chore: import upstream snapshot with attribution

pkg/checker/reserved_username.go

@@ -0,0 +1,58 @@
+/*
+ * Licensed to the Apache Software Foundation (ASF) under one
+ * or more contributor license agreements.  See the NOTICE file
+ * distributed with this work for additional information
+ * regarding copyright ownership.  The ASF licenses this file
+ * to you under the Apache License, Version 2.0 (the
+ * "License"); you may not use this file except in compliance
+ * with the License.  You may obtain a copy of the License at
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing,
+ * software distributed under the License is distributed on an
+ * "AS IS" BASIS, WITHOUT WARRANTIES OR CONDITIONS OF ANY
+ * KIND, either express or implied.  See the License for the
+ * specific language governing permissions and limitations
+ * under the License.
+ */
+
+package checker
+
+import (
+	"encoding/json"
+	"os"
+	"path/filepath"
+	"sync"
+
+	"github.com/apache/answer/configs"
+	"github.com/apache/answer/internal/base/path"
+	"github.com/apache/answer/pkg/dir"
+)
+
+var (
+	reservedUsernameMapping = make(map[string]bool)
+	reservedUsernameInit    sync.Once
+)
+
+func initReservedUsername() {
+	reservedUsernamesJsonFilePath := filepath.Join(path.ConfigFileDir, path.DefaultReservedUsernamesConfigFileName)
+	if dir.CheckFileExist(reservedUsernamesJsonFilePath) {
+		// if reserved username file exists, read it and replace configuration
+		reservedUsernamesJsonFile, err := os.ReadFile(reservedUsernamesJsonFilePath)
+		if err == nil {
+			configs.ReservedUsernames = reservedUsernamesJsonFile
+		}
+	}
+	var usernames []string
+	_ = json.Unmarshal(configs.ReservedUsernames, &usernames)
+	for _, username := range usernames {
+		reservedUsernameMapping[username] = true
+	}
+}
+
+// IsReservedUsername checks whether the username is reserved
+func IsReservedUsername(username string) bool {
+	reservedUsernameInit.Do(initReservedUsername)
+	return reservedUsernameMapping[username]
+}