Maven/cmd/mavwaked/playback.go

package main

// Reply playback, and the half-duplex gate around it (Vikunja #287).
//
// Before this, playback was `go playAudio(reply)` — fire and forget, with no
// handle on the running aplay. Two things fell out of that, and both are
// audible:
//
//  1. Self-trigger. The capture loop keeps feeding the VAD while the speaker
//     is playing, so Maven's own reply comes back in through the mic, trips
//     the VAD, and is sent to the daemon as a fresh utterance. She answers
//     herself. There is no acoustic echo canceller in this pipeline, so the
//     only correct fix is half-duplex: while she is speaking, the capture
//     side is muted.
//
//  2. No barge-in. Talking over her did nothing — there was nothing to
//     cancel, because nobody held the process handle.
//
// The two are the same mechanism seen from opposite sides, so they live
// together here. Echo suppression is unconditional (it fixes a bug). Barge-in
// is off unless -barge-in is passed, because it needs a room-specific energy
// threshold: with no echo canceller, the only way to tell "he is talking over
// her" from "the mic is hearing her" is that he is louder, and how much
// louder depends on where the mic sits relative to the speaker.

import (
	"log"
	"os/exec"
	"strconv"
	"sync"
	"time"

	"github.com/kami/maven/internal/audio"
)

// playbackMargin is the slack over the reply's own duration before a stuck
// aplay is killed. Enough for ALSA to open the device and drain its buffer,
// short enough that a busy device does not cost her a turn.
const playbackMargin = 2 * time.Second

// player plays one reply at a time and can be cut off mid-utterance.
type player interface {
	// Play starts playback of a, replacing anything already playing, and
	// returns immediately.
	Play(a audio.Audio)
	// Stop ends playback now. A no-op when nothing is playing.
	Stop()
	// Playing reports whether audio is currently going out of the speaker.
	Playing() bool
}

// aplayPlayer pipes raw PCM to aplay(1). Stop kills the child, which is what
// makes barge-in instant rather than "instant at the end of the sentence".
type aplayPlayer struct {
	mu      sync.Mutex
	cmd     *exec.Cmd
	playing bool
	// gen rises on every Play/Stop so a finishing playback cannot clear the
	// playing flag of the one that replaced it.
	gen uint64
}

func newAplayPlayer() *aplayPlayer { return &aplayPlayer{} }

func (p *aplayPlayer) Play(a audio.Audio) {
	if len(a.Bytes) == 0 {
		return
	}
	p.Stop()

	cmd := exec.Command("aplay",
		"-f", "S16_LE",
		"-r", strconv.Itoa(a.Format.SampleRate),
		"-c", strconv.Itoa(a.Format.Channels),
		"-t", "raw",
	)
	stdin, err := cmd.StdinPipe()
	if err != nil {
		log.Printf("mavwaked: aplay stdin pipe: %v", err)
		return
	}
	if err := cmd.Start(); err != nil {
		log.Printf("mavwaked: start aplay: %v", err)
		_ = stdin.Close()
		return
	}

	p.mu.Lock()
	p.gen++
	gen := p.gen
	p.cmd = cmd
	p.playing = true
	p.mu.Unlock()

	// Bound the mute window by the reply itself. Playing() gates all capture
	// now, so a wedged aplay does not merely go silent, it makes her deaf for
	// as long as the flag is set. The old ceiling was a flat 30s inherited
	// from the fire-and-forget version, where it only bounded a leaked
	// goroutine. A reply cannot legitimately take longer than it lasts.
	limit := time.Duration(a.Duration()*float64(time.Second)) + playbackMargin

	go func() {
		if _, err := stdin.Write(a.Bytes); err != nil {
			// Broken pipe is the expected outcome of Stop().
			log.Printf("mavwaked: write to aplay: %v", err)
		}
		_ = stdin.Close()

		done := make(chan error, 1)
		go func() { done <- cmd.Wait() }()
		select {
		case err := <-done:
			if err != nil {
				log.Printf("mavwaked: aplay: %v", err)
			}
		case <-time.After(limit):
			log.Printf("mavwaked: aplay did not finish %.1fs of audio within %s, killing (capture was muted the whole time)",
				a.Duration(), limit)
			if pr := cmd.Process; pr != nil {
				_ = pr.Kill()
			}
			<-done
		}

		p.mu.Lock()
		if p.gen == gen {
			p.playing = false
			p.cmd = nil
		}
		p.mu.Unlock()
	}()
}

func (p *aplayPlayer) Stop() {
	p.mu.Lock()
	cmd := p.cmd
	if cmd != nil {
		p.gen++
		p.playing = false
		p.cmd = nil
	}
	p.mu.Unlock()
	if cmd != nil && cmd.Process != nil {
		_ = cmd.Process.Kill()
	}
}

func (p *aplayPlayer) Playing() bool {
	p.mu.Lock()
	defer p.mu.Unlock()
	return p.playing
}