Polkadot P2P Authority Discovery

polkadot_p2p_authorities.md

1. Get the identifiers of the current and next authority set from the Runtime API, e.g. using the RPC interface for a PoC.

const res = await api.call.authorityDiscoveryApi.authorities()
const authorities = res.toHuman().map(a => keyring.decodeAddress(a))

Reference: https://docs.rs/sp-authority-discovery/27.0.0/sp_authority_discovery/trait.AuthorityDiscoveryApi.html

2. Load the protobuf DHT discovery types.

const disco = await protobuf.load(dirname(import.meta.url) + '/dht_disco-v2.proto')
const SignedAuthorityRecord = disco.lookupType('authority_discovery_v2.SignedAuthorityRecord')

3. Resolve peer identities for the authorities.

for (const authKey of authorities) {
  const keyHash = crypto.createHash('sha256').update(authKey).digest()
  try {
    // find the key hash in the DHT
    for await (const res of this.dht.get(keyHash)) {
      if (res.type === 5) {
        // decode with the protobuf SignedAuthorityRecord type
        const rec = SignedAuthorityRecord.decode(res.value)
        // where 0x00 = no hash, 0x36 = id length
        const id = new Uint8Array([0, 36, ...rec.peerSignature.publicKey])
        const authorityPeerId = peerIdFromBytes(id)

        console.log('Found', authorityPeerId, authKey)
        // ...
      }
    }
  } // ...
}

4. Have fun! (ಠ◡ಠ)