can't add multicast group

问题

Trying to add multicast group for ipv6, but it returns error. don't understand the problem. with ipv4 it works fine

(test_client@127.0.0.1)1> {ok, S} = gen_udp:open(3333, [binary, {active, false}, {ip, {65342,0,0,0,0,0,34048,9029}}, inet6, {multicast_loop, false}]).
{ok,#Port<0.1587>}

(test_client@127.0.0.1)4> inet:setopts(S, [{add_membership, {{65342,0,0,0,0,0,0,0}, {0,0,0,0,0,0,0,0}}}]).
{error,einval}

unfortunately this topic in erlang docs is badly documented

also have tried with addrreses like ff3c: , ff32:

UPDATE i've looked into Erlang/OTP 18.2 source code, there is using function prim_inet:is_sockopt_val(add_membership, {{65280,0,0,0,0,0,34048,9029}, {0,0,0,0,0,0,0,0}})

and it always return false, because in prim_inet:type_value_2/2 we have type ip, value {_,_,_,_,_,_,_,_} and it waits only for ipv4 {_,_,_,_}. on the one hand i know why can't add membership with ipv6 when open socket, but on other hand what to do is opened question

回答1:

It doesn't look like Erlang's driver has implemented IPV6_ADD_MEMBERSHIP, but it does have raw support so you could construct it yourself. A problem with this approach is that you are hard coding things usually defined in header files, so your solution wont be very portable.

-module(unssmraw).
-export([test/0]).


test() ->
  Port = 57100,
  Mad = <<65340:16,0:16,0:16,0:16,0:16,0:16,34048:16,9029:16>>,
  Ifindx = <<3:64/native>>,
  Ip6 = 41,
  Ip6am = 20,

  {ok, Sock} = gen_udp:open(Port, [{reuseaddr,true}, inet6, binary]),
  R3 = inet:setopts(Sock, [{raw, Ip6, Ip6am, <<Mad/binary, Ifindx/binary>> }]),
  io:format("ssm ok? ~w ~n", [R3]),
  receive
    {udp, S, A, Pr, Pk} -> io:format("watcher sees: Socket ~p Address ~p Port ~p Packet ~p ~n", [S, A, Pr, Pk]) end.

Example test sender:

echo hi | socat - UDP6-SENDTO:\"ff3c::8500:2345\":57100

Example run:

$ erl
Erlang/OTP 19 [erts-8.0.1] [source-761e467] [64-bit] [smp:2:2] [async-threads:10] [hipe] [kernel-poll:false]

Eshell V8.0.1  (abort with ^G)
1> unssmraw:test().
ssm ok? ok 
watcher sees: Socket #Port<0.453> Address {65152,0,0,0,47734,16383,65066,
                                           19977} Port 43511 Packet <<"hi\n">>  
ok

Notes on my hardcoded values

• How to find the interface index used in Ifindx:

  As of OTP 22 net:if_name2index is available to call. A language neutral description is here. I used a 64-bit since that is the size of an int on my system and it is an int in mreq in my in6.h.)

• Ip6's value is from in.h

• Ip6am is IPV6_ADD_MEMBERSHIP from in6.h.

来源：https://stackoverflow.com/questions/38376640/cant-add-multicast-group