101 Switching Protocols

GET /chat HTTP/1.1
Host: server.example.com
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==
Sec-WebSocket-Version: 13

HTTP/1.1 101 Switching Protocols
Upgrade: websocket
Connection: Upgrade
Sec-WebSocket-Accept: s3pPLMBiTxaQ9kYGzzhZRbK+xOo=

const WebSocket = require('ws');
const http = require('http');

const server = http.createServer();
const wss = new WebSocket.Server({ noServer: true });

server.on('upgrade', (request, socket, head) => {
  // Handle the upgrade request manually
  wss.handleUpgrade(request, socket, head, (ws) => {
    // The server has sent the 101 Switching Protocols response
    wss.emit('connection', ws, request);
  });
});

from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    # FastAPI automatically handles the 101 Switching Protocols handshake
    await websocket.accept()
    await websocket.send_text("Hello WebSocket!")
    await websocket.close()

package main

import (
	"net/http"
	"github.com/gorilla/websocket"
)

var upgrader = websocket.Upgrader{}

func echo(w http.ResponseWriter, r *http.Request) {
	// Upgrade automatically sends the 101 status code
	c, err := upgrader.Upgrade(w, r, nil)
	if err != nil {
		return
	}
	defer c.Close()
	for {
		mt, message, _ := c.ReadMessage()
		c.WriteMessage(mt, message)
	}
}

# Testing a WebSocket upgrade requires specific headers.
# (Note: curl natively supports WebSockets in newer versions with --include)
curl -i -N \
  -H "Connection: Upgrade" \
  -H "Upgrade: websocket" \
  -H "Sec-WebSocket-Version: 13" \
  -H "Sec-WebSocket-Key: dGhlIHNhbXBsZSBub25jZQ==" \
  http://example.com/chat