audio_streams/src/shm_streams.rs

// Copyright 2019 The ChromiumOS Authors
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

#[cfg(unix)]
use std::os::unix::io::RawFd;
use std::sync::Arc;
use std::sync::Condvar;
use std::sync::Mutex;
use std::time::Duration;
use std::time::Instant;

use remain::sorted;
use thiserror::Error;

use crate::BoxError;
use crate::SampleFormat;
use crate::StreamDirection;
use crate::StreamEffect;

type GenericResult<T> = std::result::Result<T, BoxError>;

/// `BufferSet` is used as a callback mechanism for `ServerRequest` objects.
/// It is meant to be implemented by the audio stream, allowing arbitrary code
/// to be run after a buffer offset and length is set.
pub trait BufferSet {
    /// Called when the client sets a buffer offset and length.
    ///
    /// `offset` is the offset within shared memory of the buffer and `frames`
    /// indicates the number of audio frames that can be read from or written to
    /// the buffer.
    fn callback(&mut self, offset: usize, frames: usize) -> GenericResult<()>;

    /// Called when the client ignores a request from the server.
    fn ignore(&mut self) -> GenericResult<()>;
}

#[sorted]
#[derive(Error, Debug)]
pub enum Error {
    #[error("Provided number of frames {0} exceeds requested number of frames {1}")]
    TooManyFrames(usize, usize),
}

/// `ServerRequest` represents an active request from the server for the client
/// to provide a buffer in shared memory to playback from or capture to.
pub struct ServerRequest<'a> {
    requested_frames: usize,
    buffer_set: &'a mut dyn BufferSet,
}

impl<'a> ServerRequest<'a> {
    /// Create a new ServerRequest object
    ///
    /// Create a ServerRequest object representing a request from the server
    /// for a buffer `requested_frames` in size.
    ///
    /// When the client responds to this request by calling
    /// [`set_buffer_offset_and_frames`](ServerRequest::set_buffer_offset_and_frames),
    /// BufferSet::callback will be called on `buffer_set`.
    ///
    /// # Arguments
    /// * `requested_frames` - The requested buffer size in frames.
    /// * `buffer_set` - The object implementing the callback for when a buffer is provided.
    pub fn new<D: BufferSet>(requested_frames: usize, buffer_set: &'a mut D) -> Self {
        Self {
            requested_frames,
            buffer_set,
        }
    }

    /// Get the number of frames of audio data requested by the server.
    ///
    /// The returned value should never be greater than the `buffer_size`
    /// given in [`new_stream`](ShmStreamSource::new_stream).
    pub fn requested_frames(&self) -> usize {
        self.requested_frames
    }

    /// Sets the buffer offset and length for the requested buffer.
    ///
    /// Sets the buffer offset and length of the buffer that fulfills this
    /// server request to `offset` and `length`, respectively. This means that
    /// `length` bytes of audio samples may be read from/written to that
    /// location in `client_shm` for a playback/capture stream, respectively.
    /// This function may only be called once for a `ServerRequest`, at which
    /// point the ServerRequest is dropped and no further calls are possible.
    ///
    /// # Arguments
    ///
    /// * `offset` - The value to use as the new buffer offset for the next buffer.
    /// * `frames` - The length of the next buffer in frames.
    ///
    /// # Errors
    ///
    /// * If `frames` is greater than `requested_frames`.
    pub fn set_buffer_offset_and_frames(self, offset: usize, frames: usize) -> GenericResult<()> {
        if frames > self.requested_frames {
            return Err(Box::new(Error::TooManyFrames(
                frames,
                self.requested_frames,
            )));
        }

        self.buffer_set.callback(offset, frames)
    }

    /// Ignore this request
    ///
    /// If the client does not intend to respond to this ServerRequest with a
    /// buffer, they should call this function. The stream will be notified that
    /// the request has been ignored and will handle it properly.
    pub fn ignore_request(self) -> GenericResult<()> {
        self.buffer_set.ignore()
    }
}

/// `ShmStream` allows a client to interact with an active CRAS stream.
pub trait ShmStream: Send {
    /// Get the size of a frame of audio data for this stream.
    fn frame_size(&self) -> usize;

    /// Get the number of channels of audio data for this stream.
    fn num_channels(&self) -> usize;

    /// Get the frame rate of audio data for this stream.
    fn frame_rate(&self) -> u32;

