google_bot_aware.rb

# This Rack middleware helps solving the issue with some Rails versions which do not accept
# a '*/*;q=0.6' and their variants 'Accept' request header. This header is particularly used
# by Google Bot, and if Rails doesn't like it, it will return a 500 or 406 error to Google Bot,
# which is not the best way to get your pages indexed.
#
# References:
#   - http://stackoverflow.com/questions/8881756/googlebot-receiving-missing-template-error-for-an-existing-template
#   - https://github.com/rails/rails/issues/4127
#
class GoogleBotAware
  def initialize(app)
    @app = app
  end

  def call(env)
    # If the request 'Content Accept' header indicates a '*/*' format,
    # we set the format to :html.
    # This is necessary for GoogleBot which requests / with '*/*;q=0.6' for example.
    if env["HTTP_ACCEPT"] =~ /\*\/\*;q=\d\.\d/
      env["HTTP_ACCEPT"].sub!(/\*\/\*;q=\d\.\d/, '*/*')
    end

    @app.call(env)
  end
end

google_bot_aware_spec.rb

# spec/integration/google_bot_aware_spec.rb
#
# This integration test is intended to check if your application is correctly managing
# GoogleBot's requests which may have an Accept header looking like this: '*/*;q=0.6'.
#
# This should be the case if GoogleBotAware Rack middleware is correctly loaded, and is
# correctly behaving.
#
describe "GoogleBot aware" do
  
  ['/', 'add-your-own-paths'].each do |path|

    it "should be successful for a Google-Bot-style request on '#{path}'"  do
      get path, nil, {"HTTP_ACCEPT" => "*/*;q=0.6"}
      response.should be_successful
    end
    
  end
end

rack_middlewares.rb

# config/initializers/rack_middlewares.rb
#
# This initializer configures Rack middlewares and loads custom middlewares.

require File.join(Rails.root, 'lib', 'google_bot_aware')

APP_NAME::Application.configure do
  config.middleware.use("GoogleBotAware")
end