Judge a frame against the stream its socket receives rather than the one its header claims

main.go

@@ -466,9 +466,10 @@ func (d *direction) start(wg *sync.WaitGroup, doneTx, doneRx *atomic.Bool, rxRea
 		w := &rxWorker{
 			fd:     fd,
 			batch:  batchSize,
+			stream: uint16(i),
 			spec:   d.specs[i],
 			stats:  d.rxStats[i],
-			streams: d.streams,
+			loss:   &d.streams[i],
 			ready:  rxReady,
 		}
 		wg.Add(1)

rx.go

@@ -67,9 +67,10 @@ func (s *rxStats) bucket(e int64) (frames, bytes uint64) {
 type rxWorker struct {
 	fd     int
 	batch  int
+	stream uint16
 	spec   *frameSpec
 	stats  *rxStats
-	streams []lossWindow
+	loss   *lossWindow
 	ready  *sync.WaitGroup
 }
 
@@ -115,11 +116,10 @@ func (w *rxWorker) run(done *atomic.Bool) {
 				w.stats.observe(ts, uint64(len(buf)))
 			}
 
-			// A sequence number the sender never reached got past the header
+			// The ethertype this socket is bound to already says which stream the
-			// checksum, so the frame is damaged whatever its payload says. Counted
+			// frame belongs to, so a header naming another one is damaged, as is a
-			// here rather than left to the payload check, which would report the
+			// sequence number the sender never reached.
-			// same frame twice or, if only the header was hit, not at all.
+			if p.stream != w.stream || !w.loss.observe(p.seq) {
-			if int(p.stream) < len(w.streams) && !w.streams[p.stream].observe(p.seq) {
 				w.stats.badHdr.Add(1)
 				continue
 			}