Blog Persevere

Patr: Promise-based Asynchronous Test Runner

By on September 21, 2010 12:01 am

Patr (Promise-based Asynchronous Test Runner) is a simple lightweight cross-platform test runner for promised-based applications. Patr executes tests by simply executing functions of an object and is intended to be used in combination with the “assert” module (which is available on NodeJS and Narwhal), so tests can be as simple as:

var assert = require("assert");
tests = {
  testSomething: function(){
    assert.eq(3, 3);


By on September 20, 2010 12:24 am

Promises are a well-established mechanism for modeling future or asynchronous actions. Promises allow asynchronicity while maintaining the core programming principles of composability and encapsulation. Writing asynchronous code in JavaScript can often be a confusing exercise due to the extensive need for callbacks, but promises help to define composable units of asynchronicity to encapsulate actions and reliably separate caller and callee’s concerns.


Promised-IO utilizes promises as an abstraction for I/O operations on top of Node, Narwhal/Rhino, and the browser (where possible). This serves two purposes. First, this package provides the benefits of promise usage: clean separation of concerns and proper encapsulation of eventual values. Second, Promised-IO provides a consistent normalized interface for I/O that will work on multiple platforms without sacrificing any of the advantages of asynchronous I/O, making it easy to build modules that can be used by developers on many platforms.

Nodules: Better Module/Package Handling for Node.js

By on September 15, 2010 5:25 am

Nodules is a module loader for Node that provides a powerful set of features for application development and distribution. Nodules was written to solve the two major missing pieces of functionality I needed for efficient application development: flexible dependency resolution and module reloading. Nodules runs on top of Node’s simple base module loader, and nicely compliments the base loader with additional functionality. Furthermore, it provides this functionality using idiomatic asynchronous techniques, a smart package layout, and powerful module reloading.

Real-time Comet Applications on Node with Tunguska

By on July 19, 2010 4:34 am

Node is a server-side JavaScript platform that is known for being well suited for Comet-style applications that utilize long-lived connections to allow applications to send messages from the server to the browser asynchronously. In fact, the beginning of the front page of starts out with an example of a web application that delays for a couple seconds before sending a response without any type of blocking; the code is asynchronous and efficient.

However, building a real-life real-time application involves more than just a platform that gives you asynchronous communication, there are a number of other important techniques to understand. We will look at these techniques and introduce project Tunguska that provides some helpful tools to assist in building applications. While a number of Comet projects out there attempt to provide a black box solution to Comet, Tunguska recognizes that most real-time applications involve deep integration into the application and its security, messaging, and data structures. Consequently Tunguska is a set of tools for building real-time applications rather than a closed black box that can’t easily be integrated with. Let’s look at some of these tools.

Asynchronous CommonJS Modules for the Browser (and Introducing Transporter)

By on July 16, 2010 12:15 am

Modules are an integral architectural piece of robust application development since they allow individual components to be developed with proper dependency management. Modules can specify dependencies and these can be automatically resolved and loaded to bring various pieces together automatically. In application development this is vastly more scalable and easier than having to track all the different dependencies and manually load modules or insert script tags.

The CommonJS module format is increasingly ubiquitous as the de facto module format for JavaScript. However, if CommonJS modules, by themselves, are directly executed, they require synchronous loading of modules. Synchronous loading is known to be very problematic in the browser since it locks the browser user interface, requires eval-based compilation of scripts which confuses debuggers, and is less efficient than using standard script tags.

Multi-node: Concurrent NodeJS HTTP Server

By on July 14, 2010 9:55 am

NodeJS has demonstrated impressive performance potential as an HTTP server. By combining highly optimized HTTP parsing algorithms with the speedy V8 JavaScript engine and using an event-based architecture, Node has posted eye-opening request handling numbers. However, Node historically has been limited by its inability to provide true concurrent request handling, greatly limiting its ability to leverage increasingly multiple core servers. The latest release of Node introduced new functionality for socket sharing that can be coupled with child process spawning to achieve concurrent multi-process request handling for a single TCP socket. Multi-node exists to leverage this capability to make it simple to start up a multi-process Node server.

JSGI vs Connect for Node Middleware

By on June 11, 2010 4:08 pm

JSGI (JavaScript gateway interface) is the broadly adopted standard for server-side JavaScript web applications and middleware. JSGI is designed specifically for ease of use in asynchronous, evented environments, and consequently JSGI has been a perfect fit building applications on Node. JSGI-Node has existed for sometime as lightweight JSGI server/adapter for running JSGI-based applications on Node. However, “Connect” was recently released as a new alternate middleware system for Node. This spurred me to make sure JSGI-Node was optimized, and compare the Connect middleware design to JSGI.

NoSQL Architecture

By on May 11, 2010 12:03 am

The NoSQL movement continues to gain momentum as developers continue to grow weary of traditional SQL based database management and look for advancements in storage technology. A recent article provided a great roundup of some of the great new technologies in this area, particularly focusing on the different approaches to replication and partitioning. There are excellent new technologies available, but using a NoSQL database is not just a straight substitute for a SQL server. NoSQL changes the rules in many ways, and using a NoSQL database is best accompanied by a corresponding change in application architecture.

The NoSQL database approach is characterized by a move away from the complexity of SQL based servers. The logic of validation, access control, mapping querieable indexed data, correlating related data, conflict resolution, maintaining integrity constraints, and triggered procedures is moved out of the database layer. This enables NoSQL database engines to focus on exceptional performance and scalability. Of course, these fundamental data concerns of an application don’t go away, but rather must move to a programmatic layer. One of the key advantages of the NoSQL-driven architecture is that this logic can now be codified in our own familiar, powerful, flexible turing-complete programming languages, rather than relying on the vast assortment of complex APIs and languages in a SQL server (data column, definitions, queries, stored procedures, etc).

Resource Oriented Programming

By on May 9, 2010 12:07 am

The REST architecture has become increasingly recognized for its value in creating scalable, loosely coupled systems. REST is presented as a network interaction architectural style, not a programming methodology. However, the principles of REST can actually be very meaningfully and beneficially applied in the programming realm. We will look at how the resource oriented approach of REST can be applied as principles for programming language usage and design. The motivation for looking at REST should be clear. Little in history has been as ridiculously successful and scalable as the web, and REST is a retrospective look at the principles that were employed in designing the core technologies of the web, particularly HTTP. Applying such proven principles to our application design will certainly be beneficial.

Roy Fielding‘s REST architecture is broken down into seven constraints (and the four sub-constraints of the uniform interface). The individual concepts here are certainly not new, but collectively looking at these concepts as resource oriented programming may provide an interesting new perspective. I will also look at how these principles are exemplified in Persevere 2.0 in its object store framework, Perstore, and its web stack Pintura.

Object Capability Model and Facets in Persevere

By on March 8, 2010 12:06 am

The object capability model is an approach to security that utilizes object references as the primary means of controlling access and providing authority. Capability-based security follows the principle of using unforgeable capabilities to provide access to resources. Object capability builds on capability-based security by leveraging object references as the primary representation of capabilities, which are naturally unforgeable in memory safe languages. Object capability based security is an elegant approach to security because the goals of object-oriented principles of encapsulation and information hiding are realized in virtually the same exact manner as the principle of least authority that is at the heart of object capability security. This type of security is extremely flexible and customizable since it is based on object-oriented design. Plus, writing good code naturally leads to secure code, security can be designed with object encapsulation hand-in-hand.