Add modulo comment
@@ -303,7 +303,7 @@ impl Source for CbSource {
let idx: usize = self.num_sent % self.files.len();
let file = self
.files
- .get_mut(idx)
+ .get_mut(idx) // this is safe as we do the module above
.ok_or(ErrorKind::ClientNotAvailable("cb", "No file available"))?;
let res = if let Some(line) = file.next().await {
self.num_sent += 1;
