mpt: move empty hash node in a separate type

We use them quite frequently (consider children for a new branch
node) and it is better to get rid of unneeded allocations.

Signed-off-by: Evgeniy Stratonikov <evgeniy@nspcc.ru>

pkg/core/mpt/base.go

@@ -54,8 +54,8 @@ func (b *BaseNode) getBytes(n Node) []byte {
 
 // updateHash updates hash field for this BaseNode.
 func (b *BaseNode) updateHash(n Node) {
-	if n.Type() == HashT {
-		panic("can't update hash for hash node")
+	if n.Type() == HashT || n.Type() == EmptyT {
+		panic("can't update hash for empty or hash node")
 	}
 	b.hash = hash.DoubleSha256(b.getBytes(n))
 	b.hashValid = true
@@ -86,17 +86,7 @@ func encodeBinaryAsChild(n Node, w *io.BinWriter) {
 
 // encodeNodeWithType encodes node together with it's type.
 func encodeNodeWithType(n Node, w *io.BinWriter) {
-	switch t := n.Type(); t {
-	case HashT:
-		hn := n.(*HashNode)
-		if !hn.hashValid {
-			w.WriteB(byte(EmptyT))
-			break
-		}
-		fallthrough
-	default:
-		w.WriteB(byte(t))
-	}
+	w.WriteB(byte(n.Type()))
 	n.EncodeBinary(w)
 }
 
@@ -120,11 +110,7 @@ func DecodeNodeWithType(r *io.BinReader) Node {
 	case LeafT:
 		n = new(LeafNode)
 	case EmptyT:
-		n = &HashNode{
-			BaseNode: BaseNode{
-				hashValid: false,
-			},
-		}
+		n = EmptyNode{}
 	default:
 		r.Err = fmt.Errorf("invalid node type: %x", typ)
 		return nil

pkg/core/mpt/batch.go

@@ -62,6 +62,8 @@ func (t *Trie) putBatchIntoNode(curr Node, kv []keyValue) (Node, int, error) {
 		return t.putBatchIntoExtension(n, kv)
 	case *HashNode:
 		return t.putBatchIntoHash(n, kv)
+	case EmptyNode:
+		return t.putBatchIntoEmpty(kv)
 	default:
 		panic("invalid MPT node type")
 	}
@@ -84,11 +86,9 @@ func (t *Trie) mergeExtension(prefix []byte, sub Node) (Node, error) {
 		sn.invalidateCache()
 		t.addRef(sn.Hash(), sn.bytes)
 		return sn, nil
+	case EmptyNode:
+		return sn, nil
 	case *HashNode:
-		if sn.IsEmpty() {
-			return sn, nil
-		}
-
 		n, err := t.getFromStore(sn.Hash())
 		if err != nil {
 			return sn, err
@@ -141,8 +141,8 @@ func (t *Trie) putBatchIntoExtensionNoPrefix(key []byte, next Node, kv []keyValu
 }
 
 func isEmpty(n Node) bool {
-	hn, ok := n.(*HashNode)
-	return ok && hn.IsEmpty()
+	_, ok := n.(EmptyNode)
+	return ok
 }
 
 // addToBranch puts items into the branch node assuming b is not yet in trie.
@@ -190,7 +190,7 @@ func (t *Trie) stripBranch(b *BranchNode) (Node, error) {
 	}
 	switch {
 	case n == 0:
-		return new(HashNode), nil
+		return EmptyNode{}, nil
 	case n == 1:
 		if lastIndex != lastChild {
 			return t.mergeExtension([]byte{lastIndex}, b.Children[lastIndex])
@@ -219,12 +219,13 @@ func (t *Trie) iterateBatch(kv []keyValue, f func(c byte, kv []keyValue) (int, e
 	return n, nil
 }
 
