From 3aea2c007dca22677cdef70739b9249e1c6ef326 Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Thu, 10 Jul 2025 17:30:41 +0300
Subject: [PATCH] Userspace: Add simple AudioServer and LibAudio

---
 userspace/libraries/CMakeLists.txt            |   1 +
 userspace/libraries/LibAudio/Audio.cpp        | 136 ++++++++++++
 userspace/libraries/LibAudio/AudioLoader.cpp  |  66 ++++++
 .../LibAudio/AudioLoaders/WAVLoader.cpp       | 146 +++++++++++++
 userspace/libraries/LibAudio/CMakeLists.txt   |  12 ++
 .../LibAudio/include/LibAudio/Audio.h         |  64 ++++++
 .../LibAudio/include/LibAudio/AudioLoader.h   |  32 +++
 .../include/LibAudio/AudioLoaders/WAVLoader.h |  40 ++++
 .../programs/AudioServer/AudioServer.cpp      | 200 ++++++++++++++++++
 userspace/programs/AudioServer/AudioServer.h  |  48 +++++
 userspace/programs/AudioServer/CMakeLists.txt |  11 +
 userspace/programs/AudioServer/main.cpp       | 184 ++++++++++++++++
 userspace/programs/CMakeLists.txt             |   1 +
 13 files changed, 941 insertions(+)
 create mode 100644 userspace/libraries/LibAudio/Audio.cpp
 create mode 100644 userspace/libraries/LibAudio/AudioLoader.cpp
 create mode 100644 userspace/libraries/LibAudio/AudioLoaders/WAVLoader.cpp
 create mode 100644 userspace/libraries/LibAudio/CMakeLists.txt
 create mode 100644 userspace/libraries/LibAudio/include/LibAudio/Audio.h
 create mode 100644 userspace/libraries/LibAudio/include/LibAudio/AudioLoader.h
 create mode 100644 userspace/libraries/LibAudio/include/LibAudio/AudioLoaders/WAVLoader.h
 create mode 100644 userspace/programs/AudioServer/AudioServer.cpp
 create mode 100644 userspace/programs/AudioServer/AudioServer.h
 create mode 100644 userspace/programs/AudioServer/CMakeLists.txt
 create mode 100644 userspace/programs/AudioServer/main.cpp

diff --git a/userspace/libraries/CMakeLists.txt b/userspace/libraries/CMakeLists.txt
index 6f3d2762..4a929dd0 100644
--- a/userspace/libraries/CMakeLists.txt
+++ b/userspace/libraries/CMakeLists.txt
@@ -1,4 +1,5 @@
 set(USERSPACE_LIBRARIES
+	LibAudio
 	LibC
 	LibELF
 	LibFont
diff --git a/userspace/libraries/LibAudio/Audio.cpp b/userspace/libraries/LibAudio/Audio.cpp
new file mode 100644
index 00000000..3f0ccd29
--- /dev/null
+++ b/userspace/libraries/LibAudio/Audio.cpp
@@ -0,0 +1,136 @@
+#include <BAN/ScopeGuard.h>
+
+#include <LibAudio/Audio.h>
+
+#include <fcntl.h>
+#include <stdlib.h>
+#include <sys/banan-os.h>
+#include <sys/mman.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+
+namespace LibAudio
+{
+
+	BAN::ErrorOr<Audio> Audio::load(BAN::StringView path)
+	{
+		Audio result(TRY(AudioLoader::load(path)));
+		TRY(result.initialize(256 * 1024));
+		return result;
+	}
+
+	BAN::ErrorOr<Audio> Audio::random(uint32_t samples)
+	{
+		Audio result;
+		TRY(result.initialize(samples));
+
+		result.m_audio_buffer->sample_rate = 48000;
+		result.m_audio_buffer->channels = 1;
+
+		for (size_t i = 0; i < samples - 1; i++)
+			result.m_audio_buffer->samples[i] = (rand() - RAND_MAX / 2) / (RAND_MAX / 2.0);
+		result.m_audio_buffer->head = samples - 1;
+
+		return result;
+	}
+
+	void Audio::clear()
+	{
+		if (m_audio_buffer)
+			munmap(m_audio_buffer, m_smo_size);
+		m_audio_buffer = nullptr;
+
+		if (m_smo_key != -1)
+			smo_delete(m_smo_key);
+		m_smo_key = -1;
+
+		if (m_server_fd != -1)
+			close(m_server_fd);
+		m_server_fd = -1;
+
+		m_audio_loader.clear();
+	}
+
+	Audio& Audio::operator=(Audio&& other)
+	{
+		clear();
+
+		m_server_fd    = other.m_server_fd;
+		m_smo_key      = other.m_smo_key;
+		m_smo_size     = other.m_smo_size;
+		m_audio_buffer = other.m_audio_buffer;
+		m_audio_loader = BAN::move(other.m_audio_loader);
