CODEWITHSUNDEEP
python-asyncioaiohttp
Te-jé Rodgers
Te-jé Rodgers

Reputation: 888

Detect when client closes a connection from aiohttp request handler

I have a long running request during which I push data down to a client as it is received. However, the request requires some resources that are created server side that I'd like to clean up whenever the client disconnects. I've looked through the docs, but I can't seem to find a way to detect when that happens. Any ideas?

Upvotes: 4

Views: 3004

Answers (1)

Te-jé Rodgers
Te-jé Rodgers

Reputation: 888

This isn't super obvious looking at the docs, but the key here is that the asyncio server will throw a CancelledError into handler coroutine when the connection is closed. You can catch the CancelledError wherever you wait for an asynchronous operation to complete.

Using this, I clean up after a connection with something like this:

async def passthrough_data_until_disconnect():
    await create_resources()
    while True:
        try:
            await get_next_data_item()
        except (concurrent.futures.CancelledError, 
                aiohttp.ClientDisconnectedError):
            # The request has been cancelled, due to a disconnect
            await do_cleanup()
            # Re-raise the cancellation error so the handler 
            # task gets cancelled for real
            raise
        else:
            await write_data_to_client_response()

Upvotes: 3

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