alsa.go: Add chunkingRead function to abstract reading from the alsa buffer (#440)

The chunkingRead function allows the record period to not impact on the recording buffer size of the audio. This should allow for less issues related to alsa buffer reading.

device/alsa/alsa.go

@@ -147,8 +147,8 @@ func (d *ALSA) Setup(c config.Config) error {
 		return fmt.Errorf("failed to open device: %w", err)
 	}
 
-	// Setup the device to record with desired period.
-	ab := d.dev.NewBufferDuration(time.Duration(d.RecPeriod * float64(time.Second)))
+	// Create a buffer of 1 minute for continuous recordings.
+	ab := d.dev.NewBufferDuration(time.Minute)
 	sf, err := pcm.SFFromString(ab.Format.SampleFormat.String())
 	if err != nil {
 		return fmt.Errorf("unable to get sample format from string: %w", err)
@@ -355,6 +355,13 @@ func (d *ALSA) open() error {
 // input continously records audio and writes it to the ringbuffer.
 // Re-opens the device and tries again if the ASLA device returns an error.
 func (d *ALSA) input() {
+	// Make a channel to communicate betwen continuous recording and processing.
+	// The channel has a capacity of 5 minutes of audio, which it should never reach.
+	ch := make(chan []byte, int(5*60/d.RecPeriod))
+
+	// Read audio in 1 minute sections.
+	go chunkingRead(d, ch)
+
 	for {
 		// Check mode.
 		d.mu.Lock()
@@ -407,6 +414,20 @@ func (d *ALSA) input() {
 	}
 }
 
+// chunkingRead reads continuously from the ALSA buffer in 1 minute sections. The
+// audio is then chunked into the recording period set by d.RecPeriod and sent over
+// the channel.
+func chunkingRead(d *ALSA, ch chan []byte) {
+	// Read audio in 1 minute sections.
+	d.dev.Read(d.pb.Data)
+
+	// Chunk the audio into length of RecPeriod.
+	bytesPerRecPeriod := d.dev.BytesPerFrame() * d.dev.BufferFormat().Rate * int(d.RecPeriod)
+	for i := 0; i < len(d.pb.Data); i += bytesPerRecPeriod {
+		ch <- d.pb.Data[i:i+bytesPerRecPeriod-1]
+	}
+}
+
 // Read reads from the ringbuffer, returning the number of bytes read upon success.
 func (d *ALSA) Read(p []byte) (int, error) {
 	// Ready ringbuffer for read.