一个简单的 erlang 的 udp 服务器和客户端

1. 服务器端代码如下：

-module(server).
-behaviour(gen_server).
-export([init/1, handle_call/3, handle_cast/2, handle_info/2, 
         terminate/2, code_change/3]).
-export([start/0]).

-record(state, {socket,
                port,
                local_ip,
                broad_ip}).


%% External interface:
start() ->
    io:format("start~n"),
    {ok, Server} = gen_server:start_link({local,?MODULE}, ?MODULE, [], []),
    io:format("Server: ~w~n", [Server]).


%%Internal server methods:              
init([]) ->
    Port = 15000,
    {ok, Socket} = gen_udp:open(Port, [binary,
                                       {active, true},
                                       {reuseaddr, true}]),
    {ok, #state{socket = Socket, port = Port}}.

handle_cast(process_msg, State) ->
    {noreply, State}.

handle_call(_Request, _From, State) ->
    {noreply, State}.

handle_info({udp, Socket, IP, InPortNo, Packet}, #state{socket=Socket}) ->
    io:format("whooopie, ip ~p, port ~p, got a packet ~p~n", [IP, InPortNo, Packet]),
    {noreply, #state{socket=Socket}}.

terminate(_Reason, #state{socket = LSocket}) ->
    gen_udp:close(LSocket).

code_change(_OldVsn, State, _Extra) ->
    {ok, State}.

active 一定设置为 true

运行服务器

[email protected]:~/test$ erl
Erlang/OTP 22 [erts-10.6.4] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]

Eshell V10.6.4  (abort with ^G)
1> c(server).
{ok,server}
2> 
2> 
2> 
2> server:start().
start
Server: <0.85.0>
ok
whooopie, ip {127,0,0,1}, port 40263, got a packet <<"hello">>
whooopie, ip {127,0,0,1}, port 38798, got a packet <<"hello">>
3> 

2. 客户端代码 

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

start() ->
    Port = 15000,
    {ok, Socket} = gen_udp:open(0, [binary, {active, false}]),
    gen_udp:send(Socket, "localhost", Port, "hello").

运行客户端

[email protected]:~/test$ erl
Erlang/OTP 22 [erts-10.6.4] [source] [64-bit] [smp:4:4] [ds:4:4:10] [async-threads:1]

Eshell V10.6.4  (abort with ^G)
1> c(client).
{ok,client}
2> 
2> client:start().
ok
3> client:start().
ok