output/wasapi: move COM utilities to separate headers

8 files changed, 376 insertions, 157 deletions

diff --git a/src/mixer/plugins/WasapiMixerPlugin.cxx b/src/mixer/plugins/WasapiMixerPlugin.cxx
index 1b8190c12..18c862f29 100644
--- a/src/mixer/plugins/WasapiMixerPlugin.cxx
+++ b/src/mixer/plugins/WasapiMixerPlugin.cxx
@@ -18,6 +18,8 @@
  */
 
 #include "output/plugins/wasapi/ForMixer.hxx"
+#include "output/plugins/wasapi/AudioClient.hxx"
+#include "output/plugins/wasapi/Device.hxx"
 #include "mixer/MixerInternal.hxx"
 #include "win32/ComPtr.hxx"
 #include "win32/ComWorker.hxx"
@@ -47,15 +49,8 @@ public:
 			float volume_level;
 
 			if (wasapi_is_exclusive(output)) {
-				ComPtr<IAudioEndpointVolume> endpoint_volume;
-				result = wasapi_output_get_device(output)->Activate(
-					__uuidof(IAudioEndpointVolume), CLSCTX_ALL,
-					nullptr, endpoint_volume.AddressCast());
-				if (FAILED(result)) {
-					throw FormatHResultError(result,
-								 "Unable to get device "
-								 "endpoint volume");
-				}
+				auto endpoint_volume =
+					Activate<IAudioEndpointVolume>(*wasapi_output_get_device(output));
 
 				result = endpoint_volume->GetMasterVolumeLevelScalar(
 					&volume_level);
@@ -65,15 +60,8 @@ public:
 								 "volume level");
 				}
 			} else {
-				ComPtr<ISimpleAudioVolume> session_volume;
-				result = wasapi_output_get_client(output)->GetService(
-					__uuidof(ISimpleAudioVolume),
-					session_volume.AddressCast<void>());
-				if (FAILED(result)) {
-					throw FormatHResultError(result,
-								 "Unable to get client "
-								 "session volume");
-				}
+				auto session_volume =
+					GetService<ISimpleAudioVolume>(*wasapi_output_get_client(output));
 
 				result = session_volume->GetMasterVolume(&volume_level);
 				if (FAILED(result)) {
@@ -93,15 +81,8 @@ public:
 			const float volume_level = volume / 100.0f;
 
 			if (wasapi_is_exclusive(output)) {
-				ComPtr<IAudioEndpointVolume> endpoint_volume;
-				result = wasapi_output_get_device(output)->Activate(
-					__uuidof(IAudioEndpointVolume), CLSCTX_ALL,
-					nullptr, endpoint_volume.AddressCast());
-				if (FAILED(result)) {
-					throw FormatHResultError(
-						result,
-						"Unable to get device endpoint volume");
-				}
+				auto endpoint_volume =
+					Activate<IAudioEndpointVolume>(*wasapi_output_get_device(output));
 
 				result = endpoint_volume->SetMasterVolumeLevelScalar(
 					volume_level, nullptr);
@@ -111,15 +92,8 @@ public:
 						"Unable to set master volume level");
 				}
 			} else {
-				ComPtr<ISimpleAudioVolume> session_volume;
-				result = wasapi_output_get_client(output)->GetService(
-					__uuidof(ISimpleAudioVolume),
-					session_volume.AddressCast<void>());
-				if (FAILED(result)) {
-					throw FormatHResultError(
-						result,
-						"Unable to get client session volume");
-				}
+				auto session_volume =
+					GetService<ISimpleAudioVolume>(*wasapi_output_get_client(output));
 
