Re: Network socket disconnect unreliable

[Alan Cox]

> When a network socket disconnects, this fact can't presently be
> reliably detected when using select. The exception bit is set, but this

It can be

> So, how am I supposed to know if the socket was disconnected? 
> There are of course hacks. I can just count the number of times
> that this thing looped without finding anything to do and then
> exit if it's obvious that it's hung.

If a socket is closed by the other end then it goes EOF for read once all
the data has been read. This is a portable property of sockets, its true
of BSD and its defined by posix 1003.1g drafts. So you do

	if(FD_ISSET(fd, &read_mask))
	{
		int len=read(fd, buffer, bufsize);
		if(len==0)
		{
			/* EOF - closed */
		}
		if(len<0)
		{
			if(errno==EAGAIN)
			{
				/* woken by something else */
				/* Not needed in theory but is for porting */
			}
			else
			{
				/* it broke */
			}
		}
	}

Alan