Faster Doppelganger Check (#9964)

* faster check

* potuz's review

* potuz's review

beacon-chain/rpc/prysm/v1alpha1/validator/status.go

@@ -24,6 +24,8 @@ import (
 var errPubkeyDoesNotExist = errors.New("pubkey does not exist")
 var nonExistentIndex = types.ValidatorIndex(^uint64(0))
 
+const numStatesToCheck = 2
+
 // ValidatorStatus returns the validator status of the current epoch.
 // The status response can be one of the following:
 //  DEPOSITED - validator's deposit has been recognized by Ethereum 1, not yet recognized by Ethereum.
@@ -106,9 +108,17 @@ func (vs *Server) CheckDoppelGanger(ctx context.Context, req *ethpb.DoppelGanger
 	if err != nil {
 		return nil, status.Error(codes.Internal, "Could not get head state")
 	}
+
+	currEpoch := slots.ToEpoch(headState.Slot())
+	isRecent, resp := checkValidatorsAreRecent(currEpoch, req)
+	// If all provided keys are recent we skip this check
+	// as we are unable to effectively determine if a doppelganger
+	// is active.
+	if isRecent {
+		return resp, nil
+	}
 	// We walk back from the current head state to the state at the beginning of the previous 2 epochs.
 	// Where S_i , i := 0,1,2. i = 0 would signify the current head state in this epoch.
-	currEpoch := slots.ToEpoch(headState.Slot())
 	previousEpoch, err := currEpoch.SafeSub(1)
 	if err != nil {
 		previousEpoch = currEpoch
@@ -125,18 +135,18 @@ func (vs *Server) CheckDoppelGanger(ctx context.Context, req *ethpb.DoppelGanger
 	if err != nil {
 		return nil, status.Error(codes.Internal, "Could not get older state")
 	}
-	resp := &ethpb.DoppelGangerResponse{
+	resp = &ethpb.DoppelGangerResponse{
 		Responses: []*ethpb.DoppelGangerResponse_ValidatorResponse{},
 	}
 	for _, v := range req.ValidatorRequests {
 		// If the validator's last recorded epoch was
-		// less than or equal to 2 epochs ago, this method will not
+		// less than or equal to `numStatesToCheck` epochs ago, this method will not
 		// be able to catch duplicates. This is due to how attestation
 		// inclusion works, where an attestation for the current epoch
 		// is able to included in the current or next epoch. Depending
 		// on which epoch it is included the balance change will be
 		// reflected in the following epoch.
-		if v.Epoch+2 >= currEpoch {
+		if v.Epoch+numStatesToCheck >= currEpoch {
 			resp.Responses = append(resp.Responses,
 				&ethpb.DoppelGangerResponse_ValidatorResponse{
 					PublicKey:       v.PublicKey,
@@ -322,6 +332,44 @@ func (vs *Server) validatorStatus(
 	}
 }
 
+func (vs *Server) retrieveAfterEpochTransition(ctx context.Context, epoch types.Epoch) (state.BeaconState, error) {
+	endSlot, err := slots.EpochEnd(epoch)
+	if err != nil {
+		return nil, err
+	}
+	retState, err := vs.StateGen.StateBySlot(ctx, endSlot)
+	if err != nil {
+		return nil, err
+	}
+	return transition.ProcessSlots(ctx, retState, retState.Slot()+1)
+}
+
+func checkValidatorsAreRecent(headEpoch types.Epoch, req *ethpb.DoppelGangerRequest) (bool, *ethpb.DoppelGangerResponse) {
+	validatorsAreRecent := true
+	resp := &ethpb.DoppelGangerResponse{
+		Responses: []*ethpb.DoppelGangerResponse_ValidatorResponse{},
+	}
+	for _, v := range req.ValidatorRequests {
+		// Due to how balances are reflected for individual
+		// validators, we can only effectively determine if a
+		// validator voted or not if we are able to look
+		// back more than `numStatesToCheck` epochs into the past.
+		if v.Epoch+numStatesToCheck < headEpoch {
+			validatorsAreRecent = false
+			// Zero out response if we encounter non-recent validators to
+			// guard against potential misuse.
+			resp.Responses = []*ethpb.DoppelGangerResponse_ValidatorResponse{}
+			break
+		}
+		resp.Responses = append(resp.Responses,
+			&ethpb.DoppelGangerResponse_ValidatorResponse{
+				PublicKey:       v.PublicKey,
+				DuplicateExists: false,
+			})
+	}
+	return validatorsAreRecent, resp
+}
+
 func statusForPubKey(headState state.ReadOnlyBeaconState, pubKey []byte) (ethpb.ValidatorStatus, types.ValidatorIndex, error) {
 	if headState == nil || headState.IsNil() {
 		return ethpb.ValidatorStatus_UNKNOWN_STATUS, 0, errors.New("head state does not exist")
@@ -371,15 +419,3 @@ func depositStatus(depositOrBalance uint64) ethpb.ValidatorStatus {
 	}
 	return ethpb.ValidatorStatus_DEPOSITED
 }
-
-func (vs *Server) retrieveAfterEpochTransition(ctx context.Context, epoch types.Epoch) (state.BeaconState, error) {
-	endSlot, err := slots.EpochEnd(epoch)
-	if err != nil {
-		return nil, err
-	}
-	retState, err := vs.StateGen.StateBySlot(ctx, endSlot)
-	if err != nil {
-		return nil, err
-	}
-	return transition.ProcessSlots(ctx, retState, retState.Slot()+1)
-}

beacon-chain/rpc/prysm/v1alpha1/validator/status_test.go

@@ -1170,25 +1170,10 @@ func TestServer_CheckDoppelGanger(t *testing.T) {
 			svSetup: func(t *testing.T) (*Server, *ethpb.DoppelGangerRequest, *ethpb.DoppelGangerResponse) {
 				mockGen := stategen.NewMockService()
 
-				hs, ps, os, keys := createStateSetup(t, 4, mockGen)
-				// Previous Epoch State
-				for i := 10; i < 15; i++ {
-					bal, err := ps.BalanceAtIndex(types.ValidatorIndex(i))
-					assert.NoError(t, err)
-					// Add 100 gwei, to mock an active validator
-					assert.NoError(t, ps.UpdateBalancesAtIndex(types.ValidatorIndex(i), bal-1000000000))
-				}
-
-				// Older Epoch State
-				for i := 10; i < 15; i++ {
-					bal, err := os.BalanceAtIndex(types.ValidatorIndex(i))
-					assert.NoError(t, err)
-					// Add 200 gwei, to mock an active validator
-					assert.NoError(t, os.UpdateBalancesAtIndex(types.ValidatorIndex(i), bal-2000000000))
-				}
+				hs, _, _, keys := createStateSetup(t, 4, mockGen)
 
 				vs := &Server{
-					StateGen: mockGen,
+					StateGen: nil,
 					HeadFetcher: &mockChain.ChainService{
 						State: hs,
 					},