數據緩存 · HTTP 接口設計指北

## 數據緩存大部分接口應該在響應頭中攜帶?`Last-Modified`,?`ETag`,?`Vary`,?`Date`?信息，客戶端可以在隨后請求這些資源的時候，在請求頭中使用?`If-Modified-Since`,?`If-None-Match`?等請求頭來確認資源是否經過修改。如果資源沒有進行過修改，那么就可以響應?`304 Not Modified`?并且不在響應實體中返回任何內容。 ~~~ $ curl -i http://api.example.com/#{RESOURCE_URI} HTTP/1.1 200 OK Cache-Control: public, max-age=60 Date: Thu, 05 Jul 2012 15:31:30 GMT Vary: Accept, Authorization ETag: "644b5b0155e6404a9cc4bd9d8b1ae730" Last-Modified: Thu, 05 Jul 2012 15:31:30 GMT Content ~~~ ~~~ $ curl -i http://api.example.com/#{RESOURCE_URI} -H "If-Modified-Since: Thu, 05 Jul 2012 15:31:30 GMT" HTTP/1.1 304 Not Modified Cache-Control: public, max-age=60 Date: Thu, 05 Jul 2012 15:31:45 GMT Vary: Accept, Authorization Last-Modified: Thu, 05 Jul 2012 15:31:30 GMT ~~~ ~~~ $ curl -i http://api.example.com/#{RESOURCE_URI} -H 'If-None-Match: "644b5b0155e6404a9cc4bd9d8b1ae730"' HTTP/1.1 304 Not Modified Cache-Control: public, max-age=60 Date: Thu, 05 Jul 2012 15:31:55 GMT Vary: Accept, Authorization ETag: "644b5b0155e6404a9cc4bd9d8b1ae730" Last-Modified: Thu, 05 Jul 2012 15:31:30 GMT ~~~ 相關資料： * [RFC 7232](http://tools.ietf.org/html/rfc7232) * [HTTP 緩存 - Google Developers](https://developers.google.com/web/fundamentals/performance/optimizing-content-efficiency/http-caching?hl=zh-cn) * [RFC 2616 中緩存過期時間的算法](http://tools.ietf.org/html/rfc2616#section-13.2.3),?[MDN 版](https://developer.mozilla.org/en-US/docs/Web/HTTP/Caching_FAQ),?[中文版](http://blog.csdn.net/woxueliuyun/article/details/41077671) * [HTTP 協議中 Vary 的一些研究](https://www.imququ.com/post/vary-header-in-http.html) * [Cache Control 與 ETag](https://blog.othree.net/log/2012/12/22/cache-control-and-etag/)