erlang UDP 测试

来源：互联网发布：屏幕录像软件绿色编辑：程序博客网时间：2024/06/06 11:44

无意中看到了stackoverflow.com 中提出的有关erlang UDP收发数据的问题，自己也一知半解，故直接敲代码重现问题以便修正。

stackoverflow.com 中有问题代码:

-module(udp_test).-export([start_client/3, listen/1, send/4, start_listen/1]).start_client(Host, Port, Packet) ->    {ok, Socket} = gen_udp:open(0, [{active, true}, binary]),    io:format("client opened socket=~p~n",[Socket]),    spawn(?MODULE, send, [Socket, Host, Port, Packet]).start_listen(Port) ->    {ok, Socket} = gen_udp:open(Port, [binary]),    spawn(?MODULE, listen, [Socket]).listen(Socket) ->    inet:setopts(Socket, [{active, once}]),    receive    {udp, Socket , Host, Port, Bin} ->        gen_udp:send(Socket, Host, Port, "Got Message"),        io:format("server received:~p / ~p~n",[Socket, Bin]),        listen(Socket)    end.send(Socket, Host, Port, Packet) ->    timer:send_after(1000, tryToSend),    receive    tryToSend ->        io:fwrite("Sending: ~p / to ~p / P: ~p~n", [Packet, Host, Port]),        Val = gen_udp:send(Socket, Host, Port, Packet),        io:fwrite("Value: ~p~n", [Val]),        send(Socket, Host, Port, Packet);    _ ->        io:fwrite("???~n")    end.

出现的问题是：应用程序中，以下两句代码并未执行。

gen_udp:send(Socket, Host, Port, "Got Message"),        io:format("server received:~p / ~p~n",[Socket, Bin]),

帖子给出的回答是:

For each loop it opens a new socket, the first time it uses the port to open the socket while in the following loops it uses the socket to open a new socket, which should generate an error.
You set the socket to {active,once} so you will at most receive one packet on the socket before you reset it to being active once.
经过修正，给出正确的代码如下:

-module(udp_test2).-export([server/0,start_server/0,listen/1,client/1,start_client/1, send/4]).server() ->spawn(?MODULE,start_server,[]).start_server() ->    {ok, Socket} = gen_udp:open(4000, [binary]),    listen(Socket).listen(Socket) ->    inet:setopts(Socket, [{active, once}]),    receive    {udp, Socket , Host, Port, Bin} ->        gen_udp:send(Socket, Host, Port, Bin),        io:format("server received message:~p / ~p~n",[Socket, Bin]),        listen(Socket)    end.client(Msg) ->spawn(?MODULE,start_client,[Msg]).start_client(Msg) ->    {ok, Socket} = gen_udp:open(0, [{active, true}, binary]),    io:format("client opened socket=~p~n",[Socket]),    send(Socket, "127.0.0.1", 4000, Msg).send(Socket, Host, Port, Msg) ->    timer:send_after(1000, tryToSend),    receive    tryToSend ->        io:fwrite("~nSending: ~p / to ~p / P: ~p~n", [Msg, Host, Port]),        gen_udp:send(Socket, Host, Port, Msg),        send(Socket, Host, Port, Msg);    {udp,Socket,_,_,Bin} ->        io:fwrite("client received message: ~p / ~p~n",[Socket,Bin])    end.

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