设置缓存控制是否即使没有条件请求也不会自动启用缓存？

对于以下图像： https：// upload.wikimedia.org/wikipedia/commons/7/79/2010-brown-bear.jpg

没有任何 cache-control 标头。并且根据此处，即使您不发送任何内容，它也会使用其默认值为 private 。那不是URLSession需要执行条件请求来确保其仍然有效吗？

There isn't any cache-control header. And based on here even if you don't send anything then it will use its default value which is private. That being doesn't the URLSession need to perform a conditional request to make sure its still valid?

标头中是否有任何内容可以发出这样的条件请求？因为我看不到缓存控制，最大年龄，过期。我唯一看到的是最后修改& Etag ，但是它再次需要针对服务器进行验证，或者未指定任何内容使其无限期地缓存吗？我已经阅读了此答案，但是没有讨论这种情况。

Is there anything in the headers that allows it to make such a conditional request? Because I don't see cache-control, max-age, Expires. The only things I see is are Last-Modified & Etag but again it needs to validate against the server or does not specifying anything make it cache indefinitely?! I've already read this answer, but doesn't discuss this scenario.

但是URLSession正在缓存它。 （因为如果我关闭了互联网，仍然可以下载）

Yet it's being cached by the URLSession. (Because if I turn off internet, still it gets downloaded)

我只看到的另一件事是严格的传输安全：max-年龄= 106384710 。

Only other thing I see is "Strict-Transport-Security": max-age=106384710.

这会影响缓存吗？我已经在此处并且不相信它应该。从我的角度来看，HSTS密钥的最大年龄仅用于强制在一定时间内从HTTPS访问它。一旦达到最大使用期限，则也可以通过HTTP访问。

Does that effect caching? I've already look here and don't believe it should. From what I the max-age for the HSTS key is there only to enforce it to be accessed from HTTPS for a certain period of time. Once the max-age is reached then access through HTTP is also possible.

这些都是我要返回的标头：

These are all the headers that I'm getting back:

Date : Wed, 31 Oct 2018 14:15:33 GMT
Content-Length : 215104
Access-Control-Expose-Headers: Age, Date, Content-Length, Content-Range, X-Content-Duration, X-Cache, X-Varnish
Via : 1.1 varnish (Varnish/5.1), 1.1 varnish (Varnish/5.1)    
Age : 18581
Etag : 00e21950bf432476c91b811bb685b6af
Strict-Transport-Security : max-age=106384710; includeSubDomains; preload
Accept-Ranges : bytes
Content-Type : image/jpeg
Last-Modified : Fri, 04 Oct 2013 23:30:08 GMT
Access-Control-Allow-Origin : *
Timing-Allow-Origin : *
x-analytics : https=1;nocookies=1
x-object-meta-sha1base36 : 42tq5grg9rq1ydmqd4z5hmmqj6h2309
x-varnish : 60926196 48388489, 342256851 317476424
x-cache-status : hit-front
x-trans-id : tx08ed43bbcc1946269a9a3-005bd97070
x-timestamp : 1380929407.39127
x-cache : cp1076 hit/7, cp1090 hit/7
x-client-ip : 2001:558:1400:4e:171:2a98:fad6:2579

_{由于此注释}