1. WebSockets

If you’ve already know WebSockets, feel free to skip this part

1.1 Intro

1) what is WebSockets

• Which layer: in Application Layer, just like HTTP
• TCP-based: WebSockets work on a TCP connection → can play with TCP connection properties to reduce latency
• Define: provide a full duplex communication channel over a single TCP connection

• Full duplex:
  • Simultaneous communication: can send messages between each others at the same time
  • Single persistent connection: no need to establish a new connection for every messages once connection established
  • Low latency
  • Real-time interaction

2) use case

Ideal for applications requiring real-time data update:

• Live chatting
• Video game
• Collaborative editing

3) URI schema

ws: or wss: for a secure WebSocket

1.2 How it works

1) establish WebSocket connection

1. HTTP handshake

2. Client sends Upgrade: Websocket:

   include the following in the HTTP header:

   1
   GET /chat HTTP/1.1
   2
   Host: example.com:8000
   3
   Upgrade: websocket // Request to upgrade HTTP conn to WebSocket conn
   4
   Connection: Upgrade // Request to upgrade conn (must accompany the `Upgrade` header)
   5
   Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==  // A nonce that protects against unauthorized upgrade
   6
   Sec-WebSocket-Version: 13 // 13 is the only accepted version

3. Server responds 101 Switching Protocols:

   1
   HTTP/1.1 101 Switching Protocols  // Comfirm the upgrade
   2
   Upgrade: websocket  // Comfirm switch to WebSocket
   3
   Connection: Upgrade
   4
   Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=
   5
   // Sec-WebSocket-Accept: A hashed and base64-encoded string derived
   6
   // from the client's Sec-WebSocket-Key to verify the handshake

4. Communicate messages in WebSocket format