[erlang-questions] clarify: SO_REUSEADDR under darwin?

Paul Mineiro <>
Fri Nov 9 23:21:17 CET 2007


Adding the { ip, Addr } option to gen_udp:open does make my application
work under both darwin and linux and allows me to remove the ugly raw
option that i introduced previously.

Thanks guys!

-- p

p.z. There still seems to be a call for an soreuseport option for multiply
binding unicast (to be ignored as appropriate).

On Fri, 9 Nov 2007, Per Hedeland wrote:

> "Valentin Micic" <> wrote:
> >
> >The way this worked with C/C++ was to first bind to an UDP port, using
> >"normal" interface (ip address) and then add memebership via setsockopt
> >system call. I think that something similar (undocumented as it might be)
> >should be applicable for ERLANG too. Combining it wiht gen_udp:open, may
> >create a wrong impression... I mean, you are actually receiving the traffic
> >via the "real" interface after all.
>
> Well, the only thing I've ever done with multicast is sending them (from
> Erlang though), and that didn't require any membership (on Linux), so
> take this with a grain of salt, but the unicast address(es) configured
> on the physical interface(s) shouldn't be relevant. You could/would use
> it/them with add_membership to select interface(s) in case there are
> several possible (but at least FreeBSD and Linux allows for using the
> "interface index" instead), but binding the socket to one of those
> addresses seems pointless if not "wrong", even if it works.
>
> "Serge Aleynikov" <> wrote:
> >
> >> Per Hedeland wrote:
> >>> 4> gen_udp:open(Port, [{reuseaddr, true}, {ip, {224,0,1,1}}]).
> >>> {ok,#Port<0.98>}
> >>
> >> Is this the "right" way of joining a multicast group though?
>
> No - but I didn't say that it was.:-)
>
> >>  I've been
> >> using the "undocumented" add_membership inet option to accomplish that
>
> This seems to be right - and at least per FreeBSD ip(4), you can do
> add_membership multiple times, to join the group on multiple interfaces.
> Which could perhaps be another reason to do it via inet:setopts/2
> afterwards instead, but I guess it will work to have multiple
> add_membership in the Options list for gen_udp:open/2 too. With C you
> will have to do one thing at a time.:-)
>
> >> (though haven't tried it on anything other than Win, Linux, Solaris):
> >>
> >> gen_udp:open(Port, [{reuseaddr, true}, {add_membership, {Addr,
> >> Interface}}]).
>
> (Where Interface is actually an IP address.) So this will bind to the
> wildcard address like the OP's original attempt, and won't work for
> multiple sockets on FreeBSD (probably *BSD) or Darwin.  But combining
> them should be fine:
>
> gen_udp:open(Port, [{reuseaddr, true}, {ip, Addr},
>                     {add_membership, {Addr, Interface}}]).
>
> >> I haven't checked the inet_drv, but does it actually check if in the
> >> {ip, Addr} option Addr refers to a multicast range and sets the
> >> IP_ADD_MEMBERSHIP option?
>
> No.
>
> --Per
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