How to multicast using gen_udp in Erlang?

Question

How do you use gen_udp in Erlang to do multicasting? I know its in the code, there is just no documentation behind it. Sending out data is obvious and simple. I

Answer 1

Multicast sending has been answered, receipt requires subscription to the multicast group.

It (still) seems undocumented, but has been covered on the erlang-questions mailing list before. http://www.erlang.org/pipermail/erlang-questions/2003-March/008071.html

    {ok, Socket} = gen_udp:open(Port, [binary, {active, false},
                                       {reuseaddr, true},{ip, Addr}, 
                                       {add_membership, {Addr, LAddr}}]).

where the Addr is the multicast group, and LAddr is a local interface. (code courtesy of mog)

The same options used above can be passed to inet:setopts including {drop_membership, {Addr, LAddr}} to stop listening to the group.