+
+		other.m_server_fd    = -1;
+		other.m_smo_key      = -1;
+		other.m_smo_size     = 0;
+		other.m_audio_buffer = nullptr;
+
+		return *this;
+	}
+
+	BAN::ErrorOr<void> Audio::start()
+	{
+		ASSERT(m_server_fd != -1);
+
+		const ssize_t nsend = send(m_server_fd, &m_smo_key, sizeof(m_smo_key), 0);
+		if (nsend == -1)
+			return BAN::Error::from_errno(errno);
+		ASSERT(nsend == sizeof(m_smo_key));
+
+		return {};
+	}
+
+	BAN::ErrorOr<void> Audio::initialize(uint32_t total_samples)
+	{
+		m_smo_size = sizeof(AudioBuffer) + total_samples * sizeof(AudioBuffer::sample_t);
+
+		m_smo_key = smo_create(m_smo_size, PROT_READ | PROT_WRITE);
+		if (m_smo_key == -1)
+			return BAN::Error::from_errno(errno);
+
+		m_audio_buffer = static_cast<AudioBuffer*>(smo_map(m_smo_key));
+		if (m_audio_buffer == nullptr)
+			return BAN::Error::from_errno(errno);
+		new (m_audio_buffer) AudioBuffer();
+		memset(m_audio_buffer->samples, 0, total_samples * sizeof(AudioBuffer::sample_t));
+
+		m_audio_buffer->capacity = total_samples;
+		if (m_audio_loader)
+		{
+			m_audio_buffer->channels = m_audio_loader->channels();
+			m_audio_buffer->sample_rate = m_audio_loader->sample_rate();
+		}
+
+		update();
+
+		sockaddr_un server_addr;
+		server_addr.sun_family = AF_UNIX;
+		strcpy(server_addr.sun_path, s_audio_server_socket.data());
+
+		m_server_fd = socket(AF_UNIX, SOCK_STREAM | SOCK_CLOEXEC, 0);
+		if (m_server_fd == -1)
+			return BAN::Error::from_errno(errno);
+
+		if (connect(m_server_fd, reinterpret_cast<sockaddr*>(&server_addr), sizeof(server_addr)) == -1)
+			return BAN::Error::from_errno(errno);
+
+		return {};
+	}
+
+	void Audio::update()
+	{
+		if (!m_audio_loader)
+			return;
+
+		while (m_audio_loader->samples_remaining())
+		{
+			const uint32_t next_head = (m_audio_buffer->head + 1) % m_audio_buffer->capacity;
+			if (next_head == m_audio_buffer->tail)
+				break;
+			m_audio_buffer->samples[m_audio_buffer->head] = m_audio_loader->get_sample();
+			m_audio_buffer->head = next_head;
+		}
+	}
+
+}
diff --git a/userspace/libraries/LibAudio/AudioLoader.cpp b/userspace/libraries/LibAudio/AudioLoader.cpp
new file mode 100644
index 00000000..2a7579ae
--- /dev/null
+++ b/userspace/libraries/LibAudio/AudioLoader.cpp
@@ -0,0 +1,66 @@
+#include <LibAudio/AudioLoader.h>
+#include <LibAudio/AudioLoaders/WAVLoader.h>
+
+#include <fcntl.h>
+#include <sys/mman.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+namespace LibAudio
+{
+
+	BAN::ErrorOr<BAN::UniqPtr<AudioLoader>> AudioLoader::load(BAN::StringView path)
+	{
+		if (path.empty())
+			return BAN::Error::from_errno(ENOENT);
+
+		const bool malloced = (path.data()[path.size()] != '\0');
+
+		const char* path_cstr = path.data();
+		if (malloced && (path_cstr = strndup(path.data(), path.size())) == nullptr)
+			return BAN::Error::from_errno(errno);
+		const int file_fd = open(path_cstr, O_RDONLY);
+		if (malloced)
+			free(const_cast<char*>(path_cstr));
+		if (file_fd == -1)
+			return BAN::Error::from_errno(errno);
+
+		struct stat st;
+		if (fstat(file_fd, &st) == -1)
+		{
+			close(file_fd);
+			return BAN::Error::from_errno(errno);
+		}
+
+		uint8_t* mmap_addr = static_cast<uint8_t*>(mmap(nullptr, st.st_size, PROT_READ, MAP_PRIVATE, file_fd, 0));
+		close(file_fd);
+		if (mmap_addr == MAP_FAILED)
+			return BAN::Error::from_errno(errno);
+
+		BAN::ErrorOr<BAN::UniqPtr<AudioLoader>> result_or_error { BAN::Error::from_errno(ENOTSUP) };
+
+		auto file_span = BAN::ConstByteSpan(mmap_addr, st.st_size);
+		if (WAVAudioLoader::can_load_from(file_span))
+			result_or_error = WAVAudioLoader::create(file_span);
+
+		if (result_or_error.is_error())
