    # File lib/rack/deflater.rb, line 34
        def call(env)
          status, headers, body = @app.call(env)
          headers = Utils::HeaderHash.new(headers)

          unless should_deflate?(env, status, headers, body)
            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"
            headers['Content-Encoding'] = "gzip"
            headers.delete(CONTENT_LENGTH)
            mtime = headers.key?("Last-Modified") ?
              Time.httpdate(headers["Last-Modified"]) : Time.now
            [status, headers, GzipStream.new(body, mtime)]
          when "deflate"
            headers['Content-Encoding'] = "deflate"
            headers.delete(CONTENT_LENGTH)
            [status, headers, DeflateStream.new(body)]
          when "identity"
            [status, headers, body]
          when nil
            message = "An acceptable encoding for the requested resource #{request.fullpath} could not be found."
            bp = Rack::BodyProxy.new([message]) { body.close if body.respond_to?(:close) }
            [406, {CONTENT_TYPE => "text/plain", CONTENT_LENGTH => message.length.to_s}, bp]
          end
        end