call (Rack::Deflater)

    # File lib/rack/deflater.rb, line 12
      def call(env)
        status, headers, body = @app.call(env)
        headers = Utils::HeaderHash.new(headers)

        # Skip compressing empty entity body responses and responses with
        # no-transform set.
        if Utils::STATUS_WITH_NO_ENTITY_BODY.include?(status) ||
            headers['Cache-Control'].to_s =~ /\bno-transform\b/
          return [status, headers, body]
        end

        request = Request.new(env)

        encoding = Utils.select_best_encoding(%w(gzip deflate identity),
                                              request.accept_encoding)

        # Set the Vary HTTP header.
        vary = headers["Vary"].to_s.split(",").map { |v| v.strip }
        unless vary.include?("*") || vary.include?("Accept-Encoding")
          headers["Vary"] = vary.push("Accept-Encoding").join(",")
        end

        case encoding
        when "gzip"
          mtime = if headers.key?("Last-Modified")
                    Time.httpdate(headers["Last-Modified"])
                  else
                    Time.now
                  end
          [status,
           headers.merge("Content-Encoding" => "gzip"),
           self.class.gzip(body, mtime)]
        when "deflate"
          [status,
           headers.merge("Content-Encoding" => "deflate"),
           self.class.deflate(body)]
        when "identity"
          [status, headers, body]
        when nil
          message = ["An acceptable encoding for the requested resource #{request.fullpath} could not be found."]
          [406, {"Content-Type" => "text/plain"}, message]
        end
      end