Explicit use of GENESIS_SLOT in fork choice (#4343)

beacon-chain/blockchain/forkchoice/BUILD.bazel

@@ -25,6 +25,7 @@ go_library(
         "//shared/featureconfig:go_default_library",
         "//shared/hashutil:go_default_library",
         "//shared/params:go_default_library",
+        "//shared/roughtime:go_default_library",
         "//shared/traceutil:go_default_library",
         "@com_github_gogo_protobuf//proto:go_default_library",
         "@com_github_pkg_errors//:go_default_library",

beacon-chain/blockchain/forkchoice/process_attestation.go

@@ -50,7 +50,7 @@ var ErrTargetRootNotInDB = errors.New("target root does not exist in db")
 //    assert target.root in store.blocks
 //    # Attestations cannot be from future epochs. If they are, delay consideration until the epoch arrives
 //    base_state = store.block_states[target.root].copy()
-//    assert store.time >= base_state.genesis_time + compute_start_slot_at_epoch(target.epoch) * SECONDS_PER_SLOT
+//    assert get_current_slot(store) >= compute_start_slot_at_epoch(target.epoch)
 //
 //    # Attestations must be for a known block. If block is unknown, delay consideration until the block is found
 //    assert attestation.data.beacon_block_root in store.blocks
@@ -65,7 +65,7 @@ var ErrTargetRootNotInDB = errors.New("target root does not exist in db")
 //
 //    # Attestations can only affect the fork choice of subsequent slots.
 //    # Delay consideration in the fork choice until their slot is in the past.
-//    assert store.time >= (attestation.data.slot + 1) * SECONDS_PER_SLOT
+//    assert get_current_slot(store) >= attestation.data.slot + 1
 //
 //    # Get state at the `target` to validate attestation and calculate the committees
 //    indexed_attestation = get_indexed_attestation(target_state, attestation)
@@ -80,7 +80,6 @@ func (s *Store) OnAttestation(ctx context.Context, a *ethpb.Attestation) error {
 	defer span.End()
 
 	tgt := proto.Clone(a.Data.Target).(*ethpb.Checkpoint)
-	tgtSlot := helpers.StartSlot(tgt.Epoch)
 
 	// Verify beacon node has seen the target block before.
 	if !s.db.HasBlock(ctx, bytesutil.ToBytes32(tgt.Root)) {
@@ -99,8 +98,8 @@ func (s *Store) OnAttestation(ctx context.Context, a *ethpb.Attestation) error {
 	}
 
 	// Verify Attestations cannot be from future epochs.
-	if err := helpers.VerifySlotTime(baseState.GenesisTime, tgtSlot); err != nil {
-		return errors.Wrap(err, "could not verify attestation target slot")
+	if helpers.StartSlot(tgt.Epoch) > s.currentSlot() {
+		return fmt.Errorf("could not process future attestation %d, current slot %d", helpers.StartSlot(tgt.Epoch), s.currentSlot())
 	}
 
 	// Verify attestation beacon block is known and not from the future.
@@ -115,8 +114,8 @@ func (s *Store) OnAttestation(ctx context.Context, a *ethpb.Attestation) error {
 	}
 
 	// Verify attestations can only affect the fork choice of subsequent slots.
-	if err := helpers.VerifySlotTime(baseState.GenesisTime, a.Data.Slot+1); err != nil {
-		return err
+	if a.Data.Slot+1 > s.currentSlot() {
+		return fmt.Errorf("could not process attesatin until subsequent slots %d, current slot %d", a.Data.Slot+1, s.currentSlot())
 	}
 
 	// Use the target state to to validate attestation and calculate the committees.

beacon-chain/blockchain/forkchoice/process_block.go

@@ -5,7 +5,6 @@ import (
 	"context"
 	"encoding/hex"
 	"fmt"
-	"time"
 
