fix(blockstate): if blocktree fails to search a hash in memory, load it from disk

dot/state/block.go

@@ -250,14 +250,62 @@ func (bs *BlockState) GetHashByNumber(num uint) (common.Hash, error) {
 	return common.NewHash(bh), nil
 }
 
+// GetAllDescendants gets all the descendants even if hash is not stored in memory.
+func (bs *BlockState) GetAllDescendants(hash common.Hash) ([]common.Hash, error) {
+	allDescendants, err := bs.bt.GetAllDescendants(hash)
+	if err != nil && !errors.Is(err, blocktree.ErrNodeNotFound) {
+		return nil, err
+	}
+
+	if err == nil {
+		return allDescendants, nil
+	}
+
+	header, err := bs.GetHeader(hash)
+	if err != nil {
+		return nil, fmt.Errorf("getting header from hash %s: %w", hash, err)
+	}
+
+	// TODO: Use GetBlocksByNumber after /~https://github.com/ChainSafe/gossamer/issues/2748 is done
+	nextBlock, err := bs.GetBlockByNumber(header.Number + 1)
+	if err != nil {
+		return nil, fmt.Errorf("getting block by number %d: %w", header.Number+1, err)
+	}
+
+	// next block number is not descendant of hash
+	if nextBlock.Header.ParentHash != hash {
+		return nil, nil
+	}
+
+	allDescendants = append(allDescendants, nextBlock.Header.Hash())
+
+	nextDescendants, err := bs.bt.GetAllDescendants(nextBlock.Header.Hash())
+	if err != nil && !errors.Is(err, blocktree.ErrNodeNotFound) {
+		return nil, fmt.Errorf("failed to get descendants: %w", err)
+	}
+	if err == nil {
+		allDescendants = append(allDescendants, nextDescendants...)
+		return allDescendants, nil
+	}
+
+	nextDescendants, err = bs.GetAllDescendants(nextBlock.Header.Hash())
+	if err != nil {
+		return nil, err
+	}
+
+	allDescendants = append(allDescendants, nextDescendants...)
+
+	return allDescendants, nil
+}
+
 // GetBlockHashesBySlot gets all block hashes that were produced in the given slot.
 func (bs *BlockState) GetBlockHashesBySlot(slotNum uint64) ([]common.Hash, error) {
 	highestFinalisedHash, err := bs.GetHighestFinalisedHash()
 	if err != nil {
 		return nil, fmt.Errorf("failed to get highest finalised hash: %w", err)
 	}
 
-	descendants, err := bs.bt.GetAllDescendants(highestFinalisedHash)
+	descendants, err := bs.GetAllDescendants(highestFinalisedHash)
 	if err != nil {
 		return nil, fmt.Errorf("failed to get descendants: %w", err)
 	}

lib/blocktree/blocktree.go

@@ -10,6 +10,7 @@ import (
 	"time"
 
 	"github.com/ChainSafe/gossamer/dot/types"
+
 	"github.com/ChainSafe/gossamer/lib/common"
 	"github.com/disiqueira/gotree"
 	"github.com/prometheus/client_golang/prometheus"