+		{
+			munmap(mmap_addr, st.st_size);
+			return result_or_error.release_error();
+		}
+
+		auto result = result_or_error.release_value();
+		result->m_mmap_addr = mmap_addr;
+		result->m_mmap_size = st.st_size;
+		return result;
+	}
+
+	AudioLoader::~AudioLoader()
+	{
+		if (m_mmap_addr)
+			munmap(m_mmap_addr, m_mmap_size);
+		m_mmap_addr = nullptr;
+		m_mmap_size = 0;
+	}
+
+}
diff --git a/userspace/libraries/LibAudio/AudioLoaders/WAVLoader.cpp b/userspace/libraries/LibAudio/AudioLoaders/WAVLoader.cpp
new file mode 100644
index 00000000..028aaef1
--- /dev/null
+++ b/userspace/libraries/LibAudio/AudioLoaders/WAVLoader.cpp
@@ -0,0 +1,146 @@
+#include <LibAudio/AudioLoaders/WAVLoader.h>
+
+namespace LibAudio
+{
+
+	struct WAVChunk
+	{
+		char chunk_id[4];
+		uint32_t chunk_size;
+	};
+
+	struct RIFFChunk : WAVChunk
+	{
+		char wave_id[4];
+	};
+
+	struct FormatChunk : WAVChunk
+	{
+		uint16_t wFormatTag;
+		uint16_t nChannels;
+		uint32_t nSamplePerSec;
+		uint32_t nAvgBytePerSec;
+		uint16_t nBlockAlign;
+		uint16_t wBitsPerSample;
+	};
+
+	bool WAVAudioLoader::can_load_from(BAN::ConstByteSpan data)
+	{
+		if (data.size() < sizeof(RIFFChunk))
+			return false;
+
+		const auto riff_chunk = data.as<const RIFFChunk>();
+		if (memcmp(riff_chunk.chunk_id, "RIFF", 4) != 0)
+			return false;
+		if (memcmp(riff_chunk.wave_id, "WAVE", 4) != 0)
+			return false;
+		return true;
+	}
+
+	BAN::ErrorOr<BAN::UniqPtr<AudioLoader>> WAVAudioLoader::create(BAN::ConstByteSpan data)
+	{
+		ASSERT(can_load_from(data));
+
+		{
+			const auto riff_chunk = data.as<const RIFFChunk>();
+			if (sizeof(WAVChunk) + riff_chunk.chunk_size > data.size())
+				return BAN::Error::from_errno(ENOBUFS);
+			data = data.slice(0, sizeof(WAVChunk) + riff_chunk.chunk_size);
+			data = data.slice(sizeof(RIFFChunk));
+		}
+
+		BAN::Optional<FormatChunk> format_chunk;
+		BAN::ConstByteSpan sample_data;
+
+		while (!data.empty())
+		{
+			const auto chunk = data.as<const WAVChunk>();
+			if (data.size() < sizeof(WAVChunk) + chunk.chunk_size)
+				return BAN::Error::from_errno(ENOBUFS);
+
+			if (memcmp(chunk.chunk_id, "fmt ", 4) == 0)
+				format_chunk = data.as<const FormatChunk>();
+			else if (memcmp(chunk.chunk_id, "data", 4) == 0)
+				sample_data = data.slice(sizeof(WAVChunk), chunk.chunk_size);
+
+			data = data.slice(sizeof(WAVChunk) + chunk.chunk_size);
+		}
+
+		if (!format_chunk.has_value() || sample_data.empty())
+			return BAN::Error::from_errno(EINVAL);
+
+		const auto format = static_cast<FormatCode>(format_chunk->wFormatTag);
+		const uint16_t bps = format_chunk->wBitsPerSample;
+		const uint16_t channels = format_chunk->nChannels;
+
+		if (channels == 0)
+			return BAN::Error::from_errno(EINVAL);
+
+		switch (format)
+		{
+			case FormatCode::WAVE_FORMAT_PCM:
+				if (bps != 8 && bps != 16 && bps != 32)
+					return BAN::Error::from_errno(ENOTSUP);
+				break;
+			case FormatCode::WAVE_FORMAT_IEEE_FLOAT:
+				if (bps != 32 && bps != 64)
+					return BAN::Error::from_errno(ENOTSUP);
+				break;
+			default:
+				return BAN::Error::from_errno(ENOTSUP);
+		}
+
+		if (bps / 8 * channels != format_chunk->nBlockAlign)
+			return BAN::Error::from_errno(EINVAL);
+
+		auto loader = TRY(BAN::UniqPtr<WAVAudioLoader>::create());
+		loader->m_bits_per_sample = bps;
+		loader->m_sample_format = format;
+		loader->m_channels = channels;
+		loader->m_sample_rate = format_chunk->nSamplePerSec;
+		loader->m_sample_data = sample_data;
+		loader->m_total_samples = sample_data.size() / (bps / 8);
+		loader->m_current_sample = 0;
+		return BAN::UniqPtr<AudioLoader>(BAN::move(loader));
+	}
+
+	template<typename T>
