classify audio open source errors

internal/source/source.go

@@ -178,36 +178,64 @@ type AudioFrame struct {
 func OpenAudio(domain, flowID string) (*AudioSource, error) {
 	inst, err := mxl.NewInstance(domain, "")
 	if err != nil {
-		return nil, fmt.Errorf("NewInstance: %w", err)
+		return nil, wrapError("new MXL instance", ErrorKindUnavailable, err)
 	}
 	r, err := inst.NewReader(flowID)
 	if err != nil {
 		inst.Close()
-		return nil, fmt.Errorf("NewReader: %w", err)
+		return nil, wrapError("open audio reader", ErrorKindUnavailable, err)
 	}
 	info, err := r.Info()
 	if err != nil {
 		r.Close()
 		inst.Close()
-		return nil, fmt.Errorf("Info: %w", err)
+		return nil, wrapError("get audio info", ErrorKindUnavailable, err)
 	}
 	if info.Config.Common.Format.IsDiscrete() {
 		r.Close()
 		inst.Close()
-		return nil, fmt.Errorf("flow is discrete (not audio)")
+		return nil, wrapError(
+			"validate audio flow",
+			ErrorKindInvalidConfig,
+			errors.New("audio flow is discrete"),
+		)
+	}
+	channels := uint64(info.Config.Continuous.ChannelCount)
+	if channels == 0 {
+		r.Close()
+		inst.Close()
+		return nil, wrapError(
+			"validate audio flow",
+			ErrorKindInvalidConfig,
+			errors.New("audio flow has no channels"),
+		)
+	}
+	rate := info.Config.Common.GrainRate
+	if rate.Num <= 0 || rate.Den <= 0 {
+		r.Close()
+		inst.Close()
+		return nil, wrapError(
+			"validate audio flow",
+			ErrorKindInvalidConfig,
+			fmt.Errorf("invalid audio rate: %d/%d", rate.Num, rate.Den),
+		)
 	}
 	idx := info.Runtime.HeadIndex
 	if idx == 0 {
 		r.Close()
 		inst.Close()
-		return nil, fmt.Errorf("flow has no head yet (no producer?)")
+		return nil, wrapError(
+			"open audio reader",
+			ErrorKindUnavailable,
+			errors.New("audio flow has no producer data"),
+		)
 	}
 	return &AudioSource{
 		inst:  inst,
 		r:     r,
 		info:  info,
-		rate:  info.Config.Common.GrainRate,
+		rate:  rate,
-		chans: uint64(info.Config.Continuous.ChannelCount),
+		chans: channels,
 		idx:   idx,
 	}, nil
 }