SAFE - A micro-container for Node.js SAM Implementations

SAFE implements the following services

• element wiring
• action dispatcher
• session dehydration / hydration
• enforces allowed actions and action hang back
• logging
• server side time travel

Coming up

• caching (idempotent actions)

Usage

The SAM pattern can be deployed with a variety of topologies. The blog sample implements its Actions on the client, while the Model and the State are implemented on the server.

SAFE can be used to wire the SAM elements

// note that actions can also implemented on the client
// in which case the value would be null
// var actions = null 

var actions = require('./actions') ;  
var model = require('./model') ;
var view = require('./view') ;
var state = require('./state') ;

var safe = require('sam-safe') ;

safe.init(actions,model,state,view) ;

Dispatcher

The dispatcher can be used to simplify the invocation of the server-side actions from the client's event handlers.

On the server, the dispatcher is activated via a simple call where apis.dispatch is the path you assign to the dispatcher (server-model.js):

safe.dispatcher(app,apis.dispatch) ;

In your client, add a simple dispatcher function (blog.html):

function dispatch(data) {
    
    // invoke SAFE's dispatcher
    $.post( "http://localhost:5425/app/v1/dispatch", data) 
    .done(function( representation ) {
        $( "#representation" ).html( representation );
    }        
    );
}

then route all your actions to the dispatcher (blog.js) and add the __action property to your dataset:

actions.save = (data) => {
    data.__action = 'save' ;
    actions.do(data) ; 
    return false ;
} ;

Session Management

A session manager can be plugged into SAFE to manage session rehydration/hydration.

The following implementations are available:

• DynamoDB

SAM is expecting that a session token be present in the action's dataset

data.__token = 'token_1234' ;

A dedicated session manager can be assigned during SAFE's initialization, for instance using DynamoDB session manager:

var sessionManager = require('./DDBsession') ;

safe.init(actions,model,state,view,null,null,sessionManager) ;

SAM does not validate tokens.

Allowed Actions

Currently SAFE can be used enforce global action authorization (not yet session based)

Action Hang Back

SAM inherently supports a mode where the client can call multiple allowed actions in a given step. With SAFE, the first one to present its values "wins" and prevents any other action to present its values to the model.

For instance, the Blog Sample, the save action simulates a slow behavior:

actions.save = (data,next) => {
    data.item = {title: data.title, description: data.description, id: data.id || ''} ;
    if (data.item.id !== '') {
        // simulate a slow save after
        // editing an item
        setTimeout(function() { 
            actions.present(data,next) ;
        }, 9000);
    }
    else {
        // proceed as normal when created a new item
        actions.present(data,next) ;
    }
    return false ;
} ;

When you modify a blog entry and you hit save, the action will present its data 9s later. If you hit cancel before the save action presents its values to the model, then the save action will be prevented from presenting its actions to the model.

Time Travel

Time Travel is a developer tool that allows you to put back the application state as it was in a given step. This approach was popularized by Dan Abramov as part of the Redux framework. However, in Redux time travel works only on the client while in SAFE it can run both on the client or server.

// Time Travel is initialized in a couple of lines (server-model.js)

var myTimeTraveler = safe.defaultTimeTraveler() ; // or your implementation
safe.initTimeTraveler(myTimeTraveler) ;

// add the express route to access the model versions
myTimeTraveler.init(app,your_path_to_timetravel_snapshots) ;

// SAFE's implements an in memory defaultSnapShotStore, which you can
replace with your own, including a persistent one...

SAFE's defautTimeTravel implementation adds a "Time Travel" component to all state representations.

SAFE can also be used as a server-side Time Travel store to a client application. This can be achieved with a simple node application:

var safe = require('sam-safe') ;

// SAFE adds a default set of actions,model and state
safe.init() ;

// use default time traveler
var myTimeTraveler = safe.defaultTimeTraveler() ;
safe.initTimeTraveler(myTimeTraveler) ;

safe.dispatcher(app,your_dispatcher_path) ;

myTimeTraveler.init(app,your_time_travel_path) ;


// start application 

app.listen(config.port, function() {
    console.log("registering app on port: "+config.port) ;
    //setTimeout(register(),2000) ; 
});

You can also access the time travel store via a simple api:

Return all snapshots: http://localhost:5425/dev/v1/timetravel/snapshots/

Return a single snapshot: http://localhost:5425/dev/v1/timetravel/snapshots/{index}