mpd/src/output/plugins/AoOutputPlugin.cxx

// SPDX-License-Identifier: GPL-2.0-or-later
// Copyright The Music Player Daemon Project

#include "AoOutputPlugin.hxx"
#include "../OutputAPI.hxx"
#include "lib/fmt/RuntimeError.hxx"
#include "thread/SafeSingleton.hxx"
#include "system/Error.hxx"
#include "util/IterableSplitString.hxx"
#include "util/Domain.hxx"
#include "util/StringAPI.hxx"
#include "util/StringSplit.hxx"
#include "util/StringStrip.hxx"
#include "Log.hxx"

#include <ao/ao.h>

#include <cassert>

/* An ao_sample_format, with all fields set to zero: */
static ao_sample_format OUR_AO_FORMAT_INITIALIZER;

class AoInit {
public:
	AoInit() {
		ao_initialize();
	}

	~AoInit() noexcept {
		ao_shutdown();
	}

	AoInit(const AoInit &) = delete;
	AoInit &operator=(const AoInit &) = delete;
};

class AoOutput final : AudioOutput, SafeSingleton<AoInit> {
	const size_t write_size;
	int driver;
	ao_option *options = nullptr;
	ao_device *device;

	size_t frame_size;

	std::size_t max_size;

	explicit AoOutput(const ConfigBlock &block);
	~AoOutput() override;

	AoOutput(const AoOutput &) = delete;
	AoOutput &operator=(const AoOutput &) = delete;

public:
	static AudioOutput *Create(EventLoop &, const ConfigBlock &block) {
		return new AoOutput(block);
	}

	void Open(AudioFormat &audio_format) override;
	void Close() noexcept override;

	std::size_t Play(std::span<const std::byte> src) override;
};

static constexpr Domain ao_output_domain("ao_output");


static std::system_error
MakeAoError()
{
	const char *error = "Unknown libao failure";

	switch (errno) {
	case AO_ENODRIVER:
		error = "No such libao driver";
		break;

	case AO_ENOTLIVE:
		error = "This driver is not a libao live device";
		break;

	case AO_EBADOPTION:
		error = "Invalid libao option";
		break;

	case AO_EOPENDEVICE:
		error = "Cannot open the libao device";
		break;

	case AO_EFAIL:
		error = "Generic libao failure";
		break;
	}

	return MakeErrno(errno, error);
}

AoOutput::AoOutput(const ConfigBlock &block)
	:AudioOutput(0),
	 write_size(block.GetPositiveValue("write_size", 1024U))
{
	const char *value = block.GetBlockValue("driver", "default");
	if (StringIsEqual(value, "default"))
		driver = ao_default_driver_id();
	else
		driver = ao_driver_id(value);

	if (driver < 0)
		throw FmtRuntimeError("\"{}\" is not a valid ao driver",
				      value);

	ao_info *ai = ao_driver_info(driver);
	if (ai == nullptr)
		throw std::runtime_error("problems getting driver info");

	FmtDebug(ao_output_domain, "using ao driver \"{}\" for \"{}\"\n",
		 ai->short_name, block.GetBlockValue("name", nullptr));

	value = block.GetBlockValue("options", nullptr);
	if (value != nullptr) {
		for (const std::string_view i : IterableSplitString(value, ';')) {
			const auto [n, v] = Split(Strip(i), '=');
			if (n.empty() || v.data() == nullptr)
				throw FmtRuntimeError("problems parsing option \"{}\"",
						      i);

			ao_append_option(&options, std::string{n}.c_str(),
					 std::string{v}.c_str());
		}
	}
}

AoOutput::~AoOutput()
{
	ao_free_options(options);
}

void
AoOutput::Open(AudioFormat &audio_format)
{
	ao_sample_format format = OUR_AO_FORMAT_INITIALIZER;

	switch (audio_format.format) {
	case SampleFormat::S8:
		format.bits = 8;
		break;

	case SampleFormat::S16:
		format.bits = 16;
		break;

	default:
		/* support for 24 bit samples in libao is currently
		   dubious, and until we have sorted that out,
		   convert everything to 16 bit */
		audio_format.format = SampleFormat::S16;
		format.bits = 16;
		break;
	}

	frame_size = audio_format.GetFrameSize();

	/* round down to a multiple of the frame size */
	/* no matter how small "write_size" was configured, we must
	   pass at least one frame to libao */
	max_size = std::max(write_size / frame_size, std::size_t{1}) * frame_size;

	format.rate = audio_format.sample_rate;
	format.byte_format = AO_FMT_NATIVE;
	format.channels = audio_format.channels;

	device = ao_open_live(driver, &format, options);
	if (device == nullptr)
		throw MakeAoError();
}

void
AoOutput::Close() noexcept
{
	ao_close(device);
}

std::size_t
AoOutput::Play(std::span<const std::byte> src)
{
	assert(src.size() % frame_size == 0);

	if (src.size() > max_size)
		/* round down to a multiple of the frame size */
		src = src.first(max_size);

	/* For whatever reason, libao wants a non-const pointer.
	   Let's hope it does not write to the buffer, and use the
	   union deconst hack to * work around this API misdesign. */
	char *data = const_cast<char *>((const char *)src.data());

	if (ao_play(device, data, src.size()) == 0)
		throw MakeAoError();

	return src.size();
}

const struct AudioOutputPlugin ao_output_plugin = {
	"ao",
	nullptr,
	&AoOutput::Create,
	nullptr,
};