From 7a5cfe172822de015838c6cc3274df9274e7283a Mon Sep 17 00:00:00 2001
From: Bananymous <oskari.alaranta@bananymous.com>
Date: Wed, 6 Aug 2025 01:50:41 +0300
Subject: [PATCH] LibAudio/AudioServer: Add support for playing real time audio

---
 userspace/libraries/LibAudio/Audio.cpp        | 70 +++++++++++++++----
 .../LibAudio/include/LibAudio/Audio.h         |  9 ++-
 .../programs/AudioServer/AudioServer.cpp      | 57 +++++++++++++--
 userspace/programs/AudioServer/AudioServer.h  |  6 +-
 userspace/programs/AudioServer/main.cpp       |  9 +--
 5 files changed, 123 insertions(+), 28 deletions(-)

diff --git a/userspace/libraries/LibAudio/Audio.cpp b/userspace/libraries/LibAudio/Audio.cpp
index 3f0ccd29..fbea99eb 100644
--- a/userspace/libraries/LibAudio/Audio.cpp
+++ b/userspace/libraries/LibAudio/Audio.cpp
@@ -12,6 +12,17 @@
 namespace LibAudio
 {
 
+	BAN::ErrorOr<Audio> Audio::create(uint32_t channels, uint32_t sample_rate, uint32_t sample_frames)
+	{
+		Audio result;
+		TRY(result.initialize((sample_frames + 10) * channels));
+
+		result.m_audio_buffer->sample_rate = sample_rate;
+		result.m_audio_buffer->channels = channels;
+
+		return result;
+	}
+
 	BAN::ErrorOr<Audio> Audio::load(BAN::StringView path)
 	{
 		Audio result(TRY(AudioLoader::load(path)));
@@ -69,18 +80,6 @@ namespace LibAudio
 		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);
@@ -118,11 +117,58 @@ namespace LibAudio
 		return {};
 	}
 
+	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 {};
+	}
+
+	void Audio::set_paused(bool paused)
+	{
+		ASSERT(m_server_fd != -1);
+
+		if (m_audio_buffer->paused == paused)
+			return;
+		m_audio_buffer->paused = paused;
+
+		long dummy = 0;
+		send(m_server_fd, &dummy, sizeof(dummy), 0);
+	}
+
+	size_t Audio::queue_samples(BAN::Span<const AudioBuffer::sample_t> samples)
+	{
+		size_t samples_queued = 0;
+
+		uint32_t head = m_audio_buffer->head;
+		while (samples_queued < samples.size())
+		{
+			const uint32_t next_head = (head + 1) % m_audio_buffer->capacity;
+			if (next_head == m_audio_buffer->tail)
+				break;
+			m_audio_buffer->samples[head] = samples[samples_queued++];
+			head = next_head;
+			if (samples_queued % 128 == 0)
+				m_audio_buffer->head = head;
+		}
+		if (samples_queued % 128 != 0)
+			m_audio_buffer->head = head;
+		return samples_queued;
+	}
+
 	void Audio::update()
 	{
 		if (!m_audio_loader)
 			return;
 
+		if (!m_audio_loader->samples_remaining() && !is_playing())
+			return set_paused(true);
+
 		while (m_audio_loader->samples_remaining())
 		{
 			const uint32_t next_head = (m_audio_buffer->head + 1) % m_audio_buffer->capacity;
diff --git a/userspace/libraries/LibAudio/include/LibAudio/Audio.h b/userspace/libraries/LibAudio/include/LibAudio/Audio.h
index 93f4781c..d0f1832d 100644
--- a/userspace/libraries/LibAudio/include/LibAudio/Audio.h
+++ b/userspace/libraries/LibAudio/include/LibAudio/Audio.h
@@ -18,6 +18,8 @@ namespace LibAudio
 		uint32_t sample_rate;
 		uint32_t channels;
 
+		BAN::Atomic<bool> paused { false };
+
 		uint32_t capacity;
 		BAN::Atomic<uint32_t> tail { 0 };
 		BAN::Atomic<uint32_t> head { 0 };
@@ -29,6 +31,7 @@ namespace LibAudio
 		BAN_NON_COPYABLE(Audio);
 
 	public:
+		static BAN::ErrorOr<Audio> create(uint32_t channels, uint32_t sample_rate, uint32_t sample_frames);
 		static BAN::ErrorOr<Audio> load(BAN::StringView path);
 		static BAN::ErrorOr<Audio> random(uint32_t samples);
 		~Audio() { clear(); }
@@ -37,9 +40,13 @@ namespace LibAudio
 		Audio& operator=(Audio&& other);
 
 		BAN::ErrorOr<void> start();
+		void update();
+
+		void set_paused(bool paused);
 
 		bool is_playing() const { return m_audio_buffer->tail != m_audio_buffer->head; }
-		void update();
+
+		size_t queue_samples(BAN::Span<const AudioBuffer::sample_t> samples);
 
 	private:
 		Audio() = default;
diff --git a/userspace/programs/AudioServer/AudioServer.cpp b/userspace/programs/AudioServer/AudioServer.cpp
index 358c6fb5..448e84dc 100644
--- a/userspace/programs/AudioServer/AudioServer.cpp
+++ b/userspace/programs/AudioServer/AudioServer.cpp
@@ -40,6 +40,13 @@ bool AudioServer::on_client_packet(int fd, long smo_key)
 {
 	auto& audio_buffer = m_audio_buffers[fd];
 