+	static double read_sample(BAN::ConstByteSpan data)
+	{
+		if constexpr(BAN::is_same_v<float, T> || BAN::is_same_v<double, T>)
+			return data.as<const T>();
+		else if constexpr(BAN::is_signed_v<T>)
+			return data.as<const T>() / static_cast<double>(BAN::numeric_limits<T>::max());
+		else
+			return data.as<const T>() / (BAN::numeric_limits<T>::max() / 2.0) - 1.0;
+	}
+
+	double WAVAudioLoader::get_sample()
+	{
+		ASSERT(samples_remaining() > 0);
+
+		const auto current_sample_data = m_sample_data.slice((m_bits_per_sample / 8) * m_current_sample++);
+
+		switch (m_sample_format)
+		{
+			case FormatCode::WAVE_FORMAT_PCM:
+				switch (m_bits_per_sample)
+				{
+					case 8:  return read_sample<uint8_t>(current_sample_data);
+					case 16: return read_sample<int16_t>(current_sample_data);
+					case 32: return read_sample<int32_t>(current_sample_data);
+				}
+				break;
+			case FormatCode::WAVE_FORMAT_IEEE_FLOAT:
+				switch (m_bits_per_sample)
+				{
+					case 32: return read_sample<float>(current_sample_data);
+					case 64: return read_sample<double>(current_sample_data);
+				}
+				break;
+		}
+
+		ASSERT_NOT_REACHED();
+	}
+
+}
diff --git a/userspace/libraries/LibAudio/CMakeLists.txt b/userspace/libraries/LibAudio/CMakeLists.txt
new file mode 100644
index 00000000..06fa200e
--- /dev/null
+++ b/userspace/libraries/LibAudio/CMakeLists.txt
@@ -0,0 +1,12 @@
+set(LIBAUDIO_SOURCES
+	Audio.cpp
+	AudioLoader.cpp
+	AudioLoaders/WAVLoader.cpp
+)
+
+add_library(libaudio ${LIBAUDIO_SOURCES})
+banan_link_library(libaudio ban)
+banan_link_library(libaudio libc)
+
+banan_install_headers(libaudio)
+install(TARGETS libaudio OPTIONAL)
diff --git a/userspace/libraries/LibAudio/include/LibAudio/Audio.h b/userspace/libraries/LibAudio/include/LibAudio/Audio.h
new file mode 100644
index 00000000..93f4781c
--- /dev/null
+++ b/userspace/libraries/LibAudio/include/LibAudio/Audio.h
@@ -0,0 +1,64 @@
+#pragma once
+
+#include <BAN/Atomic.h>
+#include <BAN/StringView.h>
+#include <BAN/Vector.h>
+
+#include <LibAudio/AudioLoader.h>
+
+namespace LibAudio
+{
+
+	static constexpr BAN::StringView s_audio_server_socket = "/tmp/audio-server.socket"_sv;
+
+	struct AudioBuffer
+	{
+		using sample_t = double;
+
+		uint32_t sample_rate;
+		uint32_t channels;
+
+		uint32_t capacity;
+		BAN::Atomic<uint32_t> tail { 0 };
+		BAN::Atomic<uint32_t> head { 0 };
+		sample_t samples[/* capacity */];
+	};
+
+	class Audio
+	{
+		BAN_NON_COPYABLE(Audio);
+
+	public:
+		static BAN::ErrorOr<Audio> load(BAN::StringView path);
+		static BAN::ErrorOr<Audio> random(uint32_t samples);
+		~Audio() { clear(); }
+
+		Audio(Audio&& other) { *this = BAN::move(other); }
+		Audio& operator=(Audio&& other);
+
+		BAN::ErrorOr<void> start();
+
+		bool is_playing() const { return m_audio_buffer->tail != m_audio_buffer->head; }
+		void update();
+
+	private:
+		Audio() = default;
+		Audio(BAN::UniqPtr<AudioLoader>&& audio_loader)
+			: m_audio_loader(BAN::move(audio_loader))
+		{ }
+
+		void clear();
+
+		BAN::ErrorOr<void> initialize(uint32_t total_samples);
+
+	private:
+		int m_server_fd { -1 };
+
+		BAN::UniqPtr<AudioLoader> m_audio_loader;
+
+		long m_smo_key { -1 };
+		size_t m_smo_size { 0 };
+		AudioBuffer* m_audio_buffer { nullptr };
+	};
+
+}
diff --git a/userspace/libraries/LibAudio/include/LibAudio/AudioLoader.h b/userspace/libraries/LibAudio/include/LibAudio/AudioLoader.h
new file mode 100644
index 00000000..eb3f36a3
--- /dev/null
+++ b/userspace/libraries/LibAudio/include/LibAudio/AudioLoader.h
@@ -0,0 +1,32 @@
+#pragma once
+
+#include <BAN/StringView.h>
+#include <BAN/UniqPtr.h>
+
+namespace LibAudio
+{
+
+	class AudioLoader
+	{
