Detecting disconnection¶
If in your route or websocket handler (or code called from within it)
you are awaiting and the client disconnects the await will raise a
CancelledError. This can be used to detect when a client
disconnects, to allow for cleanup, for example the sse handler from
the Tutorial: Broadcast Server Side Events uses this to remove clients on
disconnect,
@app.route('/sse')
async def sse():
queue = asyncio.Queue()
app.clients.add(queue)
async def send_events():
while True:
try:
data = await queue.get()
event = ServerSentEvent(data)
yield event.encode()
except asyncio.CancelledError:
app.clients.remove(queue)
or with only the relevant parts,
@app.route('/sse')
async def sse():
try:
await ...
except asyncio.CancelledError:
# Has disconnected
The same applies for WebSockets, streaming the request, etc…