Re: gnugk must be restarted to recognize interface is turned off/on

Hi Jan:

On Sun, Mar 27, 2016 at 4:38 PM, Jan Willamowius <[email protected]> wrote:
> the technical reason why GnuGk doesn't automatically recognize new
> interfaces is that it listens to each IP bound to your interfaces
> individually instead of listening to inaddr_any (0.0.0.0). GnuGk needs
> to do so to get full control over the IP address used for sending
> messages.

IIRC there is a trick ( I think I first saw it on ntpd, so UDP,
although I think it works in TCP too ) to react to IP changes and hava
control of the source address. You start with a socket bound to the
wildcard address ( i.e., 0.0.0.0:1719 ), and, when a packet is
received you look at the destination address ( which is your local
address ) and bind another socket to this if needed ( let's say to
192.168.1.1:1719 ) and use it for replies, and from there to receive
packets. setsockopt(IP_PKTINFO) and recvmsg where needed in the socket
used at the wildcard address, normally with a little layer to hide the
fact that the first acket for a transport address did not come from
the same socket which later was associated with it,  and some flags
where needed to have the binding survive interfaces coming up/down,
but the nice thing was that it totally abstracted the details of
interfaces and let you work with just transport addresses. I think
this works in linux, not sure about the other os though.

Francisco Olarte.

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