+		BAN_NON_COPYABLE(AudioLoader);
+		BAN_NON_MOVABLE(AudioLoader);
+
+	public:
+		static BAN::ErrorOr<BAN::UniqPtr<AudioLoader>> load(BAN::StringView path);
+		virtual ~AudioLoader();
+
+		virtual uint32_t channels() const = 0;
+		virtual uint32_t sample_rate() const = 0;
+		virtual uint32_t samples_remaining() const = 0;
+
+		virtual double get_sample() = 0;
+
+	protected:
+		AudioLoader() = default;
+
+	private:
+		void* m_mmap_addr { nullptr };
+		size_t m_mmap_size { 0 };
+	};
+
+}
diff --git a/userspace/libraries/LibAudio/include/LibAudio/AudioLoaders/WAVLoader.h b/userspace/libraries/LibAudio/include/LibAudio/AudioLoaders/WAVLoader.h
new file mode 100644
index 00000000..a81e7a97
--- /dev/null
+++ b/userspace/libraries/LibAudio/include/LibAudio/AudioLoaders/WAVLoader.h
@@ -0,0 +1,40 @@
+#pragma once
+
+#include <LibAudio/AudioLoader.h>
+
+#include <BAN/ByteSpan.h>
+
+namespace LibAudio
+{
+
+	class WAVAudioLoader : public AudioLoader
+	{
+	public:
+		enum FormatCode : uint16_t
+		{
+			WAVE_FORMAT_PCM        = 0x01,
+			WAVE_FORMAT_IEEE_FLOAT = 0x03,
+		};
+
+	public:
+		static bool can_load_from(BAN::ConstByteSpan data);
+		static BAN::ErrorOr<BAN::UniqPtr<AudioLoader>> create(BAN::ConstByteSpan data);
+
+		uint32_t channels() const override { return m_channels; }
+		uint32_t sample_rate() const override { return m_sample_rate; }
+		uint32_t samples_remaining() const override { return m_total_samples - m_current_sample; }
+
+		double get_sample() override;
+
+	private:
+		uint32_t m_channels { 0 };
+		uint32_t m_sample_rate { 0 };
+		uint32_t m_total_samples { 0 };
+
+		FormatCode m_sample_format;
+		uint16_t m_bits_per_sample { 0 };
+		size_t m_current_sample { 0 };
+		BAN::ConstByteSpan m_sample_data;
+	};
+
+}
diff --git a/userspace/programs/AudioServer/AudioServer.cpp b/userspace/programs/AudioServer/AudioServer.cpp
new file mode 100644
index 00000000..358c6fb5
--- /dev/null
+++ b/userspace/programs/AudioServer/AudioServer.cpp
@@ -0,0 +1,200 @@
+#include "AudioServer.h"
+
+#include <sys/banan-os.h>
+#include <sys/ioctl.h>
+#include <sys/mman.h>
+#include <unistd.h>
+
+AudioServer::AudioServer(int fd)
+	: m_audio_device_fd(fd)
+{
+	if (ioctl(m_audio_device_fd, SND_GET_CHANNELS, &m_channels) != 0)
+		ASSERT_NOT_REACHED();
+	if (ioctl(m_audio_device_fd, SND_GET_SAMPLE_RATE, &m_sample_rate) != 0)
+		ASSERT_NOT_REACHED();
+}
+
+BAN::ErrorOr<void> AudioServer::on_new_client(int fd)
+{
+	TRY(m_audio_buffers.emplace(fd, nullptr));
+	return {};
+}
+
+void AudioServer::on_client_disconnect(int fd)
+{
+	auto it = m_audio_buffers.find(fd);
+	ASSERT(it != m_audio_buffers.end());
+
+	if (it->value.buffer != nullptr)
+	{
+		const size_t bytes = sizeof(LibAudio::AudioBuffer) + it->value.buffer->capacity * sizeof(LibAudio::AudioBuffer::sample_t);
+		munmap(it->value.buffer, bytes);
+	}
+
+	m_audio_buffers.remove(it);
+
+	reset_kernel_buffer();
+}
+
+bool AudioServer::on_client_packet(int fd, long smo_key)
+{
+	auto& audio_buffer = m_audio_buffers[fd];
+
+	audio_buffer.buffer = static_cast<LibAudio::AudioBuffer*>(smo_map(smo_key));
+	audio_buffer.sample_frames_queued = 0;
+	if (audio_buffer.buffer == nullptr)
+	{
+		dwarnln("Failed to map audio buffer: {}", strerror(errno));
+		return false;
+	}
+
+	reset_kernel_buffer();
+
+	return true;
+}
+
+void AudioServer::update()
+{
+	uint32_t kernel_buffer_size;
+	if (ioctl(m_audio_device_fd, SND_GET_BUFFERSZ, &kernel_buffer_size) == -1)
+		ASSERT_NOT_REACHED();
+
+	const size_t kernel_samples = kernel_buffer_size / sizeof(int16_t);
+	ASSERT(kernel_samples <= m_samples_sent);
+
+	const uint32_t samples_played = m_samples_sent - kernel_samples;
