Ampersand

Moved

James Lim — Sat, 02 Feb 2019 00:00:00 -0800

New content will be available at https://medium.com/@jimjh

Building Elastic Clusters

James Lim — Mon, 04 May 2015 00:00:00 -0700

(Authors: James Lim, Adam Gray)

One of the main advantages of using a cloud provider, such as Amazon Web Services (AWS), is the ability to launch new instances on demand. However, it also means giving up control over physical machines and their retirement schedules; the cloud provider may terminate or …

dragon - an OSS File System for Hadoop

James Lim — Wed, 29 Oct 2014 00:00:00 -0700

OSS is Aliyun’s offering of a distributed, highly available storage service. dragon allows YARN applications (incl. MapReduce jobs) to read and write data to OSS through the HDFS API. This allows you to swap filesystems without modifying your YARN application, MapReduce job, Pig script, Hive script etc.

The source …

Stripe CTF 2014, Level 3 - Instant Code Search

James Lim — Sun, 06 Apr 2014 00:00:00 -0700

The task was to write, in Scala:

an indexer that scans a bunch of input files, and
a searcher that takes a query string and returns a list of lines containing it

It can be solved using the following:

In the indexer, tokenize each document, and create an inverted index …

Stripe CTF 2014, Level 2 - Defending against a DDOS attack

James Lim — Sun, 30 Mar 2014 00:00:00 -0700

If your service comes under a major DDOS attack, what would you do?

In the third level of Stripe’s CTF, participants were tasked to build a proxy to defend a couple of backend servers against a DDOS attack. The proxy needed to do the following:

distribute requests across a …

Stripe CTF 2014, Level 1

James Lim — Sat, 08 Mar 2014 00:00:00 -0800

This is the second installment of a series on Stripe's CTF 2014. You may wish to start from level 0.

Level 1

Level 1 proposed a crypto-currency named Gitcoin that used Git's SHA1 hashes. The player was provided with a git repository and asked to create a commit with a …

Stripe CTF 2014, Level 0

James Lim — Sun, 23 Feb 2014 00:00:00 -0800

I participated in a week-long CTF hosted by Stripe in Jan 2014. This series of blog posts will cover some of the problems and their solutions.

Level 0

The first level was a breeze, and mainly served as an introduction/tutorial for participating in the CTF. We were given the …

How to Create a Websocket Server in Ruby

James Lim — Wed, 21 Aug 2013 00:00:00 -0700

This is a short tutorial on creating a websocket server in Ruby using James Coglan's websocket driver. The complete example is available on github.

About Websocket Driver

The websocket-driver gem decouples the websocket protocol from the I/O layer, providing drivers that handle the websocket procotol (handshakes, upgrades etc) on …

Thoughts from Reading Code - Foreman and Pipes

James Lim — Mon, 12 Aug 2013 00:00:00 -0700

Using Pipes for Cheap IPC

A UNIX pipe is a unidirectional interprocess communication channel with a read end and a write end. You have probably used pipes in the command line. For example,

$ git ls-files | xargs grep foo

This executes both commands concurrently and creates a pipe for interprocess communication …

Thoughts from Reading Code - Foreman

James Lim — Tue, 30 Jul 2013 00:00:00 -0700

I read a lot of open source code in my free time to make myself a better engineer. Here are some of my notes from reading foreman's cli.rb.

Code Style - Raising Exceptions with a Bang

You might occasionally encounter code that looks like this:

def start(process=nil)
  raise …

Introducing Verbal, a Ruby Gem

James Lim — Sat, 27 Jul 2013 00:00:00 -0700

I recently released Verbal, a ruby gem that provides a fluent DSL for creating regular expressions. It's a fork of jehna's popular VerbalExpressions javascript library. Detailed documentation and code examples are available at rubydoc.info.

To create a regular expression that matches http, https, ftp, and sftp, one can use …

Event Tracking with Google Analytics and LaunchRock

James Lim — Fri, 19 Jul 2013 00:00:00 -0700

It's easy to create a landing page with LaunchRock, but getting meaningful analytics out of it is more difficult. For example, I still have not figured out a way to run a Google Analytics experiment on LaunchRock - using custom Javascript code in LaunchRock sometimes crashes the previewer, forcing me to …

Making Conditional Requests with Peter Murach's gem

James Lim — Fri, 19 Jul 2013 00:00:00 -0700

GitHub imposes a rate limit on API requests, and encourages developers to use conditional requests. Here is how to do that using Peter's popular github api gem.

Method A - Faraday HTTP Cache w. ActiveSupport::Cache

This uses the faraday-http-cache gem, which takes care of expiration, etags, and response statuses.

Method …

jQuery Plugin - Box Lid Menu

James Lim — Thu, 11 Jul 2013 00:00:00 -0700

Smashing Magazine wrote a piece about Toybox's navigation menu today, describing the user experience as "peeking behind the page or the lid of a toybox". I really liked the design, took a shot at creating a jQuery plugin to replicate the effect. Here is a demo.

Most of the …

A Short Tutorial on Custom Storyboard Segues

James Lim — Mon, 01 Jul 2013 00:00:00 -0700

This is a repost from my old blog.

