fix: don't close ALSA output when pausing or on EOF

Previously the output would always be closed, even when calling Pause().
This worked for the most part, somehow, but not with recent changes.

Instead, only close the output when actually getting an ALSA error that
can't be recovered from.

output/driver-alsa.go

@@ -181,10 +181,7 @@ func (out *alsaOutput) setupPcm() error {
 	// This loop continues until the PCM handle is closed and set to nil
 	// (Pause() or Close()) or there is an error.
 	pcmHandle := out.pcmHandle
-	go func() {
-		out.err <- out.outputLoop(pcmHandle)
-		_ = out.Close()
-	}()
+	go out.outputLoop(pcmHandle)
 
 	return nil
 }
@@ -228,7 +225,7 @@ func (out *alsaOutput) logParams(params *C.snd_pcm_hw_params_t) error {
 	return nil
 }
 
-func (out *alsaOutput) outputLoop(pcmHandle *C.snd_pcm_t) error {
+func (out *alsaOutput) outputLoop(pcmHandle *C.snd_pcm_t) {
 	floats := make([]float32, out.channels*out.periodSize)
 
 	for {
@@ -245,7 +242,7 @@ func (out *alsaOutput) outputLoop(pcmHandle *C.snd_pcm_t) error {
 			// (with a very fast pause+resume). In both cases, the loop should
 			// be stopped.
 			out.lock.Unlock()
-			return nil
+			return
 		}
 		availableFrames := int(C.snd_pcm_avail(pcmHandle))
 		waitForFrames := (out.periodSize + out.periodSize/8) - availableFrames
@@ -261,7 +258,7 @@ func (out *alsaOutput) outputLoop(pcmHandle *C.snd_pcm_t) error {
 		out.lock.Lock()
 		if pcmHandle != out.pcmHandle {
 			out.lock.Unlock()
-			return nil
+			return
 		}
 
 		// Read audio data. This can take a few milliseconds because it needs to
@@ -287,19 +284,31 @@ func (out *alsaOutput) outputLoop(pcmHandle *C.snd_pcm_t) error {
 				// Got an error, so must recover (even for an underrun).
 				errCode := C.snd_pcm_recover(pcmHandle, C.int(nn), 1)
 				if errCode < 0 {
-					// Failed to recover from this error.
+					// Failed to recover from this error. Close the output and
+					// report the error.
+					out.err <- out.alsaError("snd_pcm_recover", C.int(errCode))
+					out.closed = true
 					out.lock.Unlock()
-					return out.alsaError("snd_pcm_recover", C.int(errCode))
+					return
 				}
 			}
 		}
 
 		if errors.Is(err, io.EOF) {
+			// Reached EOF, move to a "paused" state.
+			out.pcmHandle = nil
+			if errCode := C.snd_pcm_close(pcmHandle); errCode < 0 {
+				out.err <- out.alsaError("snd_pcm_close", errCode)
+				out.lock.Unlock()
+			}
 			out.lock.Unlock()
-			return nil
+			return
 		} else if err != nil {
+			// Got some other error. Close the output and report the error.
+			out.err <- err
+			out.closed = true
 			out.lock.Unlock()
-			return err
+			return
 		}
 
 		out.lock.Unlock()