 				result = session_volume->SetMasterVolume(volume_level,
 									 nullptr);
diff --git a/src/output/plugins/wasapi/AudioClient.hxx b/src/output/plugins/wasapi/AudioClient.hxx
new file mode 100644
index 000000000..3ed3da319
--- /dev/null
+++ b/src/output/plugins/wasapi/AudioClient.hxx
@@ -0,0 +1,103 @@
+/*
+ * Copyright 2020-2021 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.
+ */
+
+#ifndef MPD_WASAPI_AUDIO_CLIENT_HXX
+#define MPD_WASAPI_AUDIO_CLIENT_HXX
+
+#include "win32/ComHeapPtr.hxx"
+#include "win32/ComPtr.hxx"
+#include "win32/HResult.hxx"
+
+#include <audioclient.h>
+
+inline UINT32
+GetBufferSizeInFrames(IAudioClient &client)
+{
+	UINT32 buffer_size_in_frames;
+
+	HRESULT result = client.GetBufferSize(&buffer_size_in_frames);
+	if (FAILED(result))
+		throw FormatHResultError(result,
+					 "Unable to get audio client buffer size");
+
+	return buffer_size_in_frames;
+}
+
+inline UINT32
+GetCurrentPaddingFrames(IAudioClient &client)
+{
+	UINT32 padding_frames;
+
+	HRESULT result = client.GetCurrentPadding(&padding_frames);
+	if (FAILED(result))
+		throw FormatHResultError(result,
+					 "Failed to get current padding");
+
+	return padding_frames;
+}
+
+inline ComHeapPtr<WAVEFORMATEX>
+GetMixFormat(IAudioClient &client)
+{
+	WAVEFORMATEX *f;
+
+	HRESULT result = client.GetMixFormat(&f);
+	if (FAILED(result))
+		throw FormatHResultError(result, "GetMixFormat failed");
+
+	return ComHeapPtr{f};
+}
+
+inline void
+Start(IAudioClient &client)
+{
+	HRESULT result = client.Start();
+	if (FAILED(result))
+		throw FormatHResultError(result, "Failed to start client");
+}
+
+inline void
+Stop(IAudioClient &client)
+{
+	HRESULT result = client.Stop();
+	if (FAILED(result))
+		throw FormatHResultError(result, "Failed to stop client");
+}
+
+inline void
+SetEventHandle(IAudioClient &client, HANDLE h)
+{
+	HRESULT result = client.SetEventHandle(h);
+	if (FAILED(result))
+		throw FormatHResultError(result, "Unable to set event handle");
+}
+
+template<typename T>
+inline ComPtr<T>
+GetService(IAudioClient &client)
+{
+	T *p = nullptr;
+	HRESULT result = client.GetService(IID_PPV_ARGS(&p));
+	if (FAILED(result))
+		throw FormatHResultError(result, "Unable to get service");
+
+	return ComPtr{p};
+}
+
+#endif
diff --git a/src/output/plugins/wasapi/Device.hxx b/src/output/plugins/wasapi/Device.hxx
new file mode 100644
index 000000000..863f327a7
--- /dev/null
+++ b/src/output/plugins/wasapi/Device.hxx
@@ -0,0 +1,117 @@
+/*
+ * Copyright 2020-2021 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.
+ */
+
+#ifndef MPD_WASAPI_DEVICE_COLLECTION_HXX
+#define MPD_WASAPI_DEVICE_COLLECTION_HXX
+
+#include "win32/ComPtr.hxx"
+#include "win32/HResult.hxx"
+
+#include <mmdeviceapi.h>
+
+inline ComPtr<IMMDevice>
+GetDefaultAudioEndpoint(IMMDeviceEnumerator &e)
+{
+	IMMDevice *device = nullptr;
+
+	HRESULT result = e.GetDefaultAudioEndpoint(eRender, eMultimedia,
+						   &device);
