. When a user sends a message, the client sends it over the WebSocket to the server. The server receives the message, processes it, and publishes it to the message broker.
The message broker then distributes the message to any subscribers (which could include the server itself). The server finally pushes the message out to the clients that should receive it over their respective WebSocket connections. Any relevant data like user info is saved to the database.
Building a basic real-time chat app
Now that we have an understanding of the main components, let‘s walk through the process of actually building a basic chat app from scratch. We‘ll keep things simple by focusing on the core functionality of sending and receiving messages.
Setting up the environment
First, make sure you have Node.js installed. We‘ll be using it for both the client and server. Create a new directory for the project and set up the following structure:
chat-app/
client/
public/
index.html
styles.css
src/
app.js
server/
server.jsRun npm init in both the client and server directories to set up a basic package.json file. In the client directory, install the following dependencies:
npm install express socket.io-clientAnd in the server directory:
npm install express socket.ioBuilding the client
The client in this case will be a simple web page with a form for sending messages and an area for displaying received messages. In client/public/index.html:
<!DOCTYPE html>
<html lang="en">
<head>
<meta charset="UTF-8">
<meta name="viewport" content="width=device-width, initial-scale=1.0">
<title>Real-Time Chat App</title>
<link rel="stylesheet" href="styles.css">
</head>
<body>
<div id="chat-app">
<div id="chat-window">
<div id="output"></div>
</div>
<input type="text" id="message" placeholder="Message">
<button id="send">Send</button>
</div>
<script src="/socket.io/socket.io.js"></script>
<script src="app.js"></script>
</body>
</html>And add some basic styles in client/public/styles.css:
body {
font-family: Arial, Helvetica, sans-serif;
}
#chat-app {
max-width: 600px;
margin: 30px auto;
border: 1px solid #ddd;
box-shadow: 1px 3px 5px rgba(0,0,0,0.5);
}
#chat-window {
height: 400px;
overflow: auto;
background: #f9f9f9;
}
#output p {
padding: 14px 0;
margin: 0 20px;
border-bottom: 1px solid #e9e9e9;
}
#message {
padding: 10px 20px;
box-sizing: border-box;
border: 0;
background: #eee;
display: block;
width: 100%;
}
#send {
background: #575ed8;
color: #fff;
border: 0;
padding: 12px 0;
width: 100%;
cursor: pointer;
}In client/src/app.js, set up the WebSocket connection and handle sending and receiving messages:
const socket = io();
const message = document.getElementById(‘message‘);
const send = document.getElementById(‘send‘);
const output = document.getElementById(‘output‘);
send.addEventListener(‘click‘, () => {
socket.emit(‘chat message‘, message.value);
message.value = ‘‘;
});
socket.on(‘chat message‘, (msg) => {
const p = document.createElement(‘p‘);
p.textContent = msg;
output.appendChild(p);
});Building the server
The server will use the Socket.IO library to handle WebSocket connections and messaging. Socket.IO allows sending and receiving any JSON-serializable data, which will be useful for more advanced features, but for now we‘ll just use simple strings.
In server/server.js:
const express = require(‘express‘);
const app = express();
const http = require(‘http‘).Server(app);
const io = require(‘socket.io‘)(http);
io.on(‘connection‘, (socket) => {
console.log(‘User connected‘);
socket.on(‘disconnect‘, () => {
console.log(‘User disconnected‘);
});
socket.on(‘chat message‘, (msg) => {
console.log(`Message: ${msg}`);
io.emit(‘chat message‘, msg);
});
});
app.use(express.static(__dirname + ‘/../client/public‘));
const port = process.env.PORT || 3000;
http.listen(port, () => {
console.log(`Server started on port ${port}`);
});The server uses Express to serve the static client files, and listens for Socket.IO connections. When a client connects, it sets up listeners for the disconnect event (when a client drops the connection) and the custom chat message event that we defined in the client. When a chat message is received, it re-emits it to all connected clients.
Running the app
To start the server, run the following command from the server directory:
node server.jsThen open a web browser and navigate to http://localhost:3000. You should see the chat interface. Open another browser window and navigate to the same URL to simulate a second user. Type a message and click send – the message should appear in both windows nearly instantly!
Congratulations, you‘ve built a basic real-time chat app! Of course, there are many more features you could add, such as:
- User nicknames
- User presence (showing who‘s currently online)
- Typing indicators ("User X is typing…")
- Private messaging
- Group chat rooms
Scaling real-time apps
As your app grows in features and users, you may start running into scalability issues. What if you have thousands or even millions of concurrent users? What if your chat messages need to be processed or transformed in more complex ways before being delivered?
Some common strategies for scaling real-time apps include:
- Horizontal scaling – running multiple instances of your server behind a load balancer to distribute connection and processing load
- Using a dedicated real-time messaging platform like Pusher or Ably that handles the WebSocket infrastructure and message brokering for you
- Sharding your message queues and event streams based on logical partitions like user ID or chat room
- Fan-out messaging to distribute messages to many subscribers in parallel
There are also many DevOps considerations when deploying and scaling real-time apps, such as monitoring, logging, and ensuring graceful handling of network failures and server restarts. I recommend checking out this article on the Pusher blog for a deeper dive.
Hosted real-time platforms
While it‘s certainly possible to build your own real-time messaging infrastructure from scratch, there are also a number of hosted platforms that provide real-time messaging as a service, handling the WebSocket connections, message brokering, and scaling for you. Some popular options include:
These platforms typically provide SDKs for various languages that wrap the details of WebSocket management and expose higher-level APIs for publishing and subscribing to messages.
The tradeoff is less control over your system‘s architecture and potentially higher costs at scale compared to a self-hosted solution. However, they can greatly simplify development and deployment of real-time features.
Further reading
There‘s a lot more that goes into building production-ready real-time applications. Once you have the basic messaging functionality in place, you‘ll likely want to add more advanced features, handle edge cases, ensure security and integrity of your data, and rigorously test your implementation.
Here are some additional resources to go deeper on building real-time apps:
- Socket.IO docs
- The Definitive Guide to Deploying Secure WebSocket Applications
- You Might Not Need WebSockets
- Real-Time Web Apps with Server-Sent Events
I hope this guide has given you a solid foundation for understanding and building real-time chat applications. Remember, the concepts covered here can be applied to all sorts of real-time features beyond chat. Get creative and have fun with it!