We will use the last tutorial as a base to learn how to use custom segues.

Suppose you don't want to push between view controllers. In particular, suppose you want first view controller to flip to the second view controller. To achieve …

Compiling open source libraries with Android NDK: Part 2

James Lim — Mon, 01 Jul 2013 00:00:00 -0700

This is a repost from my old blog.

For the second part of this series, we will deal with the compiling of open source libraries that have several makefiles.

Android NDK r5 added support for prebuilt libraries and also included standalone toolchains that could be used to compile open-source libraries …

Implementing a Singleton in iOS

James Lim — Mon, 01 Jul 2013 00:00:00 -0700

This is a repost from my old blog.

While I was at Apple’s Cocoa Camp over summer, one of the speakers talked rather passionately about the proper, thread-safe way to implement a singleton in iOS, which I thought deserves more attention than it currently does on the Web.

The …

Using Karma with Rails and Jenkins: Part 1

James Lim — Mon, 01 Jul 2013 00:00:00 -0700

In a recent project, I experimented with AngularJS on Rails, and managed to get Karma to work nicely with Jenkins on CloudBees. This post documents the steps I took. (Part 2 will cover e2e tests, if I get that sorted out.)

An example project is available on GitHub.

Setup

First …

Playing with Stripe CTF

James Lim — Fri, 21 Jun 2013 00:00:00 -0700

I was playing around with Stripe's source code for last year's CTF, and from what I could see online, most people solved Level 4 by using XSS in the password field. But look at the following line in srv.rb:

unless username =~ /^\w+$/
  ie("Invalid username. Usernames must match /^\w …

Experimenting with Git Hooks

James Lim — Mon, 17 Jun 2013 00:00:00 -0700

I have been trying to follow a more disciplined approach to branching in my projects to allow easier tracking and regression. For example, I learnt that it's a good idea to prefix branch names with category tokens, such as feature/, bug/, or chore/. This allows us to use wildcards when …

Deployment is Scary - Part 2

James Lim — Fri, 24 May 2013 00:00:00 -0700

The is the second installation of a series of posts about my deployment experiences with Enteract. Part 1 is available here.

In this post, I will focus on our use of Faraday and Upstart for some simple monitoring.

Faraday

We wanted a tool to monitor the web application and notify …

Predicting User Ratings on Yelp

James Lim — Tue, 14 May 2013 00:00:00 -0700

Several weeks ago, Yelp launched a dataset challenge and released data on their users and businesses in Phoenix, AZ. The challenge shared some similarities with the Netflix Prize, and I was curious to see if the Alternating Least Squares algorithm that I used for my Netflix project was versatile enough …

Deployment is Scary - Part 1

James Lim — Sun, 12 May 2013 00:00:00 -0700

As part of a class project, I was given the opportunity to field a Rails application at Spring Carnival, an annual event held by Carnegie Mellon University (official press release.) Here, I will describe a subset of the risk mitigation strategies that we used to avoid hacking and maximize uptime …

Numbering the Last Line of Align* in LaTex

James Lim — Sat, 30 Mar 2013 00:00:00 -0700

On numerous occasions, I find myself trying to number the last line (and only the last line!) of a long series of derivations in an align* environment. I usually switch to the align environment and use \notag to turn off the number on each line except the last.

There is …

Some Custom Matchers for RSpec with Shoulda

James Lim — Thu, 28 Mar 2013 00:00:00 -0700

It should have a valid factory

I use Factory Girl in my tests, and I have found it useful to check that I have valid factories for each model in my tests/specs. Here is a matcher you can use for that purpose.

Add this file to spec/support. Then …

Deploying a Thrift Server with Capistrano

James Lim — Wed, 20 Mar 2013 00:00:00 -0700

At the time of writing, I couldn't find an existing Capistrano recipe for deploying thrift servers. So here is an example that works with ubuntu.

Before you use the recipe, don't forget to update the configuration options to match your server setup. At the very least, you will need to …

Monopoly Heat Map

James Lim — Mon, 19 Nov 2012 00:00:00 -0800

I am working on a Monopoly manual for my professional writing class, and did a heat map showing the relative probabilities of landing on each square of the Monopoly board. It's done using canvas on HTML5.

Here is a preview:

Check it out here.

Passwordless Kerberized SSH for CMU's UNIX machines

James Lim — Thu, 08 Nov 2012 00:00:00 -0800

If you use SSH frequently to access unix.andrew.cmu.edu, you must have tried at some point to set up passwordless login using public/private keys. That didn't work for me, and when I did ssh -vv unix.andrew.cmu.edu, it always failed at

debug2: we did not …

Backbone, Faye, and Reaction

James Lim — Fri, 02 Nov 2012 00:00:00 -0700

I was jealous of what MeteorJS did for NodeJS developers, and decided to steal some of their ideas for Rails. The result is the reaction gem, and a demo app can be downloaded from here.

Transparent Synchronization

Using Reaction, you write your app like a usual Backbone app. However, instead …

Hello world

James Lim — Wed, 24 Oct 2012 00:00:00 -0700

This is my first blog post using Pelican.

I first tried using Wordpress, then migrated to Tumblr. Hope this works better! Old posts are still accessible at tumblr. This one is starting anew.