+	if (FAILED(result))
+		throw FormatHResultError(result,
+					 "Unable to get default device for multimedia");
+
+	return ComPtr{device};
+}
+
+inline ComPtr<IMMDeviceCollection>
+EnumAudioEndpoints(IMMDeviceEnumerator &e)
+{
+	IMMDeviceCollection *dc = nullptr;
+
+	HRESULT result = e.EnumAudioEndpoints(eRender, DEVICE_STATE_ACTIVE,
+					      &dc);
+	if (FAILED(result))
+		throw FormatHResultError(result, "Unable to enumerate devices");
+
+	return ComPtr{dc};
+}
+
+inline UINT
+GetCount(IMMDeviceCollection &dc)
+{
+	UINT count;
+
+	HRESULT result = dc.GetCount(&count);
+	if (FAILED(result))
+		throw FormatHResultError(result, "Collection->GetCount failed");
+
+	return count;
+}
+
+inline ComPtr<IMMDevice>
+Item(IMMDeviceCollection &dc, UINT i)
+{
+	IMMDevice *device = nullptr;
+
+	auto result = dc.Item(i, &device);
+	if (FAILED(result))
+		throw FormatHResultError(result, "Collection->Item failed");
+
+	return ComPtr{device};
+}
+
+inline DWORD
+GetState(IMMDevice &device)
+{
+	DWORD state;
+
+	HRESULT result = device.GetState(&state);;
+	if (FAILED(result))
+		throw FormatHResultError(result, "Unable to get device status");
+
+	return state;
+}
+
+template<typename T>
+inline ComPtr<T>
+Activate(IMMDevice &device)
+{
+	T *p = nullptr;
+	HRESULT result = device.Activate(__uuidof(T), CLSCTX_ALL,
+					 nullptr, (void **)&p);
+	if (FAILED(result))
+		throw FormatHResultError(result, "Unable to activate device");
+
+	return ComPtr{p};
+}
+
+inline ComPtr<IPropertyStore>
+OpenPropertyStore(IMMDevice &device)
+{
+	IPropertyStore *property_store = nullptr;
+
+	HRESULT result = device.OpenPropertyStore(STGM_READ, &property_store);
+	if (FAILED(result))
+		throw FormatHResultError(result,
+					 "Device->OpenPropertyStore failed");
+
+	return ComPtr{property_store};
+}
+
+#endif
diff --git a/src/output/plugins/wasapi/PropertyStore.hxx b/src/output/plugins/wasapi/PropertyStore.hxx
new file mode 100644
index 000000000..6d974087f
--- /dev/null
+++ b/src/output/plugins/wasapi/PropertyStore.hxx
@@ -0,0 +1,44 @@
+/*
+ * Copyright 2020-2021 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.
+ */
+
+#ifndef MPD_WASAPI_PROPERTY_STORE_HXX
+#define MPD_WASAPI_PROPERTY_STORE_HXX
+
+#include "win32/PropVariant.hxx"
+#include "util/AllocatedString.hxx"
+#include "util/ScopeExit.hxx"
+
+#include <propsys.h>
+
+[[gnu::pure]]
+inline AllocatedString
+GetString(IPropertyStore &ps, REFPROPERTYKEY key) noexcept
+{
+	PROPVARIANT pv;
+	PropVariantInit(&pv);
+
+	HRESULT result = ps.GetValue(key, &pv);
+	if (FAILED(result))
+		return nullptr;
+
+	AtScopeExit(&) { PropVariantClear(&pv); };
+	return ToString(pv);
+}
+
+#endif
diff --git a/src/output/plugins/wasapi/WasapiOutputPlugin.cxx b/src/output/plugins/wasapi/WasapiOutputPlugin.cxx
index 70add3c08..58a12918d 100644
--- a/src/output/plugins/wasapi/WasapiOutputPlugin.cxx
+++ b/src/output/plugins/wasapi/WasapiOutputPlugin.cxx
@@ -19,6 +19,9 @@
 
