使用Erlang建立IVR实现复杂业务逻辑
曾写过一篇使用XML实现IVR 。但当你要实现更复杂、更智能的业务逻辑时，你免不了跟数据库或其它系统交互。我们曾用Ruby借助event_socket实现过比较复杂的功能，但当业务变得更加复杂时，我们使用Erlang重写了整个逻辑。
什么是 Erlang ?
Erlang是一种函数式编程语言，它天生支持高并发，高可靠性的编程。
为什么使用 Erlang ?
Erlang 最初就是设计用来编写电信程序的，它具有OTP（开放电信平台）库，使用它可以很容易地实现FSM（有限状态机）。
我们的PBX服务器运行在办公室里，但当有电话进来时它需要到国外的一台服务器上取数据，并以此来选择坐席。呼叫过程中，它也需要更新远程的数据。我们使用HTTP与远程服务器交互。如此长距离的通信不仅会有很大的延时，而且经常会失败。FreeSWITCH本身有mod_http及mod_curl模块，并且其它嵌入式脚本语言也都有HTTP支持，但我们认为Erlang会更加健壮。而且，通过使用Erlang的轻量级进程，当一有电话进来时，我们可以一边启动IVR拨放欢迎词，一边spawn一个新进程到远程HTTP上取数据。当IVR运行到需要数据进行决策时，绝大多数情况下这些数据已经有了。即使获取数据失败，我们也可以以默认的方式进行路由。这样，客户就不会感觉到任何延迟。
实现
我们使用mod_erlang_socket的outbound模式。当有电话进来时，FreeSWITCH会通过dialplan立即把控制权交给Erlang。
<extension name="icall_fsm">
<condition field="destination_number" expression="^fsm$">
<action application="erlang" data="icall:fsm acd@192.168.1.27"/>
</condition>
</extension>
其中，Erlang程序acd运行在节点192.168.1.27上，FreeSWITCH会使用RPC调用执行icall:fsm()并在Erlang中启动一个有限状态机，它接下来会控制呼叫流程，实现进行状态转移，直到呼叫结束。并且，在呼叫过程中我们还通过db_pbx模块与数据库及远程HTTP交互。Erlang实现的FSM代码真的非常好看。
-module(icall).
-behaviour(gen_fsm).
-export([start/0, stop/0, fsm/1, init/1, welcome/2, handle_info/3, handle_event/3, terminate/3]).
-export([welcome_wait_playback/2, main_menu/2, main_menu_wait_dtmf/2, call_hst/2, call_sales/2, call_cc/2, call_extn/2,
call_cellphone/2, final_loop/2]).
-import(freeswitch_msg, [get_var/2, get_var/3, sendmsg/3]).
start() -> gen_fsm:start(icall_fsm, [], []).
stop() -> gen_fsm:send_all_state_event(self(), stop).
fsm(Ref) ->
{ok, NewPid} = ?MODULE:start(),
{Ref, NewPid}.
%% send a stop this will end up in "handle_event"
% stop() -> gen_fsm:send_all_state_event(hello, stopit).
%% -- interface end
% This initialisation routine gets called
init(State) ->
io:format("icall_fsm init ~p, PID: ~p~n", [State, self()]),
{ok, welcome, []}.
%% The state machine
welcome([], []) ->
{next_state, welcome, []};
% welcome(UUID, []) ->
% {next_state, welcome, [UUID]};
welcome({call, {event, [UUID | Data]}}, []) ->
CallerID = get_var("Channel-Caller-ID-Number", Data, "00000000"),
Pid = self(),
spawn(fun() -> fetch_cc_extn_from_crm(Pid, CallerID) end),
io:format("New call from [~p]~n", [CallerID]),
db_pbx:new_call(UUID, Data),
sendmsg(UUID, playback, "new_sales/1000.wav"),
{next_state, welcome_wait_playback, UUID}.