+	ASSERT(samples_played % m_channels == 0);
+
+	for (uint32_t i = 0; i < samples_played; i++)
+		m_samples.pop();
+	m_samples_sent -= samples_played;
+
+	const size_t max_sample_frames = (m_samples.capacity() - m_samples.size()) / m_channels;
+	const size_t queued_samples_end = m_samples.size();
+	if (max_sample_frames == 0)
+		return;
+
+	for (auto& [_, buffer] : m_audio_buffers)
+	{
+		if (buffer.buffer == nullptr)
+			continue;
+
+		const double sample_ratio = buffer.buffer->sample_rate / static_cast<double>(m_sample_rate);
+
+		if (buffer.sample_frames_queued)
+		{
+			const uint32_t buffer_sample_frames_played = BAN::Math::min<size_t>(
+				samples_played * sample_ratio / m_channels,
+				buffer.sample_frames_queued
+			);
+			buffer.buffer->tail = (buffer.buffer->tail + buffer_sample_frames_played * buffer.buffer->channels) % buffer.buffer->capacity;
+			buffer.sample_frames_queued -= buffer_sample_frames_played;
+		}
+
+		const uint32_t buffer_total_sample_frames = ((buffer.buffer->capacity + buffer.buffer->head - buffer.buffer->tail) % buffer.buffer->capacity) / buffer.buffer->channels;
+		const uint32_t buffer_sample_frames_available = (buffer_total_sample_frames - buffer.sample_frames_queued) / sample_ratio;
+		if (buffer_sample_frames_available == 0)
+			continue;
+
+		const size_t sample_frames_to_queue = BAN::Math::min<size_t>(max_sample_frames, buffer_sample_frames_available);
+		if (sample_frames_to_queue == 0)
+			continue;
+
+		while (m_samples.size() < queued_samples_end + sample_frames_to_queue * m_channels)
+			m_samples.push(0.0);
+
+		const size_t min_channels = BAN::Math::min(m_channels, buffer.buffer->channels);
+
+		const size_t buffer_tail = buffer.buffer->tail + buffer.sample_frames_queued * buffer.buffer->channels;
+		for (size_t i = 0; i < sample_frames_to_queue; i++)
+		{
+			const size_t buffer_frame = i * sample_ratio;
+			for (size_t j = 0; j < min_channels; j++)
+				m_samples[queued_samples_end + i * m_channels + j] += buffer.buffer->samples[(buffer_tail + buffer_frame * buffer.buffer->channels + j) % buffer.buffer->capacity];
+		}
+
+		buffer.sample_frames_queued += sample_frames_to_queue * sample_ratio;
+	}
+
+	send_samples();
+}
+
+void AudioServer::reset_kernel_buffer()
+{
+	uint32_t kernel_buffer_size;
+	if (ioctl(m_audio_device_fd, SND_RESET_BUFFER, &kernel_buffer_size) != 0)
+		ASSERT_NOT_REACHED();
+
+	const size_t kernel_samples = kernel_buffer_size / sizeof(int16_t);
+	ASSERT(kernel_samples <= m_samples_sent);
+
+	const uint32_t samples_played = m_samples_sent - kernel_samples;
+	ASSERT(samples_played % m_channels == 0);
+
+	m_samples_sent = 0;
+	m_samples.clear();
+
+	for (auto& [_, buffer] : m_audio_buffers)
+	{
+		if (buffer.buffer == nullptr || buffer.sample_frames_queued == 0)
+			continue;
+		const uint32_t buffer_sample_frames_played = BAN::Math::min<size_t>(
+			samples_played / m_channels,
+			buffer.sample_frames_queued
+		);
+		buffer.buffer->tail = (buffer.buffer->tail + buffer_sample_frames_played * buffer.buffer->channels) % buffer.buffer->capacity;
+		buffer.sample_frames_queued = 0;
+	}
+
+	update();
+}
+
+void AudioServer::send_samples()
+{
+	// FIXME: don't assume kernel uses 16 bit PCM
+	using kernel_sample_t = int16_t;
+
+	if (m_samples_sent >= m_samples.size())
+		return;
+
+	while (m_samples_sent < m_samples.size())
+	{
+		const size_t samples_to_send = BAN::Math::min(m_send_buffer.size() / sizeof(kernel_sample_t), m_samples.size() - m_samples_sent);
+
+		auto buffer = BAN::ByteSpan(m_send_buffer.data(), samples_to_send * sizeof(kernel_sample_t));
+
+		{
+			auto sample_buffer = buffer.as_span<kernel_sample_t>();
