lotus/chain/beacon/beacon.go

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package beacon
import (
"context"
"github.com/filecoin-project/specs-actors/actors/abi"
logging "github.com/ipfs/go-log"
"golang.org/x/xerrors"
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"github.com/filecoin-project/lotus/build"
"github.com/filecoin-project/lotus/chain/types"
)
var log = logging.Logger("beacon")
type Response struct {
Entry types.BeaconEntry
Err error
}
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// RandomBeacon represents a system that provides randomness to Lotus.
// Other components interrogate the RandomBeacon to acquire randomness that's
// valid for a specific chain epoch. Also to verify beacon entries that have
// been posted on chain.
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type RandomBeacon interface {
Entry(context.Context, uint64) <-chan Response
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VerifyEntry(types.BeaconEntry, types.BeaconEntry) error
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MaxBeaconRoundForEpoch(abi.ChainEpoch, types.BeaconEntry) uint64
}
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func ValidateBlockValues(b RandomBeacon, h *types.BlockHeader, prevEntry types.BeaconEntry) error {
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maxRound := b.MaxBeaconRoundForEpoch(h.Height, prevEntry)
if maxRound == prevEntry.Round {
if len(h.BeaconEntries) != 0 {
return xerrors.Errorf("expected not to have any beacon entries in this block, got %d", len(h.BeaconEntries))
}
return nil
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}
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last := h.BeaconEntries[len(h.BeaconEntries)-1]
if last.Round != maxRound {
return xerrors.Errorf("expected final beacon entry in block to be at round %d, got %d", maxRound, last.Round)
}
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for i, e := range h.BeaconEntries {
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if err := b.VerifyEntry(e, prevEntry); err != nil {
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return xerrors.Errorf("beacon entry %d (%d - %x (%d)) was invalid: %w", i, e.Round, e.Data, len(e.Data), err)
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}
prevEntry = e
}
return nil
}
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func BeaconEntriesForBlock(ctx context.Context, beacon RandomBeacon, round abi.ChainEpoch, prev types.BeaconEntry) ([]types.BeaconEntry, error) {
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start := build.Clock.Now()
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maxRound := beacon.MaxBeaconRoundForEpoch(round, prev)
if maxRound == prev.Round {
return nil, nil
}
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// TODO: this is a sketchy way to handle the genesis block not having a beacon entry
if prev.Round == 0 {
prev.Round = maxRound - 1
}
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cur := maxRound
var out []types.BeaconEntry
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for cur > prev.Round {
rch := beacon.Entry(ctx, cur)
select {
case resp := <-rch:
if resp.Err != nil {
return nil, xerrors.Errorf("beacon entry request returned error: %w", resp.Err)
}
out = append(out, resp.Entry)
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cur = resp.Entry.Round - 1
case <-ctx.Done():
return nil, xerrors.Errorf("context timed out waiting on beacon entry to come back for round %d: %w", round, ctx.Err())
}
}
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log.Debugw("fetching beacon entries", "took", build.Clock.Since(start), "numEntries", len(out))
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reverse(out)
return out, nil
}
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func reverse(arr []types.BeaconEntry) {
for i := 0; i < len(arr)/2; i++ {
arr[i], arr[len(arr)-(1+i)] = arr[len(arr)-(1+i)], arr[i]
}
}