Executing ruby script before rails gets loaded

rubyonrails-talk
1

I have a ruby script which instruments Net::HTTP requests in Rails applications. This works as follows: When Ruby loads the Net::HTTP class, I alias the request method. At every http request, my instrumented method gets executed. So that this works, I need to execute my script BEFORE ruby loads the standard library and BEFORE Rails gets loaded. So I need the earliest possible point in Rails where I can require my instrumentation script.

I tried the following locations:

  • config/preinitializer.rb → too late because Net::HTTP got already loaded
  • config/application.rb → also too late for the same reason
  • I put my instrumentation script at the top of the Gemfile. So that my Gemfile looks like this:

require “myinstrumentationscript” source ‘https://rubygems.org’

Bundle edge Rails instead: gem ‘rails’, github: ‘rails/rails’

gem ‘rails’, ‘4.1.1’

Use sqlite3 as the database for Active Record

gem ‘sqlite3’

Use SCSS for stylesheets

gem ‘sass-rails’, ‘~> 4.0.3’

Use Uglifier as compressor for JavaScript assets

gem ‘uglifier’, ‘>= 1.3.0’

Use CoffeeScript for .js.coffee assets and views

gem ‘coffee-rails’, ‘~> 4.0.0’

This solution works not bad, but has some drawbacks:

  • When I do “bundle install” or “bundle update” my script gets executed. But I want my script only run before Rails gets initialized.
  • The bigger problem: This solution seems only to work in Rails 4. I get at least a Gemfile error in Rails 2. So I need another location where I can load my instrumentation script.

Any help is very appreciated.

2

Martin Ennemoser wrote in post #1154169:

I have a ruby script which instruments Net::HTTP requests in Rails applications. This works as follows: When Ruby loads the Net::HTTP class, I alias the request method. At every http request, my instrumented method gets executed. So that this works, I need to execute my script BEFORE ruby loads the standard library and BEFORE Rails gets loaded. So I need the earliest possible point in Rails where I can require my instrumentation script.

Sound to me like you need to make your own Rack middleware and insert it into the stack in the appropriate place.

3

Why do you need to load before Net::HTTP? If you use something like alias_method_chain, you can inject your wrapper after-the-fact.

Hard to troubleshoot much farther without seeing how you’re hooking into Net::HTTP.

–Matt Jones

4

alias_method_chain seems very interesting. I will have a look at it, thanks.