利用自定義的erlang通訊協議編寫的入門socket程式，可實現簡單的多人線上聊天程式。

1. 服務端的程式碼：

-module(server_example).
-export([start/0,initialize_ets/0,info_lookup/1,loop/2,info_update/3,init/1,handle_call/3,terminate/2]).
-import(counter,[start/1,add/1,value/1,decrease/1,log_add/1,chat_add/1]).
-import(my_fsm,[start_count/0,count/1]).
-include("user_info.hrl"
 
).
-define(SERVER,?MODULE).

start() ->
    gen_server:start_link({local,?SERVER},?MODULE,[],[]).

init([]) ->
    initialize_ets(),
    start_parallel_server(), 
    {ok,true}.



user_online_count({add,Pid}) ->
    gen_server:call(?MODULE,{add,Pid}).

user_online_decrease({decrease,Pid}) ->
 

    gen_server:call(?MODULE,{decrease,Pid}).

personal_login_count({ladd,Name,Count}) ->
    gen_server:call(?MODULE,{ladd,Name,Count}).

personal_chat_count({cadd,Name,Count}) ->
    gen_server:call(?MODULE,{cadd,Name,Count}). 


%統計線上使用者的回撥函式
handle_call({add,Pid},_From,State) ->
    counter
 
:add({add,Pid}),
    Reply = counter:value(Pid),
    {reply,Reply,State};
handle_call({decrease,Pid},_From,State) ->
    counter:decrease(Pid),
    Reply = counter:value(Pid),
    {reply,Reply,State};
%統計個人登入次數
handle_call({ladd,Name,Count},_From,State) ->
    Pi = spawn(fun() -> counter:start({ladd,Count}) end),
    counter:add({ladd,Pi}),
    Reply = counter:log_add({value,Pi}),
    info_update(Name,4,Reply),
    {reply,Reply,State};
%個人來聊天次數
handle_call({cadd,Name,Count},_From,State) ->
     C = spawn(fun() -> counter:start({cadd,Count}) end),
     counter:add({cadd,C}),
     Reply = counter:chat_add({value,C}),
     info_update(Name,5,Reply),
     {reply,Reply,State}.

terminate(_Reason,_State) -> ok.



%開啟伺服器
start_parallel_server() ->
    {ok,Listen} = gen_tcp:listen(2345,[binary,{packet,4},{reuseaddr,true},{active,true}]),
    Pid = spawn(fun() -> counter:start({init,0}) end),%開啟統計程序,此時為0
    my_fsm:start_count(),%統計某時段的登入數
    spawn(fun() -> per_connect(Pid,Listen) end).

%每次繫結一個當前Socket後再分裂一個新的服務端程序，再接收新的請求
per_connect(Pid,Listen) ->
    {ok,Socket} = gen_tcp:accept(Listen),
    spawn(fun() -> per_connect(Pid,Listen) end),
    loop(Pid,Socket).

%初始化ets
initialize_ets() ->
    ets:new(test,[set,public,named_table,{keypos,#user.name}]),
    ets:insert(test,#user{id=01,name=laner,passwd="123456",login_times=0,chat_times=0,last_login={}}),
    ets:insert(test,#user{id=02,name=river,passwd="23456",login_times=0,chat_times=0,last_login={}}),
    ets:insert(test,#user{id=03,name=huang,passwd="3456",login_times=0,chat_times=0,last_login={}}).

%查詢ets
info_lookup(Key) ->
    %返回值是一個元組
    ets:lookup(test,Key).

%修改ets資訊
info_update(Key,Pos,Update) ->
    ets:update_element(test,Key,{Pos,Update}).





