# File lib/rack/etag.rb, line 23
    def call(env)
      status, headers, body = @app.call(env)

      if etag_status?(status) && etag_body?(body) && !skip_caching?(headers)
        original_body = body
        digest, new_body = digest_body(body)
        body = Rack::BodyProxy.new(new_body) do
          original_body.close if original_body.respond_to?(:close)
        end
        headers[ETAG_STRING] = %(W/"#{digest}") if digest
      end

      unless headers[CACHE_CONTROL]
        if digest
          headers[CACHE_CONTROL] = @cache_control if @cache_control
        else
          headers[CACHE_CONTROL] = @no_cache_control if @no_cache_control
        end
      end

      [status, headers, body]
    end