[erlang-questions] Trouble with gen_udp:fdopen

[Raimo Niskanen]

You have found a bug.

I changed the internals from using socket type to using protocol type
sometime during R11, and thought I had found all calls, but
apparently missed the ones in inet_udp.erl (and inet6_udp.erl).
They should use the atom 'udp' instead of 'dgram'.

It will be fixed in R12. A source patch is trivial.



On Sun, Sep 02, 2007 at 12:08:23PM -0600, David Baird wrote:
> Hi,
> 
> I am using otp_src_R11B-5 and I have the following code:
> 
>     #!/usr/bin/env escript
>     main(Args) ->
>         io:fwrite("Args = ~p ~n", [Args]),
>         case Args of
>           [_, "-foofd", FDStr] ->
>             FD = erlang:list_to_integer(FDStr),
>             io:fwrite("FD = ~p ~n", [FD]),
>             Res = gen_udp:fdopen(FD, []),
>             io:fwrite("Res = ~p~n", [Res])
>         end.
> 
> When I execute the script using the suid "setuid_socket_wrap.c"
> program (provided with the Erlang sources):
> 
>     /tmp/setuid_socket_wrap -d -foofd,:123 -- ./client.erl
> 
> I get this result:
> 
>     Args = ["./client.erl","-foofd","3"]
>     FD = 3
>     Res = {error,eprotonosupport}
> 
> Does anyone know what is going on?  I think the error is being raised
> in "otp_src_R11B-5/lib/kernel/src/prim_inet.erl" (but I'm not 100%
> sure):
> 
>     protocol2drv(tcp)  -> tcp_inet;
>     protocol2drv(udp)  -> udp_inet;
>     protocol2drv(sctp) -> sctp_inet;
>     protocol2drv(_) ->
>         erlang:error(eprotonosupport).
> 
> I have a suspicion that it might be an incorrect atom ("dgram" instead
> of "udp") in "otp_src_R11B-5/lib/kernel/src/inet_udp.erl:"
> 
>     open(Port, Opts) when Port >= 0, Port =< 16#ffff ->
>         case inet:udp_options(
>                [{port,Port}, {recbuf, ?RECBUF} | Opts],
>                inet) of
>             {error, Reason} -> exit(Reason);
>             {ok, R} ->
>                 Fd       = R#udp_opts.fd,
>                 BAddr    = R#udp_opts.ifaddr,
>                 BPort    = R#udp_opts.port,
>                 SockOpts = R#udp_opts.opts,
>                 inet:open(Fd,BAddr,BPort,SockOpts,udp,inet,?MODULE) %
> <- good atom
>         end.
> 
>     % <snip>
> 
>     fdopen(Fd, Opts) ->
>     inet:fdopen(Fd,
>                 optuniquify([{recbuf, ?RECBUF} | Opts]),
>                 dgram, inet, ?MODULE). % <- bad atom here
> 
> In "open," the "udp" atom is used as the Protocol (which matches
> "protocol2drv(udp)" in "prim_inet.erl").  However, "fdopen" is using a
> different atom: "dgram".  I looked at "inet_tcp.erl" and it is
> consistent, unlike "inet_udp.erl":
> 
>     do_connect({A,B,C,D}, Port, Opts, Time) when ?ip(A,B,C,D),
> is_integer(Port) ->
>         case inet:connect_options(Opts, inet) of
>       {error, Reason} -> exit(Reason);
>       {ok, R} ->
>           Fd       = R#connect_opts.fd,
>           BAddr    = R#connect_opts.ifaddr,
>           BPort    = R#connect_opts.port,
>           SockOpts = R#connect_opts.opts,
>           case inet:open(Fd,BAddr,BPort,SockOpts,tcp,inet,?MODULE) of
>           % ...
> 
>     % <snip>
> 
>     fdopen(Fd, Opts) ->
>         inet:fdopen(Fd, Opts, tcp, inet, ?MODULE).
> 
> Any suggestions?  Is this a bug or am I doing something wrong?
> 
> Thanks,
> David
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-- 

/ Raimo Niskanen, Erlang/OTP, Ericsson AB