run_before_filters

# File actionpack/lib/action_controller/filters.rb, line 585
        def run_before_filters(chain, index, nesting)
          while chain[index]
            filter, index = chain[index], index
            break unless filter # end of call chain reached

            case filter
            when BeforeFilter
              filter.call(self)  # invoke before filter
              index = index.next
              break if @before_filter_chain_aborted
            when AroundFilter
              yielded = false

              filter.call(self) do
                yielded = true
                # all remaining before and around filters will be run in this call
                index = call_filters(chain, index.next, nesting.next)
              end

              halt_filter_chain(filter, :did_not_yield) unless yielded

              break
            else
              break  # no before or around filters left
            end
          end

          index
        end