+			for (size_t i = 0; i < samples_to_send; i++)
+			{
+				sample_buffer[i] = BAN::Math::clamp<double>(
+					m_samples[m_samples_sent + i] * BAN::numeric_limits<kernel_sample_t>::max(),
+					BAN::numeric_limits<kernel_sample_t>::min(),
+					BAN::numeric_limits<kernel_sample_t>::max()
+				);
+			}
+		}
+
+		size_t nwritten = 0;
+		while (nwritten < buffer.size())
+		{
+			const ssize_t nwrite = write(
+				m_audio_device_fd,
+				buffer.data() + nwritten,
+				buffer.size() - nwritten
+			);
+			if (nwrite == -1)
+			{
+				if (errno != EAGAIN && errno != EWOULDBLOCK)
+					dwarnln("write: {}", strerror(errno));
+				break;
+			}
+			nwritten += nwrite;
+		}
+
+		m_samples_sent += nwritten / sizeof(kernel_sample_t);
+
+		if (nwritten < buffer.size())
+			break;
+	}
+}
diff --git a/userspace/programs/AudioServer/AudioServer.h b/userspace/programs/AudioServer/AudioServer.h
new file mode 100644
index 00000000..7b91d243
--- /dev/null
+++ b/userspace/programs/AudioServer/AudioServer.h
@@ -0,0 +1,48 @@
+#pragma once
+
+#include <BAN/Array.h>
+#include <BAN/ByteSpan.h>
+#include <BAN/CircularQueue.h>
+#include <BAN/HashMap.h>
+
+#include <LibAudio/Audio.h>
+
+class AudioServer
+{
+	BAN_NON_MOVABLE(AudioServer);
+	BAN_NON_COPYABLE(AudioServer);
+
+public:
+	AudioServer(int audio_device_fd);
+
+	BAN::ErrorOr<void> on_new_client(int fd);
+	void on_client_disconnect(int fd);
+	bool on_client_packet(int fd, long smo_key);
+
+	void update();
+
+private:
+	struct ClientInfo
+	{
+		LibAudio::AudioBuffer* buffer;
+		size_t sample_frames_queued { 0 };
+	};
+
+private:
+	enum class AddOrRemove { Add, Remove };
+
+	void reset_kernel_buffer();
+
+	void send_samples();
+
+private:
+	const int m_audio_device_fd;
+	uint32_t m_sample_rate;
+	uint32_t m_channels;
+
+	size_t m_samples_sent { 0 };
+	BAN::Array<uint8_t, 1024> m_send_buffer;
+	BAN::CircularQueue<double, 64 * 1024> m_samples;
+
+	BAN::HashMap<int, ClientInfo> m_audio_buffers;
+};
diff --git a/userspace/programs/AudioServer/CMakeLists.txt b/userspace/programs/AudioServer/CMakeLists.txt
new file mode 100644
index 00000000..9e072219
--- /dev/null
+++ b/userspace/programs/AudioServer/CMakeLists.txt
@@ -0,0 +1,11 @@
+set(SOURCES
+	main.cpp
+	AudioServer.cpp
+)
+
+add_executable(AudioServer ${SOURCES})
+banan_link_library(AudioServer ban)
+banan_link_library(AudioServer libc)
+banan_link_library(AudioServer libaudio)
+
+install(TARGETS AudioServer OPTIONAL)
diff --git a/userspace/programs/AudioServer/main.cpp b/userspace/programs/AudioServer/main.cpp
new file mode 100644
index 00000000..12e4362a
--- /dev/null
+++ b/userspace/programs/AudioServer/main.cpp
@@ -0,0 +1,184 @@
+#include "AudioServer.h"
+
+#include <LibAudio/Audio.h>
+
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/select.h>
+#include <sys/socket.h>
+#include <sys/stat.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+static int open_server_fd()
+{
+	struct stat st;
+	if (stat(LibAudio::s_audio_server_socket.data(), &st) != -1)
+		unlink(LibAudio::s_audio_server_socket.data());
+
+	int server_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+	if (server_fd == -1)
+	{
+		dwarnln("failed to create server socket: {}", strerror(errno));
+		return -1;
+	}
+
+	sockaddr_un server_addr;
+	server_addr.sun_family = AF_UNIX;
+	strcpy(server_addr.sun_path, LibAudio::s_audio_server_socket.data());
+	if (bind(server_fd, (sockaddr*)&server_addr, sizeof(server_addr)) == -1)
+	{
+		dwarnln("failed to bind server socket: {}", strerror(errno));
+		return -1;
+	}
+
+	if (chmod(LibAudio::s_audio_server_socket.data(), 0777) == -1)
+	{
+		dwarnln("failed to set server socket permissions: {}", strerror(errno));