 #include "WasapiOutputPlugin.hxx"
 #include "ForMixer.hxx"
+#include "AudioClient.hxx"
+#include "Device.hxx"
+#include "PropertyStore.hxx"
 #include "output/OutputAPI.hxx"
 #include "lib/icu/Win32.hxx"
 #include "mixer/MixerList.hxx"
@@ -35,7 +38,6 @@
 #include "util/ScopeExit.hxx"
 #include "util/StringBuffer.hxx"
 #include "win32/Com.hxx"
-#include "win32/ComHeapPtr.hxx"
 #include "win32/ComPtr.hxx"
 #include "win32/ComWorker.hxx"
 #include "win32/HResult.hxx"
@@ -254,7 +256,6 @@ private:
 	void EnumerateDevices();
 	void GetDevice(unsigned int index);
 	unsigned int SearchDevice(std::string_view name);
-	void GetDefaultDevice();
 };
 
 WasapiOutput &wasapi_output_downcast(AudioOutput &output) noexcept {
@@ -288,13 +289,8 @@ void WasapiOutputThread::Work() noexcept {
 
 			UINT32 write_in_frames = buffer_size_in_frames;
 			if (!is_exclusive) {
-				UINT32 data_in_frames;
-				if (HRESULT result =
-					    client->GetCurrentPadding(&data_in_frames);
-				    FAILED(result)) {
-					throw FormatHResultError(
-						result, "Failed to get current padding");
-				}
+				UINT32 data_in_frames =
+					GetCurrentPaddingFrames(*client);
 
 				if (data_in_frames >= buffer_size_in_frames) {
 					continue;
@@ -366,20 +362,12 @@ void WasapiOutput::DoDisable() noexcept {
 void WasapiOutput::DoOpen(AudioFormat &audio_format) {
 	client.reset();
 
-	DWORD state;
-	if (HRESULT result = device->GetState(&state); FAILED(result)) {
-		throw FormatHResultError(result, "Unable to get device status");
-	}
-	if (state != DEVICE_STATE_ACTIVE) {
+	if (GetState(*device) != DEVICE_STATE_ACTIVE) {
 		device.reset();
 		OpenDevice();
 	}
 
-	if (HRESULT result = device->Activate(__uuidof(IAudioClient), CLSCTX_ALL, nullptr,
-					      client.AddressCast());
-	    FAILED(result)) {
-		throw FormatHResultError(result, "Unable to activate audio client");
-	}
+	client = Activate<IAudioClient>(*device);
 
 	if (audio_format.channels > 8) {
 		audio_format.channels = 8;
@@ -453,13 +441,8 @@ void WasapiOutput::DoOpen(AudioFormat &audio_format) {
 		    FAILED(result)) {
 			if (result == AUDCLNT_E_BUFFER_SIZE_NOT_ALIGNED) {
 				// https://docs.microsoft.com/en-us/windows/win32/api/audioclient/nf-audioclient-iaudioclient-initialize
-				UINT32 buffer_size_in_frames = 0;
-				result = client->GetBufferSize(&buffer_size_in_frames);
-				if (FAILED(result)) {
-					throw FormatHResultError(
-						result,
-						"Unable to get audio client buffer size");
-				}
+				UINT32 buffer_size_in_frames =
+					GetBufferSizeInFrames(*client);
 				buffer_duration =
 					std::ceil(double(buffer_size_in_frames *
 							 hundred_ns(s(1)).count()) /
@@ -469,14 +452,7 @@ void WasapiOutput::DoOpen(AudioFormat &audio_format) {
 					"Aligned buffer duration: %I64u ns",
 					size_t(ns(hundred_ns(buffer_duration)).count()));
 				client.reset();
-				result = device->Activate(__uuidof(IAudioClient),
-							  CLSCTX_ALL, nullptr,
-							  client.AddressCast());
-				if (FAILED(result)) {
-					throw FormatHResultError(
-						result,
-						"Unable to activate audio client");
-				}
+				client = Activate<IAudioClient>(*device);
 				result = client->Initialize(
 					AUDCLNT_SHAREMODE_EXCLUSIVE,
 					AUDCLNT_STREAMFLAGS_EVENTCALLBACK,
@@ -501,27 +477,15 @@ void WasapiOutput::DoOpen(AudioFormat &audio_format) {
 		}
 	}
 
-	ComPtr<IAudioRenderClient> render_client;
-	if (HRESULT result = client->GetService(IID_PPV_ARGS(render_client.Address()));
-	    FAILED(result)) {
-		throw FormatHResultError(result, "Unable to get new render client");
-	}
+	auto render_client = GetService<IAudioRenderClient>(*client);
 
