ethdb: add NewBatch

ethdb/memory_database.go

@@ -95,3 +95,26 @@ func (db *MemDatabase) LastKnownTD() []byte {
 func (db *MemDatabase) Flush() error {
 	return nil
 }
+
+func (db *MemDatabase) NewBatch() Batch {
+	return &memBatch{db: db}
+}
+
+type kv struct{ k, v []byte }
+
+type memBatch struct {
+	db     *MemDatabase
+	writes []kv
+}
+
+func (w *memBatch) Put(key, value []byte) error {
+	w.writes = append(w.writes, kv{key, common.CopyBytes(value)})
+	return nil
+}
+
+func (w *memBatch) Write() error {
+	for _, kv := range w.writes {
+		w.db.db[string(kv.k)] = kv.v
+	}
+	return nil
+}