command: new command "readcomments" lists arbitrary file tags

Makefile.am

@@ -85,6 +85,7 @@ src_mpd_SOURCES = \
 	src/command/PlayerCommands.cxx src/command/PlayerCommands.hxx \
 	src/command/PlaylistCommands.cxx src/command/PlaylistCommands.hxx \
 	src/command/DatabaseCommands.cxx src/command/DatabaseCommands.hxx \
+	src/command/FileCommands.cxx src/command/FileCommands.hxx \
 	src/command/OutputCommands.cxx src/command/OutputCommands.hxx \
 	src/command/MessageCommands.cxx src/command/MessageCommands.hxx \
 	src/command/OtherCommands.cxx src/command/OtherCommands.hxx \

NEWS

@@ -3,6 +3,7 @@ ver 0.18 (2012/??/??)
   - allow tilde paths for socket
   - default filesystem charset is UTF-8 instead of ISO-8859-1
 * protocol:
+  - new command "readcomments" lists arbitrary file tags
   - new command "toggleoutput"
   - search for album artist falls back to the artist tag
   - re-add the "volume" command

doc/protocol.xml

@@ -1582,6 +1582,32 @@ OK
             </para>
           </listitem>
         </varlistentry>
+        <varlistentry id="command_readcomments">
+          <term>
+            <cmdsynopsis>
+              <command>readcomments</command>
+              <arg><replaceable>URI</replaceable></arg>
+            </cmdsynopsis>
+          </term>
+          <listitem>
+            <para>
+              Read "comments" (i.e. key-value pairs) from the file
+              specified by "URI".  This "URI" can be a path relative
+              to the music directory or a URL in the form
+              "file:///foo/bar.ogg".
+            </para>
+            <para>
+              The response consists of lines in the form "KEY: VALUE".
+              Comments with suspicious characters (e.g. newlines) are
+              ignored silently.
+            </para>
+            <para>
+              The meaning of these depends on the codec, and not all
+              decoder plugins support it.  For example, on Ogg files,
+              this lists the Vorbis comments.
+            </para>
+          </listitem>
+        </varlistentry>
         <varlistentry id="command_search">
           <term>
             <cmdsynopsis>

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