HTTP Caching

HTTP Caching
http://railscasts.com/episodes/321-http-caching?view=asciicast

這篇來講說在rails 上實作HTTP Caching的機制

首先可以用 curl這個命令來看到說request後respond了什麼

terminal

$ curl -I http://localhost:3000/
HTTP/1.1 200 OK 
Content-Type: text/html; charset=utf-8
X-Ua-Compatible: IE=Edge
Etag: "d3132af4f574ff53eb69e6fa5523fe2a"
Cache-Control: max-age=0, private, must-revalidate
X-Request-Id: 2cb31eeec2b1beda8e1342f8caa90acd
X-Runtime: 0.018216
Content-Length: 0
Server: WEBrick/1.3.1 (Ruby/1.9.2/2011-07-09)
Date: Fri, 03 Feb 2012 21:09:22 GMT
Connection: Keep-Alive
Set-Cookie: _store_session=BAh7B0kiD3Nlc3Npb25faWQGOgZFRkkiJWQ2N2U5MGEwMWZhNGU4ZTI2NzIxOTYxOWE1ODYyNzcxBjsAVEkiEF9j

這邊要看的有幾個
1.Etag
2.Last-Modified
3.Cache-Control

Cache-Control: max-age=0, private, must-revalidate

程式碼
可透過fresh_when來設定

fresh_when does a couple of things 

1.checks the Etag matches or not

2.If matches : send a 304 Not Modified response instead of rendering the actual template

3.If not matches , the page will rendered as normal

Rack:cache -->This is known as a reverse proxy cache or gateway cache

rails 已經自動將他包進來在production環境

如果你要在development上使用

/config/environments/development.rb

config.action_controller.perform_caching = true

如果是敏感性資料時

可以設定當目前為public時 不要顯現

/app/views/layouts/application.html.erb

<%= csrf_meta_tag unless response.cache_control[:public] %>