将大程序分在多个文件中
为了演示需要，我们将前面几节中 messager 程序分布到五个文件中：
mess_config.hrl
配置所需数据头文件
mess_interface.hrl
客户端与 messager 之间的接口定义
user_interface.erl
用户接口函数
mess_client.erl
messager 系统客户端的函数
mess_server.erl
messager 服务端的函数
除了完成上述工作外，我们使用记录重新定义了 shell 、客户端以及服务端的消息格式。此外，我们还引入了下面这些宏：
%%%----FILE mess_config.hrl----
%%% Configure the location of the server node,
-define(server_node, messenger@super).
%%%----END FILE----
%%%----FILE mess_interface.hrl----
%%%Message interface between client and server and client shell for
%%% messenger program
%%%Messages from Client to server received in server/1 function.
-record(logon,{client_pid, username}).
-record(message,{client_pid, to_name, message}).
%%% {'EXIT', ClientPid, Reason} (client terminated or unreachable.
%%% Messages from Server to Client, received in await_result/0 function
-record(abort_client,{message}).
%%% Messages are: user_exists_at_other_node,
%%% you_are_not_logged_on
-record(server_reply,{message}).
%%% Messages are: logged_on
%%% receiver_not_found
%%% sent (Message has been sent (no guarantee)
%%% Messages from Server to Client received in client/1 function
-record(message_from,{from_name, message}).
%%% Messages from shell to Client received in client/1 function
%%% spawn(mess_client, client, [server_node(), Name])
-record(message_to,{to_name, message}).
%%% logoff
%%%----END FILE----
%%%----FILE mess_interface.hrl----
%%% Message interface between client and server and client shell for
%%% messenger program
%%%Messages from Client to server received in server/1 function.
-record(logon,{client_pid, username}).
-record(message,{client_pid, to_name, message}).
%%% {'EXIT', ClientPid, Reason} (client terminated or unreachable.
%%% Messages from Server to Client, received in await_result/0 function
-record(abort_client,{message}).
%%% Messages are: user_exists_at_other_node,
%%% you_are_not_logged_on
-record(server_reply,{message}).
%%% Messages are: logged_on
%%% receiver_not_found
%%% sent (Message has been sent (no guarantee)
%%% Messages from Server to Client received in client/1 function
-record(message_from,{from_name, message}).
%%% Messages from shell to Client received in client/1 function
%%% spawn(mess_client, client, [server_node(), Name])
-record(message_to,{to_name, message}).
%%% logoff
%%%----END FILE----
%%%----FILE mess_client.erl----
%%% The client process which runs on each user node
-module(mess_client).
-export([client/2]).
-include("mess_interface.hrl").
client(Server_Node, Name) ->
{messenger, Server_Node} ! #logon{client_pid=self(), username=Name},
await_result(),
client(Server_Node).
client(Server_Node) ->
receive
logoff ->
exit(normal);
#message_to{to_name=ToName, message=Message} ->
{messenger, Server_Node} !
#message{client_pid=self(), to_name=ToName, message=Message},
await_result();
{message_from, FromName, Message} ->
io:format("Message from ~p: ~p~n", [FromName, Message])
end,
client(Server_Node).
%%% wait for a response from the server
await_result() ->
receive
#abort_client{message=Why} ->
io:format("~p~n", [Why]),
exit(normal);
#server_reply{message=What} ->
io:format("~p~n", [What])
after 5000 ->
io:format("No response from server~n", []),
exit(timeout)
end.
%%%----END FILE---
%%%----FILE mess_server.erl----
%%% This is the server process of the messenger service
-module(mess_server).
-export([start_server/0, server/0]).
-include("mess_interface.hrl").
server() ->
process_flag(trap_exit, true),
server([]).
%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...]
server(User_List) ->
io:format("User list = ~p~n", [User_List]),
receive
#logon{client_pid=From, username=Name} ->
New_User_List = server_logon(From, Name, User_List),
server(New_User_List);
{'EXIT', From, _} ->
New_User_List = server_logoff(From, User_List),
server(New_User_List);
#message{client_pid=From, to_name=To, message=Message} ->
server_transfer(From, To, Message, User_List),
server(User_List)
end.
%%% Start the server
start_server() ->
register(messenger, spawn(?MODULE, server, [])).
%%% Server adds a new user to the user list
server_logon(From, Name, User_List) ->
%% check if logged on anywhere else
case lists:keymember(Name, 2, User_List) of
true ->
From ! #abort_client{message=user_exists_at_other_node},
User_List;
false ->
From ! #server_reply{message=logged_on},
link(From),
[{From, Name} | User_List] %add user to the list
end.
%%% Server deletes a user from the user list
server_logoff(From, User_List) ->
lists:keydelete(From, 1, User_List).
%%% Server transfers a message between user
server_transfer(From, To, Message, User_List) ->
%% check that the user is logged on and who he is
case lists:keysearch(From, 1, User_List) of
false ->
From ! #abort_client{message=you_are_not_logged_on};
{value, {_, Name}} ->
server_transfer(From, Name, To, Message, User_List)
end.
%%% If the user exists, send the message
server_transfer(From, Name, To, Message, User_List) ->
%% Find the receiver and send the message
case lists:keysearch(To, 2, User_List) of
false ->
From ! #server_reply{message=receiver_not_found};
{value, {ToPid, To}} ->
ToPid ! #message_from{from_name=Name, message=Message},
From ! #server_reply{message=sent}
end.
%%%----END FILE---