welcome_wait_playback({call_event, {event, [UUID | Data]} }, UUID) ->
Name = get_var("Event-Name", Data),
App = get_var("Application", Data),
error_logger:info_msg("welcome_wait_playback: Pid ~p: UUID ~p, Event ~p~n",[self(), UUID, Name]),
case Name of
"CHANNEL_EXECUTE_COMPLETE" when App =:= "playback" ->
NextState = route_time_condition(UUID),
gen_fsm:send_event(self(), UUID),
{next_state, NextState, UUID};
_ ->
{next_state, welcome_wait_playback, UUID}
end.
main_menu(UUID, UUID) ->
sendmsg(UUID, play_and_get_digits, "1 1 3 5000 # new_sales/1001.wav new_sales/9004.wav menu_number [1-5]"),
db_pbx:log(UUID, "MainMenu", ""),
gen_fsm:send_event(self(), {call_event, {event, [UUID]}}),
{next_state, main_menu_wait_dtmf, UUID}.
main_menu_wait_dtmf({call_event, {event, [UUID | Data]} }, UUID) ->
Name = get_var("Event-Name", Data),
App = get_var("Application", Data),
error_logger:info_msg("Pid ~p: UUID ~p, Event ~p, State: main_menu_wait_dtmf~n",[self(), UUID, Name]),
case Name of
"CHANNEL_EXECUTE_COMPLETE" when App =:= "play_and_get_digits" ->
MenuNumber = get_var("variable_menu_number", Data),
db_pbx:log(UUID, "MainMenu", MenuNumber),
case MenuNumber of
"1" ->
gen_fsm:send_event(self(), UUID),
{next_state, call_hst, UUID};
"5" ->
%<min> <max> <tries> <timeout> <terminators> <file> <invalid_file> <var_name> <regexp>
sendmsg(UUID, play_and_get_digits, "3 3 3 5000 # new_sales/2002.wav new_sales/9004.wav extn_number [68]\\d\\d"),
{next_state, call_extn, no_extn};
X when X == "2"; X == "3"; X == "4" ->
gen_fsm:send_event(self(), UUID),
{next_state, call_sales, UUID};
_ ->
sendmsg(UUID, playback, "new_sales/9003.wav"),
timer:sleep(5000),
sendmsg(UUID, hangup, ""),
{next_state, final_loop, UUID}
end;
_ ->
{next_state, main_menu_wait_dtmf, UUID}
end.
call_hst(UUID, UUID) ->
transfer(UUID, "fifo_hst"),
{next_state, final_loop, UUID}.
call_cellphone(UUID, UUID) ->
transfer(UUID, "fifo_cellphone"),
{next_state, final_loop, UUID}.
call_sales(UUID, UUID) ->
case get(cc_extn) of
undefined ->
transfer(UUID, "fifo_sales"),
db_pbx:log(UUID, "SalesFifo", ""),
{next_state, final_loop, UUID};
Extn ->
play_intransfer(UUID),
sendmsg(UUID, set, "ringback=${us-ring}"),
sendmsg(UUID, set, "continue_on_fail=true"),
sendmsg(UUID, set, "hangup_after_bridge=true"),
sendmsg(UUID, bridge, "user/" ++ Extn),
db_pbx:log(UUID, "CallCC", Extn),
{next_state, call_cc, Extn}
end.
call_cc({call_event, {event, [UUID | Data]} }, Extn) ->
Name = get_var("Event-Name", Data),
App = get_var("Application", Data),
error_logger:info_msg("Pid ~p: UUID ~p, Event ~p, Extn ~p~n",[self(), UUID, Name, Extn]),
case Name of
"CHANNEL_EXECUTE_COMPLETE" when App =:= "bridge" ->
HangupCause = get_var("variable_originate_disposition", Data),
DialedUser = get_var("variable_dialed_user", Data),
sendmsg(UUID, play_and_get_digits, "1 1 2 5000 # new_sales/8" ++ Extn ++
".wav new_sales/9004.wav cc_menu_number [12]"),
db_pbx:log(UUID, "CCFailure", HangupCause),
{next_state, call_cc, Extn};
"CHANNEL_EXECUTE_COMPLETE" when App =:= "play_and_get_digits" ->
CCMenuNumber = get_var("variable_cc_menu_number", Data),
case CCMenuNumber of
"1" -> sendmsg(UUID, transfer, "Playcell_" ++ Extn);
"2" -> sendmsg(UUID, transfer, "VM_" ++ Extn);
_ -> sendmsg(UUID, transfer, "Quit")
end,
{next_state, final_loop, UUID};
_ ->
{next_state, call_cc, Extn}
end.
