command: new command "readcomments" lists arbitrary file tags

src/command/AllCommands.cxx

@@ -23,6 +23,7 @@
 #include "PlayerCommands.hxx"
 #include "PlaylistCommands.hxx"
 #include "DatabaseCommands.hxx"
+#include "FileCommands.hxx"
 #include "OutputCommands.hxx"
 #include "MessageCommands.hxx"
 #include "OtherCommands.hxx"
@@ -127,6 +128,7 @@ static const struct command commands[] = {
 	{ "prio", PERMISSION_CONTROL, 2, -1, handle_prio },
 	{ "prioid", PERMISSION_CONTROL, 2, -1, handle_prioid },
 	{ "random", PERMISSION_CONTROL, 1, 1, handle_random },
+	{ "readcomments", PERMISSION_READ, 1, 1, handle_read_comments },
 	{ "readmessages", PERMISSION_READ, 0, 0, handle_read_messages },
 	{ "rename", PERMISSION_CONTROL, 2, 2, handle_rename },
 	{ "repeat", PERMISSION_CONTROL, 1, 1, handle_repeat },

src/command/FileCommands.cxx

@@ -0,0 +1,122 @@
+/*
+ * Copyright (C) 2003-2013 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.
+ */
+
+#include "config.h"
+#include "FileCommands.hxx"
+#include "CommandError.hxx"
+#include "protocol/Ack.hxx"
+#include "protocol/Result.hxx"
+#include "ClientFile.hxx"
+#include "Client.hxx"
+#include "util/CharUtil.hxx"
+#include "util/Error.hxx"
+#include "tag/TagHandler.hxx"
+#include "TagFile.hxx"
+#include "Mapper.hxx"
+#include "fs/AllocatedPath.hxx"
+
+#include <assert.h>
+
+gcc_pure
+static bool
+IsValidName(const char *p)
+{
+	if (!IsAlphaASCII(*p))
+		return false;
+
+	while (*++p) {
+		const char ch = *p;
+		if (!IsAlphaASCII(ch) && ch != '_' && ch != '-')
+			return false;
+	}
+
+	return true;
+}
+
+gcc_pure
+static bool
+IsValidValue(const char *p)
+{
+	while (*p) {
+		const char ch = *p++;
+
+		if ((unsigned char)ch >= 0x20)
+			return false;
+	}
+
+	return true;
+}
+
+static void
+print_pair(const char *key, const char *value, void *ctx)
+{
+	Client &client = *(Client *)ctx;
+
+	if (IsValidName(key) && IsValidValue(value))
+		client_printf(client, "%s: %s\n", key, value);
+}
+
+static constexpr tag_handler print_comment_handler = {
+	nullptr,
+	nullptr,
+	print_pair,
+};
+
+CommandResult
+handle_read_comments(Client &client, gcc_unused int argc, char *argv[])
+{
+	assert(argc == 2);
+
+	const char *const uri = argv[1];
+
+	AllocatedPath path_fs = AllocatedPath::Null();
+
+	if (memcmp(uri, "file:///", 8) == 0) {
+		/* read comments from arbitrary local file */
+		const char *path_utf8 = uri + 7;
+		path_fs = AllocatedPath::FromUTF8(path_utf8);
+		if (path_fs.IsNull()) {
+			command_error(client, ACK_ERROR_NO_EXIST,
+				      "unsupported file name");
+			return CommandResult::ERROR;
+		}
+
+		Error error;
+		if (!client_allow_file(client, path_fs, error))
+			return print_error(client, error);
+	} else if (*uri != '/') {
+		path_fs = map_uri_fs(uri);
+		if (path_fs.IsNull()) {
+			command_error(client, ACK_ERROR_NO_EXIST,
+				      "No such file");
+			return CommandResult::ERROR;
+		}
+	} else {
+		command_error(client, ACK_ERROR_NO_EXIST, "No such file");
+		return CommandResult::ERROR;
+	}
+
+	if (!tag_file_scan(path_fs.c_str(), &print_comment_handler, &client)) {
+		command_error(client, ACK_ERROR_NO_EXIST,
+			      "Failed to load file");
+		return CommandResult::ERROR;
+	}
+
+	return CommandResult::OK;
+}

src/command/FileCommands.hxx

@@ -0,0 +1,30 @@
+/*
+ * Copyright (C) 2003-2012 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.
+ */
+
+#ifndef MPD_FILE_COMMANDS_HXX
+#define MPD_FILE_COMMANDS_HXX
+
+#include "CommandResult.hxx"
+
+class Client;
+
+CommandResult
+handle_read_comments(Client &client, int argc, char *argv[]);
+
+#endif