sansa

sansa

Object graph serialization library for Node.js, written in CoffeeScript.

Motivation

When using JSON to serialize complex object graphs, it is easy to create a very large block of JSON with full representations of embedded objects. Even worse, it is easy to create an object graph with cycles, which leads to a TypeError: Converting circular structure to JSON.

There is no easy way to overcome these problems. The best we can hope for is to remove all the cycles from our object graphs and be careful how we call JSON.stringify();

sansa's Solution

sansa breaks the object graph serialization problem into the problem of serializing a number of small objects. The simple contents (boolean, number, string, etc.) are serialized directly to JSON. References to other objects are converted to UUIDs. Referenced objects are then serialized recursively.

Object Graph with Cycles in JSON

{ "a": { "b": { "a": ... TypeError: Converting circular structure to JSON

Object Graph with Cycles in sansa

{
  "uuid": "4cdc768b-1164-40d6-b2f4-4b319bc289d2",
  "a": "»211379b8-b9c0-4202-9c4b-a399aa18e11b"
}

{
  "uuid": "211379b8-b9c0-4202-9c4b-a399aa18e11b",
  "b": "»4cdc768b-1164-40d6-b2f4-4b319bc289d2"
}

Component API

sansa provides two components in its main module:

var sansa = require('sansa');
var Arya = sansa.Arya;
var AryaMemory = sansa.AryaMemory;

AryaMemory

AryaMemory is an in-memory JSON store. Its functions can be provided directly to Arya for object graph de/serialization.

An AryaMemory is constructed like any other object in JavaScript:

var mem = new AryaMemory();

AryaMemory.input(uuid, callback)

Obtain the JSON for the provided object's UUID.

• uuid String: The UUID of the object for which to obtain JSON
• callback Function: function callback(err, json)
  • err Error: An error, if any (AryaMemory never passes an Error)
  • json String: The JSON of the requested object

Example:

mem.input('a94beae2-881e-4e26-9fb4-de4f0f478abf', function(err, json) {
  if(err != null) {
    // handle error
  }
  // do something with json
});

AryaMemory.output(uuid, json, callback)

Store the JSON of an object under the provided UUID.

• uuid String: The UUID of the object to put in the JSON store
• json String: The JSON of the object to put in the JSON store
• callback Function: function callback(err)
  • err Error: An error, if any (AryaMemory never passes an Error)

Example:

mem.output('a94beae2-881e-4e26-9fb4-de4f0f478abf', '{}', function(err) {
  if(err != null) {
    // handle error
  }
});

Arya

Arya is the object responsible for serialization and deserialization of object graphs.

An Arya is constructed like any other object in JavaScript:

var arya = new Arya();

Arya.load(uuid, src, callback)

Load an object graph from a JSON store. Caller provides the UUID of the object to be returned (uuid), a callback to the JSON store (src), and the callback to be provided with the object after deserialization (callback).

• uuid String: The UUID of the object to load
• src Function: function src(uuid, callback)
  • uuid String: The UUID of the object to be loaded from the JSON store
  • callback Function: function callback(err, json)
    • err Error: An error, if any occur while reading from the store
    • json String: The JSON of the requested object
• callback Function: function callback(err, obj)
  • err Error: An error, if any are encountered while loading
  • obj Object: The object and connected object graph, loaded from JSON

Example:

arya.load('a94beae2-881e-4e26-9fb4-de4f0f478abf', mem.input, function(err, obj) {
  if(err != null) {
    // handle error
  }
  // do something with obj (an object with attached object graph)
});

Arya.register(name, constr, proxy)

Register a constructor or constructor proxy with Arya.

• name String: the name of the constructor
• constr Function: the constructor, or a constructor proxy function
• proxy Boolean: true, iff the function provided is a constructor proxy

When serializing an object graph from JavaScript objects into JSON, sansa will record the type of an object with a named constructor. When deserializing the object graph back from the JSON, sansa will need a reference to the constructor in order to re-create the object.

