From e44f64bea0901b551658e512be953a21c01fb364 Mon Sep 17 00:00:00 2001
From: Neil Alexander <neilalexander@users.noreply.github.com>
Date: Thu, 25 Jan 2018 17:44:56 +0000
Subject: [PATCH] Fix MTU issues with TAP adapters

---
 src/yggdrasil/tun.go         | 17 +++++++++++------
 src/yggdrasil/tun_windows.go | 21 ++++++++++++++++++++-
 2 files changed, 31 insertions(+), 7 deletions(-)

diff --git a/src/yggdrasil/tun.go b/src/yggdrasil/tun.go
index d23ced7e..871fb3c0 100644
--- a/src/yggdrasil/tun.go
+++ b/src/yggdrasil/tun.go
@@ -5,6 +5,7 @@ package yggdrasil
 import ethernet "github.com/songgao/packets/ethernet"
 
 const IPv6_HEADER_LENGTH = 40
+const ETHER_HEADER_LENGTH = 14
 
 type tunInterface interface {
 	IsTUN() bool
@@ -40,13 +41,13 @@ func (tun *tunDevice) write() error {
 				ethernet.NotTagged,  // VLAN tagging
 				ethernet.IPv6,       // Ethertype
 				len(data))           // Payload length
-			copy(frame[14:], data[:])
+			copy(frame[ETHER_HEADER_LENGTH:], data[:])
 			if _, err := tun.iface.Write(frame); err != nil {
-				return err
+				panic(err)
 			}
 		} else {
 			if _, err := tun.iface.Write(data); err != nil {
-				return err
+				panic(err)
 			}
 		}
 		util_putBytes(data)
@@ -54,15 +55,19 @@ func (tun *tunDevice) write() error {
 }
 
 func (tun *tunDevice) read() error {
-	buf := make([]byte, tun.mtu)
+	mtu := tun.mtu
+	if tun.iface.IsTAP() {
+		mtu += ETHER_HEADER_LENGTH
+	}
+	buf := make([]byte, mtu)
 	for {
 		n, err := tun.iface.Read(buf)
 		if err != nil {
-			return err
+			panic(err)
 		}
 		o := 0
 		if tun.iface.IsTAP() {
-			o = 14
+			o = ETHER_HEADER_LENGTH
 			b := make([]byte, n)
 			copy(b, buf)
 			tun.ndp.recv <- b
diff --git a/src/yggdrasil/tun_windows.go b/src/yggdrasil/tun_windows.go
index 005806ca..b7906224 100644
--- a/src/yggdrasil/tun_windows.go
+++ b/src/yggdrasil/tun_windows.go
@@ -39,12 +39,31 @@ func (tun *tunDevice) setup(ifname string, addr string, mtu int) error {
 	}
 	tun.iface = iface
 	tun.mtu = mtu
+	err = tun.setupMTU(tun.mtu)
+	if err != nil {
+		panic(err)
+	}
 	return tun.setupAddress(addr)
 }
 
+func (tun *tunDevice) setupMTU(mtu int) error {
+	// Set MTU
+	cmd := exec.Command("netsh", "interface", "ipv6", "set", "subinterface",
+		fmt.Sprintf("interface=%s", tun.iface.Name()),
+		fmt.Sprintf("mtu=%d", mtu),
+		"store=active")
+	tun.core.log.Printf("netsh command: %v", strings.Join(cmd.Args, " "))
+	output, err := cmd.CombinedOutput()
+	if err != nil {
+		tun.core.log.Printf("Windows netsh failed: %v.", err)
+		tun.core.log.Println(string(output))
+		return err
+	}
+	return nil
+}
+
 func (tun *tunDevice) setupAddress(addr string) error {
 	// Set address
-	// addr = strings.TrimRight(addr, "/8")
 	cmd := exec.Command("netsh", "interface", "ipv6", "add", "address",
 		fmt.Sprintf("interface=%s", tun.iface.Name()),
 		fmt.Sprintf("addr=%s", addr),