[erlang-questions] Erlang udp server can't receive accept packets

[Attila Rajmund Nohl]

Hello!

As the gen_udp documentation states: "If the socket is not in an
active mode, data can be retrieved through the recv/2,3 calls.".
Unless I'm mistaken, you pass the "{active, false}" option to the
server - maybe you should try "{active, true}" or {active, once}".


2017-05-15 11:27 GMT+02:00 yuzhu chen <billcyz@REDACTED>:
>
> I've posted the same question on stackoverflow, but haven't got answers yet. So I posted this question again in here hoping for a solution.
>
>
>
> down votefavorite
>
> I have one simple udp server written in gen_server behaviour. When I run it, and try to send message by using gen_udp:send, the server replies nothing, seems like the udp server didn't accept packet successfully. Here is my code
>
> gen_udp_server.erl:
>
> -module(gen_udp_server).
> -behaviour(gen_server).
> -export([init/1, handle_call/3, handle_cast/2, handle_info/2, terminate/2, code_change/3]).
>
> -export([start_link/1]).
>
> -define(SERVER, ?MODULE).
>
> -record(state, {socket,
>                 port,
>                 local_ip,
>                 broad_ip}).
>
> start_link(Port) ->
>     {ok, Socket} = gen_udp:open(Port, [binary,
>
> {active, false},
>                                        {reuseaddr, true}]),
>     gen_server:start_link(?MODULE, [Socket, Port], []).
>
> init([Socket, Port]) ->
>     {ok, #state{socket = Socket, port = Port}}.
>
> handle_cast(_Request, State) ->
>     {noreply, State}.
>
> handle_call(_Request, _From, State) ->
>     {noreply, State}.
>
> handle_info({udp, _Socket, _Addr, _Port, Data}, #state{socket = Socket} = State) ->
>     inet:setopts(Socket, [{active, once}]),
>     io:format("Server received data ~p from socket ~p~n", [Data, Socket]),
>     {ok, State}.
>
> terminate(_Reason, {socket = LSocket}) ->
>     gen_udp:close(LSocket).
>
> code_change(_OldVsn, State, _Extra) ->
>     {ok, State}.
>
> Starting server on server 192.168.146.129: gen_udp_server:start_link(10000).
>
> Sending message from 192.168.146.128:
>
> {ok, Socket} = gen_udp:open(4399, [binary, {active, false}]).
> gen_udp:send(Socket, {192,168,146,129}, 10000, "hello").
>
> The udp server should print some message when it receives packets, but my one failed. Can anyone help me?
>
>
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