Implement symmetric difference iterator

utils/iterator.go

@@ -1 +1,155 @@
 package utils
+
+import (
+	"bytes"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/trie"
+)
+
+type symmDiffIterator struct {
+	a, b       iterState // Nodes returned are those in b - a and a - b (keys only)
+	yieldFromA bool      // Whether next node comes from a
+	count      int       // Number of nodes scanned on either trie
+}
+
+// NewDifferenceIterator constructs a trie.NodeIterator that iterates over the exclusive elements in b that
+// are not in a. Returns the iterator, and a pointer to an integer recording the number
+// of nodes seen.
+func NewSymmetricDifferenceIterator(a, b trie.NodeIterator) (*symmDiffIterator, *int) {
+	it := &symmDiffIterator{
+		a: iterState{a, true},
+		b: iterState{b, true},
+	}
+	return it, &it.count
+}
+
+// pairs an iterator with a cache of its valid status
+type iterState struct {
+	trie.NodeIterator
+	valid bool
+}
+
+func (st *iterState) Next(descend bool) bool {
+	st.valid = st.NodeIterator.Next(descend)
+	return st.valid
+}
+
+func (it *symmDiffIterator) curr() *iterState {
+	if it.yieldFromA {
+		return &it.a
+	}
+	return &it.b
+}
+
+// FromA returns true if the current node is sourced from A.
+func (it *symmDiffIterator) FromA() bool {
+	return it.yieldFromA
+}
+
+func (it *symmDiffIterator) Hash() common.Hash {
+	return it.curr().Hash()
+}
+
+func (it *symmDiffIterator) Parent() common.Hash {
+	return it.curr().Parent()
+}
+
+func (it *symmDiffIterator) Leaf() bool {
+	return it.curr().Leaf()
+}
+
+func (it *symmDiffIterator) LeafKey() []byte {
+	return it.curr().LeafKey()
+}
+
+func (it *symmDiffIterator) LeafBlob() []byte {
+	return it.curr().LeafBlob()
+}
+
+func (it *symmDiffIterator) LeafProof() [][]byte {
+	return it.curr().LeafProof()
+}
+
+func (it *symmDiffIterator) Path() []byte {
+	return it.curr().Path()
+}
+
+func (it *symmDiffIterator) NodeBlob() []byte {
+	return it.curr().NodeBlob()
+}
+
+func (it *symmDiffIterator) AddResolver(resolver trie.NodeResolver) {
+	panic("not implemented")
+}
+
+func (it *symmDiffIterator) Next(bool) bool {
+	// NodeIterators start in a "pre-valid" state, so you have to call Next before they point to a
+	// valid node. This delays advancing the sub-iterators until they are so initialized by seek.
+	if it.count != 0 {
+		if it.curr().Next(true) {
+			it.count++
+		}
+	}
+	it.seek()
+	return it.a.valid || it.b.valid
+}
+
+func (it *symmDiffIterator) seek() {
+	// Invariants:
+	// - At the end of the function, the sub-iterator with the lexically lesser path
+	// points to the next element
+	// - Said sub-iterator never points to an element present in the other
+	for {
+		if !it.b.valid {
+			it.yieldFromA = true
+			return
+		}
+		if !it.a.valid {
+			it.yieldFromA = false
+			return
+		}
+
+		switch compareNodes(&it.a, &it.b) {
+		case -1:
+			it.yieldFromA = true
+			return
+		case 1:
+			it.yieldFromA = false
+			return
+		case 0:
+			if it.a.Next(true) {
+				it.count++
+			}
+			if it.b.Next(true) {
+				it.count++
+			}
+		}
+	}
+}
+
+func (it *symmDiffIterator) Error() error {
+	if err := it.a.Error(); err != nil {
+		return err
+	}
+	return it.b.Error()
+}
+
+// Compares nodes with equal paths by value
+func compareNodes(a, b trie.NodeIterator) int {
+	if cmp := bytes.Compare(a.Path(), b.Path()); cmp != 0 {
+		return cmp
+	}
+	if a.Leaf() && !b.Leaf() {
+		return -1
+	} else if b.Leaf() && !a.Leaf() {
+		return 1
+	}
+	if cmp := bytes.Compare(a.Hash().Bytes(), b.Hash().Bytes()); cmp != 0 {
+		return cmp
+	}
+	if a.Leaf() && b.Leaf() {
+		return bytes.Compare(a.LeafBlob(), b.LeafBlob())
+	}
+	return 0
+}

