Author a sibling block in case best block's slot is same as current s…

…lot (#2726)

dot/services.go

@@ -175,6 +175,7 @@ func (nb nodeBuilder) createBABEService(cfg *Config, st *state.Service, ks keyst
 	cs *core.Service, telemetryMailer telemetry.Client) (babe.ServiceIFace, error) {
 	return nb.createBABEServiceWithBuilder(cfg, st, ks, cs, telemetryMailer, babe.Builder{})
 }
+
 func (nodeBuilder) createBABEServiceWithBuilder(cfg *Config, st *state.Service, ks keystore.Keystore,
 	cs *core.Service, telemetryMailer telemetry.Client, newBabeService ServiceBuilder) (babe.
 	ServiceIFace, error) {

dot/types/authority.go

@@ -16,7 +16,9 @@ import (
 
 // Authority struct to hold authority data
 type Authority struct {
-	Key    crypto.PublicKey
+	Key crypto.PublicKey
+	// Weight exists for potential improvements in the protocol and could
+	// have a use-case in the future. In polkadot all authorities have the weight = 1.
 	Weight uint64
 }
 

lib/babe/babe.go

@@ -467,6 +467,30 @@ func (b *Service) handleSlot(epoch, slotNum uint64,
 		return errNilParentHeader
 	}
 
+	atGenesisBlock := b.blockState.GenesisHash().Equal(parentHeader.Hash())
+	if !atGenesisBlock {
+		bestBlockSlotNum, err := b.blockState.GetSlotForBlock(parentHeader.Hash())
+		if err != nil {
+			return fmt.Errorf("could not get slot for block %s: %w", parentHeader.Hash(), err)
+		}
+
+		if bestBlockSlotNum > slotNum {
+			return errLaggingSlot
+		}
+
+		if bestBlockSlotNum == slotNum {
+			// pick parent of best block instead to handle slot
+			newParentHeader, err := b.blockState.GetHeader(parentHeader.ParentHash)
+			if err != nil {
+				return fmt.Errorf("could not get header for hash %s: %w", parentHeader.ParentHash, err)
+			}
+			if newParentHeader == nil {
+				return errNilParentHeader
+			}
+			parentHeader = newParentHeader
+		}
+	}
+
 	// there is a chance that the best block header may change in the course of building the block,
 	// so let's copy it first.
 	parent, err := parentHeader.DeepCopy()

