from_file_by_path (Gem::Format)

    # File lib/rubygems/format.rb, line 37
      def self.from_file_by_path(file_path, security_policy = nil)
        format = nil

        unless File.exist?(file_path)
          raise Gem::Exception, "Cannot load gem at [#{file_path}] in #{Dir.pwd}"
        end

        # check for old version gem
        if File.read(file_path, 20).include?("MD5SUM =")
          require 'rubygems/old_format'

          format = Gem::OldFormat.from_file_by_path(file_path)
        else
          open file_path, Gem.binary_mode do |io|
            format = from_io io, file_path, security_policy
          end
        end

        return format
      end