+func (t *Trie) putBatchIntoEmpty(kv []keyValue) (Node, int, error) {
+	common := lcpMany(kv)
+	stripPrefix(len(common), kv)
+	return t.newSubTrieMany(common, kv, nil)
+}
+
 func (t *Trie) putBatchIntoHash(curr *HashNode, kv []keyValue) (Node, int, error) {
-	if curr.IsEmpty() {
-		common := lcpMany(kv)
-		stripPrefix(len(common), kv)
-		return t.newSubTrieMany(common, kv, nil)
-	}
 	result, err := t.getFromStore(curr.hash)
 	if err != nil {
 		return curr, 0, err
@@ -242,7 +243,7 @@ func (t *Trie) newSubTrieMany(prefix []byte, kv []keyValue, value []byte) (Node,
 	if len(kv[0].key) == 0 {
 		if len(kv[0].value) == 0 {
 			if len(kv) == 1 {
-				return new(HashNode), 1, nil
+				return EmptyNode{}, 1, nil
 			}
 			node, n, err := t.newSubTrieMany(prefix, kv[1:], nil)
 			return node, n + 1, err

pkg/core/mpt/batch_test.go

@@ -68,8 +68,8 @@ func testPut(t *testing.T, ps pairs, tr1, tr2 *Trie) {
 
 func TestTrie_PutBatchLeaf(t *testing.T) {
 	prepareLeaf := func(t *testing.T) (*Trie, *Trie) {
-		tr1 := NewTrie(new(HashNode), false, newTestStore())
-		tr2 := NewTrie(new(HashNode), false, newTestStore())
+		tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+		tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 		require.NoError(t, tr1.Put([]byte{0}, []byte("value")))
 		require.NoError(t, tr2.Put([]byte{0}, []byte("value")))
 		return tr1, tr2
@@ -97,8 +97,8 @@ func TestTrie_PutBatchLeaf(t *testing.T) {
 
 func TestTrie_PutBatchExtension(t *testing.T) {
 	prepareExtension := func(t *testing.T) (*Trie, *Trie) {
-		tr1 := NewTrie(new(HashNode), false, newTestStore())
-		tr2 := NewTrie(new(HashNode), false, newTestStore())
+		tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+		tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 		require.NoError(t, tr1.Put([]byte{1, 2}, []byte("value1")))
 		require.NoError(t, tr2.Put([]byte{1, 2}, []byte("value1")))
 		return tr1, tr2
@@ -144,8 +144,8 @@ func TestTrie_PutBatchExtension(t *testing.T) {
 
 func TestTrie_PutBatchBranch(t *testing.T) {
 	prepareBranch := func(t *testing.T) (*Trie, *Trie) {
-		tr1 := NewTrie(new(HashNode), false, newTestStore())
-		tr2 := NewTrie(new(HashNode), false, newTestStore())
+		tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+		tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 		require.NoError(t, tr1.Put([]byte{0x00, 2}, []byte("value1")))
 		require.NoError(t, tr2.Put([]byte{0x00, 2}, []byte("value1")))
 		require.NoError(t, tr1.Put([]byte{0x10, 3}, []byte("value2")))
@@ -175,8 +175,8 @@ func TestTrie_PutBatchBranch(t *testing.T) {
 			require.IsType(t, (*ExtensionNode)(nil), tr1.root)
 		})
 		t.Run("non-empty child is last node", func(t *testing.T) {
-			tr1 := NewTrie(new(HashNode), false, newTestStore())
-			tr2 := NewTrie(new(HashNode), false, newTestStore())
+			tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+			tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 			require.NoError(t, tr1.Put([]byte{0x00, 2}, []byte("value1")))
 			require.NoError(t, tr2.Put([]byte{0x00, 2}, []byte("value1")))
 			require.NoError(t, tr1.Put([]byte{0x00}, []byte("value2")))
@@ -222,8 +222,8 @@ func TestTrie_PutBatchBranch(t *testing.T) {
 
 func TestTrie_PutBatchHash(t *testing.T) {
 	prepareHash := func(t *testing.T) (*Trie, *Trie) {
-		tr1 := NewTrie(new(HashNode), false, newTestStore())
-		tr2 := NewTrie(new(HashNode), false, newTestStore())
+		tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+		tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 		require.NoError(t, tr1.Put([]byte{0x10}, []byte("value1")))
 		require.NoError(t, tr2.Put([]byte{0x10}, []byte("value1")))
 		require.NoError(t, tr1.Put([]byte{0x20}, []byte("value2")))
@@ -257,8 +257,8 @@ func TestTrie_PutBatchHash(t *testing.T) {
 
 func TestTrie_PutBatchEmpty(t *testing.T) {
 	t.Run("good", func(t *testing.T) {
-		tr1 := NewTrie(new(HashNode), false, newTestStore())
-		tr2 := NewTrie(new(HashNode), false, newTestStore())
+		tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+		tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 		var ps = pairs{
 			{[]byte{0}, []byte("value0")},
 			{[]byte{1}, []byte("value1")},
@@ -273,15 +273,15 @@ func TestTrie_PutBatchEmpty(t *testing.T) {
 			{[]byte{2}, nil},
 			{[]byte{3}, []byte("replace3")},
 		}
-		tr1 := NewTrie(new(HashNode), false, newTestStore())
-		tr2 := NewTrie(new(HashNode), false, newTestStore())
+		tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+		tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 		testIncompletePut(t, ps, 4, tr1, tr2)
 	})
 }
 