    /// Waits until the next server message indicating action is required.
    ///
    /// For playback streams, this will be `AUDIO_MESSAGE_REQUEST_DATA`, meaning
    /// that we must set the buffer offset to the next location where playback
    /// data can be found.
    /// For capture streams, this will be `AUDIO_MESSAGE_DATA_READY`, meaning
    /// that we must set the buffer offset to the next location where captured
    /// data can be written to.
    /// Will return early if `timeout` elapses before a message is received.
    ///
    /// # Arguments
    ///
    /// * `timeout` - The amount of time to wait until a message is received.
    ///
    /// # Return value
    ///
    /// Returns `Some(request)` where `request` is an object that implements the
    /// [`ServerRequest`](ServerRequest) trait and which can be used to get the
    /// number of bytes requested for playback streams or that have already been
    /// written to shm for capture streams.
    ///
    /// If the timeout occurs before a message is received, returns `None`.
    ///
    /// # Errors
    ///
    /// * If an invalid message type is received for the stream.
    fn wait_for_next_action_with_timeout(
        &mut self,
        timeout: Duration,
    ) -> GenericResult<Option<ServerRequest>>;
}

/// `SharedMemory` specifies features of shared memory areas passed on to `ShmStreamSource`.
pub trait SharedMemory {
    type Error: std::error::Error;

    /// Creates a new shared memory file descriptor without specifying a name.
    fn anon(size: u64) -> Result<Self, Self::Error>
    where
        Self: Sized;

    /// Gets the size in bytes of the shared memory.
    ///
    /// The size returned here does not reflect changes by other interfaces or users of the shared
    /// memory file descriptor..
    fn size(&self) -> u64;

    /// Returns the underlying raw fd.
    #[cfg(unix)]
    fn as_raw_fd(&self) -> RawFd;
}

/// `ShmStreamSource` creates streams for playback or capture of audio.
pub trait ShmStreamSource<E: std::error::Error>: Send {
    /// Creates a new [`ShmStream`](ShmStream)
    ///
    /// Creates a new `ShmStream` object, which allows:
    /// * Waiting until the server has communicated that data is ready or
    ///   requested that we make more data available.
    /// * Setting the location and length of buffers for reading/writing audio data.
    ///
    /// # Arguments
    ///
    /// * `direction` - The direction of the stream, either `Playback` or `Capture`.
    /// * `num_channels` - The number of audio channels for the stream.
    /// * `format` - The audio format to use for audio samples.
    /// * `frame_rate` - The stream's frame rate in Hz.
    /// * `buffer_size` - The maximum size of an audio buffer. This will be the
    ///                   size used for transfers of audio data between client
    ///                   and server.
    /// * `effects` - Audio effects to use for the stream, such as echo-cancellation.
    /// * `client_shm` - The shared memory area that will contain samples.
    /// * `buffer_offsets` - The two initial values to use as buffer offsets
    ///                      for streams. This way, the server will not write
    ///                      audio data to an arbitrary offset in `client_shm`
    ///                      if the client fails to update offsets in time.
    ///
    /// # Errors
    ///
    /// * If sending the connect stream message to the server fails.
    #[allow(clippy::too_many_arguments)]
    fn new_stream(
        &mut self,
        direction: StreamDirection,
        num_channels: usize,
        format: SampleFormat,
        frame_rate: u32,
        buffer_size: usize,
        effects: &[StreamEffect],
        client_shm: &dyn SharedMemory<Error = E>,
        buffer_offsets: [u64; 2],
    ) -> GenericResult<Box<dyn ShmStream>>;

    /// Get a list of file descriptors used by the implementation.
    ///
    /// Returns any open file descriptors needed by the implementation.
    /// This list helps users of the ShmStreamSource enter Linux jails without
    /// closing needed file descriptors.
    #[cfg(unix)]
    fn keep_fds(&self) -> Vec<RawFd> {
        Vec::new()
    }
}

/// Class that implements ShmStream trait but does nothing with the samples
pub struct NullShmStream {
    num_channels: usize,
    frame_rate: u32,
    buffer_size: usize,
    frame_size: usize,
    interval: Duration,
    next_frame: Duration,
    start_time: Instant,
}

impl NullShmStream {
    /// Attempt to create a new NullShmStream with the given number of channels,
    /// format, frame_rate, and buffer_size.
    pub fn new(
        buffer_size: usize,
        num_channels: usize,
        format: SampleFormat,
        frame_rate: u32,
    ) -> Self {
        let interval = Duration::from_millis(buffer_size as u64 * 1000 / frame_rate as u64);
        Self {
            num_channels,
            frame_rate,
            buffer_size,
            frame_size: format.sample_bytes() * num_channels,
            interval,
            next_frame: interval,
            start_time: Instant::now(),
        }
    }
}

impl BufferSet for NullShmStream {
    fn callback(&mut self, _offset: usize, _frames: usize) -> GenericResult<()> {
        Ok(())
    }

