force.rb

class UnicodeEnforcer
  def new(app)
    @app = app
  end
  
  def call(env)
    return @app.call(env) unless env["Content-Type"] =~ "utf-8"
    req = Rack::Request.new(env)
    req.params = force_encoding(req.params)
    @app.call(env)
  end
  
  def force_encoding(on)
    case on
      when String
        on.force_encoding(Encoding::UTF8)
      when Array
        on.map(&method(:force_encoding))
      when Hash
        on.inject({}) do | n, (k, v) |
          n.merge(force_encoding(k) => force_encoding(v))
        end
      else
        on
    end
  end
end