nih-plug/src/wrapper/standalone/backend/jack.rs

use std::sync::Arc;

use anyhow::{Context, Result};
use atomic_refcell::AtomicRefCell;
use crossbeam::channel;
use jack::{
    AudioIn, AudioOut, Client, ClientOptions, ClosureProcessHandler, Control, MidiIn, MidiOut, Port,
};

use super::super::config::WrapperConfig;
use super::Backend;
use crate::buffer::Buffer;
use crate::context::Transport;
use crate::midi::{MidiConfig, NoteEvent};
use crate::plugin::Plugin;

/// Uses JACK audio and MIDI.
pub struct Jack {
    config: WrapperConfig,
    /// The JACK client, wrapped in an option since it needs to be transformed into an `AsyncClient`
    /// and then back into a regular `Client`.
    client: Option<Client>,

    inputs: Arc<Vec<Port<AudioIn>>>,
    outputs: Arc<AtomicRefCell<Vec<Port<AudioOut>>>>,
    midi_input: Option<Arc<Port<MidiIn>>>,
    midi_output: Option<Arc<AtomicRefCell<Port<MidiOut>>>>,
}

/// A simple message to tell the audio thread to shut down, since the actual processing happens in
/// these callbacks.
enum Task {
    Shutdown,
}

impl Backend for Jack {
    fn run(
        &mut self,
        mut cb: impl FnMut(&mut Buffer, Transport, &[NoteEvent], &mut Vec<NoteEvent>) -> bool
            + 'static
            + Send,
    ) {
        let client = self.client.take().unwrap();
        let buffer_size = client.buffer_size();

        let mut buffer = Buffer::default();
        unsafe {
            buffer.with_raw_vec(|output_slices| {
                output_slices.resize_with(self.outputs.borrow().len(), || &mut []);
            })
        }

        let mut input_events = Vec::with_capacity(2048);
        let mut output_events = Vec::with_capacity(2048);

        let (control_sender, control_receiver) = channel::bounded(32);
        let config = self.config.clone();
        let inputs = self.inputs.clone();
        let outputs = self.outputs.clone();
        let midi_input = self.midi_input.clone();
        let midi_output = self.midi_output.clone();
        let process_handler = ClosureProcessHandler::new(move |client, ps| {
            // In theory we could handle `num_frames <= buffer_size`, but JACK will never chop up
            // buffers like that so we'll just make it easier for ourselves by not supporting that
            let num_frames = ps.n_frames();
            if num_frames != buffer_size {
                nih_error!(
                    "Buffer size changed from {buffer_size} to {num_frames}. Buffer size changes \
                     are currently not supported, aborting..."
                );
                control_sender.send(Task::Shutdown).unwrap();
                return Control::Quit;
            }

            let mut transport = Transport::new(client.sample_rate() as f32);
            transport.tempo = Some(config.tempo as f64);
            transport.time_sig_numerator = Some(config.timesig_num as i32);
            transport.time_sig_denominator = Some(config.timesig_denom as i32);

            if let Ok(jack_transport) = client.transport().query() {
                transport.pos_samples = Some(jack_transport.pos.frame() as i64);
                transport.playing = jack_transport.state == jack::TransportState::Rolling;

                if let Some(bbt) = jack_transport.pos.bbt() {
                    transport.tempo = Some(bbt.bpm);
                    transport.time_sig_numerator = Some(bbt.sig_num as i32);
                    transport.time_sig_denominator = Some(bbt.sig_denom as i32);

                    transport.pos_beats = Some(
                        (bbt.bar as f64 * 4.0)
                            + (bbt.beat as f64 / bbt.sig_denom as f64 * 4.0)
                            + (bbt.tick as f64 / bbt.ticks_per_beat),
                    );
                    transport.bar_number = Some(bbt.bar as i32);
                }
            }

            // Just like all of the plugin backends, we need to grab the output slices and copy the
            // inputs to the outputs
            let mut outputs = outputs.borrow_mut();
            for (input, output) in inputs.iter().zip(outputs.iter_mut()) {
                // XXX: Since the JACK bindings let us do this, presumably these two can't alias,
                //      right?
                output.as_mut_slice(ps).copy_from_slice(input.as_slice(ps));
            }

