WebSocket

• Normal HTTP: A client makes a request → server sends a response → connection closes.

• WebSocket: After an HTTP handshake, the connection upgrades to a WebSocket and stays open. Both client and server can now send messages anytime (full-duplex communication).

• So instead of repeated requests (polling), you get a persistent, low-latency channel.

Flow

1. Client asks the server: Upgrade: websocket
2. Server agrees and switches protocols
3. From then on, client and server exchange frames (messages) freely

Request

GET /ws HTTP/1.1
Host: example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: <random>
Sec-WebSocket-Version: 13

Response

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: <derived from client key>

Protocol

• WebSocket is a protocol, standardized by RFC 6455
• It defines how a client and server establish a connection (the HTTP upgrade handshake).
• It defines how data is framed (text or binary messages broken into frames).
• It defines control frames (like ping, pong, close).

• It defines full-duplex communication over a single TCP connection.

• wss://

• ws://