class Rack::ETag

def call(env)
  status, headers, body = @app.call(env)
  headers = Utils::HeaderHash[headers]
  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