+		return -1;
+	}
+
+	if (listen(server_fd, SOMAXCONN) == -1)
+	{
+		dwarnln("failed to make server socket listening: {}", strerror(errno));
+		return -1;
+	}
+
+	return server_fd;
+}
+
+static uint64_t get_current_ms()
+{
+	timespec ts;
+	clock_gettime(CLOCK_MONOTONIC, &ts);
+	return ts.tv_sec * 1000 + ts.tv_nsec / 1000000;
+}
+
+int main()
+{
+	constexpr int non_terminating_signals[] {
+		SIGCONT,
+		SIGSTOP,
+		SIGTSTP,
+		SIGTTIN,
+		SIGTTOU,
+	};
+	for (int sig = _SIGMIN; sig <= _SIGMAX; sig++)
+		signal(sig, exit);
+	for (int sig : non_terminating_signals)
+		signal(sig, SIG_DFL);
+
+	const int audio_device_fd = open("/dev/audio0", O_RDWR | O_NONBLOCK);
+	if (audio_device_fd == -1)
+	{
+		dwarnln("failed to open audio device: {}", strerror(errno));
+		return 1;
+	}
+
+	auto* audio_server = new AudioServer(audio_device_fd);
+	if (audio_server == nullptr)
+	{
+		dwarnln("Failed to allocate AudioServer: {}", strerror(errno));
+		return 1;
+	}
+
+	const int server_fd = open_server_fd();
+	if (server_fd == -1)
+		return 1;
+
+	struct ClientInfo
+	{
+		int fd;
+	};
+
+	BAN::Vector<ClientInfo> clients;
+
+	dprintln("AudioServer started");
+
+	constexpr uint64_t update_interval_ms = 100;
+	uint64_t next_update_ms = get_current_ms() + update_interval_ms;
+
+	for (;;)
+	{
+		fd_set fds;
+		FD_ZERO(&fds);
+		FD_SET(server_fd, &fds);
+
+		int max_fd = server_fd;
+		for (const auto& client : clients)
+		{
+			max_fd = BAN::Math::max(max_fd, client.fd);
+			FD_SET(client.fd, &fds);
+		}
+
+		const uint64_t current_ms = get_current_ms();
+		if (current_ms >= next_update_ms)
+		{
+			audio_server->update();
+			next_update_ms = current_ms + update_interval_ms;
+		}
+
+		const uint64_t timeout_ms = next_update_ms - current_ms;
+
+		timeval timeout {
+			.tv_sec = static_cast<time_t>(timeout_ms / 1000),
+			.tv_usec = static_cast<suseconds_t>((timeout_ms % 1000) * 1000)
+		};
+		if (select(max_fd + 1, &fds, nullptr, nullptr, &timeout) == -1)
+		{
+			dwarnln("select: {}", strerror(errno));
+			break;
+		}
+
+		if (FD_ISSET(server_fd, &fds))
+		{
+			const int client_fd = accept(server_fd, nullptr, nullptr);
+			if (client_fd == -1)
+			{
+				dwarnln("accept: {}", strerror(errno));
+				continue;
+			}
+
+			if (auto ret = clients.emplace_back(client_fd); ret.is_error())
+			{
+				dwarnln("Failed to add client: {}", ret.error());
+				close(client_fd);
+				continue;
+			}
+
+			if (auto ret = audio_server->on_new_client(client_fd); ret.is_error())
+			{
+				dwarnln("Failed to initialize client: {}", ret.error());
+				clients.pop_back();
+				close(client_fd);
+				continue;
+			}
+		}
+
+		for (size_t i = 0; i < clients.size(); i++)
+		{
+			auto& client = clients[i];
+			if (!FD_ISSET(client.fd, &fds))
+				continue;
+
+			long smo_key;
+			const ssize_t nrecv = recv(client.fd, &smo_key, sizeof(smo_key), 0);
+
+			if (nrecv < static_cast<ssize_t>(sizeof(smo_key)) || !audio_server->on_client_packet(client.fd, smo_key))
+			{
+				if (nrecv == 0)
+					;
+				else if (nrecv < 0)
+					dwarnln("recv: {}", strerror(errno));
+				else if (nrecv < static_cast<ssize_t>(sizeof(smo_key)))
+					dwarnln("client sent only {} bytes, {} expected", nrecv, sizeof(smo_key));
+
+				audio_server->on_client_disconnect(client.fd);
+				close(client.fd);
+				clients.remove(i--);
+				continue;
+			}
+		}
+	}
+}
diff --git a/userspace/programs/CMakeLists.txt b/userspace/programs/CMakeLists.txt
index 7b775a4d..54f823fb 100644
--- a/userspace/programs/CMakeLists.txt
+++ b/userspace/programs/CMakeLists.txt
@@ -1,4 +1,5 @@
 set(USERSPACE_PROGRAMS
+	AudioServer
 	bananfetch
 	basename
 	cat