fs/io/TextFile: add interface LineReader

src/fs/io/LineReader.hxx

+/*
+ * Copyright 2003-2021 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#pragma once
+
+class LineReader
+{
+public:
+	/**
+	 * Reads a line from the input file, and strips trailing
+	 * space.  There is a reasonable maximum line length, only to
+	 * prevent denial of service.
+	 *
+	 * @return a pointer to the line, or nullptr on end-of-file
+	 */
+	virtual char *ReadLine() = 0;
+};

src/fs/io/TextFile.hxx

@@ -20,6 +20,7 @@
 #ifndef MPD_TEXT_FILE_HXX
 #define MPD_TEXT_FILE_HXX
 
+#include "LineReader.hxx"
 #include "config.h"
 
 #include <memory>
@@ -29,7 +30,7 @@ class FileReader;
 class AutoGunzipReader;
 class BufferedReader;
 
-class TextFile {
+class TextFile final : public LineReader {
 	const std::unique_ptr<FileReader> file_reader;
 
 #ifdef ENABLE_ZLIB
@@ -45,14 +46,8 @@ public:
 
 	~TextFile() noexcept;
 
-	/**
-	 * Reads a line from the input file, and strips trailing
-	 * space.  There is a reasonable maximum line length, only to
-	 * prevent denial of service.
-	 *
-	 * @return a pointer to the line, or nullptr on end-of-file
-	 */
-	char *ReadLine();
+	/* virtual methods from class LineReader */
+	char *ReadLine() override;
 };
 
 #endif