handle the case when epoch data is nil (#2590)

Fixes #2584

dot/state/epoch.go

@@ -17,9 +17,11 @@ import (
 )
 
 var (
-	ErrEpochNotInMemory = errors.New("epoch not found in memory map")
-	errHashNotInMemory  = errors.New("hash not found in memory map")
-	errHashNotPersisted = errors.New("hash with next epoch not found in database")
+	ErrEpochNotInMemory   = errors.New("epoch not found in memory map")
+	errHashNotInMemory    = errors.New("hash not found in memory map")
+	errEpochDataNotFound  = errors.New("epoch data not found in the database")
+	errHashNotPersisted   = errors.New("hash with next epoch not found in database")
+	errNoPreRuntimeDigest = errors.New("header does not contain pre-runtime digest")
 )
 
 var (
@@ -225,7 +227,7 @@ func (s *EpochState) GetEpochForBlock(header *types.Header) (uint64, error) {
 		return (slotNumber - firstSlot) / s.epochLength, nil
 	}
 
-	return 0, errors.New("header does not contain pre-runtime digest")
+	return 0, errNoPreRuntimeDigest
 }
 
 // SetEpochData sets the epoch data for a given epoch
@@ -251,14 +253,19 @@ func (s *EpochState) GetEpochData(epoch uint64, header *types.Header) (*types.Ep
 
 	if err != nil && !errors.Is(err, chaindb.ErrKeyNotFound) {
 		return nil, fmt.Errorf("failed to get epoch data from database: %w", err)
-	} else if header == nil {
-		// if no header is given then skip the lookup in-memory
-		return epochData, nil
 	}
 
-	epochData, err = s.getEpochDataFromMemory(epoch, header)
-	if err != nil {
-		return nil, fmt.Errorf("failed to get epoch data from memory: %w", err)
+	//  lookup in-memory only if header is given
+	if header != nil && errors.Is(err, chaindb.ErrKeyNotFound) {
+		epochData, err = s.getEpochDataFromMemory(epoch, header)
+		if err != nil {
+			return nil, fmt.Errorf("failed to get epoch data from memory: %w", err)
+		}
+	}
+
+	if epochData == nil {
+		return nil, fmt.Errorf("%w: for epoch %d and header with hash %s",
+			errEpochDataNotFound, epoch, header.Hash())
 	}
 
 	return epochData, nil
@@ -543,6 +550,10 @@ func (s *EpochState) StoreBABENextConfigData(epoch uint64, hash common.Hash, nex
 // check if the header is in the database then it's been finalized and
 // thus we can also set the corresponding EpochData in the database
 func (s *EpochState) FinalizeBABENextEpochData(finalizedHeader *types.Header) error {
+	if finalizedHeader.Number == 0 {
+		return nil
+	}
+
 	s.nextEpochDataLock.Lock()
 	defer s.nextEpochDataLock.Unlock()
 
@@ -600,6 +611,10 @@ func (s *EpochState) FinalizeBABENextEpochData(finalizedHeader *types.Header) er
 // check if the header is in the database then it's been finalized and
 // thus we can also set the corresponding NextConfigData in the database
 func (s *EpochState) FinalizeBABENextConfigData(finalizedHeader *types.Header) error {
+	if finalizedHeader.Number == 0 {
+		return nil
+	}
+
 	s.nextConfigDataLock.Lock()
 	defer s.nextConfigDataLock.Unlock()
 

lib/babe/verify.go

@@ -341,6 +341,7 @@ func (b *verifier) verifyAuthorshipRight(header *types.Header) error {
 	}
 
 	// check if the producer has equivocated, ie. have they produced a conflicting block?
+	// hashes is hashes of all blocks with same block number as header.Number
 	hashes := b.blockState.GetAllBlocksAtDepth(header.ParentHash)
 
 	for _, hash := range hashes {
@@ -364,6 +365,7 @@ func (b *verifier) verifyAuthorshipRight(header *types.Header) error {
 			existingBlockProducerIndex = d.AuthorityIndex
 		}
 
+		// same authority won't produce two different blocks at the same block number
 		if currentBlockProducerIndex == existingBlockProducerIndex && hash != header.Hash() {
 			return ErrProducerEquivocated
 		}

pkg/scale/varying_data_type.go

@@ -12,7 +12,7 @@ type VaryingDataTypeValue interface {
 	Index() uint
 }
 
-// VaryingDataTypeSlice is used to represent []VaryingDataType.  SCALE requires knowledge
+// VaryingDataTypeSlice is used to represent []VaryingDataType. SCALE requires knowledge
 // of the underlying data, so it is required to have the VaryingDataType required for decoding
 type VaryingDataTypeSlice struct {
 	VaryingDataType