Tuesday, October 28, 2008

Openssl, when checking a digest...

I've been working on my own implementation of SHA-1 hashing function. In the bigger picture I've put together a mostly working OAuth client using Groovy, and part of that is using HMAC-SHA1 to compute a secret value. Well I started by using the built in Java version but decided i would create my own... this is good exercise.

So first thing I did was write some unit tests. I needed SHA1 hashes to start with to make sure that my algorithm implementation works. The obvious choices are either sha1sum or openssl. I'm on a iMac running Leopard, and by default openssl is installed. I used that to compute some hash values. Unfortunately for me I spent a lot of time trying to get my algorithm working when it was already working. The problem was I computed the values wrong with openssl. I used the following:

echo "the quick fox jumps the brown dog" | openssl sha1

Which gave me a incorrect value. Why you ask? Well I didn't remember the -n flag and a newline character was being included in the string passed to openssl. Ooops! Well once I added the -n flag everything was fine and I now have a number of hash values to use in my tests.

Thursday, October 16, 2008

Eclipse, Tomcat, Sysdeo and the DevLoader (and a little Maven)

If you are developing a webapp in Eclipse there is a very good chance you are using Sysdeo. If you are not there is a very good chance you have not yet learned a proper way to debug a Java web application (or maybe you are using Jetty?). Sysdeo is really the only good open source, free Eclipse plugin for developing with Tomcat. It allows a simple way to debug your code in Eclipse while it runs in Tomkitty, a very nice thing.

Now the problem with the plugin out right is your project must be laid out like an exploded war... YUCK! This is because Sysdeo will be looking for the lib files under WEB-INF/lib and such. Often I've seen this lead to some truly horrible project organization, where jsp and Ant build files co-mingle in the same folder!?!

Most of us use a sane Ant or Maven project layout that is standardized across all our Java projects. If you want to continue doing so and leverage the benefits of Sysdeo then you will need the DevLoader installed.

If you haven't downloaded and installed the Sysdeo plugin do so now, I will wait ;)

Go here to get Sysdeo!

Ok once installed you should see 3 icons under the Eclipse menu bar that look very familiar (they are Tomcats!). The first icon starts Tomcat, the second stops it and the third restarts. Now open the Eclipse preferences menu. You should see the "Tomcat" entry. Open it and configure the plugin based on your Tomcat installation. You will want the "Context Declaration mode" to be "context" in my experience. It just makes things a lot cleaner if you use Tomcat for other projects/apps, where they each have individual files rather being crammed in server.xml. That should be about all you need to know. Oh the sub-menu 'Source path' is for adding the source files used in debugging, so make sure your project is in there if you want to be able to see the files while debugging.

Next up the DevLoader. It came with the Sysdeo plugin when you download it! You should find a zip file in the the Sysdeo zip aptly named Devloader.zip. Unzip it. It will create an org folder, within lies some classes. Jar this sucker up:

jar cf devloader.jar org/

This should create a jar for the DevLoader. Now throw this in your Tomcat instance's lib folder.

Great now you have almost everything you need to get started. Lets go over an example of a Maven project being used.

In Maven the webapp files go in src/main/webapp by convention, and sources go in src/main/java, and the resource files (xml, properties) go into src/main/resources. For your Maven project you would right click the project and select properties. You should now notice a 'Tomcat' entry in the config options. Select this.

Enable the "Is a Tomcat Project" checkbox. For the 'context name' use whatever sane value you prefer. Near the bottom area you will want to enter 'src/main/webapp' for the app root. This is where most jsp, html, javascrpt, css and whatnot will be. You will be able to update these and see the result. Now the last thing we need to do is activate the devloader. Here is a picture of what that looks like:

So really all you do is add the jar files needed. Thats it. Now save. If you are not going to create a context file yourself, and you enabled 'can update context definition' in the projects tomcat properties you can right click the project and select "tomcat project > update context definition". This will automatically create the proper context file for Tomcat, so that it uses the DevLoader and your project. You almost certainly will want to do this. Note you can further alter the automatically created context file afterwards.

Monday, October 13, 2008

Sorting using Haskell

Last Friday night I had some fun writing sorts in Haskell. Yes thats right I spent my Friday night working on some rudimentary algorithms in an obscure computer language. Lets just say I'm in to that kinda thing. Oh well it beats being addicted to cough syrup.

So Haskell is fun. There I said it. It is the kinda language which lends much balance to ones style, is one is a imperitive/OO language flunky. The ideas in Haskell seem bizarre at first but become beautiful as they sink in. Sink they do, lets look at the first sort, the almighty BUBBLE SORT

-- Implementation of a bubble sort in Haskell
bubbleSort :: (Ord t) => [t] -> [t] -- signature
bubbleSort a = loop (length a) bubble a

bubble :: (Ord t) => [t] -> [t]
bubble (a:b:c) | a < b = a : bubble (b:c)
| otherwise = b : bubble (a:c)
bubble (a:[]) = [a]
bubble [] = []

loop :: (Num a, Ord a) => a -> (t -> t) -> t -> t
loop num f x | num > 0 = loop (num-1) f x'
| otherwise = x
where x' = f x

I imagine that looks weird. Well it should, if you are unaccustomed to Haskell. The syntax is much different than any OO language. I've had people tell me Python is too weird looking. Well this would just frighten those types of people silly. Lets talk about this code

The first thing to point out is the signature. In leyman's terms this says "take a list of something and return a list of something". The last [t] is going to be what is returned. The '(Ord t)' says that t must be of the typeclass 'Ord' as in 'Ordinality' which is related to being able to compare values. Don't worry too much about that for now, just know it allows us to do things like '>', '<', '==' and so on.

The rest is easy to explain. The bubbleSort function will loop x times, x being the length of the list to be sorted. For a list of 10 elements we loop 10 times. Each time we loop we call bubble. See the loop function takes a number (a) and a function (t -> t), and finally a value (t). What we end up doing here is calling loop again with the number decremented by one. We call bubble on the value, then passing the result right back into bubble IF the number is greater than 0.

This bubble function will go through the list comparing each pair elements, starting with the first and second, and swapping them if the first is greater than the second. This causes the largest value to 'bubble up' to the top of the list.