feat(protonvpn): Added ProtonVPN feature selection

[kvanzuijlen]

I know it's not completely done yet (missing tests, missing todo's for moving feature-related stuff to the new Features struct, docs, etc) but I wanted to open a PR to see if you agree with my chosen direction.

Closes #1582, partially #1103

[qdm12]

Nice it's looking pretty good, just a few minor comments 😉 👍

[kvanzuijlen]

Hi,

I applied (most of) your suggestions from the code review. I also added minimal unit tests (basically added to all the _test files) for all files changed in this PR. I also built my own image and started using it already. It seems to work, as far as I can tell.

[kvanzuijlen]

@qdm12 I've been running this code for a couple of days now myself (https://github.com/users/kvanzuijlen/packages/container/package/gluetun) and as far as I can tell it now fully works :).

[qdm12]

1. I rebased your branch on master

2. Extracting features was actually semi-functional... but fear not, it's Go's switch which behaves strangely compared to other programming languages. When encountering a true case in the switch, it gets out of the switch and doesn't try other cases. That means if the features bits match one feature, it won't find other features. This is fixed by assigning the features struct fields directly without a switch:

   features := features{
   	secureCore: featuresBits&1 != 0,
   	tor:        featuresBits&2 != 0,
   	p2p:        featuresBits&4 != 0,
   	stream:     featuresBits&8 != 0,
   	// ipv6: featuresBits&16 != 0, - unused.
   }

   FYI this could also been fixed using the fallthrough keyword at the end of each case block in the switch 😉

3. IPv6 only filter got removed. It's a bit of a confusing option IPV6_ONLY and also does not seem to be used.

4. Re-updated servers data

5. Added new environment variable options to Dockerfile

   SECURE_CORE_ONLY= \
   TOR_ONLY= \
   P2P_ONLY= \

The merge-base changed after approval.

[qdm12]

@kvanzuijlen are you aware of a difference between 'p2p' and 'port forwarding' in terms of feature for Protonvpn? I'm looking at #1103 (comment) and thinking of removing P2P_ONLY in favor of PORT_FORWARD_ONLY. Also are all p2p servers able to port forward?

EDIT: Please answer on #1103 😉 Since I don't get notified for this PR anymore