call_extn({call_event, {event, [UUID | Data]} }, no_extn) ->
Name = get_var("Event-Name", Data),
App = get_var("Application", Data),
error_logger:info_msg("Pid ~p: UUID ~p, Event ~p, State: call_extn",[self(), UUID, Name]),
case Name of
"CHANNEL_EXECUTE_COMPLETE" when App =:= "play_and_get_digits" ->
Extn = get_var("variable_extn_number", Data),
db_pbx:log(UUID, "CallExtn", Extn),
gen_fsm:send_event(self(), UUID),
{next_state, call_extn, Extn};
_ ->
{next_state, call_extn, no_extn}
end;
call_extn(UUID, Extn) ->
io:format("Calling extn: ~p~n", [Extn]),
% sendmsg(UUID, set, "campon=true"),
sendmsg(UUID, set, "ringback=${us-ring}"),
sendmsg(UUID, set, "continue_on_fail=true"),
sendmsg(UUID, set, "hangup_after_bridge=true"),
DialString = "user/" ++ Extn,
sendmsg(UUID, bridge, DialString),
{next_state, call_cc, Extn}.
final_loop({call_event, {event, [UUID | Data]} }, UUID) ->
Name = get_var("Event-Name", Data),
error_logger:info_msg("final_loop Pid ~p: UUID ~p, Event ~p~n",[self(), UUID, Name]),
{next_state, final_loop, UUID};
final_loop(UUID, UUID) ->
{next_state, final_loop, UUID}.
handle_info({cc_extn, error}, State, Data) ->
{next_state, State, Data};
handle_info({cc_extn, Extn}, State, Data) ->
put(cc_extn, Extn),
io:format("Found CC Extn: ~p~n", [Extn]),
{next_state, State, Data};
handle_info(call_hangup, State, Args) ->
io:format("Hangup ~p ~p ~n", [State, Args]),
{stop, normal, State};
handle_info({E, {event, [UUID | Data]}} = Event, State, StateData) ->
Name = get_var("Event-Name", Data),
App = list_to_atom(get_var("Application", Data, "undefined")),
error_logger:info_msg("handle_info: ~p ~p ~p ~p~n~p~n",[self(), UUID, Name, State, StateData]),
case Name of
"CHANNEL_HANGUP_COMPLETE"->
db_pbx:hangup(UUID, Data),
% {next_state, final_loop, UUID};
{stop, normal, UUID};
"CUSTOM" ->
SubClass = get_var("Event-Subclass", Data),
Action = get_var("FIFO-Action", Data),
io:format("Fifo: ~p ~p~n", [SubClass, Action]),
case SubClass of
"fifo::info" when Action =:= "bridge-caller" ->
db_pbx:process(UUID, Data);
_ -> ok
end,
{next_state, State, StateData};
_ ->
List = [welcome, welcome_wait_playback, main_menu_wait_dtmf, call_cc, call_extn],
case lists:any(fun(Elem) -> Elem =:= State end, List) of
true ->
gen_fsm:send_event(self(), Event);
_ -> ok
end,
{next_state, State, StateData}
end;
handle_info(Info, State, Data) ->
io:format("Got Other Info: ~p ~p ~p ~n", [Info, State, Data]).
handle_event(stop, _StateName, StateData) ->
{stop, normal, StateData}.
terminate(normal, _StateName, _StateData) ->
io:format("Stop with reason: normal ~p ~p~n", [_StateName, _StateData]),
ok;
terminate(Reason, _StateName, _StateData) ->
io:format("Stop with reason: ~p ~p ~p~n", [Reason, _StateName, _StateData]),
ok.
