Devp2p: Per-Message debugging for ETH and other protocols / Improved docs

[holgerd77]

This PR adds per-message debugging on the devp2p library for the ETH protocol as well as other protocols. This should hopefully significantly help us on a more targeted debugging along client development.

Per-Message debugging can be used as follows, see also the additions to the docs for more information:

DEBUG=devp2p:eth:BLOCK_HEADERS,devp2p:eth:GET_BLOCK_HEADERS npm run client:start

Example output:

[codecov]

Codecov Report

Merging #1449 (457a4f8) into master (4c9d34b) will increase coverage by 1.22%.
The diff coverage is 80.14%.

Flag	Coverage Δ
block	86.76% <ø> (+0.13%)	⬆️
blockchain	83.56% <ø> (+0.06%)	⬆️
client	82.61% <ø> (-0.28%)	⬇️
common	94.39% <ø> (+0.19%)	⬆️
devp2p	82.46% <80.14%> (+0.02%)	⬆️
ethash	86.56% <ø> (ø)
tx	88.36% <ø> (+0.11%)	⬆️
vm	82.78% <ø> (+3.45%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[holgerd77]

Added LES as well.

This now also works for RLPx messages with e.g. DEBUG=devp2p:rlpx:peer:DISCONNECT npm run client:start:

[holgerd77]

For DPT server messages DEBUG=devp2p:dpt:server:findneighbours npm run client:start:

[holgerd77]

And a special logger to log along the RLPx peer DISCONNECT reason, e.g. DEBUG=devp2p:rlpx:peer:DISCONNECT:TOO_MANY_PEERS npm run client:start. Think this might likely be pretty useful on certain occasions:

[holgerd77]

Aaaand two final debuggers which are very close to my heart and which I think will be super useful:

An IP based per-peer debugger, e.g. DEBUG=devp2p:3.209.45.79 npm run client:start:

And a special debugger only debugging the message exchange with the first successfully connected peer, used with DEBUG=devp2p:FIRST_PEER npm run client:start:

Ok. Ready for review. 😄

[acolytec3]

This is beautiful, I like it, and I approve this message. I dig all the additional debug visibility. I kinda wish I had all of this when I started on the snappy/NEW_BLOCK stuff 😉

[holgerd77]

@acolytec3 Yes, totally looking forward to use this stuff myself 😄, thanks for approving!

[holgerd77]

(pain has grown too strong here over the months... 😜)