3.0.x monkeypatch for fixing Invalid Char 500s

rails_routing_invalid_chars_fix.rb

# Fix for a Rails - Ruby 1.9 bug
# Rails Router, now that it's UTF-8 default, blows up when routing requests
# with invalid chars in the URL; it should properly return a 400 error
# Have to monkey-patch the fix in, since it's not scheduled for release until
# Rails 4.0.
# Adapted Andrew White (pixeltrix)'s fix at 
# https://github.com/rails/rails/commit/3fc561a1f71edf1c2bae695cafa03909d24a5ca3,
# but edited to work in 3.0.x.
# 3.1.x, 3.2.x compatibility unknown
require 'action_dispatch/routing/route_set'

module ActionDispatch
  module Routing
    class RouteSet
      class Dispatcher
        def call_with_invalid_char_handling(env)
          params = env[PARAMETERS_KEY]

          # If any of the path parameters has a invalid encoding then
          # raise since it's likely to trigger errors further on.
          params.each do |key, value|
            if value.is_a?(String) and !value.valid_encoding?
              return [400, {'X-Cascade' => 'pass'}, []]
            end
          end
          call_without_invalid_char_handling(env)
        end

        alias_method_chain :call, :invalid_char_handling
      end
    end
  end
end

My friend @rgarver made a change that will repair the encoding and allow the request to still be served for common encoding problems (eg, extended ascii / windows 1252).

See my fork of this gist to see how it's done.