Groovy scripts and JVM Security

Posted March 24, 2010, under Technology
2 comments

Groovy is a very cool dynamic language for the JVM. Because it runs on the JVM, it also has the great security features as well.

Let’s see how we can run trusted code and allow a dynamic (possibly user defined) script to execute with limited permissions. We will also see how the script can call functions in our trusted code and how we can elevate privileges to allow the untrusted script to get access to trusted data.

Setting up a security policy

We are going to create a java policy file that gives our script and groovy full access, but no permissions for our untrusted scripts

~/.java.policy

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grant codeBase "file:/Users/chris/securegroovy/trusted.groovy" {
  permission java.security.AllPermission;
};

grant codeBase "file:${groovy.home}/-" {
    permission java.security.AllPermission;
};

grant codeBase "file:/restrictedScript" {

};

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Getting started with Scala using SBT

Posted February 10, 2010, under Technology
3 comments

One of my biggest gripes with Java (and all the languages that run on the JVM) is getting my project setup and building it. Maven is not my favorite, and ant..well..I don’t like it either. Fortunately, if you want to start a new project in Scala, there is a great build tool available that takes a lot of the pain out of project management and building – SBT, simple-build-tool.

sbt is a simple build tool for Scala projects that aims to do the basics well. It requires Java 1.5 or later.

Installing SBT

I’m using Mac OS X, but the following instructions should be pretty much the same on any Unix based OS.

You can find the latest version of SBT here.

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cd ~
wget http://simple-build-tool.googlecode.com/files/sbt-launcher-0.5.6.jar
sudo mv sbt-launcher-0.5.6.jar /usr/local/bin/sbt-launcher.jar
echo "java -Xmx512M -jar /usr/local/bin/sbt-launcher.jar \"\$@\"" | sudo tee /usr/local/bin/sbt
sudo chmod +x /usr/local/bin/sbt

This will install the SBT jar and create a script called sbt that will allow you to run the sbt jar.

Just type sbt and press enter, and you now have access to sbt.

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$ sbt
Project does not exist, create new project? (y/N/s) : n

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AjaxTask – a rails plugin for managing background tasks

Posted February 9, 2010, under Technology
One comment

SOAP, Background Tasks, and AJAX

Recently in Rails I’ve been interacting with various SOAP services and running them in the background with Workling. I needed to relay the SOAP response to the client’s web browser, so I decided to use AJAX to poll the status of my background tasks.

This is great if you have < 30 second background tasks running, but don't want to block a user (and a request).

The Solution

I created a Rails plugin, called AjaxTask, that has two components:

  • Methods to use in your controller to define a task handler and create tasks
  • Javascript library to manage the AJAX between the browser and the handler.

GitHub Link: http://github.com/chrismoos/ajaxtask

In a nutshell, the client initiates a task, the handler responds with a task ID, and the client polls at a user defined interval until the task has finished, or has an error.

The plugin takes the pain out of implementing the handler, as well as the Javascript. All you have to do is run code for your task, and periodically update the status.

I am using Workling to run my background tasks, as well as maintain the status using Workling’s return store.

Okay, enough with the intro, here is the example.

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MySQL and partitioning tables with millions of rows

Posted January 31, 2010, under moostrax, Technology
7 comments

The Problem

I’ve been running a mobile GPS tracking service, MoosTrax (formerly BlackBerry Tracker), for a few years and have encountered a large amount of data in the process.

A user’s phone sends its location to the server and it is stored in a MySQL database. Each “location” entry is stored as a single row in a table.

Right now there are approximately 12 million rows in the location table, and things are getting slow now, as a full table scan can take ~3-4 minutes on my limited hardware. This means that if a user is pulling a location from history it could potentially block all other users (as the table is locked) access to the site until the query is complete.

Partitioning

Partitioning allows you to store parts of your table in their own logical space. With partitioning, you want to divide up your rows based on how you access them. If you partition your rows and you are still hitting all the partitions, it does you no good. The goal is that when you query, you will only have to look at a subset of the data to get a result, and not the whole table.

There are various ways in MySQL to partition a database, such as:

  • RANGE – rows are partitioned based on the range of a column (i.e date, 2006-2007, 2007-20008, etc,.)
  • HASH – hashes a column and depending on the result of the hash, has a different partition
  • LIST, KEY

Choosing the partition type is important, so I looked at how my application looks up a user’s location.

Getting a user’s current location

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Location.find(:all, :conditions => {:device_id => @device.id}, :order => "date_added desc", :limit => 6)

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Why I didn’t like Java 5 years ago, and why I don’t like it now

Posted December 7, 2009, under Technology
No comments yet

Update 2011 – Reading this post bothers me, as I’m using Java a lot now and can’t complain at all! I can say that I’ve worked on some pretty bad Java projects that may have given me a bad taste for the language. Java is an excellent language and I have only good things to say about it now (for the most part!).

Then

I started out programming in C, which taught me a lot about the fundamentals of computer science. I learned about types, memory management, functions, and logic. As I began to evaluate other programming languages to try out, I of course ended up trying Java. My first impression of it was how heavy it felt. Of course, this was when 4GB of memory wasn’t standard in a desktop, and memory allocations and processing power — were still relatively precious.

I remember trying out Swing and that only made me more disgusted with Java, as a Swing application felt horribly slow.

Java users don’t have to worry about memory management (technically), as the garbage collection system takes care of it for the user. I think this was a huge benefit for novice developers, because dealing with memory management definitely isn’t fun — and usually presents issues if not done properly.

The next thing I tried in Java was creating a web application. I bought a book on J2EE and as I began learning the ins and outs, I began to hate it with a passion. The amount of configuration and boiler plate code to get something simple up and running, was a huge turn off to me. I was disgusted with the concept of EJBs and all the various patterns in J2EE.

After a short while, J2EE was gone with the wind for me. I moved on to scripting languages, such as the notoriously shitty PHP, which was still in my opinion, more practical than Java…but I wouldn’t settle on a good web framework and language until Python and Ruby really caught my eye.

Now

Flash forward to today…and I’m still not liking Java.

It is still plagued with lots of configuration, descriptors, assembly, and boiler plate code. And now that memory is relatively cheap and available, Java still eats it like a fat boy eating at McDonalds. PermGen errors, anyone? The JVM has moved forward a lot in the past years, but its still a memory hog, and I feel like it abstracts so much low level coding that developers tend to not pay attention to the performance of a system — just throw more hardware at the JVM.

My productivity in Java is much lower than most other languages — even C. When building enterprise software in Java the complexity of getting it setup and going seems like too much at times.

DAO’s, interfaces, implementations, proxies — its just boring to me.

Ever used a BlackBerry? It feels slow to me…and I bet if it was coded in C it would be a lot snappier…same goes for Android. I’m currently using an iPhone now and it definitely feels the most repsonsive out of all 3.

What do you think about Java? Any recommendations on feeling more productive and not slowed down?

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