Re: [Cppcms-users] Problem with cppcms::application::add() method

[Daniel V. <chi...@gm...>]

Hello.

I use the latest cppcms revision.

I answer between the lines below.

Thanks.


On Thu, 2010-11-11 at 12:39 -0800, Artyom wrote:

> >
> >void application::add(application &app,std::string regex,int part)
> >{
> >        add(app);
> >        url_dispatcher().mount(regex,app,part);
> >}
> >
> >The code above has an error, the correct code is:
> >dispatcher().mount(regex,app,part);
> >

You write "url_dispatcher()" in the above method definition.  As you
know  url_dispatcher() makes an anonymous instance of
cppcms::url_dispatcher class. I suspect that your intentions are to call
dispatcher() method instead. 


> 
> add or attach member functions do only one thing - they share the http::context
> class between all connected applications.
> 
> Otherwise you'll just have an exception trying to access anything like request() 
> 
> or response() of any class that wasn't added.
> 
> On the other hand url_dispatching is just a simple way to "split" your main
> function according to requests between its own member function and other sub 
> applications.
> 
> There are different tasks and they both required (unless you wan't to do 
> something on
> your own in main rather then standard URL-dispatching)

They are diferent task, I understand, but  the method add(application
&app,std::string regex,int part) makes these two tasks. 

> 
> > Second problem:
> >
> > When I attach or add an application B to an application A,
> > the method "void B::main(std::string url)" is never 
> > called on url dispatch stage.
> 
> When you mount a sub application you just extract sub expression and
> pass it to mounted application. I.e.
> 
>    add(users_app)
>    add(uploads)
>    urd_dispatched().mount("/users(/.*)",users_app,1);
>    urd_dispatched().mount("/uploads(/.*)",uploads,1);

I can't use that interface because the mount() method is private.
The code

        add(users_app);
        dispatcher().mount("/users(/.*)",u,1);

raise the error

        cppcms/url_dispatcher.h:160: error: ‘void
        cppcms::url_dispatcher::mount(std::string, cppcms::application&,
        int)’ is private
        main.cpp:30: error: within this context

For that reason I use the shortcut method add(application
&app,std::string regex,int part).


> And then in constructor of users you mount
> 
>    url_dispatcher().attach("/login",&users_class::login,this);
> 
> when you hit /users/login
> 
> /users/login is matched against "/users(/.*)" regex and passed to 
> users_app.main()
> with parameter "/login"
> 
> then it matched by users_app's url_disptacher against "/login" regex and passed 
> to login
> member function of users_app instance.
> 
> So you need both steps and understand how they work.
> 
> > This behaviour causes problems when adding cppcms::rpc::json_rpc_server 
> > application because the parsing of the request is made in json_rpc_server::main 
> >
> > method.
> > The result is that the application does not work.
> 
> adding application has nothing to do with URL dispatching, url_disptaching just 
> allows
> you to forward request to other app's main function.

I wrote an small example that reproduces the issue:

        #include <cppcms/application.h>
        #include <cppcms/service.h>
        #include <cppcms/applications_pool.h>
        #include <cppcms/url_dispatcher.h>
        #include <cppcms/http_response.h>
        #include <iostream>
        
        class users : public cppcms::application
        {
        public:
            users(cppcms::service& srv): application(srv) {
                dispatcher().assign("/login$", &users::login, this);
            }
            void main(std::string url) {
                response().out() << "into users::main(\""<< url
        <<"\")\n";
                cppcms::application::main(url);
            }
            void login() {
                response().out() << "into users::login()\n";
            }
        };
        
        class main_app : public cppcms::application
        {
        public:
            main_app(cppcms::service& srv) : application(srv), u(srv) {
                add(u,"/users(/.*)",1);
                //add(u);
                //dispatcher().mount("/users(/.*)",u,1);
            }
            void main(std::string url) {
                response().out() << "into main_app::main(\""<< url
        <<"\")\n";
                cppcms::application::main(url);
            }
        private:
            users u;
        };
        
        int main(int argc, char **argv)
        {
            try {
                cppcms::service srv(argc, argv);
                srv.applications_pool().mount(
                    cppcms::applications_factory<main_app>());
                srv.run();
        
            }
            catch(std::exception const &e) {
                std::cerr << e.what() << std::endl;
                return 1;
            }
            return 0;
        }

Test cases:

A - Test url: .../users/login
     result: "into users::login()"

    That's ok.

B - Test url: .../users/foo
    result: "into main_app::main("/users/foo")"

    That's no ok, because the espected result is "into
users::main("/foo")". The users::main() method is never called.

    Am I wrong?

If you don't change "url_dispatcher()" to "dispatcher()" in
add(application &app,std::string regex,int part) definition then the A
test also fails.



> > in cppcms::rpc::json_rpc_server application: URL mapping with 
> > dispatcher().assign() method does not work because main method overwriting.
> 
> When you develop json_rpc server you suppose to rather bind member function
> by remote procedure functions (i.e. RPC service function = member function)
> rather then using URL-dispatching method suitable for ordinary web applications.
>     
> So it is done by design.
> 
> Artyom
> 
> 
> 
>       
> 
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