    fn ignore(&mut self) -> GenericResult<()> {
        Ok(())
    }
}

impl ShmStream for NullShmStream {
    fn frame_size(&self) -> usize {
        self.frame_size
    }

    fn num_channels(&self) -> usize {
        self.num_channels
    }

    fn frame_rate(&self) -> u32 {
        self.frame_rate
    }

    fn wait_for_next_action_with_timeout(
        &mut self,
        timeout: Duration,
    ) -> GenericResult<Option<ServerRequest>> {
        let elapsed = self.start_time.elapsed();
        if elapsed < self.next_frame {
            if timeout < self.next_frame - elapsed {
                std::thread::sleep(timeout);
                return Ok(None);
            } else {
                std::thread::sleep(self.next_frame - elapsed);
            }
        }
        self.next_frame += self.interval;
        Ok(Some(ServerRequest::new(self.buffer_size, self)))
    }
}

/// Source of `NullShmStream` objects.
#[derive(Default)]
pub struct NullShmStreamSource;

impl NullShmStreamSource {
    pub fn new() -> Self {
        Self::default()
    }
}

impl<E: std::error::Error> ShmStreamSource<E> for NullShmStreamSource {
    fn new_stream(
        &mut self,
        _direction: StreamDirection,
        num_channels: usize,
        format: SampleFormat,
        frame_rate: u32,
        buffer_size: usize,
        _effects: &[StreamEffect],
        _client_shm: &dyn SharedMemory<Error = E>,
        _buffer_offsets: [u64; 2],
    ) -> GenericResult<Box<dyn ShmStream>> {
        let new_stream = NullShmStream::new(buffer_size, num_channels, format, frame_rate);
        Ok(Box::new(new_stream))
    }
}

#[derive(Clone)]
pub struct MockShmStream {
    num_channels: usize,
    frame_rate: u32,
    request_size: usize,
    frame_size: usize,
    request_notifier: Arc<(Mutex<bool>, Condvar)>,
}

impl MockShmStream {
    /// Attempt to create a new MockShmStream with the given number of
    /// channels, frame_rate, format, and buffer_size.
    pub fn new(
        num_channels: usize,
        frame_rate: u32,
        format: SampleFormat,
        buffer_size: usize,
    ) -> Self {
        #[allow(clippy::mutex_atomic)]
        Self {
            num_channels,
            frame_rate,
            request_size: buffer_size,
            frame_size: format.sample_bytes() * num_channels,
            request_notifier: Arc::new((Mutex::new(false), Condvar::new())),
        }
    }

    /// Call to request data from the stream, causing it to return from
    /// `wait_for_next_action_with_timeout`. Will block until
    /// `set_buffer_offset_and_frames` is called on the ServerRequest returned
    /// from `wait_for_next_action_with_timeout`, or until `timeout` elapses.
    /// Returns true if a response was successfully received.
    pub fn trigger_callback_with_timeout(&mut self, timeout: Duration) -> bool {
        let (lock, cvar) = &*self.request_notifier;
        let mut requested = lock.lock().unwrap();
        *requested = true;
        cvar.notify_one();
        let start_time = Instant::now();
        while *requested {
            requested = cvar.wait_timeout(requested, timeout).unwrap().0;
            if start_time.elapsed() > timeout {
                // We failed to get a callback in time, mark this as false.
                *requested = false;
                return false;
            }
        }

        true
    }

    fn notify_request(&mut self) {
        let (lock, cvar) = &*self.request_notifier;
        let mut requested = lock.lock().unwrap();
        *requested = false;
        cvar.notify_one();
    }
}

impl BufferSet for MockShmStream {
    fn callback(&mut self, _offset: usize, _frames: usize) -> GenericResult<()> {
        self.notify_request();
        Ok(())
    }

    fn ignore(&mut self) -> GenericResult<()> {
        self.notify_request();
        Ok(())
    }
}

impl ShmStream for MockShmStream {
    fn frame_size(&self) -> usize {
        self.frame_size
    }

    fn num_channels(&self) -> usize {
        self.num_channels
    }

    fn frame_rate(&self) -> u32 {
        self.frame_rate
    }

    fn wait_for_next_action_with_timeout(
        &mut self,
        timeout: Duration,
    ) -> GenericResult<Option<ServerRequest>> {
        {
            let start_time = Instant::now();
            let (lock, cvar) = &*self.request_notifier;
            let mut requested = lock.lock().unwrap();
            while !*requested {
                requested = cvar.wait_timeout(requested, timeout).unwrap().0;
                if start_time.elapsed() > timeout {
                    return Ok(None);
                }
            }
        }

