command: add command "getvol"

Closes https://github.com/MusicPlayerDaemon/MPD/issues/979

NEWS

@@ -1,4 +1,6 @@
 ver 0.23 (not yet released)
+* protocol
+  - new command "getvol"
 
 ver 0.22.1 (not yet released)
 * output

doc/protocol.rst

@@ -522,6 +522,16 @@ Playback options
     Sets volume to ``VOL``, the range of
     volume is 0-100.
 
+:command:`getvol`
+
+    Read the volume.  The result is a ``volume:`` line like in
+    :ref:`status <command_status>`.  If there is no mixer, MPD will
+    emit an empty response.  Example::
+
+      getvol
+      volume: 42
+      OK
+
 :command:`single {STATE}` [#since_0_15]_
     Sets single state to ``STATE``,
     ``STATE`` should be ``0``, ``1`` or ``oneshot`` [#since_0_20]_.

src/command/AllCommands.cxx

@@ -113,6 +113,7 @@ static constexpr struct command commands[] = {
 #ifdef ENABLE_CHROMAPRINT
 	{ "getfingerprint", PERMISSION_READ, 1, 1, handle_getfingerprint },
 #endif
+	{ "getvol", PERMISSION_READ, 0, 0, handle_getvol },
 	{ "idle", PERMISSION_READ, 0, -1, handle_idle },
 	{ "kill", PERMISSION_ADMIN, -1, -1, handle_kill },
 #ifdef ENABLE_DATABASE

src/command/OtherCommands.cxx

@@ -318,6 +318,18 @@ handle_rescan(Client &client, Request args, Response &r)
 	return handle_update(client, args, r, true);
 }
 
+CommandResult
+handle_getvol(Client &client, Request, Response &r)
+{
+	auto &partition = client.GetPartition();
+
+	const auto volume = volume_level_get(partition.outputs);
+	if (volume >= 0)
+		r.Format("volume: %i\n", volume);
+
+	return CommandResult::OK;
+}
+
 CommandResult
 handle_setvol(Client &client, Request args, Response &r)
 {

src/command/OtherCommands.hxx

@@ -47,6 +47,9 @@ handle_update(Client &client, Request request, Response &response);
 CommandResult
 handle_rescan(Client &client, Request request, Response &response);
 
+CommandResult
+handle_getvol(Client &client, Request request, Response &response);
+
 CommandResult
 handle_setvol(Client &client, Request request, Response &response);