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| -rw-r--r-- | step-04/messenger.erl | 166 |
1 files changed, 166 insertions, 0 deletions
diff --git a/step-04/messenger.erl b/step-04/messenger.erl new file mode 100644 index 0000000..06288dd --- /dev/null +++ b/step-04/messenger.erl @@ -0,0 +1,166 @@ +%%% Message passing utility. +%%% User interface: +%%% logon(Name) +%%% One user at a time can log in from each Erlang node in the +%%% system messenger: and choose a suitable Name. If the Name +%%% is already logged in at another node or if someone else is +%%% already logged in at the same node, login will be rejected +%%% with a suitable error message. +%%% logoff() +%%% Logs off anybody at that node +%%% message(ToName, Message) +%%% sends Message to ToName. Error messages if the user of this +%%% function is not logged on or if ToName is not logged on at +%%% any node. +%%% +%%% One node in the network of Erlang nodes runs a server which maintains +%%% data about the logged on users. The server is registered as "messenger" +%%% Each node where there is a user logged on runs a client process registered +%%% as "mess_client" +%%% +%%% Protocol between the client processes and the server +%%% ---------------------------------------------------- +%%% +%%% To server: {ClientPid, logon, UserName} +%%% Reply {messenger, stop, user_exists_at_other_node} stops the client +%%% Reply {messenger, logged_on} logon was successful +%%% +%%% To server: {ClientPid, logoff} +%%% Reply: {messenger, logged_off} +%%% +%%% To server: {ClientPid, logoff} +%%% Reply: no reply +%%% +%%% To server: {ClientPid, message_to, ToName, Message} send a message +%%% Reply: {messenger, stop, you_are_not_logged_on} stops the client +%%% Reply: {messenger, receiver_not_found} no user with this name logged on +%%% Reply: {messenger, sent} Message has been sent (but no guarantee) +%%% +%%% To client: {message_from, Name, Message}, +%%% +%%% Protocol between the "commands" and the client +%%% ---------------------------------------------- +%%% +%%% Started: messenger:client(Server_Node, Name) +%%% To client: logoff +%%% To client: {message_to, ToName, Message} +%%% +%%% Configuration: change the server_node() function to return the +%%% name of the node where the messenger server runs + +-module(messenger). +-export([start_server/0, server/1, logon/1, logoff/0, message/2, client/2]). + +%%% Change the function below to return the name of the node where the +%%% messenger server runs +server_node() -> + messenger@akili. + +%%% This is the server process for the "messenger" +%%% the user list has the format [{ClientPid1, Name1},{ClientPid22, Name2},...] +server(User_List) -> + receive + {From, logon, Name} -> + New_User_List = server_logon(From, Name, User_List), + server(New_User_List); + {From, logoff} -> + New_User_List = server_logoff(From, User_List), + server(New_User_List); + {From, message_to, To, Message} -> + server_transfer(From, To, Message, User_List), + io:format("list is now: ~p~n", [User_List]), + server(User_List) + end. + +%%% Start the server +start_server() -> + register(messenger, spawn(messenger, 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 ! {messenger, stop, user_exists_at_other_node}, %reject logon + User_List; + false -> + From ! {messenger, logged_on}, + [{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 ! {messenger, stop, you_are_not_logged_on}; + {value, {From, 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 ! {messenger, receiver_not_found}; + {value, {ToPid, To}} -> + ToPid ! {message_from, Name, Message}, + From ! {messenger, sent} + end. + + +%%% User Commands +logon(Name) -> + case whereis(mess_client) of + undefined -> + register(mess_client, + spawn(messenger, client, [server_node(), Name])); + _ -> already_logged_on + end. + +logoff() -> + mess_client ! logoff. + +message(ToName, Message) -> + case whereis(mess_client) of % Test if the client is running + undefined -> + not_logged_on; + _ -> mess_client ! {message_to, ToName, Message}, + ok +end. + + +%%% The client process which runs on each server node +client(Server_Node, Name) -> + {messenger, Server_Node} ! {self(), logon, Name}, + await_result(), + client(Server_Node). + +client(Server_Node) -> + receive + logoff -> + {messenger, Server_Node} ! {self(), logoff}, + exit(normal); + {message_to, ToName, Message} -> + {messenger, Server_Node} ! {self(), message_to, ToName, 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 + {messenger, stop, Why} -> % Stop the client + io:format("~p~n", [Why]), + exit(normal); + {messenger, What} -> % Normal response + io:format("~p~n", [What]) + end. |