+	if (smo_key == 0)
+	{
+		if (audio_buffer.buffer)
+			reset_kernel_buffer();
+		return true;
+	}
+
 	audio_buffer.buffer = static_cast<LibAudio::AudioBuffer*>(smo_map(smo_key));
 	audio_buffer.sample_frames_queued = 0;
 	if (audio_buffer.buffer == nullptr)
@@ -53,8 +60,11 @@ bool AudioServer::on_client_packet(int fd, long smo_key)
 	return true;
 }
 
-void AudioServer::update()
+uint64_t AudioServer::update()
 {
+	// FIXME: get this from the kernel
+	static constexpr uint64_t kernel_buffer_ms = 50;
+
 	uint32_t kernel_buffer_size;
 	if (ioctl(m_audio_device_fd, SND_GET_BUFFERSZ, &kernel_buffer_size) == -1)
 		ASSERT_NOT_REACHED();
@@ -72,14 +82,17 @@ void AudioServer::update()
 	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;
+		return kernel_buffer_ms;
 
+	size_t max_sample_frames_to_queue = max_sample_frames;
+
+	bool anyone_playing = false;
 	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);
+		const sample_t sample_ratio = buffer.buffer->sample_rate / static_cast<sample_t>(m_sample_rate);
 
 		if (buffer.sample_frames_queued)
 		{
@@ -91,13 +104,38 @@ void AudioServer::update()
 			buffer.sample_frames_queued -= buffer_sample_frames_played;
 		}
 
+		if (buffer.buffer->paused)
+			continue;
+		anyone_playing = true;
+
+		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;
+		max_sample_frames_to_queue = BAN::Math::min<size_t>(max_sample_frames_to_queue, buffer_sample_frames_available);
+	}
+
+	if (!anyone_playing)
+		return 60'000;
+
+	// FIXME: this works but if any client stops producing audio samples
+	//        the whole audio server halts
+	const uint32_t samples_per_10ms = m_sample_rate / 100;
+	if (max_sample_frames_to_queue < samples_per_10ms)
+		return 1;
+
+	for (auto& [_, buffer] : m_audio_buffers)
+	{
+		if (buffer.buffer == nullptr || buffer.buffer->paused)
+			continue;
+
+		const sample_t sample_ratio = buffer.buffer->sample_rate / static_cast<sample_t>(m_sample_rate);
+
 		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)
+		const size_t sample_frames_to_queue = BAN::Math::min<size_t>(max_sample_frames_to_queue, buffer_sample_frames_available);
+		if (sample_frames_to_queue < samples_per_10ms)
 			continue;
 
 		while (m_samples.size() < queued_samples_end + sample_frames_to_queue * m_channels)
@@ -113,10 +151,17 @@ void AudioServer::update()
 				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;
+		buffer.sample_frames_queued += BAN::Math::min<uint32_t>(
+			buffer_total_sample_frames,
+			BAN::Math::ceil(sample_frames_to_queue * sample_ratio)
+		);
 	}
 
 	send_samples();
+
+	const double play_ms = 1000.0 * m_samples_sent / m_channels / m_sample_rate;
+	const uint64_t wake_ms = BAN::Math::max<uint64_t>(play_ms, kernel_buffer_ms) - kernel_buffer_ms;
+	return wake_ms;
 }
 
 void AudioServer::reset_kernel_buffer()
diff --git a/userspace/programs/AudioServer/AudioServer.h b/userspace/programs/AudioServer/AudioServer.h
index 7b91d243..44bb7562 100644
--- a/userspace/programs/AudioServer/AudioServer.h
+++ b/userspace/programs/AudioServer/AudioServer.h
@@ -19,7 +19,7 @@ public:
 	void on_client_disconnect(int fd);
 	bool on_client_packet(int fd, long smo_key);
 
-	void update();
+	uint64_t update();
 
 private:
 	struct ClientInfo
@@ -28,6 +28,8 @@ private:
 		size_t sample_frames_queued { 0 };
 	};
 
+	using sample_t = LibAudio::AudioBuffer::sample_t;
+
 private:
 	enum class AddOrRemove { Add, Remove };
 
@@ -42,7 +44,7 @@ private:
 
 	size_t m_samples_sent { 0 };
 	BAN::Array<uint8_t, 1024> m_send_buffer;
-	BAN::CircularQueue<double, 64 * 1024> m_samples;
+	BAN::CircularQueue<sample_t, 64 * 1024> m_samples;
 
 	BAN::HashMap<int, ClientInfo> m_audio_buffers;
 };
diff --git a/userspace/programs/AudioServer/main.cpp b/userspace/programs/AudioServer/main.cpp
index 12e4362a..65915087 100644
--- a/userspace/programs/AudioServer/main.cpp
+++ b/userspace/programs/AudioServer/main.cpp
@@ -96,8 +96,7 @@ int main()
 
 	dprintln("AudioServer started");
 
-	constexpr uint64_t update_interval_ms = 100;
-	uint64_t next_update_ms = get_current_ms() + update_interval_ms;
+	uint64_t next_update_ms = get_current_ms();
 
 	for (;;)
 	{
@@ -113,11 +112,7 @@ int main()
 		}
 
 		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;
-		}
+		next_update_ms = current_ms + audio_server->update();
 
 		const uint64_t timeout_ms = next_update_ms - current_ms;