http - Understand the weak comparison function

Question

HTTP 1.1 defines a weak comparison function for cache validators:

in order to be considered equal, both validators MUST be identical in every way, but either or both of them MAY be tagged as "weak" without affecting the result.

I understand that following statement (for two ETags) is true:

W/"Foo" = "Foo"

Now I'm wondering what real world use case might exist where a server compares a weak ETag against a strong one.

Answer 1

在某些情况下，服务器首先分配一个弱 etag，然后将其提升为一个强 etag（通过删除“W/”前缀）。一个示例是 Apache moddav（或者它是普通的 httpd？），当配置为根据所服务文件的文件系统时间戳创建实体标签时。