An alternate title for this post could be: How to run non Ruby executable from a gem, or How to wrap a C executable, in a Node module, then wrap it again in a Ruby gem, but seriously it should be: How to do something not very smart.

In one of my client projects we are running acceptance tests using Calabash. The process is quite smooth but there is a bottle neck: if you want to run the tests on a device you need to install the latest build embedding the Calabash server manually.

This is quite annoying, and because of the manual labour involved is not really portable in a CI environment.

Lucky enough the PhoneGap community has a tool called ios-deploy that enables the deploy of an ipa to a connected device from the command line. As a note: ios-deploy is a fork of an older project called fruitstrap that is no longer maintained but still pops up when googling something like “run on device from command line”.

Being PhoneGap a Javascript community ios-deploy is distributed via npm. Now, I love Node.js, and io.js, but the usual iOS project already has to deal with a Podfile, and if you want to handle your CocoaPod version properly a Gemfile too. Adding a package.json would be too much.

So what I did is packaging the ios-deploy node module into a gem. It all was possible because what the module actually does is packaging an executable file, generated from a C source.

This sounds awful, and it is awful, and you should think twice before doing it. But let’s go on for the sake of sharing the experience…

After generating the gem scaffold with bundle gem ios-deploy, and npm install ios-deploy, my first step has bee to create the bin folder a naively simlinking the executable there.

This of course didn’t work, the error I got was:

invalid multibyte char (UTF-8) (SyntaxError)

Which is an error a lot of people used to get before Ruby 2, and happens when the file is missing the encoding definition.

Of course! We’re talking about Ruby gems here, and the executable in the bin folder has to be a ruby file.

The second step then was to create a very simple Ruby file that simply runs the executable form the node_modules/ios-deploy folder:

absolute_pwd = File.expand_path(File.dirname(__FILE__))
exec "#{absolute_pwd}/../node_modules/ios-deploy/ios-deploy"

This worked fine, but when running something like ios-deploy --list the list option wasn’t passed to ios-deploy. The reason is simple, the options are passed to the Ruby executable, not to the real one.

The fix for this was to pass down the options to the ios-deploy invocation made with exec, and this is one way to do it:

absolute_pwd = File.expand_path(File.dirname(__FILE__))
command = "#{absolute_pwd}/../node_modules/ios-deploy/ios-deploy"
ARGV.each do |parameter|
  command += " #{parameter}"
exec command

That’s it folks, how to wrap in a Ruby gem a Node module that wraps a C executable.

If you’re curious about this the gem is acutally published, and you can find it here.

Food for thoughts

  • Instead of writing dirty stuff like this, wouldn’t it be better if ios-deploy was distributed via homebrew?
  • Can the code be written in a better way? I don’t think exec is the best way to run shell commands from a Ruby script.