            // And the buffer's slices need to point to the JACK output ports
            unsafe {
                buffer.with_raw_vec(|output_slices| {
                    for (output_slice, output) in output_slices.iter_mut().zip(outputs.iter_mut()) {
                        // SAFETY: This buffer is only read from after in this callback, and the
                        //         reference passed to `cb` cannot outlive that function call
                        *output_slice = &mut *(output.as_mut_slice(ps) as *mut _);
                    }
                })
            }

            input_events.clear();
            if let Some(midi_input) = &midi_input {
                input_events.extend(midi_input.iter(ps).filter_map(|midi| {
                    // This should always be three bytes, but we get an unsized slice
                    let midi_data: [u8; 3] = midi.bytes.try_into().ok()?;
                    NoteEvent::from_midi(midi.time, midi_data).ok()
                }));
            }

            output_events.clear();
            if cb(&mut buffer, transport, &input_events, &mut output_events) {
                if let Some(midi_output) = &midi_output {
                    let mut midi_output = midi_output.borrow_mut();
                    let mut midi_writer = midi_output.writer(ps);
                    for event in output_events.drain(..) {
                        let timing = event.timing();
                        if let Some(midi_data) = event.as_midi() {
                            let write_result = midi_writer.write(&jack::RawMidi {
                                time: timing,
                                bytes: &midi_data,
                            });
                            nih_debug_assert!(write_result.is_ok(), "The MIDI buffer is full");
                        }
                    }
                }

                Control::Continue
            } else {
                control_sender.send(Task::Shutdown).unwrap();
                Control::Quit
            }
        });
        // TODO: What can go wrong here that would cause an error?
        let async_client = client.activate_async((), process_handler).unwrap();

        // The process callback happens on another thread, so we need to block this thread until we
        // get the request to shut down or until the process callback runs into an error
        #[allow(clippy::never_loop)]
        loop {
            match control_receiver.recv() {
                Ok(Task::Shutdown) => break,
                Err(err) => {
                    nih_debug_assert_failure!("Error reading from channel: {}", err);
                    break;
                }
            }
        }

        // And put the client back where it belongs in case this function is called a second time
        let (client, _, _) = async_client.deactivate().unwrap();
        self.client = Some(client);
    }
}

impl Jack {
    /// Initialize the JACK backend. Returns an error if this failed for whatever reason. The plugin
    /// generic argument is to get the name for the client, and to know whether or not the
    /// standalone should expose JACK MIDI ports.
    pub fn new<P: Plugin>(config: WrapperConfig) -> Result<Self> {
        let (client, status) = Client::new(P::NAME, ClientOptions::NO_START_SERVER)
            .context("Error while initializing the JACK client")?;
        if !status.is_empty() {
            anyhow::bail!("The JACK server returned an error: {status:?}");
        }

        let mut inputs = Vec::new();
        for port_no in 1..config.input_channels + 1 {
            inputs.push(client.register_port(&format!("input_{port_no}"), AudioIn)?);
        }

        let mut outputs = Vec::new();
        for port_no in 1..config.output_channels + 1 {
            let port = client.register_port(&format!("output_{port_no}"), AudioOut)?;

            // We don't connect the inputs automatically to avoid feedback loops, but this should be
            // safe. And if this fails, then that's fine.
            let system_playback_port_name = &format!("system:playback_{port_no}");
            let _ = client.connect_ports_by_name(&port.name()?, system_playback_port_name);

            outputs.push(port);
        }

        let midi_input = if P::MIDI_INPUT >= MidiConfig::Basic {
            Some(Arc::new(client.register_port("midi_input", MidiIn)?))
        } else {
            None
        };

        let midi_output = if P::MIDI_OUTPUT >= MidiConfig::Basic {
            Some(Arc::new(AtomicRefCell::new(
                client.register_port("midi_output", MidiOut)?,
            )))
        } else {
            None
        };

        // This option can either be set to a single port all inputs should be connected to, or a
        // comma separated list of ports
        if let Some(port_name) = &config.connect_jack_inputs {
            if port_name.contains(',') {
                for (port_name, input) in port_name.split(',').zip(&inputs) {
                    if let Err(err) = client.connect_ports_by_name(port_name, &input.name()?) {
                        nih_error!("Could not connect to '{port_name}': {err}");
                        break;
                    }
                }
            } else {
                for input in &inputs {
                    if let Err(err) = client.connect_ports_by_name(port_name, &input.name()?) {
                        nih_error!("Could not connect to '{port_name}': {err}");
                        break;
                    }
                }
            }
        }

        if let (Some(port), Some(port_name)) = (&midi_input, &config.connect_jack_midi_input) {
            if let Err(err) = client.connect_ports_by_name(port_name, &port.name()?) {
                nih_error!("Could not connect to '{port_name}': {err}");
            }
        }
        if let (Some(port), Some(port_name)) = (&midi_output, &config.connect_jack_midi_output) {
            if let Err(err) = client.connect_ports_by_name(&port.borrow().name()?, port_name) {
                nih_error!("Could not connect to '{port_name}': {err}");
            }
        }

        Ok(Self {
            config,
            client: Some(client),

            inputs: Arc::new(inputs),
            outputs: Arc::new(AtomicRefCell::new(outputs)),
            midi_input,
            midi_output,
        })
    }
}