output/Interface: add "attributes" map

These attributes are printed in the "outputs" response, and the new
command "outputset" allows setting new values.

No attributes are currently implemented.

Makefile.am

@@ -1390,7 +1390,6 @@ OUTPUT_LIBS = \
 OUTPUT_API_SRC = \
 	src/output/Client.hxx \
 	src/output/OutputAPI.hxx \
-	src/output/Interface.hxx \
 	src/output/Filtered.cxx src/output/Filtered.hxx \
 	src/output/Registry.cxx src/output/Registry.hxx \
 	src/output/MultipleOutputs.cxx src/output/MultipleOutputs.hxx \
@@ -1407,6 +1406,7 @@ OUTPUT_API_SRC = \
 	src/output/Init.cxx
 
 liboutput_plugins_a_SOURCES = \
+	src/output/Interface.cxx src/output/Interface.hxx \
 	src/output/Timer.cxx src/output/Timer.hxx \
 	src/output/plugins/NullOutputPlugin.cxx \
 	src/output/plugins/NullOutputPlugin.hxx

NEWS

@@ -3,6 +3,7 @@ ver 0.21 (not yet released)
   - "tagtypes" can be used to hide tags
   - "find" and "search" can sort
   - "outputs" prints the plugin name
+  - "outputset" sets runtime attributes
   - close connection when client sends HTTP request
 * tags
   - new tag "OriginalDate"

doc/protocol.xml

@@ -2523,6 +2523,7 @@ outputid: 0
 outputname: My ALSA Device
 plugin: alsa
 outputenabled: 0
+attribute: dop=0
 OK
             </screen>
             <para>
@@ -2547,6 +2548,24 @@ OK
             </itemizedlist>
           </listitem>
         </varlistentry>
+
+        <varlistentry id="command_outputset">
+          <term>
+            <cmdsynopsis>
+              <command>outputset</command>
+              <arg choice="req"><replaceable>ID</replaceable></arg>
+              <arg choice="req"><replaceable>NAME</replaceable></arg>
+              <arg choice="req"><replaceable>VALUE</replaceable></arg>
+            </cmdsynopsis>
+          </term>
+          <listitem>
+            <para>
+              Set a runtime attribute.  These are specific to the
+              output plugin, and supported values are usually printed
+              in the <command>outputs</command> response.
+            </para>
+          </listitem>
+        </varlistentry>
       </variablelist>
     </section>
 

src/command/AllCommands.cxx

@@ -138,6 +138,7 @@ static constexpr struct command commands[] = {
 	{ "next", PERMISSION_CONTROL, 0, 0, handle_next },
 	{ "notcommands", PERMISSION_NONE, 0, 0, handle_not_commands },
 	{ "outputs", PERMISSION_READ, 0, 0, handle_devices },
+	{ "outputset", PERMISSION_ADMIN, 3, 3, handle_outputset },
 	{ "partition", PERMISSION_READ, 1, 1, handle_partition },
 	{ "password", PERMISSION_NONE, 1, 1, handle_password },
 	{ "pause", PERMISSION_CONTROL, 0, 1, handle_pause },

src/command/OutputCommands.cxx

@@ -25,6 +25,8 @@
 #include "client/Client.hxx"
 #include "client/Response.hxx"
 #include "Partition.hxx"
+#include "IdleFlags.hxx"
+#include "util/CharUtil.hxx"
 
 CommandResult
 handle_enableoutput(Client &client, Request args, Response &r)
@@ -68,6 +70,54 @@ handle_toggleoutput(Client &client, Request args, Response &r)
 	return CommandResult::OK;
 }
 
+static bool
+IsValidAttributeNameChar(char ch) noexcept
+{
+	return IsAlphaNumericASCII(ch) || ch == '_';
+}
+
+gcc_pure
+static bool
+IsValidAttributeName(const char *s) noexcept
+{
+	do {
+		if (!IsValidAttributeNameChar(*s))
+			return false;
+	} while (*++s);
+
+	return true;
+}
+
+CommandResult
+handle_outputset(Client &client, Request request, Response &response)
+{
+	assert(request.size == 3);
+	const unsigned i = request.ParseUnsigned(0);
+
+	auto &partition = client.GetPartition();
+	auto &outputs = partition.outputs;
+	if (i >= outputs.Size()) {
+		response.Error(ACK_ERROR_NO_EXIST, "No such audio output");
+		return CommandResult::ERROR;
+	}
+
+	auto &ao = outputs.Get(i);
+
+	const char *const name = request[1];
+	if (!IsValidAttributeName(name)) {
+		response.Error(ACK_ERROR_ARG, "Illegal attribute name");
+		return CommandResult::ERROR;
+	}
+
+	const char *const value = request[2];
+
+	ao.SetAttribute(name, value);
+
+	partition.EmitIdle(IDLE_OUTPUT);
+
+	return CommandResult::OK;
+}
+
 CommandResult
 handle_devices(Client &client, gcc_unused Request args, Response &r)
 {

src/command/OutputCommands.hxx

@@ -35,6 +35,9 @@ handle_disableoutput(Client &client, Request request, Response &response);
 CommandResult
 handle_toggleoutput(Client &client, Request request, Response &response);
 
