Use go 1.17 ability to re-use LZW writer

[relistan]

A busy Sidecar is spending like 6% of its CPU time allocating LZW writers! These had a dumb interface in the stdlib and it was improved in 1.17 with the addition of a Reset() function. This update re-uses both the bytes.Buffer and the lzw.Writer which should save a lot of allocs! This is only called from a loop over a channel so there should not be synchronization issues.

[relistan]

Updating Go found all these issues in the existing code

[mihaitodor]

Awesome! Nice find. Looks like this should be fixed upstream too: https://github.com/hashicorp/memberlist/blob/696ff46201c1b64d31b60d57971d07d8cf15df7a/util.go#L240

Not sure if relevant, but I noticed this error is unchecked with golangci-lint:

memberlist/memberlist.go

Line 354 in cfac2b5

_, publicIfs, err := sockaddr.IfByRFC("6890", ifAddrs)

Otherwise

[relistan]

Awesome! Nice find. Looks like this should be fixed upstream too: https://github.com/hashicorp/memberlist/blob/696ff46201c1b64d31b60d57971d07d8cf15df7a/util.go#L240

@mihaitodor thanks, yeah I had looked at the upstream first and saw they hadn't done anything to improve this. Because the upstream SWIM implementation does nowhere near as much gossiping, I suspect that this is not as much of an issue.

[relistan]

Sadly, looks like this does need a pooling setup. Appears to be used in a goroutine.

[mihaitodor]

Ugh... You know, I was thinking to ask about that when I reviewed it. I recall implementing something like that somewhere, but I can't recall where.