 	"github.com/gogo/protobuf/proto"
 	"github.com/pkg/errors"
@@ -21,6 +20,7 @@ import (
 	"github.com/prysmaticlabs/prysm/shared/featureconfig"
 	"github.com/prysmaticlabs/prysm/shared/hashutil"
 	"github.com/prysmaticlabs/prysm/shared/params"
+	"github.com/prysmaticlabs/prysm/shared/roughtime"
 	"github.com/prysmaticlabs/prysm/shared/traceutil"
 	"github.com/sirupsen/logrus"
 	"go.opencensus.io/trace"
@@ -35,7 +35,7 @@ import (
 //    assert block.parent_root in store.block_states
 //    pre_state = store.block_states[block.parent_root].copy()
 //    # Blocks cannot be in the future. If they are, their consideration must be delayed until the are in the past.
-//    assert store.time >= pre_state.genesis_time + block.slot * SECONDS_PER_SLOT
+//    assert get_current_slot(store) >= block.slot
 //    # Add new block to the store
 //    store.blocks[signing_root(block)] = block
 //    # Check block is a descendant of the finalized block
@@ -254,8 +254,8 @@ func (s *Store) getBlockPreState(ctx context.Context, b *ethpb.BeaconBlock) (*pb
 	}
 
 	// Verify block slot time is not from the feature.
-	if err := helpers.VerifySlotTime(preState.GenesisTime, b.Slot); err != nil {
-		return nil, err
+	if b.Slot > s.currentSlot() {
+		return nil, fmt.Errorf("could not process future block %d, current slot %d", b.Slot, s.currentSlot())
 	}
 
 	// Verify block is a descendent of a finalized block.
@@ -498,9 +498,14 @@ func (s *Store) shouldUpdateJustified(ctx context.Context, newJustifiedCheckpt *
 	return true, nil
 }
 
-// currentSlot returns the current slot based on time.
+// currentSlot returns the current slot number.
 func (s *Store) currentSlot() uint64 {
-	return (uint64(time.Now().Unix()) - s.genesisTime) / params.BeaconConfig().SecondsPerSlot
+	return params.BeaconConfig().GenesisSlot + s.slotsSinceGenesis()
+}
+
+// slotsSinceGenesis returns how many slots has passed since genesis time.
+func (s *Store) slotsSinceGenesis() uint64 {
+	return (uint64(roughtime.Now().Unix()) - s.genesisTime) / params.BeaconConfig().SecondsPerSlot
 }
 
 // updates justified check point in store if a better check point is known

beacon-chain/blockchain/forkchoice/process_block_test.go

@@ -64,7 +64,7 @@ func TestStore_OnBlock(t *testing.T) {
 			name:          "block is from the feature",
 			blk:           &ethpb.BeaconBlock{ParentRoot: randomParentRoot[:], Slot: params.BeaconConfig().FarFutureEpoch},
 			s:             &pb.BeaconState{},
-			wantErrString: "could not process slot from the future",
+			wantErrString: "could not process future block",
 		},
 		{
 			name:          "could not get finalized block",

shared/params/config.go

@@ -27,6 +27,7 @@ type BeaconChainConfig struct {
 	MinGenesisActiveValidatorCount uint64 `yaml:"MIN_GENESIS_ACTIVE_VALIDATOR_COUNT"` // MinGenesisActiveValidatorCount defines how many validator deposits needed to kick off beacon chain.
 	MinGenesisTime                 uint64 `yaml:"MIN_GENESIS_TIME"`                   // MinGenesisTime is the time that needed to pass before kicking off beacon chain. Currently set to Jan/3/2020.
 	TargetAggregatorsPerCommittee  uint64 // TargetAggregatorsPerCommittee defines the number of aggregators inside one committee.
+	GenesisSlot                    uint64 // GenesisSlot is the slot number when beacon chain starts.
 
 	// Gwei value constants.
 	MinDepositAmount          uint64 `yaml:"MIN_DEPOSIT_AMOUNT"`          // MinDepositAmount is the maximal amount of Gwei a validator can send to the deposit contract at once.
@@ -124,6 +125,7 @@ var defaultBeaconConfig = &BeaconChainConfig{
 	MinGenesisActiveValidatorCount: 16384,
 	MinGenesisTime:                 1578009600,
 	TargetAggregatorsPerCommittee:  16,
+	GenesisSlot:                    0,
 
 	// Gwei value constants.
 	MinDepositAmount:          1 * 1e9,