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

From: Cliff Green (cliffg_at_[hidden])
Date: 2007-06-28 20:08:48

  Andrej van der Zee <mavdzee_at_[hidden]> 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?

Cliff