        Ok(Some(ServerRequest::new(self.request_size, self)))
    }
}

/// Source of `MockShmStream` objects.
#[derive(Clone, Default)]
pub struct MockShmStreamSource {
    last_stream: Arc<(Mutex<Option<MockShmStream>>, Condvar)>,
}

impl MockShmStreamSource {
    pub fn new() -> Self {
        Default::default()
    }

    /// Get the last stream that has been created from this source. If no stream
    /// has been created, block until one has.
    pub fn get_last_stream(&self) -> MockShmStream {
        let (last_stream, cvar) = &*self.last_stream;
        let mut stream = last_stream.lock().unwrap();
        loop {
            match &*stream {
                None => stream = cvar.wait(stream).unwrap(),
                Some(ref s) => return s.clone(),
            };
        }
    }
}

impl<E: std::error::Error> ShmStreamSource<E> for MockShmStreamSource {
    fn new_stream(
        &mut self,
        _direction: StreamDirection,
        num_channels: usize,
        format: SampleFormat,
        frame_rate: u32,
        buffer_size: usize,
        _effects: &[StreamEffect],
        _client_shm: &dyn SharedMemory<Error = E>,
        _buffer_offsets: [u64; 2],
    ) -> GenericResult<Box<dyn ShmStream>> {
        let (last_stream, cvar) = &*self.last_stream;
        let mut stream = last_stream.lock().unwrap();

        let new_stream = MockShmStream::new(num_channels, frame_rate, format, buffer_size);
        *stream = Some(new_stream.clone());
        cvar.notify_one();
        Ok(Box::new(new_stream))
    }
}

// Tests that run only for Unix, where `base::SharedMemory` is used.
#[cfg(all(test, unix))]
pub mod tests {
    use super::*;

    struct MockSharedMemory {}

    impl SharedMemory for MockSharedMemory {
        type Error = super::Error;

        fn anon(_: u64) -> Result<Self, Self::Error> {
            Ok(MockSharedMemory {})
        }

        fn size(&self) -> u64 {
            0
        }

        #[cfg(unix)]
        fn as_raw_fd(&self) -> RawFd {
            0
        }
    }

    #[test]
    fn mock_trigger_callback() {
        let stream_source = MockShmStreamSource::new();
        let mut thread_stream_source = stream_source.clone();

        let buffer_size = 480;
        let num_channels = 2;
        let format = SampleFormat::S24LE;
        let shm = MockSharedMemory {};

        let handle = std::thread::spawn(move || {
            let mut stream = thread_stream_source
                .new_stream(
                    StreamDirection::Playback,
                    num_channels,
                    format,
                    44100,
                    buffer_size,
                    &[],
                    &shm,
                    [400, 8000],
                )
                .expect("Failed to create stream");

            let request = stream
                .wait_for_next_action_with_timeout(Duration::from_secs(5))
                .expect("Failed to wait for next action");
            match request {
                Some(r) => {
                    let requested = r.requested_frames();
                    r.set_buffer_offset_and_frames(872, requested)
                        .expect("Failed to set buffer offset and frames");
                    requested
                }
                None => 0,
            }
        });

        let mut stream = stream_source.get_last_stream();
        assert!(stream.trigger_callback_with_timeout(Duration::from_secs(1)));

        let requested_frames = handle.join().expect("Failed to join thread");
        assert_eq!(requested_frames, buffer_size);
    }

    #[test]
    fn null_consumption_rate() {
        let frame_rate = 44100;
        let buffer_size = 480;
        let interval = Duration::from_millis(buffer_size as u64 * 1000 / frame_rate as u64);

        let shm = MockSharedMemory {};

        let start = Instant::now();

        let mut stream_source = NullShmStreamSource::new();
        let mut stream = stream_source
            .new_stream(
                StreamDirection::Playback,
                2,
                SampleFormat::S24LE,
                frame_rate,
                buffer_size,
                &[],
                &shm,
                [400, 8000],
            )
            .expect("Failed to create stream");

        let timeout = Duration::from_secs(5);
        let request = stream
            .wait_for_next_action_with_timeout(timeout)
            .expect("Failed to wait for first request")
            .expect("First request should not have timed out");
        request
            .set_buffer_offset_and_frames(276, 480)
            .expect("Failed to set buffer offset and length");

        // The second call should block until the first buffer is consumed.
        let _request = stream
            .wait_for_next_action_with_timeout(timeout)
            .expect("Failed to wait for second request");
        let elapsed = start.elapsed();
        assert!(
            elapsed > interval,
            "wait_for_next_action_with_timeout didn't block long enough: {:?}",
            elapsed
        );

        assert!(
            elapsed < timeout,
            "wait_for_next_action_with_timeout blocked for too long: {:?}",
            elapsed
        );
    }
}