-	UINT32 buffer_size_in_frames;
-	if (HRESULT result = client->GetBufferSize(&buffer_size_in_frames);
-	    FAILED(result)) {
-		throw FormatHResultError(result,
-					 "Unable to get audio client buffer size");
-	}
+	const UINT32 buffer_size_in_frames = GetBufferSizeInFrames(*client);
 
 	watermark = buffer_size_in_frames * 3 * FrameSize();
 	thread.emplace(client.get(), std::move(render_client), FrameSize(),
 		       buffer_size_in_frames, is_exclusive);
 
-	if (HRESULT result = client->SetEventHandle(thread->event.handle());
-	    FAILED(result)) {
-		throw FormatHResultError(result, "Unable to set event handler");
-	}
+	SetEventHandle(*client, thread->event.handle());
 
 	thread->Start();
 }
@@ -531,9 +495,7 @@ void WasapiOutput::Close() noexcept {
 
 	try {
 		COMWorker::Async([&]() {
-			if (HRESULT result = client->Stop(); FAILED(result)) {
-				throw FormatHResultError(result, "Failed to stop client");
-			}
+			Stop(*client);
 		}).get();
 		thread->CheckException();
 	} catch (std::exception &err) {
@@ -595,10 +557,7 @@ size_t WasapiOutput::Play(const void *chunk, size_t size) {
 			is_started = true;
 			thread->Play();
 			COMWorker::Async([&]() {
-				if (HRESULT result = client->Start(); FAILED(result)) {
-					throw FormatHResultError(
-						result, "Failed to start client");
-				}
+				Start(*client);
 			}).wait();
 		}
 
@@ -660,7 +619,7 @@ void WasapiOutput::OpenDevice() {
 	}
 
 	if (!device) {
-		GetDefaultDevice();
+		device = GetDefaultAudioEndpoint(*enumerator);
 	}
 
 	device_desc.clear();
@@ -735,13 +694,10 @@ void WasapiOutput::FindExclusiveFormatSupported(AudioFormat &audio_format) {
 /// run inside COMWorkerThread
 void WasapiOutput::FindSharedFormatSupported(AudioFormat &audio_format) {
 	HRESULT result;
-	ComHeapPtr<WAVEFORMATEX> mixer_format;
 
 	// In shared mode, different sample rate is always unsupported.
-	result = client->GetMixFormat(mixer_format.Address());
-	if (FAILED(result)) {
-		throw FormatHResultError(result, "GetMixFormat failed");
-	}
+	auto mixer_format = GetMixFormat(*client);
+
 	audio_format.sample_rate = mixer_format->nSamplesPerSec;
 	device_format = GetFormats(audio_format).front();
 
@@ -846,66 +802,30 @@ void WasapiOutput::EnumerateDevices() {
 
 	HRESULT result;
 
-	ComPtr<IMMDeviceCollection> device_collection;
-	result = enumerator->EnumAudioEndpoints(eRender, DEVICE_STATE_ACTIVE,
-						device_collection.Address());
-	if (FAILED(result)) {
-		throw FormatHResultError(result, "Unable to enumerate devices");
-	}
+	const auto device_collection = EnumAudioEndpoints(*enumerator);
 
-	UINT count;
-	result = device_collection->GetCount(&count);
-	if (FAILED(result)) {
-		throw FormatHResultError(result, "Collection->GetCount failed");
-	}
+	const UINT count = GetCount(*device_collection);
 
 	device_desc.reserve(count);
 	for (UINT i = 0; i < count; ++i) {
-		ComPtr<IMMDevice> enumerated_device;
-		result = device_collection->Item(i, enumerated_device.Address());
-		if (FAILED(result)) {
-			throw FormatHResultError(result, "Collection->Item failed");
-		}
-
-		ComPtr<IPropertyStore> property_store;
-		result = enumerated_device->OpenPropertyStore(STGM_READ,
-							      property_store.Address());
-		if (FAILED(result)) {
-			throw FormatHResultError(result,
-						 "Device->OpenPropertyStore failed");
-		}
+		const auto enumerated_device = Item(*device_collection, i);
 
-		PROPVARIANT var_name;
-		PropVariantInit(&var_name);
-		AtScopeExit(&) { PropVariantClear(&var_name); };
+		const auto property_store =
+			OpenPropertyStore(*enumerated_device);
 
