http - Pragma 和 Cache-Control header 之间的区别？

Question

我在 Wikipedia 上阅读了有关 Pragma header 的信息其中说:

"The Pragma: no-cache header field is an HTTP/1.0 header intended for use in requests. It is a means for the browser to tell the server and any intermediate caches that it wants a fresh version of the resource, not for the server to tell the browser not to cache the resource. Some user agents do pay attention to this header in responses, but the HTTP/1.1 RFC specifically warns against relying on this behavior."

但是我一直不明白它的作用是什么？值为 no-cache 的 Cache-Control header 与值为 no-cache< 的 Pragma 有什么区别?

Answer 1

Pragma 是 HTTP/1.0 实现，cache-control 是相同概念的 HTTP/1.1 实现。它们都是为了防止客户端缓存响应。较旧的客户端可能不支持 HTTP/1.1，这就是该 header 仍在使用的原因。