Piye cara nangani WebSocket ing FastAPI?

Question

Accepted Answer

FastAPI ndhukung **WebSocket** kanggo komunikasi bidirectional real-time (chat, live updates, notifikasi) nganggo decorator `@app.websocket`. Beda karo model request-response HTTP, koneksine WebSocket tetep mbukak, supaya server lan client bisa ngirim pesan kanthi bebas.

## Endpoint WebSocket dasar

```python
from fastapi import WebSocket, WebSocketDisconnect

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()                  # accept the connection
    try:
        while True:
            data = await websocket.receive_text()    # receive a message from the client
            await websocket.send_text(f"Echo: {data}")  # send a message back
    except WebSocketDisconnect:
        print("client disconnected")           # handle disconnection (cleanup)
```

Polane: `accept()` koneksine, banjur loop — `receive_text()`/`receive_json()` maca pesan, `send_text()`/`send_json()` ngirim. Eksepsi `WebSocketDisconnect` nuduhake kliene ilang (ngendi sampeyan bebersih).

## Broadcasting menyang klien akeh (contone chat)

```python
class ConnectionManager:
    def __init__(self): self.active: list[WebSocket] = []
    async def connect(self, ws): await ws.accept(); self.active.append(ws)
    def disconnect(self, ws): self.active.remove(ws)
    async def broadcast(self, msg):
        for conn in self.active:
            await conn.send_text(msg)          # send to ALL connected clients

manager = ConnectionManager()

@app.websocket("/chat")
async def chat(ws: WebSocket):
    await manager.connect(ws)
    try:
        while True:
            msg = await ws.receive_text()
            await manager.broadcast(msg)        # everyone gets the message
    except WebSocketDisconnect:
        manager.disconnect(ws)                  # remove on disconnect
```

Manage daftar koneksine aktif ngidini sampeyan **broadcast** menyang kabeh klien — basis fitur chat lan live-update.

## Caveat scaling

```text
⚠️ WebSocket connections are STATEFUL and live on ONE server instance.
To scale across multiple instances, use a Redis Pub/Sub (or similar) backplane so
messages/broadcasts reach clients connected to OTHER instances.
(Like sessions, don't keep connection state only in one process when scaling horizontally.)
```

## Kepapa dadi penting

WebSocket gawe fitur **bidirectional, real-time** — chat, live notifications, presence, collaborative editing, live dashboards — sing HTTP model request-response ora bisa gawe (server bisa push menyang klien, ora mung mbalas).

Ngerti suportan WebSocket FastAPI regane kanggo ngun aplikasi interaktif modern: decorator `@app.websocket` karo loop accept/receive/send nutupi komunikasi real-time dasar, lan manaj koneksine aktif gawe **broadcasting** (inti fitur multi-user kaya chat).

Fundasi async FastAPI pas kanggo WebSocket.

Critical penting yaiku **caveat scaling**: koneksine WebSocket stateful lan kabedhel single server instance, dadi scaling lintas instansi akeh butuh **Redis Pub/Sub backplane** kanggo relay pesan antarane instansi — pitfall umum, amarga (kaya sessions) status koneksine ora bisa manggon siji proses memori nalika jalanake instansi akeh.

Ngerti pola WebSocket dasar, broadcasting, disconnect handling, lan scaling consideration dadi penting senior-level knowledge kanggo ngun pengalaman real-time, interactive sing saya-saya dikarepake ing aplikasi modern.