open_uri_or_path (Gem::RemoteFetcher)

    # File lib/rubygems/remote_fetcher.rb, line 255
      def open_uri_or_path(uri, last_modified = nil, head = false, depth = 0)
        raise "block is dead" if block_given?

        uri = URI.parse uri unless URI::Generic === uri

        # This check is redundant unless Gem::RemoteFetcher is likely
        # to be used directly, since the scheme is checked elsewhere.
        # - Daniel Berger
        unless ['http', 'https', 'file'].include?(uri.scheme)
         raise ArgumentError, 'uri scheme is invalid'
        end

        if uri.scheme == 'file'
          path = uri.path

          # Deal with leading slash on Windows paths
          if path[0].chr == '/' && path[1].chr =~ /[a-zA-Z]/ && path[2].chr == ':'
             path = path[1..-1]
          end

          return Gem.read_binary(path)
        end

        fetch_type = head ? Net::HTTP::Head : Net::HTTP::Get
        response   = request uri, fetch_type, last_modified

        case response
        when Net::HTTPOK, Net::HTTPNotModified then
          head ? response : response.body
        when Net::HTTPMovedPermanently, Net::HTTPFound, Net::HTTPSeeOther,
             Net::HTTPTemporaryRedirect then
          raise FetchError.new('too many redirects', uri) if depth > 10

          open_uri_or_path(response['Location'], last_modified, head, depth + 1)
        else
          raise FetchError.new("bad response #{response.message} #{response.code}", uri)
        end
      end