+CommandResult
+handle_outputset(Client &client, Request request, Response &response);
+
 CommandResult
 handle_devices(Client &client, Request request, Response &response);
 

src/output/Control.cxx

@@ -76,6 +76,18 @@ AudioOutputControl::GetMixer() const noexcept
 	return output->mixer;
 }
 
+const std::map<std::string, std::string>
+AudioOutputControl::GetAttributes() const noexcept
+{
+	return output->GetAttributes();
+}
+
+void
+AudioOutputControl::SetAttribute(std::string &&name, std::string &&value)
+{
+	output->SetAttribute(std::move(name), std::move(value));
+}
+
 bool
 AudioOutputControl::LockSetEnabled(bool new_value) noexcept
 {

src/output/Control.hxx

@@ -30,6 +30,8 @@
 
 #include <utility>
 #include <exception>
+#include <string>
+#include <map>
 
 #ifndef NDEBUG
 #include <assert.h>
@@ -324,6 +326,9 @@ public:
 	void BeginDestroy() noexcept;
 	void FinishDestroy() noexcept;
 
+	const std::map<std::string, std::string> GetAttributes() const noexcept;
+	void SetAttribute(std::string &&name, std::string &&value);
+
 	/**
 	 * Enables the device, but don't wait for completion.
 	 *

src/output/Filtered.cxx

@@ -40,6 +40,18 @@ FilteredAudioOutput::SupportsPause() const noexcept
 	return output->SupportsPause();
 }
 
+const std::map<std::string, std::string>
+FilteredAudioOutput::GetAttributes() const noexcept
+{
+	return output->GetAttributes();
+}
+
+void
+FilteredAudioOutput::SetAttribute(std::string &&_name, std::string &&_value)
+{
+	output->SetAttribute(std::move(_name), std::move(_value));
+}
+
 void
 FilteredAudioOutput::Enable()
 {

src/output/Filtered.hxx

@@ -25,6 +25,7 @@
 
 #include <memory>
 #include <string>
+#include <map>
 #include <chrono>
 
 class PreparedFilter;
@@ -167,6 +168,9 @@ public:
 	gcc_pure
 	bool SupportsPause() const noexcept;
 
+	const std::map<std::string, std::string> GetAttributes() const noexcept;
+	void SetAttribute(std::string &&name, std::string &&value);
+
 	/**
 	 * Throws #std::runtime_error on error.
 	 */

src/output/Interface.cxx

@@ -0,0 +1,30 @@
+/*
+ * Copyright 2003-2017 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 "Interface.hxx"
+#include "Compiler.h"
+
+#include <stdexcept>
+
+void
+AudioOutput::SetAttribute(gcc_unused std::string &&name,
+			  gcc_unused std::string &&value)
+{
+	throw std::invalid_argument("Unsupported attribute");
+}

src/output/Interface.hxx

@@ -20,7 +20,10 @@
 #ifndef MPD_AUDIO_OUTPUT_INTERFACE_HXX
 #define MPD_AUDIO_OUTPUT_INTERFACE_HXX
 
+#include <map>
+#include <string>
 #include <chrono>
+#include <stdexcept>
 
 struct AudioFormat;
 struct Tag;
@@ -57,6 +60,22 @@ public:
 		return flags & FLAG_NEED_FULLY_DEFINED_AUDIO_FORMAT;
 	}
 
+	/**
+	 * Returns a map of runtime attributes.
+	 *
+	 * This method must be thread-safe.
+	 */
+	virtual const std::map<std::string, std::string> GetAttributes() const noexcept {
+		return {};
+	}
+
+	/**
+	 * Manipulate a runtime attribute on client request.
+	 *
+	 * This method must be thread-safe.
+	 */
+	virtual void SetAttribute(std::string &&name, std::string &&value);
+
 	/**
 	 * Enable the device.  This may allocate resources, preparing
 	 * for the device to be opened.

src/output/Print.cxx

@@ -41,5 +41,9 @@ printAudioDevices(Response &r, const MultipleOutputs &outputs)
 			 i,
 			 ao.GetName(), ao.GetPluginName(),
 			 ao.IsEnabled());
+
+		for (const auto &a : ao.GetAttributes())
+			r.Format("attribute: %s=%s\n",
+				 a.first.c_str(), a.second.c_str());
 	}
 }