lotus/chain/beacon/drand/drand.go

package drand

import (
	"context"
	"fmt"
	"sync"
	"time"

	"github.com/filecoin-project/lotus/chain/beacon"
	"github.com/filecoin-project/lotus/chain/types"
	"github.com/filecoin-project/specs-actors/actors/abi"
	"golang.org/x/xerrors"

	logging "github.com/ipfs/go-log"

	dbeacon "github.com/drand/drand/beacon"
	"github.com/drand/drand/core"
	dkey "github.com/drand/drand/key"
	dnet "github.com/drand/drand/net"
	dproto "github.com/drand/drand/protobuf/drand"
)

var log = logging.Logger("drand")

var drandServers = []string{
	"drand-test1.nikkolasg.xyz:5001",
}

type drandPeer struct {
	addr string
	tls  bool
}

func (dp *drandPeer) Address() string {
	return dp.addr
}

func (dp *drandPeer) IsTLS() bool {
	return dp.tls
}

type DrandBeacon struct {
	client dnet.Client
	peers  []dnet.Peer

	pubkey *dkey.DistPublic

	// seconds
	interval time.Duration

	drandGenTime uint64
	filGenTime   uint64
	filRoundTime uint64

	cacheLk    sync.Mutex
	localCache map[uint64]types.BeaconEntry
}

func NewDrandBeacon(genesisTs, interval uint64) (*DrandBeacon, error) {
	if genesisTs == 0 {
		panic("what are you doing this cant be zero")
	}
	db := &DrandBeacon{
		client:     dnet.NewGrpcClient(),
		localCache: make(map[uint64]types.BeaconEntry),
	}
	for _, ds := range drandServers {
		db.peers = append(db.peers, &drandPeer{addr: ds, tls: true})
	}

	groupResp, err := db.client.Group(context.TODO(), db.peers[0], &dproto.GroupRequest{})
	if err != nil {
		return nil, xerrors.Errorf("failed to get group response from beacon peer: %w", err)
	}

	kgroup, err := core.ProtoToGroup(groupResp)
	if err != nil {
		return nil, xerrors.Errorf("failed to parse group response: %w", err)
	}

	// TODO: verify these values are what we expect them to be
	db.pubkey = kgroup.PublicKey
	db.interval = kgroup.Period
	db.drandGenTime = uint64(kgroup.GenesisTime)
	db.filRoundTime = interval
	db.filGenTime = genesisTs

	// TODO: the stream currently gives you back *all* values since drand genesis.
	// Having the stream in the background is merely an optimization, so not a big deal to disable it for now
	//go db.handleStreamingUpdates()

	return db, nil
}

func (db *DrandBeacon) handleStreamingUpdates() {
	for {
		ch, err := db.client.PublicRandStream(context.Background(), db.peers[0], &dproto.PublicRandRequest{})
		if err != nil {
			log.Warnf("failed to get public rand stream: %s", err)
			log.Warnf("trying again in 10 seconds")
			time.Sleep(time.Second * 10)
			continue
		}

		for e := range ch {
			fmt.Println("Entry: ", e.Round, e.Signature)
			db.cacheValue(e.Round, types.BeaconEntry{
				Round: e.Round,
				Data:  e.Signature,
			})
		}
		log.Warn("drand beacon stream broke, reconnecting in 10 seconds")
		time.Sleep(time.Second * 10)
	}
}

func (db *DrandBeacon) Entry(ctx context.Context, round uint64) <-chan beacon.Response {
	fmt.Println("requesting drand entry: ", round)
	// check cache, it it if there, otherwise query the endpoint
	resp, err := db.client.PublicRand(ctx, db.peers[0], &dproto.PublicRandRequest{Round: round})

	var br beacon.Response
	if err != nil {
		br.Err = err
	} else {
		br.Entry.Round = resp.GetRound()
		br.Entry.Data = resp.GetSignature()
	}

	out := make(chan beacon.Response, 1)
	out <- br
	close(out)

	return out
}

func (db *DrandBeacon) cacheValue(round uint64, e types.BeaconEntry) {
	db.cacheLk.Lock()
	defer db.cacheLk.Unlock()
	db.localCache[round] = e
}

func (db *DrandBeacon) getCachedValue(round uint64) *types.BeaconEntry {
	db.cacheLk.Lock()
	defer db.cacheLk.Unlock()
	v, ok := db.localCache[round]
	if !ok {
		return nil
	}
	return &v
}

func (db *DrandBeacon) VerifyEntry(curr types.BeaconEntry, prev types.BeaconEntry) error {
	if prev.Round == 0 {
		// TODO handle genesis better
		return nil
	}
	b := &dbeacon.Beacon{
		PreviousRound: prev.Round,
		PreviousSig:   prev.Data,
		Round:         curr.Round,
		Signature:     curr.Data,
	}
	//log.Warnw("VerifyEntry", "beacon", b)
	return dbeacon.VerifyBeacon(db.pubkey.Key(), b)
}

func (db *DrandBeacon) MaxBeaconRoundForEpoch(filEpoch abi.ChainEpoch, prevEntry types.BeaconEntry) uint64 {
	fmt.Println("MAX BEACON ROUND FOR EPOCH: ", filEpoch)
	fmt.Println("filecoin genesis time: ", db.filGenTime)
	fmt.Println("drand genesis time: ", db.drandGenTime)
	// TODO: sometimes the genesis time for filecoin is zero and this goes negative
	latestTs := ((uint64(filEpoch) * db.filRoundTime) + db.filGenTime) - db.filRoundTime
	dround := (latestTs - db.drandGenTime) / uint64(db.interval.Seconds())
	fmt.Println("max beacon round will be: ", dround)
	return dround
}

var _ beacon.RandomBeacon = (*DrandBeacon)(nil)