실시간 채팅 Pub/Sub

// npm install socket.io @socket.io/redis-adapter
import { createAdapter } from '@socket.io/redis-adapter'

const pub = redis
const sub = redis.duplicate()
await sub.subscribe('socket.io#/#')

io.adapter(createAdapter(pub, sub))

// 채팅 룸 처리
io.on('connection', (socket) => {
  socket.on('join', (room) => socket.join(room))

  socket.on('message', async ({ room, msg }) => {
    // 메시지 저장 (최근 50개)
    await redis.lpush(`chat:${room}`, JSON.stringify(msg))
    await redis.ltrim(`chat:${room}`, 0, 49)
    io.to(room).emit('message', msg)
  })
})