From 6687e6b4d60b4b87636a54a814e92bca8f6c2295 Mon Sep 17 00:00:00 2001
From: Artem Tsebrovskiy <awskii@users.noreply.github.com>
Date: Tue, 15 Mar 2022 20:01:51 +0300
Subject: [PATCH] during computeCommitment exits with RootHash when there are
 no updates to apply (#366)

---
 aggregator/aggregator.go               |  6 +++
 commitment/hex_patricia_hashed.go      |  3 +-
 commitment/hex_patricia_hashed_test.go | 66 +++++++++++++++++++++++++-
 3 files changed, 73 insertions(+), 2 deletions(-)

diff --git a/aggregator/aggregator.go b/aggregator/aggregator.go
index a3a4d659c..97465cc2e 100644
--- a/aggregator/aggregator.go
+++ b/aggregator/aggregator.go
@@ -2326,6 +2326,11 @@ func (w *Writer) computeCommitment(trace bool) ([]byte, error) {
 		j++
 		return true
 	})
+
+	if len(updates) == 0 {
+		return w.a.hph.RootHash()
+	}
+
 	w.a.hph.Reset()
 	w.a.hph.ResetFns(w.branchFn, w.accountFn, w.storageFn, w.lockFn, w.unlockFn)
 	w.a.hph.SetTrace(trace)
@@ -2376,6 +2381,7 @@ func (w *Writer) computeCommitment(trace bool) ([]byte, error) {
 			}
 		}
 	}
+
 	var rootHash []byte
 	if rootHash, err = w.a.hph.RootHash(); err != nil {
 		return nil, err
diff --git a/commitment/hex_patricia_hashed.go b/commitment/hex_patricia_hashed.go
index 1d3d7da7b..d124e7977 100644
--- a/commitment/hex_patricia_hashed.go
+++ b/commitment/hex_patricia_hashed.go
@@ -27,9 +27,10 @@ import (
 	"strings"
 
 	"github.com/holiman/uint256"
+	"golang.org/x/crypto/sha3"
+
 	"github.com/ledgerwatch/erigon-lib/common/length"
 	"github.com/ledgerwatch/erigon-lib/rlp"
-	"golang.org/x/crypto/sha3"
 )
 
 // keccakState wraps sha3.state. In addition to the usual hash methods, it also supports
diff --git a/commitment/hex_patricia_hashed_test.go b/commitment/hex_patricia_hashed_test.go
index 0e5e6dbb7..b42816534 100644
--- a/commitment/hex_patricia_hashed_test.go
+++ b/commitment/hex_patricia_hashed_test.go
@@ -17,6 +17,7 @@
 package commitment
 
 import (
+	"bytes"
 	"encoding/binary"
 	"encoding/hex"
 	"fmt"
@@ -24,8 +25,9 @@ import (
 	"testing"
 
 	"github.com/holiman/uint256"
-	"github.com/ledgerwatch/erigon-lib/common"
 	"golang.org/x/crypto/sha3"
+
+	"github.com/ledgerwatch/erigon-lib/common"
 )
 
 // In memory commitment and state to use with the tests
@@ -481,3 +483,65 @@ func TestEmptyState(t *testing.T) {
 		fmt.Printf("%x => %s\n", CompactToHex([]byte(key)), branchToString(branchNodeUpdate))
 	}
 }
+
+func TestEmptyUpdateState(t *testing.T) {
+	ms := NewMockState(t)
+	hph := NewHexPatriciaHashed(1, ms.branchFn, ms.accountFn, ms.storageFn, ms.lockFn, ms.unlockFn)
+	hph.SetTrace(false)
+	plainKeys, hashedKeys, updates := NewUpdateBuilder().
+		Balance("00", 4).
+		Balance("01", 5).
+		Build()
+	if err := ms.applyPlainUpdates(plainKeys, updates); err != nil {
+		t.Fatal(err)
+	}
+	branchNodeUpdates, err := hph.ProcessUpdates(plainKeys, hashedKeys, updates)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rh, err := hph.RootHash()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	fmt.Printf("root %v\n", hex.EncodeToString(rh))
+
+	ms.applyBranchNodeUpdates(branchNodeUpdates)
+
+	fmt.Println("1. Updates applied")
+	var keys []string
+	for key := range branchNodeUpdates {
+		keys = append(keys, key)
+	}
+	sort.Strings(keys)
+	for _, key := range keys {
+		branchNodeUpdate := branchNodeUpdates[key]
+		fmt.Printf("%x => %s\n", CompactToHex([]byte(key)), branchToString(branchNodeUpdate))
+	}
+
+	// generate empty updates and do NOT reset tree
+	//hph.Reset()
+	hph.SetTrace(true)
+	plainKeys, hashedKeys, updates = NewUpdateBuilder().Build()
+	if err := ms.applyPlainUpdates(plainKeys, updates); err != nil {
+		t.Fatal(err)
+	}
+
+	branchNodeUpdates, err = hph.ProcessUpdates(plainKeys, hashedKeys, updates)
+	if err != nil {
+		t.Fatal(err)
+	}
+	ms.applyBranchNodeUpdates(branchNodeUpdates)
+	fmt.Println("2. empty updates applied without state reset")
+
+	firstRH := rh
+	rh, err = hph.RootHash()
+	if err != nil {
+		t.Fatal(err)
+	}
+	if !bytes.Equal(firstRH, rh) {
+		t.Fatalf("expected root hash [%v] after update but got [%v]", hex.EncodeToString(firstRH), hex.EncodeToString(rh))
+	}
+	fmt.Printf("root %v\n", hex.EncodeToString(rh))
+}