Additional checks on mirrors

[nirik]

From downstream report:

"Some mirrors make it difficult to create further downstream local caching proxies
by including "Cache-Control: no-cache", "Cache-Control: max-age=0" headers
and setting Expires to right now.

wget -S -O /dev/stdout 'https://mirrors.uni-ruse.bg/fedora/linux/'
--2020-04-28 12:56:08-- https://mirrors.uni-ruse.bg/fedora/linux/
Resolving mirrors.uni-ruse.bg (mirrors.uni-ruse.bg)... 91.210.88.42, 2001:67c:220c::2a
Connecting to mirrors.uni-ruse.bg (mirrors.uni-ruse.bg)|91.210.88.42|:443... connected.
HTTP request sent, awaiting response...
HTTP/1.1 200 OK
Server: nginx
Date: Tue, 28 Apr 2020 10:56:02 GMT
Content-Type: text/html
Transfer-Encoding: chunked
Connection: keep-alive
Expires: Tue, 28 Apr 2020 10:56:02 GMT
Cache-Control: max-age=0
Cache-Control: no-cache
Length: unspecified [text/html]

I have also seen one https mirror downgrade connections to http via a 301
Location: redirect, but I cannot find it right now.

Additionally, it seems that some mirrors in the public mirror list are not
actual mirrors but rather caching proxies (note the X-Cache-Status: MISS):

wget -S -O /dev/stdout 'https://fedora.mirror.garr.it/fedora/linux/releases/'
--2020-04-28 12:49:52-- https://fedora.mirror.garr.it/fedora/linux/releases/
Resolving fedora.mirror.garr.it (fedora.mirror.garr.it)... 90.147.160.72, 90.147.160.73, 90.147.160.70, ...
Connecting to fedora.mirror.garr.it (fedora.mirror.garr.it)|90.147.160.72|:443... connected.
HTTP request sent, awaiting response...
HTTP/1.1 200 OK
Server: nginx Date: Tue, 28 Apr 2020 10:49:51 GMT
Content-Type: text/html Transfer-Encoding: chunked
Connection: keep-alive
Vary: Accept-Encoding
Vary: Accept-Encoding
X-Cache-Status: MISS
Length: unspecified [text/html]

The above may or may not be a problem, but it could at least be noted in the
mirror list. I use a local caching proxy due to metered internet and many
installations. This requirement makes the Ruse university mirror unusable for me."

[Hirenpanera]

Hii
Mera one question he