RULES_ENGINE.md

Overview

"A business rules engine is a software system that executes one or more business rules in a runtime production environment. The rules might come from legal regulation ("An employee can be fired for any reason or no reason but not for an illegal reason"), company policy ("All customers that spend more than $100 at one time will receive a 10% discount"), or other sources. A business rule system enables these company policies and other operational decisions to be defined, tested, executed and maintained separately from application code." -- Wikipedia

Example

#include <string>
#include <memory>
#include <cstdlib>
#include <functional>
#include <restbed>

using namespace std;
using namespace restbed;

class HostRule : public Rule
{
    public:
        HostRule( void ) : Rule( )
        {
            return;
        }
        
        virtual ~HostRule( void )
        {
            return;
        }
        
        bool condition( const shared_ptr< Session > ) final override
        {
            return true;
        }
        
        void action( const shared_ptr< Session > session, const function< void ( const shared_ptr< Session > ) >& callback ) final override
        {
            const auto request = session->get_request( );
            
            if ( not request->has_header( "Host" ) )
            {
                session->close( BAD_REQUEST, "Bad Request! Host header required.", { { "Content-Length", "34" }, { "Content-Type", "text/plain" } } );
            }
            else
            {
                callback( session );
            }
        }
};

class AcceptRule : public Rule
{
    public:
        AcceptRule( void ) : Rule( )
        {
            return;
        }
        
        virtual ~AcceptRule( void )
        {
            return;
        }
        
        bool condition( const shared_ptr< Session > session ) final override
        {
            return session->get_request( )->has_header( "Accept" );
        }
        
        void action( const shared_ptr< Session > session, const function< void ( const shared_ptr< Session > ) >& callback ) final override
        {
            const auto request = session->get_request( );
            const auto type = request->get_header( "Accept", String::lowercase );
            
            if ( type not_eq "text/plain" and type not_eq "*/*" )
            {
                session->close( NOT_ACCEPTABLE,
                                "Not Acceptable, must be 'text/plain' or '*/*'.",
                { { "Content-Length", "46" }, { "Content-Type", "text/plain" } } );
            }
            else
            {
                callback( session );
            }
        }
};

void get_method_handler( const shared_ptr< Session > session )
{
    session->close( OK, "Hello, World!", { { "Content-Length", "13" }, { "Content-Type", "text/plain" } } );
}

int main( const int, const char** )
{
    auto resource = make_shared< Resource >( );
    resource->set_path( "/resource" );
    resource->add_rule( make_shared< AcceptRule >( ) );
    resource->set_method_handler( "GET", get_method_handler );
    
    auto settings = make_shared< Settings >( );
    settings->set_port( 1984 );
    settings->set_default_header( "Connection", "close" );
    
    Service service;
    service.publish( resource );
    service.add_rule( make_shared< HostRule >( ) );
    service.start( settings );
    
    return EXIT_SUCCESS;
}

Build

$ clang++ -o example example.cpp -l restbed

Execution

$ ./example

$ curl -w'\n' -v -X GET 'http://localhost:1984/resource'

$ curl -w'\n' -v -X GET 'http://localhost:1984/resource' -H"Host:"

$ curl -w'\n' -v -X GET 'http://localhost:1984/resource' -H"Accept: application/json"