CAF (Cloud Assistant Framework)

Co-design permanent, active, stateful, reliable cloud proxies with your web app.

See http://www.cafjs.com

CAF Lib Conduit

Conduits are functional processing pipelines assembled in a series-parallel task graph. Each task implements an asynchronous action that uses standard node.js callback conventions, and data flows through pipelines by folding a map in a graph traversal that respects task dependencies. Map entries are labelled with the originating task, enabling communication between tasks. Unique labels can be chosen by the application or assigned by the library. Tasks can explicitly declare these dependencies and 'conduit' will check for data races or dangling references at build time. Labels can be made unique by scoping with a prefix, and 'conduit' will rewrite the dependencies for you.

An error in any of the tasks aborts the traversal, returning in a callback this error and previous (or parallel) results already in the map.

The structure and configuration of conduits can be serialized, and later on, after parsing, can be bound to a different set of implementation methods. This simplifies uploading conduits (from the browser to a CA) in a secure manner, and modify their behavior based on the execution context.

API

Conduits are immutable data structures and reusing pipeline elements never creates side-effects. Task graphs are built using a stack, similar to an HP calculator with reverse polish notation (RPN), but only two operators __seq__(n) and __par__(n). For example:

var conduit = require('caf_conduit')

// declare method names that implement tasks
c = conduit.newInstance(['foo','bar'])

// first argument provides arguments for the invoked task
// second argument, an optional object with read dependencies
// third argument, an optional label for the results
// returns a new conduit (a conduit object is immutable) 
c = c.foo({'arg':1}, null, 'fx0')
     .foo({'arg':2}, {'prev': 'fx0'}, 'fx1')
     .foo({'arg':4}, {'prev': 'fx1'}, 'fx2')
     .__seq__(3)
     .bar({'arg':2}, null,  'bx')
     .bar({'arg':4}, null, 'b1x')
     .__seq__()
     .__par__()
           

will execute in parallel two sequences of 3 foos and 2 bars.

And this can be composed with another conduit as follows:

b = conduit.newInstance(['foo','bar'])
b = b.foo({'arg':1}, null, 'ffx')
     .__push__(c)
     .__seq__()
     

Or we can use it as a template, and prefix labels to avoid collisions:

cClone = c.__scope__('myspace/')
// and now labels are of the form 'myspace/fx0', 'myspace/fx1'...

Serializing a conduit:

var st = b.__stringify__()
var c = conduit.parse(st);
 

Adding methods to implement tasks:

var actions = {
                'foo' : function(acc, args, deps, label, cb) {
                  // acc should be treated as read-only
                  //
                  // Note that deps.prev `happened-before` this task
                  //   because conduit checks for races.
                  var whatever = (deps && deps.prev && acc[deps.prev] && 
                                  acc[deps.prev].data &&
                                  acc[deps.prev].data.whatever) || 0;
                  // Never use `return xx`, use the callback to return.
                  // New `whatever` will be added to acc by this library.
                  cb(null, {'whatever': whatever + 1})
                 },
                 'bar' : function(acc, args, deps, label, cb) {
                  ...
                 }
               }
b = b.__behavior__(actions)

Executing the task graph:

var acc = {}
b.__fold__(acc, function(err, data) {
                    // data refers to `acc` with an entry for each
                    //  task (key is the given label or a unique string,
                    //        value is {err: <err>, data: <whatever>,
                    //                  meta: {name:string, args:[],
                    //                         deps:[]}})
                    // where meta just records call arguments
                    ...
});

Configuration Example

framework.json

None

ca.json

None