fileserver/lib/restbed-4.8/documentation/example/SESSION_MANAGER.md

Overview
--------

"Sessions are a simple way to store data for individual users against a unique session ID. This can be used to persist state information between requests. Session IDs are normally sent to the browser via session cookies and the ID is used to retrieve existing session data. The absence of an ID or session cookie lets PHP know to create a new session, and generate a new session ID." -- [PHP Group](http://php.net/manual/en/session.examples.basic.php)

Example
-------

```C++
#include <map>
#include <mutex>
#include <chrono>
#include <string>
#include <memory>
#include <random>
#include <cstdlib>
#include <restbed>

using namespace std;
using namespace restbed;

class InMemorySessionManager : public SessionManager
{
    public:
        InMemorySessionManager( void ) : m_sessions_lock( ),
            m_sessions( )
        {
            return;
        }
        
        ~InMemorySessionManager( void )
        {
            return;
        }
        
        void start( const shared_ptr< const Settings >& )
        {
            return;
        }
        
        void create( const function< void ( const shared_ptr< Session > ) >& callback )
        {
            static const string charset = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
            static uniform_int_distribution< > selector( 0, 35 );
            
            auto seed = static_cast< unsigned int >( chrono::high_resolution_clock::now( ).time_since_epoch( ).count( ) );
            static mt19937 generator( seed );
            
            string key = "";
            
            for ( int index = 0; index < 32; index++ )
            {
                key += charset.at( selector( generator ) );
            }
            
            callback( make_shared< Session >( key ) );
        }
        
        void load( const shared_ptr< Session > session, const function< void ( const shared_ptr< Session > ) >& callback )
        {
            const auto request = session->get_request( );
            
            unique_lock< mutex > lock( m_sessions_lock );
            auto previous_session = m_sessions.find( request->get_header( "SessionID" ) );
            
            if ( previous_session not_eq m_sessions.end( ) )
            {
                const auto id = previous_session->second->get_id( );
                session->set_id( id );
                
                for ( const auto key : previous_session->second->keys( ) )
                {
                    session->set( key, previous_session->second->get( key ) );
                }
            }
            
            lock.unlock( );
            
            const auto key = session->get_id( );
            session->set_header( "SessionID", key );
            
            callback( session );
        }
        
        void save( const shared_ptr< Session > session, const function< void ( const shared_ptr< Session > ) >& callback )
        {
            unique_lock< mutex > lock( m_sessions_lock );
            m_sessions[ session->get_id( ) ] = session;
            lock.unlock( );
            
            callback( session );
        }
        
        void stop( void )
        {
            return;
        }
        
    private:
        mutex m_sessions_lock;
        
        map< string, shared_ptr< Session > > m_sessions;
};

void get_method_handler( const shared_ptr< Session > session )
{
    string body = "Previous Session Data\n";
    
    for ( const auto key : session->keys( ) )
    {
        string value = session->get( key );
        body += key + "=" + value + "\n";
    }
    
    const auto request = session->get_request( );
    
    for ( const auto query_parameter : request->get_query_parameters( ) )
    {
        session->set( query_parameter.first, query_parameter.second );
    }
    
    session->close( OK, body, { { "Connection", "close" } } );
}

int main( const int, const char** )
{
    auto resource = make_shared< Resource >( );
    resource->set_path( "/resource" );
    resource->set_method_handler( "GET", get_method_handler );
    
    auto settings = make_shared< Settings >( );
    settings->set_port( 1984 );
    
    Service service;
    service.publish( resource );
    service.set_session_manager( make_shared< InMemorySessionManager >( ) );
    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?location=UK'
>
> $ curl -w'\n' -v -X GET 'http://localhost:1984/resource' -H"SessionID: <Previously returned SessionID header value>"