lib/babe/babe_integration_test.go

@@ -15,6 +15,7 @@ import (
 	"github.com/ChainSafe/gossamer/dot/types"
 	"github.com/ChainSafe/gossamer/internal/log"
 	"github.com/ChainSafe/gossamer/lib/babe/mocks"
+	"github.com/ChainSafe/gossamer/lib/common"
 	"github.com/ChainSafe/gossamer/lib/crypto/sr25519"
 	"github.com/ChainSafe/gossamer/lib/genesis"
 	"github.com/ChainSafe/gossamer/lib/runtime"
@@ -293,3 +294,173 @@ func TestService_PauseAndResume(t *testing.T) {
 	err = bs.Stop()
 	require.NoError(t, err)
 }
+
+func TestService_HandleSlotWithLaggingSlot(t *testing.T) {
+	cfg := &ServiceConfig{
+		Authority: true,
+		Lead:      true,
+	}
+	babeService := createTestService(t, cfg)
+
+	err := babeService.Start()
+	require.NoError(t, err)
+	defer func() {
+		_ = babeService.Stop()
+	}()
+
+	// add a block
+	parentHash := babeService.blockState.GenesisHash()
+	rt, err := babeService.blockState.GetRuntime(nil)
+	require.NoError(t, err)
+
+	epochData, err := babeService.initiateEpoch(testEpochIndex)
+	require.NoError(t, err)
+
+	ext := runtime.NewTestExtrinsic(t, rt, parentHash, parentHash, 0, "System.remark", []byte{0xab, 0xcd})
+	block := createTestBlock(t, babeService, emptyHeader, [][]byte{common.MustHexToBytes(ext)},
+		1, testEpochIndex, epochData)
+
+	babeService.blockState.AddBlock(block)
+	time.Sleep(babeService.constants.slotDuration * 1)
+
+	header, err := babeService.blockState.BestBlockHeader()
+	require.NoError(t, err)
+
+	bestBlockSlotNum, err := babeService.blockState.GetSlotForBlock(header.Hash())
+	require.NoError(t, err)
+
+	slotnum := uint64(1)
+	slot := Slot{
+		start:    time.Now(),
+		duration: 1 * time.Second,
+		number:   slotnum,
+	}
+	testVRFOutputAndProof := &VrfOutputAndProof{}
+	preRuntimeDigest, err := types.NewBabePrimaryPreDigest(
+		0, slot.number,
+		testVRFOutputAndProof.output,
+		testVRFOutputAndProof.proof,
+	).ToPreRuntimeDigest()
+
+	require.NoError(t, err)
+
+	err = babeService.handleSlot(
+		babeService.epochHandler.epochNumber,
+		bestBlockSlotNum-1,
+		babeService.epochHandler.epochData.authorityIndex,
+		preRuntimeDigest)
+
+	require.ErrorIs(t, err, errLaggingSlot)
+}
+
+func TestService_HandleSlotWithSameSlot(t *testing.T) {
+	alice := keyring.Alice().(*sr25519.Keypair)
+	bob := keyring.Bob().(*sr25519.Keypair)
+
+	// Create babe service for alice
+	cfgAlice := &ServiceConfig{
+		Authority: true,
+		Lead:      true,
+		Keypair:   alice,
+	}
+	cfgAlice.AuthData = []types.Authority{
+		{
+			Key:    alice.Public().(*sr25519.PublicKey),
+			Weight: 1,
+		},
+		{
+			Key:    bob.Public().(*sr25519.PublicKey),
+			Weight: 1,
+		},
+	}
+
+	// Create babe service for bob
+	cfgBob := &ServiceConfig{
+		Authority: true,
+		Lead:      true,
+		Keypair:   bob,
+	}
+	cfgBob.AuthData = []types.Authority{
+		{
+			Key:    alice.Public().(*sr25519.PublicKey),
+			Weight: 1,
+		},
+		{
+			Key:    bob.Public().(*sr25519.PublicKey),
+			Weight: 1,
+		},
+	}
+
+	babeServiceBob := createTestService(t, cfgBob)
+
+	err := babeServiceBob.Start()
+	require.NoError(t, err)
+	defer func() {
+		_ = babeServiceBob.Stop()
+	}()
+
+	time.Sleep(babeServiceBob.constants.slotDuration * 5)
+
+	// create a block using bob
+	parentHash := babeServiceBob.blockState.GenesisHash()
+	rt, err := babeServiceBob.blockState.GetRuntime(nil)
+	require.NoError(t, err)
+
+	epochData, err := babeServiceBob.initiateEpoch(testEpochIndex)
+	require.NoError(t, err)
+
+	ext := runtime.NewTestExtrinsic(t, rt, parentHash, parentHash, 0, "System.remark", []byte{0xab, 0xcd})
+	block := createTestBlock(t, babeServiceBob, emptyHeader, [][]byte{common.MustHexToBytes(ext)},
+		1, testEpochIndex, epochData)
+
+	err = babeServiceBob.Stop()
+	require.NoError(t, err)
+
+	babeServiceAlice := createTestService(t, cfgAlice)
+
+	err = babeServiceAlice.Start()
+	require.NoError(t, err)
+	defer func() {
+		_ = babeServiceAlice.Stop()
+	}()
+	time.Sleep(babeServiceAlice.constants.slotDuration * 1)
+
+	// Add block created by Bob to Alice
+	babeServiceAlice.blockState.AddBlock(block)
+
+	time.Sleep(babeServiceAlice.constants.slotDuration * 1)
+
+	bestBlockHeader, err := babeServiceAlice.blockState.BestBlockHeader()
+	require.NoError(t, err)
+
+	require.Equal(t, block.Header.Hash().String(), bestBlockHeader.Hash().String())
+
+	// If the slot we are claiming is same as slot in best header, test that we don't
+	// through any error and can claim slot.
+	bestBlockSlotNum, err := babeServiceAlice.blockState.GetSlotForBlock(bestBlockHeader.Hash())
+	require.NoError(t, err)
+
+	err = babeServiceAlice.Stop()
+	require.NoError(t, err)
+
+	slot := Slot{
+		start:    time.Now(),
+		duration: 1 * time.Second,
+		number:   bestBlockSlotNum,
+	}
+	testVRFOutputAndProof := &VrfOutputAndProof{}
+	preRuntimeDigest, err := types.NewBabePrimaryPreDigest(
+		0, slot.number,
+		testVRFOutputAndProof.output,
+		testVRFOutputAndProof.proof,
+	).ToPreRuntimeDigest()
+	require.NoError(t, err)
+
+	err = babeServiceAlice.handleSlot(
+		babeServiceAlice.epochHandler.epochNumber,
+		bestBlockSlotNum,
+		babeServiceAlice.epochHandler.epochData.authorityIndex,
+		preRuntimeDigest)
+	require.NoError(t, err)
+
+}

lib/babe/errors.go

@@ -71,6 +71,7 @@ var (
 	errInvalidSlotTechnique       = errors.New("invalid slot claiming technique")
 	errNoBABEAuthorityKeyProvided = errors.New("cannot create BABE service as authority; no keypair provided")
 	errLastDigestItemNotSeal      = errors.New("last digest item is not seal")
+	errLaggingSlot                = errors.New("cannot claim slot, current slot is smaller than slot of best block")
 
 	other         Other
 	invalidCustom InvalidCustom

lib/genesis/test_utils.go

@@ -13,6 +13,7 @@ import (
 	"github.com/ChainSafe/gossamer/lib/common"
 	"github.com/ChainSafe/gossamer/lib/trie"
 	"github.com/ChainSafe/gossamer/lib/utils"
+	"github.com/ChainSafe/gossamer/pkg/scale"
 	"github.com/stretchr/testify/require"
 )
 
@@ -100,8 +101,22 @@ func newGenesisTrieAndHeader(t *testing.T, gen *Genesis) (*trie.Trie, *types.Hea
 	genTrie, err := NewTrieFromGenesis(gen)
 	require.NoError(t, err)
 
+	babeDigest := types.NewBabeDigest()
+	err = babeDigest.Set(types.BabePrimaryPreDigest{AuthorityIndex: 0})
+	require.NoError(t, err)
+
+	bdEnc, err := scale.Marshal(babeDigest)
+	require.NoError(t, err)
+
+	digest := types.NewDigest()
+	err = digest.Add(types.PreRuntimeDigest{
+		ConsensusEngineID: types.BabeEngineID,
+		Data:              bdEnc,
+	})
+	require.NoError(t, err)
+
 	genesisHeader, err := types.NewHeader(common.NewHash([]byte{0}),
-		genTrie.MustHash(), trie.EmptyHash, 0, types.NewDigest())
+		genTrie.MustHash(), trie.EmptyHash, 0, digest)
 	require.NoError(t, err)
 
 	return genTrie, genesisHeader