Make json parsing more strict

internal/misc/json.go

@@ -0,0 +1,34 @@
+// This file is Free Software under the Apache-2.0 License
+// without warranty, see README.md and LICENSES/Apache-2.0.txt for details.
+//
+// SPDX-License-Identifier: Apache-2.0
+//
+// SPDX-FileCopyrightText: 2023 German Federal Office for Information Security (BSI) <https://www.bsi.bund.de>
+// Software-Engineering: 2023 Intevation GmbH <https://intevation.de>
+
+package misc
+
+import (
+	"encoding/json"
+	"fmt"
+	"io"
+)
+
+// StrictJSONParse provides JSON parsing with stronger validation.
+func StrictJSONParse(jsonData io.Reader, target interface{}) error {
+	decoder := json.NewDecoder(jsonData)
+
+	decoder.DisallowUnknownFields()
+
+	err := decoder.Decode(target)
+	if err != nil {
+		return fmt.Errorf("strictJSONParse: %w", err)
+	}
+
+	token, err := decoder.Token()
+	if err != io.EOF {
+		return fmt.Errorf("strictJSONParse: unexpected trailing data after JSON: token: %v, err: %v", token, err)
+	}
+
+	return nil
+}