I am rewriting an older server using Streams, and one of the problems I never manage to solve was the disconnection issue.
I have made this really simple server example:

import asyncio

async def handle_client(reader, writer):
    address = writer.get_extra_info('peername')
    print(f"Connection: {address}")

    try:
        while True:
            data = await reader.read(1024)
            if not data:
                print(f"Disconnected: {address}.")
                break
            print(f"{address} Send: {data.decode()}")

            writer.write('????n'.encode())
            await writer.drain()
    except Exception as e:
        print(f"Something bad happened: {e}")
    finally:
        print(f"Closed: {address}")
        writer.close()
        await writer.wait_closed()


async def main():
    server = await asyncio.start_server(handle_client, '0.0.0.0', 5678)

    async with server:
        await server.serve_forever()

asyncio.run(main())

If I connect using netcat, everything works, if I close the netcat or the terminal, it knows the connection has ended. But if I disconnect my client network, it will never know that my client is offline. I know this is a lower level limitation, but I am thinking in ways to solve this.

Currently, my best approach was using a timeout for force a disconnection, like this example:

import asyncio

async def handle_client(reader, writer):
    address = writer.get_extra_info('peername')
    print(f"Connection: {address}")

    try:
        while True:
            data = await asyncio.wait_for(reader.read(1024), timeout=10.0)
            if not data:
                print(f"Disconnected: {address}.")
                break
            print(f"{address} Send: {data.decode()}")

            writer.write('????n'.encode())
            await writer.drain()
    except asyncio.TimeoutError:
        print(f"Timeout: {address}")
    except Exception as e:
        print(f"Something bad happened: {e}")
    finally:
        print(f"Closed: {address}")
        writer.close()
        await writer.wait_closed()

async def main():
    server = await asyncio.start_server(handle_client, '0.0.0.0', 5678)

    async with server:
        await server.serve_forever()

asyncio.run(main())

This works, but I would need to fine-tune my application to fit all devices (and unfortunately, most of those devices that send me data were build in a time that you paid per byte send, so their keep alive interval is ridiculous long).

Is there a better way to know when there was a disconnection without needing to wait several minutes for a timeout?

Thank you for your attention.