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.. _detecting_disconnection:
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 :ref:`broadcast_tutorial` uses this to remove clients on
disconnect,
.. code-block:: python
@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,
.. code-block:: python
@app.route('/sse')
async def sse():
try:
await ...
except asyncio.CancelledError:
# Has disconnected
The same applies for WebSockets, streaming the request, etc...
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