 // For the sake of coverage.
 func TestTrie_InvalidNodeType(t *testing.T) {
-	tr := NewTrie(new(HashNode), false, newTestStore())
+	tr := NewTrie(EmptyNode{}, false, newTestStore())
 	var b Batch
 	b.Add([]byte{1}, []byte("value"))
 	tr.root = Node(nil)
@@ -289,8 +289,8 @@ func TestTrie_InvalidNodeType(t *testing.T) {
 }
 
 func TestTrie_PutBatch(t *testing.T) {
-	tr1 := NewTrie(new(HashNode), false, newTestStore())
-	tr2 := NewTrie(new(HashNode), false, newTestStore())
+	tr1 := NewTrie(EmptyNode{}, false, newTestStore())
+	tr2 := NewTrie(EmptyNode{}, false, newTestStore())
 	var ps = pairs{
 		{[]byte{1}, []byte{1}},
 		{[]byte{2}, []byte{3}},
@@ -312,11 +312,10 @@ var _ = printNode
 // `spew.Dump()`.
 func printNode(prefix string, n Node) {
 	switch tn := n.(type) {
+	case EmptyNode:
+		fmt.Printf("%s empty\n", prefix)
+		return
 	case *HashNode:
-		if tn.IsEmpty() {
-			fmt.Printf("%s empty\n", prefix)
-			return
-		}
 		fmt.Printf("%s %s\n", prefix, tn.Hash().StringLE())
 	case *BranchNode:
 		for i, c := range tn.Children {

pkg/core/mpt/branch.go

@@ -27,7 +27,7 @@ var _ Node = (*BranchNode)(nil)
 func NewBranchNode() *BranchNode {
 	b := new(BranchNode)
 	for i := 0; i < childrenCount; i++ {
-		b.Children[i] = new(HashNode)
+		b.Children[i] = EmptyNode{}
 	}
 	return b
 }

pkg/core/mpt/empty.go

@@ -0,0 +1,53 @@
+package mpt
+
+import (
+	"encoding/json"
+	"errors"
+
+	"github.com/nspcc-dev/neo-go/pkg/io"
+	"github.com/nspcc-dev/neo-go/pkg/util"
+)
+
+// EmptyNode represents empty node.
+type EmptyNode struct{}
+
+// DecodeBinary implements io.Serializable interface.
+func (e EmptyNode) DecodeBinary(*io.BinReader) {
+}
+
+// EncodeBinary implements io.Serializable interface.
+func (e EmptyNode) EncodeBinary(*io.BinWriter) {
+}
+
+// MarshalJSON implements Node interface.
+func (e EmptyNode) MarshalJSON() ([]byte, error) {
+	return []byte(`{}`), nil
+}
+
+// UnmarshalJSON implements Node interface.
+func (e EmptyNode) UnmarshalJSON(bytes []byte) error {
+	var m map[string]interface{}
+	err := json.Unmarshal(bytes, &m)
+	if err != nil {
+		return err
+	}
+	if len(m) != 0 {
+		return errors.New("expected empty node")
+	}
+	return nil
+}
+
+// Hash implements Node interface.
+func (e EmptyNode) Hash() util.Uint256 {
+	panic("can't get hash of an EmptyNode")
+}
+
+// Type implements Node interface.
+func (e EmptyNode) Type() NodeType {
+	return EmptyT
+}
+
+// Bytes implements Node interface.
+func (e EmptyNode) Bytes() []byte {
+	return nil
+}

pkg/core/mpt/hash.go

@@ -35,9 +35,6 @@ func (h *HashNode) Hash() util.Uint256 {
 	return h.hash
 }
 
-// IsEmpty returns true if h is an empty node i.e. contains no hash.
-func (h *HashNode) IsEmpty() bool { return !h.hashValid }
-
 // Bytes returns serialized HashNode.
 func (h *HashNode) Bytes() []byte {
 	return h.getBytes(h)
@@ -60,9 +57,6 @@ func (h HashNode) EncodeBinary(w *io.BinWriter) {
 