%接收資訊並處理
loop(Pid,Socket) ->
    io:format("receiving...~n"), 
    receive
        {tcp,Socket,Bin} ->
            <<State:4,Str1:2/binary,Str2:2/binary>> = Bin,
            %case binary_to_term(Bin) of
            case State of
                %登入
                    0000 -> %{Name,Passwd} = binary_to_term(Str),
                            Name = binary_to_term(Str1),
                            case info_lookup(Name) of
                                [{user,Uid,Pname,Pwd,Logc,ChatC,Lastlog}] -> S = term_to_binary(success),
                                                                            N = term_to_binary(Name),
                                                                            Packet = <<0000:4,(byte_size(S)):16,S/binary,(byte_size(N)):16,N/binary>>, 
                                                                            gen_tcp:send(Socket,Packet),
                                                                            my_fsm:count(0),
                                                                            %取到了名字和密碼之後傳送成功的標識並增加登入次數
                                                                            Reply = user_online_count({add,Pid}),
                                                                            io:format("~p users online ~n",[Reply]),
                                                                            Reply1 = personal_login_count({ladd,Name,Logc}),
                                                                            io:format("user ~p have logged ~p times ~n",[Name,Reply1]),
                                                                            loop(Pid,Socket);
                                %為空表示該使用者沒有記錄    
                                [{}] -> io:format("you haved not registered yet"),
                                        F = term_to_binary(failed),
                                        N = term_to_binary(Name),
                                        Packet = <<0000:4,(byte_size(F)):16,F/binary,(byte_size(N)):16,N/binary>>,
                                        gen_tcp:send(Socket,Packet),
                                        loop(Pid,Socket)
                            end;
                %接收資訊
                    0001 ->
                            Name = binary_to_term(Str1),
                            Msg = binary_to_term(Str2),
                            [#user{chat_times=Ccount}] = info_lookup(Name),
                            Reply = personal_chat_count({cadd,Name,Ccount}),
                            io:format("User ~p :~p~n",[Name,Msg]),
                            io:format("User ~p have chatted with his friend on line ~p times ~n",[Name,Reply]),
                            N = term_to_binary({ok,received}),
                            Len = byte_size(N),
                            Packet = <<0001:4,Len:16,N/binary>>,
                            gen_tcp:send(Socket,Packet),
                            loop(Pid,Socket);
                %退出
                    0002 ->
                        Name = binary_to_term(Str2),    
                        io:format("~p~n",[info_lookup(Name)]),
                        [#user{login_times=Logc,last_login=LastLo}] = info_lookup(Name),
                        Last = calendar:now_to_local_time(erlang:now()),
                        Reply = user_online_decrease({decrease,Pid}),
                        N = term_to_binary(ok),
                        Packet = <<0002:4,(byte_size(N)):16,N/binary>>,
                        gen_tcp:send(Socket,Packet),
                        %修改最後登入時間
                        info_update(Name,6,Last),
                        io:format("last time ~p logined is ~p~n",[Name,Last]),
                        io:format("~p users online~n",[Reply])



            end;

        {tcp_closed,Socket} ->
                              io:format("Server socket closed~n")
    end.

2.客戶端的程式碼

-module(client_example).
-export([get_socket/0,client_login/1,send_message/1,logout/1]).

%獲取socket
get_socket() ->
    {ok,Socket} = gen_tcp:connect("localhost",2345,[binary,{packet,4}]),
    register(client,spawn(fun() -> handle(Socket) end)).

%登入介面
client_login({Name,Password}) ->
    client ! {self(),{login,Name,Password}},
        receive
            Response -> ok
        end.


%聊天傳送介面
send_message({Name,Msg}) -> 
    client ! {self(),{msg,Name,Msg}},
        receive
            Response -> ok
        end.

%退出介面
logout(Name) ->
    client ! {self(),{logout,Name}},
        receive
            Response -> ok
        end.

handle(Socket) ->
    receive
        %來自控制程序的請求
        {From,Request} ->
            case Request of
                %登入的請求協議號0000
                {login,Name,Password} ->
                    N = term_to_binary(Name),
                    P = term_to_binary(Password),
                    Packet = <<0000:4,(byte_size(N)):16,N/binary,(byte_size(P)):16,P/binary>>,
                    gen_tcp:send(Socket,Packet),
                    receive
                        %來自服務端socket響應
                        {tcp,Socket,Bin} ->
                            <<State:4,S:2/binary,N:2/binary>> = Bin,
                            case binary_to_term(S) of
                                success ->
                                    From ! {"you have login successfully"},
                                    io:format("you have login successfully ~n");
                                failed ->
                                    From ! {"you haved login failed,please try again"},
                                    gen_tcp:close(Socket)
                            end
                    after 5000 ->
                        ok
                    end,
                    handle(Socket);
                %傳送資訊協議號0001
                {msg,Name,Msg} ->
                    io:format("my message:~p~n",[Msg]),
                    N = term_to_binary(Name),
                    M = term_to_binary(Msg),
                    Packet = <<0001:4,(byte_size(N)):16,N/binary,(byte_size(M)):16,M/binary>>,
                    gen_tcp:send(Socket,Packet),
                        receive
                            {tcp,Socket,Bin} ->
                                <<State:4,N:2/binary>> = Bin,
                                case binary_to_term(N) of
                                {ok,received} -> 
                                    From ! {"ok,you can send next message ~n"}
                                end
                        after 3000 ->
                            ok
                        end,
                        handle(Socket);
                %登出協議號0002
                {logout,Name} ->
                    L = term_to_binary({logout}),
                    N = term_to_binary({Name}),
                    Packet = <<0002:4,(byte_size(L)):16,L/binary,(byte_size(N)):16,N/binary>>,
                    gen_tcp:send(Socket,Packet),
                        receive
                            {tcp,Socket,Bin} ->
                                <<State:4,N:2/binary>> = Bin,
                                case binary_to_term(N) of
                                    ok ->
                                        From ! {"ok,you will logout successfully ~n"}
                                end
                        after 5000 ->
                            ok
                        end,
                        gen_tcp:close(Socket)
                    % 關閉socket時只有再次連線新socket才能開啟
            end
    end.

客戶端與服務端的通訊協議為自定義形式，協議號佔4位，資料部分分為兩部分，一部分為個人姓名，另一部分為資訊，如登入密碼或者聊天資訊，或者登出標誌。如：

封包時的協議：<<0000:4,byte_size(Name):16,Name/binary,byte_size(Msg):16,Msg/binary>>