utils/iterator_test.go

@@ -0,0 +1,97 @@
+package utils_test
+
+import (
+	"testing"
+
+	"github.com/cerc-io/plugeth-statediff/utils"
+	"github.com/ethereum/go-ethereum/core/rawdb"
+	"github.com/ethereum/go-ethereum/trie"
+
+	"github.com/stretchr/testify/assert"
+)
+
+type kvs struct{ k, v string }
+
+var (
+	testdata1 = []kvs{
+		{"bar", "b"},
+		{"barb", "ba"},
+		{"bard", "bc"},
+		{"bars", "bb"},
+		{"fab", "z"},
+		{"foo", "a"},
+		{"food", "ab"},
+	}
+
+	testdata2 = []kvs{
+		{"aardvark", "c"},
+		{"bar", "b"},
+		{"barb", "bd"},
+		{"bars", "be"},
+		{"fab", "z"},
+		{"foo", "a"},
+		{"foos", "aa"},
+		{"jars", "d"},
+	}
+)
+
+func TestSymmetricDifferenceIterator(t *testing.T) {
+	t.Run("with no difference", func(t *testing.T) {
+		db := trie.NewDatabase(rawdb.NewMemoryDatabase())
+		tree := trie.NewEmpty(db)
+		di, count := utils.NewSymmetricDifferenceIterator(tree.NodeIterator(nil), tree.NodeIterator(nil))
+		for di.Next(true) {
+			t.Errorf("iterator should not yield any elements")
+		}
+		assert.Equal(t, 0, *count)
+
+		tree.MustUpdate([]byte("foo"), []byte("bar"))
+		di, count = utils.NewSymmetricDifferenceIterator(tree.NodeIterator(nil), tree.NodeIterator(nil))
+		for di.Next(true) {
+			t.Errorf("iterator should not yield any elements")
+		}
+		assert.NotEqual(t, 0, count)
+	})
+
+	dba := trie.NewDatabase(rawdb.NewMemoryDatabase())
+	triea := trie.NewEmpty(dba)
+	for _, val := range testdata1 {
+		triea.MustUpdate([]byte(val.k), []byte(val.v))
+	}
+	dbb := trie.NewDatabase(rawdb.NewMemoryDatabase())
+	trieb := trie.NewEmpty(dbb)
+	for _, val := range testdata2 {
+		trieb.MustUpdate([]byte(val.k), []byte(val.v))
+	}
+
+	onlyA := make(map[string]string)
+	onlyB := make(map[string]string)
+	it, _ := utils.NewSymmetricDifferenceIterator(triea.NodeIterator(nil), trieb.NodeIterator(nil))
+	for it.Next(true) {
+		if !it.Leaf() {
+			continue
+		}
+		key, value := string(it.LeafKey()), string(it.LeafBlob())
+		if it.FromA() {
+			onlyA[key] = value
+		} else {
+			onlyB[key] = value
+		}
+	}
+
+	expectedOnlyA := map[string]string{
+		"barb": "ba",
+		"bard": "bc",
+		"bars": "bb",
+		"food": "ab",
+	}
+	expectedOnlyB := map[string]string{
+		"aardvark": "c",
+		"barb":     "bd",
+		"bars":     "be",
+		"foos":     "aa",
+		"jars":     "d",
+	}
+	assert.Equal(t, expectedOnlyA, onlyA)
+	assert.Equal(t, expectedOnlyB, onlyB)
+}