 // MarshalJSON implements json.Marshaler.
 func (h *HashNode) MarshalJSON() ([]byte, error) {
-	if !h.hashValid {
-		return []byte(`{}`), nil
-	}
 	return []byte(`{"hash":"` + h.hash.StringLE() + `"}`), nil
 }
 

pkg/core/mpt/node.go

@@ -68,7 +68,7 @@ func (n *NodeObject) UnmarshalJSON(data []byte) error {
 
 	switch len(m) {
 	case 0:
-		n.Node = new(HashNode)
+		n.Node = EmptyNode{}
 	case 1:
 		if v, ok := m["hash"]; ok {
 			var h util.Uint256

pkg/core/mpt/node_test.go

@@ -78,9 +78,6 @@ func TestNode_Serializable(t *testing.T) {
 			t.Run("Raw", getTestFuncEncode(true, h, new(HashNode)))
 			t.Run("WithType", getTestFuncEncode(true, &NodeObject{h}, new(NodeObject)))
 		})
-		t.Run("Empty", func(t *testing.T) { // compare nodes, not hashes
-			testserdes.EncodeDecodeBinary(t, new(HashNode), new(HashNode))
-		})
 		t.Run("InvalidSize", func(t *testing.T) {
 			buf := io.NewBufBinWriter()
 			buf.BinWriter.WriteBytes(make([]byte, 13))
@@ -111,7 +108,7 @@ func TestInvalidJSON(t *testing.T) {
 	t.Run("InvalidChildrenCount", func(t *testing.T) {
 		var cs [childrenCount + 1]Node
 		for i := range cs {
-			cs[i] = new(HashNode)
+			cs[i] = EmptyNode{}
 		}
 		data, err := json.Marshal(cs)
 		require.NoError(t, err)

pkg/core/mpt/proof.go

@@ -49,13 +49,11 @@ func (t *Trie) getProof(curr Node, path []byte, proofs *[][]byte) (Node, error)
 			return n, nil
 		}
 	case *HashNode:
-		if !n.IsEmpty() {
-			r, err := t.getFromStore(n.Hash())
-			if err != nil {
-				return nil, err
-			}
-			return t.getProof(r, path, proofs)
+		r, err := t.getFromStore(n.Hash())
+		if err != nil {
+			return nil, err
 		}
+		return t.getProof(r, path, proofs)
 	}
 	return nil, ErrNotFound
 }

pkg/core/mpt/trie.go

@@ -35,7 +35,7 @@ var ErrNotFound = errors.New("item not found")
 // This also has the benefit, that every `Put` can be considered an atomic operation.
 func NewTrie(root Node, enableRefCount bool, store *storage.MemCachedStore) *Trie {
 	if root == nil {
-		root = new(HashNode)
+		root = EmptyNode{}
 	}
 
 	return &Trie{
@@ -75,11 +75,10 @@ func (t *Trie) getWithPath(curr Node, path []byte) (Node, []byte, error) {
 		}
 		n.Children[i] = r
 		return n, bs, nil
+	case EmptyNode:
 	case *HashNode:
-		if !n.IsEmpty() {
-			if r, err := t.getFromStore(n.hash); err == nil {
-				return t.getWithPath(r, path)
-			}
+		if r, err := t.getFromStore(n.hash); err == nil {
+			return t.getWithPath(r, path)
 		}
 	case *ExtensionNode:
 		if bytes.HasPrefix(path, n.key) {
@@ -187,14 +186,13 @@ func (t *Trie) putIntoExtension(curr *ExtensionNode, path []byte, val Node) (Nod
 	return b, nil
 }
 
