Question

我是一个二郎新手。我尝试使用gen_udp构建服务器以维护在线客户端的在线/离线状态。所有客户端都将udp数据发送到udp服务器，服务器从所有客户端接收udp数据，如果服务器在5秒内没有收到数据，则服务器标记该客户端脱机。

-module(client_states_manager).
-export([start/0]).

start() ->
        spawn(fun() -> server(8080) end).

server(Port) ->
        {ok, Socket} = gen_udp:open(Port, [binary, {active, false}]),
        io:format("server opened socket:~p~n",[Socket]),
        loop(Socket).

loop(Socket) ->
        inet:setopts(Socket, [{active, once}]),
        receive
                {udp, Socket, Host, Port, Bin} ->
                        io:format("server received:~p from ~w~n",[Bin, Host]), 
%%% How to detect if Host is in a list variable (lists:member), if Host is not already in OnlineHosts variable, lists:append it to OnlineHosts                          
                        %gen_udp:send(Socket, Host, Port, Bin),
                        loop(Socket)
        end.


displayOnlineHosts(Hosts) ->
        io:format("There are online hosts ~p~n",[Hosts]).

这是用于测试的客户端ruby脚本：

require "socket"

sender = UDPSocket.new
host = ARGV[0]
port = ARGV[1] || 8080

puts "Connect to #{host}:#{port}"

n = 0
loop do
    sender.send("message #{n}", 0, host, port)
    n = n + 1
end

谁会给我一些启动的灵感？非常感谢。

Answer 1

您必须将OnlineHosts变量传递给loop函数并相应地更新其值。可能是这样的：

server(Port) ->
        {ok, Socket} = gen_udp:open(Port, [binary, {active, false}]),
        io:format("server opened socket:~p~n",[Socket]),
        loop(Socket, []).

loop(Socket, OnlineHosts) ->
        inet:setopts(Socket, [{active, once}]),
        receive
                {udp, Socket, Host, Port, Bin} ->
                        io:format("server received:~p from ~w~n",[Bin, Host]), 
%%% How to detect if Host is in a list variable (lists:member), if Host is not already in OnlineHosts variable, lists:append it to OnlineHosts
                        case lists:member(Host, OnlineHosts) of
                             true ->
                                  loop(Socket, OnlineHosts);
                             false ->
                                  %gen_udp:send(Socket, Host, Port, Bin),
                                  loop(Socket, [Host | OnlineHosts])
                        end
        end.

如何使用gen_udp构建udp服务器来显示在线客户端？

1 个答案: