How to multicast using gen_udp in Erlang?
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.
I try to get this example running on my PC. What could happen, if I get always the message {error,eaddrnotavail} by opening the receive socket?
Example 1: This works:
{ok, Socket} = gen_udp:open(?PORT, [{reuseaddr,true}, {ip,?SERVER_IP},
{multicast_ttl,4}, {multicast_loop,false}, binary]),
Example 2: Getting an runtime Error:
{ok, Socket} = gen_udp:open(?PORT, [{reuseaddr,true}, {ip,?MULTICAST_IP},
{multicast_ttl,4}, {multicast_loop,false}, binary]),
% --> {error,eaddrnotavail}
-define(SERVER_IP, {10,31,123,123}). % The IP of the current computer
-define(PORT, 5353).
-define(MULTICAST_IP, {224,0,0,251}).
Here is example code on how to listen in on Bonjour / Zeroconf traffic.
-module(zcclient).
-export([open/2,start/0]).
-export([stop/1,receiver/0]).
open(Addr,Port) ->
{ok,S} = gen_udp:open(Port,[{reuseaddr,true}, {ip,Addr}, {multicast_ttl,4}, {multicast_loop,false}, binary]),
inet:setopts(S,[{add_membership,{Addr,{0,0,0,0}}}]),
S.
close(S) -> gen_udp:close(S).
start() ->
S=open({224,0,0,251},5353),
Pid=spawn(?MODULE,receiver,[]),
gen_udp:controlling_process(S,Pid),
{S,Pid}.
stop({S,Pid}) ->
close(S),
Pid ! stop.
receiver() ->
receive
{udp, _Socket, IP, InPortNo, Packet} ->
io:format("~n~nFrom: ~p~nPort: ~p~nData: ~p~n",[IP,InPortNo,inet_dns:decode(Packet)]),
receiver();
stop -> true;
AnythingElse -> io:format("RECEIVED: ~p~n",[AnythingElse]),
receiver()
end.