4.3.3. Handling a Validation Response
rfc 7234 4.3.3. Handling a Validation Response
Cache handling of a response to a conditional request is dependent
upon its status code:
o A 304 (Not Modified) response status code indicates that the
stored response can be updated and reused; see Section 4.3.4.
o A full response (i.e., one with a payload body) indicates that
none of the stored responses nominated in the conditional request
is suitable. Instead, the cache MUST use the full response to
satisfy the request and MAY replace the stored response(s).
o However, if a cache receives a 5xx (Server Error) response while
attempting to validate a response, it can either forward this
response to the requesting client, or act as if the server failed
to respond. In the latter case, the cache MAY send a previously
stored response (see Section 4.2.4).
这一小节主要讲，cache发起了条件请求，收到对于response以后可以处理的情况。
rfc中没有cover到的情况
显然这里并没有cover到当收到response时所有的情况
