Setting RLPx subprotocol version to 0 crashes

[oskarth]

Problem

If I set wakuVersion (or whisperVersion) to 0 like this: https://github.com/oskarth/nim-eth/blob/waku-zero/eth/p2p/rlpx_protocols/waku_protocol.nim#L56-L57

I get the following crash:

[Suite] Waku connections
INF 2019-11-15 17:01:52+08:00 RLPx listener up                           tid=10758 self=enode://23cb2baaab4231bc85271e540c6161549199b78c7f66c2997ca7f0722650a8fcf5e005ff8b34043959bd5e8e0c27a1b868c8a870282a0f8bc18d5c1617084225@127.0.0.1:30304
Traceback (most recent call last)
/home/oskarth/git/nim-eth/tests/p2p/test_waku_connect.nim(26) test_waku_connect
/home/oskarth/.nimble/pkgs/chronos-2.3.2/chronos/asyncloop.nim(933) waitFor
/home/oskarth/.nimble/pkgs/chronos-2.3.2/chronos/asyncloop.nim(274) poll
/home/oskarth/git/nim-eth/eth/p2p/rlpx.nim(1029) rlpxConnect
/home/oskarth/git/nim-eth/eth/p2p/rlpx.nim(899) postHelloSteps
/home/oskarth/git/nim-eth/eth/p2p/p2p_protocol_dsl.nim(305) WakuPeerConnected
/home/oskarth/.choosenim/toolchains/nim-0.20.0/lib/system/gc.nim(238) asgnRef
/home/oskarth/.choosenim/toolchains/nim-0.20.0/lib/system/gc.nim(183) incRef
SIGSEGV: Illegal storage access. (Attempt to read from nil?)
Error: execution of an external program failed: '/home/oskarth/git/nim-eth/tests/p2p/test_waku_connect -vvv'

Solution

I can't find in docs/p2p.md or https://github.com/ethereum/devp2p/blob/master/rlpx.md that suggest that this should be invalid. Either:

1. Make version 0 valid, or:

2. Give a better validation/compile error, and add to docs that this is a requirement

Notes

I didn't debug or try to fix this further, but seems like a bug in the P2P DSL.

Additionally, and separately, I noticed that p2p/docs.md says subprotocols should be 3 letters. In devp2p/rlpx.md it just says "short ASCII name" as far as I can tell. I can't tell if this a spec constraint and I'm looking in the wrong place, or what's going on there. Didn't look into it too much. Some validation there might be useful too.