# File lib/rack/etag.rb, line 10
    def call(env)
      status, headers, body = @app.call(env)

      if !headers.has_key?('ETag')
        parts = []
        body.each { |part| parts << part.to_s }
        headers['ETag'] = %("#{Digest::MD5.hexdigest(parts.join(""))}")
        [status, headers, parts]
      else
        [status, headers, body]
      end
    end