How does Uvicorn handle WebSocket connections?

Uvicorn has native WebSocket support, making it suitable for real-time applications like chat, live dashboards, and collaborative tools. WebSocket connections are handled via the websockets or wsproto library.

# Pure ASGI WebSocket application
async def app(scope, receive, send):
    if scope["type"] == "websocket":
        # Accept the WebSocket connection
        await send({"type": "websocket.accept"})
        while True:
            event = await receive()
            if event["type"] == "websocket.receive":
                data = event.get("text") or event.get("bytes")
                # Echo the message back
                await send({"type": "websocket.send", "text": data})
            elif event["type"] == "websocket.disconnect":
                break

# FastAPI WebSocket example
from fastapi import FastAPI, WebSocket

app = FastAPI()

@app.websocket("/ws")
async def websocket_endpoint(websocket: WebSocket):
    await websocket.accept()
    while True:
        data = await websocket.receive_text()
        await websocket.send_text(f"Echo: {data}")

Note: the WSGI interface (--interface wsgi) always disables WebSocket support because WSGI does not define a WebSocket protocol. Use the ASGI interface for WebSocket-capable applications.

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