[erlang-questions] Behavior for writing web applications

[narasimham placements]

Hi Kiran,
 Check Yaws documentation, you can find even better and simple way to handle
web applications for your requirements.

On Sat, May 22, 2010 at 6:06 PM, kiran khaladkar
<khaladkar.kiran@REDACTED>wrote:

> Hi,
>
> When working on erlang for almost more than 2 years now, I felt using there
> could have been more generic behaviours than the standard one’s i.e.
> gen_server, gen_fsm, gen_event. I wanted a behaviour that is suited for
> writing web applications
> Following is the attempt to write such a behaviour
>
>
>
> %%%-------------------------------------------------------------------------
> %%% Author: Kiran Khaladkar
> %%% Description: Behavior for writing web applications.
> %%% Created: Sat 5th Dec 2009
>
> %%%-------------------------------------------------------------------------
>
> -module(gen_app).
> -export([behavior_info/1, start/3, start/2]).
> -behavior(gen_server).
>
> -record(gen_app_state, {app_name :: atom(),         %%stores app name
>            cookie :: string(),         %%cookie to be stored to refer to
> client
>            app_state :: tuple()         %%state maintained by the apps
> extending this behavior
>                   }).
>
> -export([init/1, handle_call/3, handle_cast/2, handle_info/2,
>         terminate/2, code_change/3]).
>
> -export([get_info/1, get_cookie/1, set_cookie/2, handle_sync_request/2,
> handle_async_request/2]).
>
> behavior_info(callbacks) ->
>    [{init,1}, {handle_request, 2}, {respond, 1},{terminate,1}].
>
> %% Function: start/3
> %% Description: starts the application by AppName with Params and Options.
> %%        Options are gen_app process options
> %% Return: {ok, Pid}
> start(AppName, Param, Options) ->
>    gen_server:start_link(?MODULE, {AppName,Param}, Options).
>
> %% Function: start/2
> %% Description: Starts the application by AppName with params but without
> Options
> %% Return: {ok, Pid}
> start(AppName, Param) ->
>    gen_server:start_link(?MODULE, {AppName, Param}, []).
>
> init({AppName, Param}) ->
>    {ok, AppInitCookie, AppInitState} = AppName:init(Param),
>    {ok, #gen_app_state{app_name = AppName, cookie = AppInitCookie,
> app_state = AppInitState}}.
>
> %% Function: get_info/1
> %% Return: returns state of the gen_app
> get_info(AppId) ->
>    gen_app:handle_sync_request(AppId, get_state).
>
> get_cookie(AppId) ->
>    handle_sync_request(AppId, get_cookie).
>
> set_cookie(AppId, Cookie) ->
>    handle_sync_request(AppId, {set_cookie, Cookie}).
>
> %% Funtion: handle_async_request(/2
> %% Description: API to handle asynchronous calls that return immidiately
> without results.
> %% Rerurn: {noreply, State}
> handle_async_request(AppId, Reqest) ->
>    gen_server:handle_cast(AppId, {app_req, Reqest}),
>    {ok, processing}.
>
> %% Function: handle_sync_request/2
> %% Description: API to handle synchronous calls that return the result of
> the
> %%        request after completion of the processing of that request
> %% Return: {reply, Reply, NewState} after completion of the processing
> handle_sync_request(AppId, Request) ->
>    gen_server:handle_call(AppId, {app_req, Request}).
>
> %% Funtion: handle_cast/2
> %% Desciption: handle cast messages to gen_app process
> %% Return: {noreply, #state{}}
> handle_cast({app_req, Request}, #gen_app_state{app_name=AppName,
> app_state=AppState}=State) ->
>    {ok, NewAppState, Response}=AppName:handle_request(Request, AppState),
>    AppName:respond(Response),
>    {noreply, State#gen_app_state{app_state=NewAppState}};
>
> handle_cast(_Msg, _State) ->
>    {noreplay, _State}.
>
> %% Funtion: handle_call/3
> %% Desciption: handle cast messages to gen_app process
> %% Return: {noreply, #state{}}
> handle_call(get_state,_From, State) ->
>    {reply, app_state, State};
>
> handle_call({app_req, Req},_From, #gen_app_state{app_name = AppName,
> app_state = AppState} = State) ->
>    {ok, NewAppState, Response}=AppName:handle_request(Req, AppState),
>    AppName:respond(Response),
>    {reply, ok, State#gen_app_state{app_state=NewAppState}};
>
> handle_call(get_cookie, _From, State) ->
>    {reply, State#gen_app_state.cookie, State};
>
> handle_call({set_cookie, Cookie}, _From, State)->
>    {reply, ok, State#gen_app_state{cookie = Cookie}};
>
> handle_call(_Msg,_From, _State) ->
>    Reply = _Msg,
>    {reply, Reply, _State}.
>
> handle_info(_Info, _State) ->
>    {noreply, _State}.
>
> code_change(_OldVsn, State, _Extra) ->
>    {ok, State}.
>
> terminate(Reason, #gen_app_state{app_name=AppName, app_state=AppState} =
> _State) ->
>    AppName:terminate(Reason, AppState).
>
> Need your comments on this...
> regards,
> Kiran
>