Re: [Boost-users] ASIO: Detecting broken connections

On 6/29/07, Cliff Green wrote:

Andrej van der Zee wrote:

...

I was wondering how I can find out with ASIO whether a connection is broken. I have a client connected to the server that continuously streams data.

The canonical way to consistently detect broken TCP connections is to always have a read on the socket - it will return 0 on broken connection (in usual BSD sockets type reads - I would expect an appropriate error parameter set in ASIO). Since you're doing async operations this is pretty easy.

Many times a write will only buffer the data (at the OS / TCP driver level), and an error is not detected until a later write (and if the client socket is in a "half shutdown" mode, it might be quite a while before the TCP keepalive timer pops and the socket is fully destroyed).

This is absent special ASIO capabilities - if ASIO is doing a read "on your behalf", then the problem is the "not completely destroyed connection", which is an OS / TCP "feature" and nothing that ASIO can help with. I haven't found specific details relating to this in ASIO, but that may only be because I haven't read enough of the ASIO documentation.

Chris K (or others), clarifications, corrections, or comments?

You test for a disconnection with Asio the same way you would with BSD sockets - you need to leave a long-running read operating going. Check out this post from the Asio-users mailing list: http://osdir.com/ml/lib.boost.asio.user/2006-11/msg00035.html Richard Cliff

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