API version checking using Sinatra's before filter; supports nested resources

gistfile1.rb

require 'sinatra'

# Set the version of the API being run here
#
MAJOR_VERSION = 1
MINOR_VERSION = 0

helpers do
  def version_compatible?(nums)
    return MAJOR_VERSION == nums[0].to_i && MINOR_VERSION >= nums[1].to_i
  end
end

# Enforce compatibility before the call. Rewrite the
# URL in the request to remove the API versioning stuff
#
before %r{/api/v(\d)\.(\d)} do
  if version_compatible?(params[:captures])
    elements = request.fullpath.split('/')
    new_path = ""
    (3..elements.size).each do |i|
      new_path << "/#{elements[i]}"
    end
    request.path_info = new_path
  else
    halt 400, "Version not compatible with this server"
  end
end

# Reach this route using
#   http://localhost:4567/api/vX.Y/hello
#
get '/hello' do
  "Hello there, compatible client."
end

Thanks for spotting that one, I appreciate the feedback! -- In the meantime I had found another approach using regex and post_match that I incorporated into https://github.com/oisin/plink but never updated the gist...