+func (t *Trie) putIntoEmpty(path []byte, val Node) (Node, error) {
+	return t.newSubTrie(path, val, true), nil
+}
+
 // putIntoHash puts val to trie if current node is a HashNode.
 // It returns Node if curr needs to be replaced and error if any.
 func (t *Trie) putIntoHash(curr *HashNode, path []byte, val Node) (Node, error) {
-	if curr.IsEmpty() {
-		hn := t.newSubTrie(path, val, true)
-		return hn, nil
-	}
-
 	result, err := t.getFromStore(curr.hash)
 	if err != nil {
 		return nil, err
@@ -227,6 +225,8 @@ func (t *Trie) putIntoNode(curr Node, path []byte, val Node) (Node, error) {
 		return t.putIntoExtension(n, path, val)
 	case *HashNode:
 		return t.putIntoHash(n, path, val)
+	case EmptyNode:
+		return t.putIntoEmpty(path, val)
 	default:
 		panic("invalid MPT node type")
 	}
@@ -257,8 +257,7 @@ func (t *Trie) deleteFromBranch(b *BranchNode, path []byte) (Node, error) {
 	b.invalidateCache()
 	var count, index int
 	for i := range b.Children {
-		h, ok := b.Children[i].(*HashNode)
-		if !ok || !h.IsEmpty() {
+		if !isEmpty(b.Children[i]) {
 			index = i
 			count++
 		}
@@ -307,10 +306,9 @@ func (t *Trie) deleteFromExtension(n *ExtensionNode, path []byte) (Node, error)
 		t.removeRef(nxt.Hash(), nxt.bytes)
 		n.key = append(n.key, nxt.key...)
 		n.next = nxt.next
+	case EmptyNode:
+		return nxt, nil
 	case *HashNode:
-		if nxt.IsEmpty() {
-			return nxt, nil
-		}
 		n.next = nxt
 	default:
 		n.next = r
@@ -327,17 +325,16 @@ func (t *Trie) deleteFromNode(curr Node, path []byte) (Node, error) {
 	case *LeafNode:
 		if len(path) == 0 {
 			t.removeRef(curr.Hash(), curr.Bytes())
-			return new(HashNode), nil
+			return EmptyNode{}, nil
 		}
 		return curr, nil
 	case *BranchNode:
 		return t.deleteFromBranch(n, path)
 	case *ExtensionNode:
 		return t.deleteFromExtension(n, path)
+	case EmptyNode:
+		return n, nil
 	case *HashNode:
-		if n.IsEmpty() {
-			return n, nil
-		}
 		newNode, err := t.getFromStore(n.Hash())
 		if err != nil {
 			return nil, err
@@ -350,7 +347,7 @@ func (t *Trie) deleteFromNode(curr Node, path []byte) (Node, error) {
 
 // StateRoot returns root hash of t.
 func (t *Trie) StateRoot() util.Uint256 {
-	if hn, ok := t.root.(*HashNode); ok && hn.IsEmpty() {
+	if isEmpty(t.root) {
 		return util.Uint256{}
 	}
 	return t.root.Hash()
@@ -486,9 +483,11 @@ func (t *Trie) Collapse(depth int) {
 }
 
 func collapse(depth int, node Node) Node {
-	if _, ok := node.(*HashNode); ok {
+	switch node.(type) {
+	case *HashNode, EmptyNode:
 		return node
-	} else if depth == 0 {
+	}
+	if depth == 0 {
 		return NewHashNode(node.Hash())
 	}
 

pkg/core/mpt/trie_test.go

@@ -239,8 +239,7 @@ func isValid(curr Node) bool {
 			if !isValid(n.Children[i]) {
 				return false
 			}
-			hn, ok := n.Children[i].(*HashNode)
-			if !ok || !hn.IsEmpty() {
+			if !isEmpty(n.Children[i]) {
 				count++
 			}
 		}
@@ -342,7 +341,7 @@ func testTrieDelete(t *testing.T, enableGC bool) {
 			})
 
 			require.NoError(t, tr.Delete([]byte{0xAB}))
-			require.True(t, tr.root.(*HashNode).IsEmpty())
+			require.IsType(t, EmptyNode{}, tr.root)
 		})
 
 		t.Run("MultipleKeys", func(t *testing.T) {
@@ -505,12 +504,11 @@ func TestTrie_Collapse(t *testing.T) {
 		require.Equal(t, NewLeafNode([]byte("value")), tr.root)
 	})
 	t.Run("Hash", func(t *testing.T) {
-		t.Run("Empty", func(t *testing.T) {
-			tr := NewTrie(new(HashNode), false, newTestStore())
+		t.Run("EmptyNode", func(t *testing.T) {
+			tr := NewTrie(EmptyNode{}, false, newTestStore())
 			require.NotPanics(t, func() { tr.Collapse(1) })
-			hn, ok := tr.root.(*HashNode)
+			_, ok := tr.root.(EmptyNode)
 			require.True(t, ok)
-			require.True(t, hn.IsEmpty())
 		})
 
 		h := random.Uint256()