WebSocket

Why WebSockets Were Needed

With polling/long polling:

• Client keeps asking the server repeatedly
• Many unnecessary HTTP requests
• Higher latency
• Waste of bandwidth

WebSockets solve this by creating:

A persistent, full-duplex (two-way) connection over a single TCP connection.

What Is a WebSocket?

A WebSocket is a protocol that allows:

• Continuous connection between client and server
• Bi-directional communication
• Low latency messaging
• Minimal overhead after connection is established

Instead of:

request → response → close

You get:

open connection → send/receive anytime → close when done

How WebSockets Work

1 Starts as HTTP

The connection begins as a normal HTTP request. In order to start the connection, clients sends a http GET request with a upgrade header, so that the server know that this is a upgrade request.

Client sends:

GET /chat HTTP/1.1
Host: example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: random_key
Sec-WebSocket-Version: 13

This is called the HTTP Upgrade request.

2 Server Upgraded the Connection

If server supports WebSockets. It responds with status 101 and return error code if not.

If any code other than 101 is returned from the server, Clients has to end the connection.

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: generated_key

Now:

• HTTP is done.
• The TCP connection remains open.
• Communication switches to WebSocket protocol.

3 Persistent Full-Duplex Communication

Now both sides can send messages anytime:

Client ⇄ Server

No repeated HTTP headers.

No repeated handshakes.

Jut lightweight frames.

WebSocket Frames

After upgrade, data is sent in frames.

Each frame contains:

• Opcode (text, binary, ping, pong, close)
• Payload length
• Masking key (for client messages)
• Actual data

Example text frame:

{ "message": "Hello!" }

Binary data (e.g., file chunks) also supported.

Connection Lifecycle

1. Client connects
2. Server accepts
3. Messages flow both ways
4. Either side can close connection

Close frame includes a status code (e.g., 1000 = normal closure).

Security

WebSockets can be:

• ws:// (plain)
• wss:// (secure, uses TLS)

Secure WebSockets (wss://) use the same TLS handshake as HTTPS.