As of sansa v0.3.2, failure to register a constructor that is necessary for deserialization will be passed as an error. (Thanks to @qbradq)

If there are no special conditions, and a simple no-argument call to new will suffice, then you can just pass the constructor itself to Arya. sansa will handle the call to new internally:

var ComplexNumber = function ComplexNumber(real, imag) {
    // do something with the real and imag values here
};

arya.register("ComplexNumber", ComplexNumber);

If there are special conditions for calling the constructor, you may instead pass a constructor proxy to Arya. sansa WILL NOT call new for you in this case. Your proxy function must do that. You pass true as the third argument, in order to indicate that the function provided is a proxy.

var ComplexNumber = function ComplexNumber(real, imag) {
    // do something with the real and imag values here
};

var complexProxy = function complexProxy() {
    var num = new ComplexNumber(1, 0);
    return num;
};

arya.register("ComplexNumber", complexProxy, true);

The constructor proxy function is provided with four arguments:

function constructorProxy(dObj, json, uuid, context)

• dObj Object: the raw result of JSON.parse
• json String: the JSON for this object
• uuid String: the UUID of the object
• context Object: sansa's own context object

sansa's context object contains references to the incomplete object graph that is currently under construction. It represents everything sansa knows about the object graph at the time of the call to the constructor proxy.

All of this is really advanced usage. Most of the time, you can simply ignore the parameters to the constructor proxy function.

Arya.save(obj, sink, next)

Serialize an object graph to JSON

• obj Object: object in graph to be stored
• sink Function: function sink(uuid, json, callback)
  • uuid String: The UUID of the object to put in the JSON store
  • json String: The JSON of the object to put in the JSON store
  • callback Function: function callback(err)
    • err Error: An error, if any occurs while writing to the store
• next Function: function next(uuid, json, callback)
  • err Error: An error, if any occurs while serializing the object graph
  • uuid String: the UUID of the object as stored in the JSON store

Example:

arya.save({ name: "Bob" }, mem.output, function(err, uuid) {
  if(err != null) {
    // handle error
  }
  // do something with the uuid (the uuid of the provided object)
});

Limitations

If you make use of fields or values that begin with the character '»' you might run into trouble unless you modify sansa.

Reserved field: uuid

sansa tags every object in the graph with the field 'uuid'. If you are using that field to store an actual v4 UUID in String form, that is no problem. sansa can reuse your own identifiers. If you need that field for something other than a v4 UUID in String form, you'll need to modify sansa so that it can work with your objects.

Reserved field: »type

sansa makes use of the character '»' to create special tags in the JSON. There is one special key:

/^»type$/       Used to store the name of an object's constructor

Reserved value: /^»[0-9]+$/

sansa interprets the regular expression /^»[0-9]+$/ to be a Date object stored in the format of milliseconds after the unix epoch.

Reserved value: /^»[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/

sansa interprets the regular expression /^»[0-9a-f]{8}-[0-9a-f]{4}-4[0-9a-f]{3}-[89ab][0-9a-f]{3}-[0-9a-f]{12}$/ to be a reference to another object.

Identical constructor names

sansa has no special way of telling identically named (but differently scoped) constructors apart. For example, if you have two packages which both define a Point class, each with different constructors, you may need to modify sansa in order to serialize and deserialize your object graphs correctly.

Circular arrays

Object graphs with circular object references aren't a problem for sansa. However, circular array references are difficult to serialize to JSON without some ugly hacks to properly restore them.

var arrayA = [1, 2, 3];
var arrayB = [4, 5, 6];
arrayA[3] = arrayB;
arrayB[3] = arrayA;
var Arya = require('sansa').Arya;
var arya = new Arya();
arya.save(arrayA, mem.output, function(err, uuid) {
    // there will be an error passed here!
});

Attempting to serialize this will result in an error. However the following would be just fine:

var a = { array: [1, 2, 3] };
var b = { array: [4, 5, 6] };
a.array[3] = b;
b.array[3] = a;
var Arya = require('sansa').Arya;
var arya = new Arya();
arya.save(a, mem.output, function(err, uuid) {
    // no error here, just a uuid
});

If you need circular arrays, you'll need to modify sansa to accomodate your objects, or your objects to accomodate sansa.

Development

In order to make modifications to sansa, you'll need to establish a development environment:

git clone https://github.com/blinkdog/sansa.git
cd sansa
./configure
npm install
cake rebuild

Code Coverage

You can see the istanbul coverage report for sansa with a task in the cake file:

cake coverage

This task will attempt to open the coverage report in a new tab in Mozilla Firefox. If you use another browser, you'll need to modify the Cakefile to specify your preferred command for viewing the coverage report.

Source files

The source files are located in src/main/coffee.

The test source files are located in src/test/coffee.

License

sansa
Copyright 2015-2016 Patrick Meade.

This program is free software: you can redistribute it and/or modify it under the terms of the GNU Affero General Public License as published by the Free Software Foundation, either version 3 of the License, or (at your option) any later version.

This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public License for more details.

You should have received a copy of the GNU Affero General Public License along with this program. If not, see http://www.gnu.org/licenses/.