[PM-2752] Throttle incoming connections from the same ip

[KonradStaniec]

Description

Create a possibility to throttle incoming connections from the same ip.

Some of design decisions:

• I did not add maxSize property to cache as it with typical throttling times (like lets say 30s) it would be really hard to use up all host memory. (Ip4 address takes 4bytes, so 1M of them would take only 4Mb + some overhead for java object fields)
• I decided to use caffeine cache with exipreAfterWrite property. The similar effect could be accomplished by using java concurrent hash map, and scheduling clearing on netty eventLoops, but ultimately I think cache solution is clearer and worth bringing another dependency
• I decided to not give user of the group option to sent a message when closing the channel which violates throttling restrictions. By default we are treating connections which violates throttling restrictions as hostile and want to give it as little information as possilbe.

[aakoshh]

Nice one!

[aakoshh]

The projects we use Scalanet in already use guava, which also has a timed cache. Shouldn't we stick to that?

[KonradStaniec]

hmm there is only some old versions of guava - 21, which is from 12-Jan-2017, and also it exports only some wierd annotation library part - com.google.errorprone:error_prone_annotations.

Taking those into account I would stick with caffeine.

[aakoshh]

Maybe we should upgrade then, there's version 30 from Dec 2020.

Looking at caffeine on Maven it has the same error_prone_annotations dependency, there's even an issue for it, which references the guava issue.

[aakoshh]

But it sounds like Caffeine is a bit better, like no extra thread for cleanups, so if you prefer it then 👍

[KonradStaniec]

Sure we can, I do not have strong preference here. As long it has putIfAbsent and timed eviction it is good enough.

[aakoshh]

The CacheBuilder has an example of expire after write, and apparently the asMap with putIfAbsent is still the way.

I also read that Caffeine handles async loading natively, whereas Guava is synchronous.

[aakoshh]

Looks good. I'm sorry for suggesting a confusing name, see my comment about another option.

[KonradStaniec]

so ultimately lets go with isQuotaAvailable and caffeine cache :)