drop ECN support for this release

overlay/batch/batch.go

@@ -19,11 +19,9 @@ type RxBatcher interface {
 type TxBatcher interface {
 	// Reserve creates a pkt to borrow
 	Reserve(sz int) []byte
-	// Commit borrows pkt and records its destination plus the 2-bit
-	// IP-level ECN codepoint to set on the outer (carrier) header. The
-	// caller must keep pkt valid until the next Flush. Pass 0 (Not-ECT)
-	// to leave the outer ECN field unset.
-	Commit(pkt []byte, dst netip.AddrPort, outerECN byte)
+	// Commit borrows pkt and records its destination. The caller must
+	// keep pkt valid until the next Flush.
+	Commit(pkt []byte, dst netip.AddrPort)
 	// Flush emits every queued packet via the underlying batch writer in arrival order and reports how many were
 	// actually written. A short count means some destinations were undeliverable, not that the batch failed.
 	// After Flush returns, borrowed payload slices may be recycled.

overlay/batch/tx_batch.go

@@ -6,7 +6,7 @@ const SendBatchCap = 128
 
 // batchWriter is the minimal subset of udp.Conn needed by SendBatch to flush.
 type batchWriter interface {
-	WriteBatch(bufs [][]byte, addrs []netip.AddrPort, outerECNs []byte) (int, error)
+	WriteBatch(bufs [][]byte, addrs []netip.AddrPort) (int, error)
 }
 
 // SendBatch accumulates encrypted UDP packets and flushes them via WriteBatch.
@@ -16,7 +16,6 @@ type SendBatch struct {
 	out   batchWriter
 	bufs  [][]byte
 	dsts  []netip.AddrPort
-	ecns  []byte
 	arena *Arena
 }
 
@@ -26,7 +25,6 @@ func NewSendBatch(out batchWriter, batchCap, arenaSize int) *SendBatch {
 		out:   out,
 		bufs:  make([][]byte, 0, batchCap),
 		dsts:  make([]netip.AddrPort, 0, batchCap),
-		ecns:  make([]byte, 0, batchCap),
 		arena: NewArena(arenaSize),
 	}
 }
@@ -40,10 +38,9 @@ func (b *SendBatch) Reserve(sz int) []byte {
 // bounding how long the first packet of a large read batch waits.
 func (b *SendBatch) Len() int { return len(b.bufs) }
 
-func (b *SendBatch) Commit(pkt []byte, dst netip.AddrPort, outerECN byte) {
+func (b *SendBatch) Commit(pkt []byte, dst netip.AddrPort) {
 	b.bufs = append(b.bufs, pkt)
 	b.dsts = append(b.dsts, dst)
-	b.ecns = append(b.ecns, outerECN)
 }
 
 // Flush writes every queued packet and reports how many actually went out. A short count means some destinations
@@ -52,12 +49,11 @@ func (b *SendBatch) Flush() (int, error) {
 	var err error
 	written := 0
 	if len(b.bufs) > 0 {
-		written, err = b.out.WriteBatch(b.bufs, b.dsts, b.ecns)
+		written, err = b.out.WriteBatch(b.bufs, b.dsts)
 	}
 	clear(b.bufs)
 	b.bufs = b.bufs[:0]
 	b.dsts = b.dsts[:0]
-	b.ecns = b.ecns[:0]
 	b.arena.Reset()
 	return written, err
 }

overlay/batch/tx_batch_test.go

@@ -8,10 +8,9 @@ import (
 type fakeBatchWriter struct {
 	bufs  [][]byte
 	addrs []netip.AddrPort
-	ecns  []byte
 }
 
-func (w *fakeBatchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort, ecns []byte) (int, error) {
+func (w *fakeBatchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort) (int, error) {
 	// Snapshot — SendBatch.Flush nils its slot pointers right after WriteBatch
 	// returns, so tests must capture data before that happens.
 	w.bufs = make([][]byte, len(bufs))
@@ -21,7 +20,6 @@ func (w *fakeBatchWriter) WriteBatch(bufs [][]byte, addrs []netip.AddrPort, ecns
 		w.bufs[i] = cp
 	}
 	w.addrs = append(w.addrs[:0], addrs...)
-	w.ecns = append(w.ecns[:0], ecns...)
 	return len(bufs), nil
 }
 
@@ -36,7 +34,7 @@ func TestSendBatchReserveCommitFlush(t *testing.T) {
 			t.Fatalf("slot %d: cap=%d want 32", i, cap(slot))
 		}
 		pkt := append(slot[:0], byte(i), byte(i+1), byte(i+2))
-		b.Commit(pkt, ap, 0)
+		b.Commit(pkt, ap)
 	}
 	if _, err := b.Flush(); err != nil {
 		t.Fatalf("Flush: %v", err)
@@ -77,7 +75,7 @@ func TestSendBatchSlotsDoNotOverlap(t *testing.T) {
 	for i := 0; i < 3; i++ {
 		s := b.Reserve(8)
 		pkt := append(s[:0], byte(0xA0+i), byte(0xB0+i))
-		b.Commit(pkt, ap, 0)
+		b.Commit(pkt, ap)
 	}
 	if _, err := b.Flush(); err != nil {
 		t.Fatalf("Flush: %v", err)
@@ -98,11 +96,11 @@ func TestSendBatchGrowPreservesCommitted(t *testing.T) {
 
 	s1 := b.Reserve(4)
 	pkt1 := append(s1[:0], 0x11, 0x22, 0x33, 0x44)
-	b.Commit(pkt1, ap, 0)
+	b.Commit(pkt1, ap)
 
 	s2 := b.Reserve(8) // exceeds remaining cap, triggers grow
 	pkt2 := append(s2[:0], 0xA, 0xB, 0xC, 0xD, 0xE)
-	b.Commit(pkt2, ap, 0)
+	b.Commit(pkt2, ap)
 
 	// pkt1 must still be intact even though backing reallocated.
 	if pkt1[0] != 0x11 || pkt1[3] != 0x44 {