Today we spent some time figuring out how to bind a UDP Socket to a specific
interface, as opposed to any or 0.0.0.0. This special case is needed when a
server holds multiple IP addresses. If you do not bind to a specific one, you
will of course still receive incoming datagrams on any interface, but when you
answer you could use a different server source address than the one the client
sent to in the first place. That might lead to trouble, as it did for us.
We had to read through the (Linux) socket plugin code [1] to figure this out
(and it might not work on other platforms). It turns out that
Socket>>#primSocket: aHandle listenOn: portNumber backlogSize: backlog
interface: ifAddr does not just work for TCP but also for UDP (we left backlog
size to 1, it is not used).
In code (on a private helper class):
UDPListener>>#port: port bindingAddress: address
self socket: Socket newUDP.
self socket
primSocket: self socket socketHandle
listenOn: port
backlogSize: 1
interface: address
And yes, this is ugly.
Sven
[1]
https://github.com/pharo-project/pharo-vm/blob/master/platforms/unix/plugins/SocketPlugin/sqUnixSocket.c
