Monday, November 14, 2011

Roboinstaller: Install roboguice dependencies in your device

Yesterday I wrote about a crazy idea of installing your application dependencies in the device to make the builds faster. This is just an example of what's possible.

After yesterday's idea I decided to give it a try and install in my rooted nexus one all the roboguice dependencies to see if my build times improved. To test it out I Manfred Moser's roboguice sample code called: roboguice-calculator.

Mike: I was going to test with the Astroboy roboguice's demo, but I didn't feel like dealing with hg. Plz move roboguice to git :)

To do this I have separated the whole process in steps.

Pre-dexing step

First of all, you need to get a pre-dexed jar files of all the dependencies. You can pre-dex your jar files with the following line:

dx -JXmx1024M -JXms1024M -JXss4M --no-optimize --debug --dex --output=./my_dep_dex.jar my_dep.jar

Creating the permissions XMLs
Once you get all your dependencies pre-dexed, you need to create the permissions XMLs which looks like this:

<library name="my.dependency"
file="/data/data/com.nasatrainedmonkeys.roboinstaller/files/my_dependency_dex.jar" />

Installing the dependencies
After some hacking to the scala-android-libs src code I had the code ready to install dependencies on the device.

Modifying the AndroidManifest
Inside the tag you need to add all your dependencies with the <uses-library> tag. It should look like this:

<uses-library name="my.dependency"/>

Modifying the pom.xml
The last step is setting the scope to provided using provided tag.

Building the ordinary app: Total time: 22.212s

With this hack: Total time: 10.431s

Since mvn doesn't create a jar file with all the dependencies inside, I failed on my first try because the guice dependency needed the javax.inject jar file. I guess there should be a way to create a "fat-jar" with every dependency inside. If that's possible pre-dexing a dependency would be much more easier.

Future work
This has shown the approach is totally useful. Next step is to create an android app that can install pre-dexed files and create the xml without needing to recompile the whole application. This approach would also take me to separate my application into different libraries to develop as fast as possible :)

Source code
I have placed the installer code and the sample application with the modifications in this github repo: Roboinstaller

Installing dependencies on the device

This last two weeks I have been giving it a try to Scala on Android. While learning how to do it, I found something interesting I would like to share.

Developing Android apps using scala

The big problem of developing in Scala is that Android doesn't provide a way to install dependencies on the device. So, if you want to use Scala you need to place the scala's jar in your apk.

Placing the scala jar inside the apk bring another problem, apk size. To fix this, scala developers use proguard to remove all unused classes from the scala jar.

Using proguard to remove unused classes works like charm but it brings a third problem. Compilation time. For me, it takes a whole minute to compile an application with a single Activity coded in scala.

Coding scala in Android is as frustrating as testing android apps :)

While looking for a solution for this, I asked a question in stackoverflow and it was answered by @jberkel. He pointed me to a project called scala-android-libs created by Johannes Rudolph.

What this project does is very interesting. It installs the scala's jars in a rooted device and allows the application to use it through the AndroidManifest tag uses-library.

How does it work?

It creates a serie of XMLs in /system/etc/permissions that look like this:

file="/data/data/" />

This means that if inside the AndroidManifest the app says:

It will be able to use the scala_actors.jar file inside the /data/data/ folder as a dependency.

Since now we have the jar installed in our device, we can avoid the proguard step and the build times are very similar to build an ordinary java app.

Taking it further
Every time I develop an android application I start creating a maven project because I know that I will use certain dependencies. After learning about this approach I thought about leaving my dependencies inside the device.

Why don't extending scala-android-libs approach to provide a way to manage dependencies inside the device to make the build times faster?
Perhaps having an android app that allows to install/remove jar files and automatically generate this XMLs with the proper permissions.

What do you think?
Would you use it?