HTTP cache

What is mandatory caching

Do not initiate http request , Use local cache directly , For example, enter in the browser address bar , Use the browser's refresh button , stay Expires or max-age In the case of the entry into force , Trigger strong cache .

Files that are not frequently modified , Usually use strong cache

Negotiate the cache , Corresponding cache

Before using the local cache , Negotiate with the server first , Check whether the cache file is up to date . Ask the head to carry If-None-Match or If-Modified-Since, You can also carry them all

Negotiate cache related header Field

The negotiation cache is determined by the server whether the cache resource is available , So the client and server communicate through some kind of identification , So that the server can judge whether the request resource can be accessed by cache , This mainly involves the following two groups header Field , These two groups of partners are in pairs , That is, the response header of the first request is attached with a certain field （Last-Modified perhaps Etag）, Then the subsequent request will be accompanied by the corresponding request field （If-Modified-Since perhaps If-None-Match）, If the response header does not Last-Modified perhaps Etag Field , Then the request header will not have a corresponding field .