Executing ruby script before rails gets loaded

[Martin Ennemoser]

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.

 

 

[Robert Walker]

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.

http://guides.rubyonrails.org/rails_on_rack.html

--
Posted via http://www.ruby-forum.com/.

[Matt Jones]

On Monday, 4 August 2014 08:57:19 UTC-4, Martin Ennemoser wrote:

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.

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

[Martin Ennemoser]

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