trie: polish commit function (ethereum#21692)

* trie: polish commit function

* trie: fix typo

trie/stacktrie.go

@@ -17,6 +17,7 @@
 package trie
 
 import (
+	"errors"
 	"fmt"
 	"sync"
 
@@ -26,6 +27,8 @@ import (
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
+var ErrCommitDisabled = errors.New("no database for committing")
+
 var stPool = sync.Pool{
 	New: func() interface{} {
 		return NewStackTrie(nil)
@@ -391,14 +394,18 @@ func (st *StackTrie) Hash() (h common.Hash) {
 	return common.BytesToHash(st.val)
 }
 
-// Commit will commit the current node to database db
-func (st *StackTrie) Commit(db ethdb.KeyValueStore) common.Hash {
-	oldDb := st.db
-	st.db = db
-	defer func() {
-		st.db = oldDb
-	}()
+// Commit will firstly hash the entrie trie if it's still not hashed
+// and then commit all nodes to the associated database. Actually most
+// of the trie nodes MAY have been committed already. The main purpose
+// here is to commit the root node.
+//
+// The associated database is expected, otherwise the whole commit
+// functionality should be disabled.
+func (st *StackTrie) Commit() (common.Hash, error) {
+	if st.db == nil {
+		return common.Hash{}, ErrCommitDisabled
+	}
 	st.hash()
 	h := common.BytesToHash(st.val)
-	return h
+	return h, nil
 }

trie/trie_test.go

@@ -831,7 +831,10 @@ func TestCommitSequenceStackTrie(t *testing.T) {
 		// Flush memdb -> disk (sponge)
 		db.Commit(root, false, nil)
 		// And flush stacktrie -> disk
-		stRoot := stTrie.Commit(stTrie.db)
+		stRoot, err := stTrie.Commit()
+		if err != nil {
+			t.Fatalf("Failed to commit stack trie %v", err)
+		}
 		if stRoot != root {
 			t.Fatalf("root wrong, got %x exp %x", stRoot, root)
 		}