-		result = property_store->GetValue(PKEY_Device_FriendlyName, &var_name);
-		if (FAILED(result)) {
-			throw FormatHResultError(result,
-						 "PropertyStore->GetValue failed");
-		}
+		auto name = GetString(*property_store,
+				      PKEY_Device_FriendlyName);
+		if (name == nullptr)
+			continue;
 
-		device_desc.emplace_back(
-			i, WideCharToMultiByte(CP_UTF8,
-					       std::wstring_view(var_name.pwszVal)));
+		device_desc.emplace_back(i, std::move(name));
 	}
 }
 
 /// run inside COMWorkerThread
 void WasapiOutput::GetDevice(unsigned int index) {
-	HRESULT result;
-
-	ComPtr<IMMDeviceCollection> device_collection;
-	result = enumerator->EnumAudioEndpoints(eRender, DEVICE_STATE_ACTIVE,
-						device_collection.Address());
-	if (FAILED(result)) {
-		throw FormatHResultError(result, "Unable to enumerate devices");
-	}
-
-	result = device_collection->Item(index, device.Address());
-	if (FAILED(result)) {
-		throw FormatHResultError(result, "Collection->Item failed");
-	}
+	const auto device_collection = EnumAudioEndpoints(*enumerator);
+	device = Item(*device_collection, index);
 }
 
 /// run inside COMWorkerThread
@@ -926,17 +846,6 @@ unsigned int WasapiOutput::SearchDevice(std::string_view name) {
 	return iter->first;
 }
 
-/// run inside COMWorkerThread
-void WasapiOutput::GetDefaultDevice() {
-	HRESULT result;
-	result = enumerator->GetDefaultAudioEndpoint(eRender, eMultimedia,
-						     device.Address());
-	if (FAILED(result)) {
-		throw FormatHResultError(result,
-					 "Unable to get default device for multimedia");
-	}
-}
-
 static bool wasapi_output_test_default_device() { return true; }
 
 const struct AudioOutputPlugin wasapi_output_plugin = {
diff --git a/src/win32/PropVariant.cxx b/src/win32/PropVariant.cxx
new file mode 100644
index 000000000..5fa728eeb
--- /dev/null
+++ b/src/win32/PropVariant.cxx
@@ -0,0 +1,40 @@
+/*
+ * Copyright 2020-2021 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.
+ */
+
+#include "PropVariant.hxx"
+#include "lib/icu/Win32.hxx"
+#include "util/AllocatedString.hxx"
+#include "util/ScopeExit.hxx"
+
+AllocatedString
+ToString(const PROPVARIANT &pv) noexcept
+{
+	// TODO: VT_BSTR
+
+	switch (pv.vt) {
+	case VT_LPSTR:
+		return AllocatedString{static_cast<const char *>(pv.pszVal)};
+
+	case VT_LPWSTR:
+		return WideCharToMultiByte(CP_UTF8, pv.pwszVal);
+
+	default:
+		return nullptr;
+	}
+}
diff --git a/src/win32/PropVariant.hxx b/src/win32/PropVariant.hxx
new file mode 100644
index 000000000..54da5e988
--- /dev/null
+++ b/src/win32/PropVariant.hxx
@@ -0,0 +1,31 @@
+/*
+ * Copyright 2020-2021 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.
+ */
+
+#ifndef MPD_WIN32_PROPVARIANT_HXX
+#define MPD_WIN32_PROPVARIANT_HXX
+
+#include <propidl.h>
+
+class AllocatedString;
+
+[[gnu::pure]]
+AllocatedString
+ToString(const PROPVARIANT &pv) noexcept;
+
+#endif
diff --git a/src/win32/meson.build b/src/win32/meson.build
index 5f8eaf6b7..28f958a8a 100644
--- a/src/win32/meson.build
+++ b/src/win32/meson.build
@@ -7,6 +7,7 @@ win32 = static_library(
   'win32',
   'ComWorker.cxx',
   'HResult.cxx',
+  'PropVariant.cxx',
   'WinEvent.cxx',
   include_directories: inc,
 )