%% private
route_time_condition(UUID) ->
case db_pbx:get_time_condition("sales_icall") of
{Action, Args} ->
case Action of
% "idp_acd:" ++ ErlAction ->
% Fun = list_to_atom(ErlAction),
% db_pbx:log(UUID, "TimeCondition", ErlAction ++ " " ++ Args),
% ?MODULE:Fun(UUID, Args);
Action ->
db_pbx:log(UUID, "TimeCondition", Action ++ " " ++ Args),
sendmsg(UUID, list_to_atom(Action), Args),
final_loop
end;
_ ->
{Date, {Hour, Min, _Sec}} = erlang:localtime(),
Weekday = calendar:day_of_the_week(Date),
route_work_time(UUID, Weekday, Hour, Min)
end.
route_work_time(UUID, Weekday, Hour, Min)
when Weekday > 5 andalso Hour > 10 andalso (Hour < 20 orelse ( Min < 30 andalso Hour < 21) ) ->
db_pbx:log(UUID, "Weekend", "10:00 - 20:30"),
main_menu;
route_work_time(UUID, Weekday, Hour, Min) when Hour > 9 andalso (Hour < 20 orelse (Min < 30 andalso Hour < 21 ))->
db_pbx:log(UUID, "Workday", "Weekend 9:00 - 20:30"),
main_menu;
route_work_time(UUID, _Weekday, Hour, Min) when (Hour > 21 orelse (Hour > 20 andalso Min > 30)) andalso Hour < 23 ->
db_pbx:log(UUID, "Time", "20:30 - 23:00"),
call_hst;
route_work_time(UUID, _Weekday, _Hour, _Min) ->
db_pbx:log(UUID, "NonWorktime", "Cellphone"),
call_cellphone.
transfer(UUID, Dest) ->
transfer(UUID, Dest, "XML", "new_sales").
transfer(UUID, Dest, Dialplan, Context) ->
sendmsg(UUID, transfer, Dest ++ " " ++ Dialplan ++ " " ++ Context).
play_intransfer(UUID) ->
sendmsg(UUID, playback, "new_sales/1002.wav"),
timer:sleep(3000).
fetch_cc_extn_from_crm(Pid, CallerID) ->
Extn = case helpers:http_fetch(?CRM_APP, "/voip/cdrs?caller_id=" ++ CallerID) of
{error, _} -> error;
Number -> Number
end,
Pid ! {cc_extn, Extn}.
其它讨论
1） Erlang在这里是完全异步的。所以，当你通知FreeSWITCH执行一个application时（如playback），你必须等待收到CHANEL_EXECUTE_COMPLETE事件再进行下一步操作。这比起直接在dialplan或lua脚本中要麻烦一些，但正因为你是异步的，你可以随时终止正在执行的application。当然，如果你非要同步并且你知道某程序要执行多长时间时（如你知道要playback的声音文件的长度），你也可以用timer:sleep延时一下。
2）当我们觉得不再需要Erlang的特性时，我们会把流程转到dialplan，毕竟修改XML要容易些。
3）mod_fifo在Erlang中不能很好工作，除非你在fifo结束时将流程transfer到其它地方。因为channel在送到Erlang关是park的，而fifo中bridge到另一分机时无法解除park状态。这也是为什么我们在最后都送流程再送回dialplan。
4）代码已经很清晰了，但我想，如果有时间能现写个gen_fs_behaviour之类的东东把FreeSWITCH的事件消息包装一下会更好看。
本文也有一个英文版本：http://www.dujinfang.com/past/2010/4/22/build-a-complex-hence-powerful-freeswitch-ivr-in-erlang/
