Document Waku existing light node behavior

[oskarth]

Problem

Waku adds a light node status that isn't documented in the existing Whisper docs. This makes it hard for clients to implement and reason about wrt connectivity, privacy guarantees and perf.

Acceptance criteria

• Document light node behavior in Waku 0 spec
• Add implementation status matrix per implementation, see Implementation matrix for Whisper/Waku clients status-im/specs#63
• Briefly on rationale and implications for privacy

Details

See https://github.com/status-im/whisper/blob/8be20fd33d56bce7a886a93101984d5a1fe101af/whisperv6/peer.go#L80 and https://github.com/status-im/whisper/blob/8be20fd33d56bce7a886a93101984d5a1fe101af/whisperv6/api.go#L194

And https://github.com/status-im/nim-eth/blob/c64a370fe7a49d8d8d287d043870ecec1251676e/eth/p2p/rlpx_protocols/whisper_protocol.nim#L780

Possible Solutions

Look at details and amend EIP627 in https://github.com/vacp2p/specs/pull/28/files

Notes

Check with @adamb and @kdeme if there are any gotchas here

[oskarth]

@decanus do you want to take a look at this one?

[decanus]

So I added light node description in specs/light-node. This documents both the behaviour in geth and nimbus which are identical. Its rather simple, one thing left to look at is the handshake. Would also make sense to discuss with core to see which functionality is used in the app.

cc @kdeme

[oskarth]

@decanus Seems like this is modifying the existing waku spec, can we add it to existing PR? It'll get messy quickly if we have too many branches IMO.

[decanus]

@oskarth I can just merge it yea.

[decanus]

Important to note that status clients run in light mode.

[oskarth]

Current docs https://github.com/status-im/specs/blob/master/status-client-spec.md#mobile-nodes

Note inconsistent terms and different MUST/MAY usage cc @adambabik

[oskarth]

@decanus what's state of this?

[decanus]

Although compact, seems good imo: https://github.com/vacp2p/specs/blob/master/waku.md#light-node