GenRandomKey function

[guillaumemichel]

Add a GenRandomKey(targetCpl) function similar to GenRandPeerID(targetCpl) but not requiring the list of precomputed hash preimages.

This function generates a random Kademlia key (32 bytes), whose first targetCpl bits are shared with the local key of the routing table.

It is useful as we get to replace string oriented requests with byte oriented requests in go-libp2p-kad-dht). It is a prerequisite for the Double Hash DHT implementation.

[guillaumemichel]

@Jorropo I updated the code with your suggestions, and reduced the amount of inline comments. Let me know what you think now 😄

[Jorropo]

Minus a last final change this LGTM

[Jorropo]

@guillaumemichel I'm surprised you are not removing the older preimage based implementation.

This makes me worry of how you are gonna implement the double hashing impl.

Will you do a V2 branch ? (so both modules live in two different branches but can be imported together). Or stay on v0 branch and "manually" write code that handle both DHTs at once.

[guillaumemichel]

Good point @Jorropo! IMO this new function is generic enough to be used in other projects, and even the go-libp2p-kbucket repo is pretty generic, so no need to deprecate anything now.

It will certainly be useful to create a V2 branch for both go-libp2p-kbucket and go-libp2p-kad-dht in order to allow kubo to use both the old and the new DHT during the transition period.