allow for multiple traffic types inside the session at the tuntap level, only implement typeSessionTraffic for now

src/tuntap/iface.go

@@ -50,6 +50,8 @@ func (tun *TunAdapter) read() {
 		if srcAddr != tun.addr && srcSubnet != tun.subnet {
 			continue // Wrong soruce address
 		}
+		bs = buf[begin-1 : end]
+		bs[0] = typeSessionTraffic
 		if dstAddr.IsValid() {
 			tun.store.sendToAddress(dstAddr, bs)
 		} else if dstSubnet.IsValid() {
@@ -61,12 +63,24 @@ func (tun *TunAdapter) read() {
 func (tun *TunAdapter) write() {
 	var buf [TUN_OFFSET_BYTES + 65535]byte
 	for {
-		bs := buf[TUN_OFFSET_BYTES:]
+		bs := buf[TUN_OFFSET_BYTES-1:]
 		n, from, err := tun.core.ReadFrom(bs)
 		if err != nil {
 			return
 		}
-		bs = bs[:n]
+		if n == 0 {
+			continue
+		}
+		switch bs[0] {
+		case typeSessionTraffic:
+			// This is what we want to handle here
+		default:
+			continue
+		}
+		bs = bs[1:n]
+		if len(bs) == 0 {
+			continue
+		}
 		if bs[0]&0xf0 != 0x60 {
 			continue // not IPv6
 		}
@@ -99,7 +113,7 @@ func (tun *TunAdapter) write() {
 		if srcAddr != info.address && srcSubnet != info.subnet {
 			continue // bad remote address/subnet
 		}
-		bs = buf[:TUN_OFFSET_BYTES+n]
+		bs = buf[:TUN_OFFSET_BYTES+len(bs)]
 		n, err = tun.iface.Write(bs, TUN_OFFSET_BYTES)
 		if err != nil {
 			tun.Act(nil, func() {

src/tuntap/tun.go

@@ -150,8 +150,8 @@ func (tun *TunAdapter) _start() error {
 		return nil
 	}
 	mtu := current.IfMTU
-	if tun.core.MTU() < uint64(mtu) {
+	if tun.maxSessionMTU() < mtu {
-		mtu = MTU(tun.core.MTU())
+		mtu = tun.maxSessionMTU()
 	}
 	if err := tun.setup(current.IfName, addr, mtu); err != nil {
 		return err
@@ -216,11 +216,6 @@ func (tun *TunAdapter) oobHandler(fromKey, toKey ed25519.PublicKey, data []byte)
 	}
 }
 
-const (
-	typeKeyLookup   = 1
-	typeKeyResponse = 2
-)
-
 func (tun *TunAdapter) sendKeyLookup(partial ed25519.PublicKey) {
 	sig := ed25519.Sign(tun.core.PrivateKey(), partial[:])
 	bs := append([]byte{typeKeyLookup}, sig...)
@@ -232,3 +227,8 @@ func (tun *TunAdapter) sendKeyResponse(dest ed25519.PublicKey) {
 	bs := append([]byte{typeKeyResponse}, sig...)
 	tun.core.SendOutOfBand(dest, bs)
 }
+
+func (tun *TunAdapter) maxSessionMTU() MTU {
+	const sessionTypeOverhead = 1
+	return MTU(tun.core.MTU() - sessionTypeOverhead)
+}

src/tuntap/types.go

@@ -0,0 +1,14 @@
+package tuntap
+
+// Out-of-band packet types
+const (
+	typeKeyDummy = iota
+	typeKeyLookup
+	typeKeyResponse
+)
+
+// In-band packet types
+const (
+	typeSessionDummy = iota
+	typeSessionTraffic
+)