feat: detect default limit changes in go-libp2p-resource-manager

[lidel]

Part of #8761, based on #8680

What

This PR removes hardcoded defaults and switches to ones from go-libp2p.

To safeguard against silent changes that could impact our users, adds a simple check that will scream loud and clear every time go-libp2p libraries change any of the limit defaults related to go-libp2p-resource-manager. This was suggested during recent go-ipfs sync.

How

• relevant structs are serialized to JSON zand compared
• if there are any unexpected changes, go-ipfs will refuse to start, forcing us to review impact of go-libp2p update
• diff between expected and actual limits is returned in JSON Patch format
  • Initially, I just printed JSON for "before" and "after" and compared normalized strings,
    but given how many values we have it was difficult to spot the change.
  • Makes it easier to apply changes on top of expected limits in rcmgr_defaults.go

Demo

Assuming next version of go-libp2p changed:

• DefaultLimits in go-libp2p-resource-manager
  • SystemBaseLimit/FD from 512 to 1024
  • SystemBaseLimit/StreamsInbound from 4095 to 1024
• SetDefaultServiceLimits in go-libp2p
  • StreamLimits/Memory from 16777216 to 0
  • SystemLimits/Streams from 16384 to 42

The daemon will refuse to start until the changes are reviewed, and expected values are updated in rcmgr_defaults.go:

$ LIBP2P_RCMGR=1 ipfs daemon
Initializing daemon...
go-ipfs version: 0.13.0-dev-024bf885e-dirty
Repo version: 12
System version: amd64/linux
Golang version: go1.16.9
2022-04-07T23:47:00.068+0200	ERROR	p2pnode	libp2p/rcmgr_defaults.go:85	===> OOF! go-libp2p-resource-manager changed DefaultLimits
=> changes ('test' represents the old value):
  {"op":"test","path":"/SystemBaseLimit/FD","value":512}
  {"op":"replace","path":"/SystemBaseLimit/FD","value":1024}
  {"op":"test","path":"/SystemBaseLimit/StreamsInbound","value":4095}
  {"op":"replace","path":"/SystemBaseLimit/StreamsInbound","value":1024}
=> go-libp2p-resource-manager DefaultLimits update needs a review:
Please inspect if changes impact go-ipfs users, and update expectedDefaultLimits in rcmgr_defaults.go to remove this message
2022-04-07T23:47:00.068+0200	ERROR	p2pnode	libp2p/rcmgr_defaults.go:107	===> OOF! go-libp2p changed DefaultServiceLimits
=> changes ('test' represents the old value):
  {"op":"test","path":"/StreamLimits/Memory","value":16777216}
  {"op":"replace","path":"/StreamLimits/Memory","value":0}
  {"op":"test","path":"/SystemLimits/Streams","value":16384}
  {"op":"replace","path":"/SystemLimits/Streams","value":42}
=> go-libp2p SetDefaultServiceLimits update needs a review:
Please inspect if changes impact go-ipfs users, and update expectedDefaultServiceLimits in rcmgr_defaults.go to remove this message
2022-04-07T23:47:00.068+0200	FATAL	p2pnode	libp2p/rcmgr_defaults.go:115	daemon will refuse to run with the resource manager until this is resolved

[BigLep]

Good stuff @lidel ! Conceptually this makes sense to me. I'll let others approve from a code regard.

[guseggert]

This is amazing, thanks!