internal/pipewire: unmarshal nil pointer correctly

This now calls unmarshalCheckTypeBounds to advance to the next message. Additionally, handling for None value is relocated to a function for reuse by other types.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pipewire/pod.go

@@ -384,19 +384,16 @@ func unmarshalValue(data []byte, v reflect.Value, wireSizeP *Word) error {
 		return nil
 
 	case reflect.Pointer:
-		if len(data) < SizePrefix {
+		if ok, err := unmarshalHandleNone(&data, wireSizeP); err != nil {
-			return ErrEOFPrefix
+			return err
-		}
+		} else if ok {
-		switch SPAKind(binary.NativeEndian.Uint32(data[SizeSPrefix:])) {
-		case SPA_TYPE_None:
 			v.SetZero()
 			return nil
-
-		default:
-			v.Set(reflect.New(v.Type().Elem()))
-			return unmarshalValue(data, v.Elem(), wireSizeP)
 		}
 
+		v.Set(reflect.New(v.Type().Elem()))
+		return unmarshalValue(data, v.Elem(), wireSizeP)
+
 	case reflect.String:
 		*wireSizeP = 0
 		if err := unmarshalCheckTypeBounds(&data, SPA_TYPE_String, wireSizeP); err != nil {
@@ -422,6 +419,29 @@ func unmarshalValue(data []byte, v reflect.Value, wireSizeP *Word) error {
 	}
 }
 
+// unmarshalHandleNone establishes prefix bounds and, for a value of type [SPA_TYPE_None],
+// validates its size and skips the header. This is for unmarshalling values that can be nil.
+func unmarshalHandleNone(data *[]byte, wireSizeP *Word) (bool, error) {
+	if len(*data) < SizePrefix {
+		return false, ErrEOFPrefix
+	}
+
+	if SPAKind(binary.NativeEndian.Uint32((*data)[SizeSPrefix:])) != SPA_TYPE_None {
+		return false, nil
+	}
+
+	*wireSizeP = 0
+	if err := unmarshalCheckTypeBounds(data, SPA_TYPE_None, wireSizeP); err != nil {
+		return true, err
+	}
+
+	if len(*data) != 0 {
+		return true, TrailingGarbageError(*data)
+	}
+
+	return true, nil
+}
+
 // An InconsistentSizeError describes an inconsistent size prefix encountered
 // in data passed to [Unmarshal].
 type InconsistentSizeError struct{ Prefix, Expect Word }