batched tun interface

overlay/batch/passthrough.go

@@ -0,0 +1,52 @@
+package batch
+
+import (
+	"io"
+
+	"github.com/slackhq/nebula/udp"
+)
+
+// Passthrough is a RxBatcher that doesn't batch anything, it just accumulates and then sends packets.
+type Passthrough struct {
+	out    io.Writer
+	slots  [][]byte
+	arena  *Arena
+	cursor int
+}
+
+const passthroughBaseNumSlots = 128
+
+// DefaultPassthroughArenaCap is the recommended arena capacity for a
+// standalone Passthrough batcher: 128 slots × udp.MTU ≈ 1.1 MiB.
+const DefaultPassthroughArenaCap = passthroughBaseNumSlots * udp.MTU
+
+func NewPassthrough(w io.Writer, arena *Arena) *Passthrough {
+	return &Passthrough{
+		out:   w,
+		slots: make([][]byte, 0, passthroughBaseNumSlots),
+		arena: arena,
+	}
+}
+
+func (p *Passthrough) Reserve(sz int) []byte {
+	return p.arena.Reserve(sz)
+}
+
+func (p *Passthrough) Commit(pkt []byte) error {
+	p.slots = append(p.slots, pkt)
+	return nil
+}
+
+func (p *Passthrough) Flush() error {
+	var firstErr error
+	for _, s := range p.slots {
+		_, err := p.out.Write(s)
+		if err != nil && firstErr == nil {
+			firstErr = err
+		}
+	}
+	clear(p.slots)
+	p.slots = p.slots[:0]
+	p.arena.Reset()
+	return firstErr
+}