From ef93b63dfcfd5f30c185bfcf0dc7a3725c7267cd Mon Sep 17 00:00:00 2001
From: gary rong <garyrong0905@gmail.com>
Date: Wed, 23 Sep 2020 16:03:21 +0800
Subject: [PATCH] trie: support empty range proof (#21199)

---
 trie/proof.go      | 21 +++++++++++++++++----
 trie/proof_test.go | 33 +++++++++++++++++++++++++++++++++
 2 files changed, 50 insertions(+), 4 deletions(-)

diff --git a/trie/proof.go b/trie/proof.go
index 6fc21fc1f7ee..326235a3fdea 100644
--- a/trie/proof.go
+++ b/trie/proof.go
@@ -393,7 +393,7 @@ func hasRightElement(node node, key []byte) bool {
 // (unless firstProof is an existent proof).
 //
 // Expect the normal case, this function can also be used to verify the following
-// range proofs(note this function doesn't accept zero element proof):
+// range proofs:
 //
 // - All elements proof. In this case the left and right proof can be nil, but the
 //   range should be all the leaves in the trie.
@@ -401,15 +401,16 @@ func hasRightElement(node node, key []byte) bool {
 // - One element proof. In this case no matter the left edge proof is a non-existent
 //   proof or not, we can always verify the correctness of the proof.
 //
+// - Zero element proof(left edge proof should be a non-existent proof). In this
+//   case if there are still some other leaves available on the right side, then
+//   an error will be returned.
+//
 // Except returning the error to indicate the proof is valid or not, the function will
 // also return a flag to indicate whether there exists more accounts/slots in the trie.
 func VerifyRangeProof(rootHash common.Hash, firstKey []byte, keys [][]byte, values [][]byte, firstProof ethdb.KeyValueReader, lastProof ethdb.KeyValueReader) (error, bool) {
 	if len(keys) != len(values) {
 		return fmt.Errorf("inconsistent proof data, keys: %d, values: %d", len(keys), len(values)), false
 	}
-	if len(keys) == 0 {
-		return errors.New("empty proof"), false
-	}
 	// Ensure the received batch is monotonic increasing.
 	for i := 0; i < len(keys)-1; i++ {
 		if bytes.Compare(keys[i], keys[i+1]) >= 0 {
@@ -431,6 +432,18 @@ func VerifyRangeProof(rootHash common.Hash, firstKey []byte, keys [][]byte, valu
 		}
 		return nil, false // no more element.
 	}
+	// Special case, there is a provided left edge proof and zero key/value
+	// pairs, ensure there are no more accounts / slots in the trie.
+	if len(keys) == 0 {
+		root, val, err := proofToPath(rootHash, nil, firstKey, firstProof, true)
+		if err != nil {
+			return err, false
+		}
+		if val != nil || hasRightElement(root, firstKey) {
+			return errors.New("more entries available"), false
+		}
+		return nil, false
+	}
 	// Special case, there is only one element and left edge
 	// proof is an existent one.
 	if len(keys) == 1 && bytes.Equal(keys[0], firstKey) {
diff --git a/trie/proof_test.go b/trie/proof_test.go
index db0e4051c8bf..4d76f3f783a4 100644
--- a/trie/proof_test.go
+++ b/trie/proof_test.go
@@ -571,6 +571,39 @@ func TestHasRightElement(t *testing.T) {
 	}
 }
 
+// TestEmptyRangeProof tests the range proof with "no" element.
+// The first edge proof must be a non-existent proof.
+func TestEmptyRangeProof(t *testing.T) {
+	trie, vals := randomTrie(4096)
+	var entries entrySlice
+	for _, kv := range vals {
+		entries = append(entries, kv)
+	}
+	sort.Sort(entries)
+
+	var cases = []struct {
+		pos int
+		err bool
+	}{
+		{len(entries) - 1, false},
+		{500, true},
+	}
+	for _, c := range cases {
+		firstProof := memorydb.New()
+		first := increseKey(common.CopyBytes(entries[c.pos].k))
+		if err := trie.Prove(first, 0, firstProof); err != nil {
+			t.Fatalf("Failed to prove the first node %v", err)
+		}
+		err, _ := VerifyRangeProof(trie.Hash(), first, nil, nil, firstProof, nil)
+		if c.err && err == nil {
+			t.Fatalf("Expected error, got nil")
+		}
+		if !c.err && err != nil {
+			t.Fatalf("Expected no error, got %v", err)
+		}
+	}
+}
+
 // mutateByte changes one byte in b.
 func mutateByte(b []byte) {
 	for r := mrand.Intn(len(b)); ; {