Re: [Boost-users] [asio] Socket closed notification?

Andrew Maclean writes:

On Tue, Dec 15, 2009 at 2:50 PM, Scott Gifford wrote:

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Jonathan Franklin writes:

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On Mon, Dec 14, 2009 at 10:52 AM, Nicola Michael Gutberlet wrote:

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I’m using TCP sockets and wonder, if there’s a possibility to get an automatic notification when one side of a socket is closed (even if the other side is crashed / not closed properly).

You generally have to do a read on the socket to reliably detect when the other side has closed (or crashed).

And a write, too, or else use TCP keepalives.  Otherwise a crashed client which is never sending anything will not send any error indication for you to read.

Do you have any ideas on how to do this within the ASIO framework?

Sure, just use any of the read functions and see if they return an error. In my application, I use read_until(), but any function that reads should do. Jonathan Franklin writes: [...]

Unfortunately, write isn't reliable since it will always succeed until you fill up your send buffer.

Well, OK, maybe a write and a flush. Certainly there are othe buffers, but typically a TCP implementation will time out at some point if it has some pending data which is not acknowledged, and typically once data is flushed to the TCP layer it will try to write it and begin waiting for its timeout. ----Scott.