Use transaction when necessary

cmd/data/db.go

@@ -89,12 +89,19 @@ func (db *DB) CheckPassword(id int64, pass string) error {
 }
 
 func (db *DB) ChangePassword(id int64, oldPass, newPass string) error {
+	tx, err := db.Begin()
+	if err != nil {
+		return fmt.Errorf("error starting transaction: %v", err)
+	}
+
 	if err := db.CheckPassword(id, oldPass); err != nil {
+		tx.Rollback()
 		return fmt.Errorf("error checking password: %v", err)
 	}
 
 	newHashedPass, err := bcrypt.GenerateFromPassword([]byte(newPass), bcrypt.DefaultCost)
 	if err != nil {
+		tx.Rollback()
 		return fmt.Errorf("error creating password hash: %v", err)
 	}
 
@@ -104,9 +111,14 @@ func (db *DB) ChangePassword(id int64, oldPass, newPass string) error {
     WHERE id = ?
     `
 	if _, err = db.Exec(query, string(newHashedPass), id); err != nil {
+		tx.Rollback()
 		return fmt.Errorf("error updating password in DB: %v", err)
 	}
 
+	if err = tx.Commit(); err != nil {
+		return fmt.Errorf("error committing transaction: %v", err)
+	}
+
 	return nil
 }