From ec60dd136a54a4dfbb0fa82933989ea939c1b15d Mon Sep 17 00:00:00 2001
From: Christoph Haas <christoph.h@sprinternet.at>
Date: Fri, 18 Dec 2020 22:07:55 +0100
Subject: [PATCH] fix default mtu handling

---
 internal/server/usermanager.go | 3 +++
 internal/wireguard/net.go      | 4 +++-
 2 files changed, 6 insertions(+), 1 deletion(-)

diff --git a/internal/server/usermanager.go b/internal/server/usermanager.go
index a4070ba..0de1759 100644
--- a/internal/server/usermanager.go
+++ b/internal/server/usermanager.go
@@ -390,6 +390,9 @@ func (u *UserManager) validateOrCreateDevice(dev wgtypes.Device, ipAddresses []s
 		device.Mtu = 0
 		device.PersistentKeepalive = 16 // Default
 		device.IPsStr = strings.Join(ipAddresses, ", ")
+		if mtu == wireguard.WireGuardDefaultMTU {
+			mtu = 0
+		}
 		device.Mtu = mtu
 
 		res := u.db.Create(&device)
diff --git a/internal/wireguard/net.go b/internal/wireguard/net.go
index 3eca03c..57b5d11 100644
--- a/internal/wireguard/net.go
+++ b/internal/wireguard/net.go
@@ -7,6 +7,8 @@ import (
 	"github.com/milosgajdos/tenus"
 )
 
+const WireGuardDefaultMTU = 1420
+
 func (m *Manager) GetIPAddress() ([]string, error) {
 	wgInterface, err := tenus.NewLinkFrom(m.Cfg.DeviceName)
 	if err != nil {
@@ -107,7 +109,7 @@ func (m *Manager) SetMTU(mtu int) error {
 	}
 
 	if mtu == 0 {
-		mtu = 1420 // WireGuard default MTU
+		mtu = WireGuardDefaultMTU
 	}
 
 	if err := wgInterface.SetLinkMTU(mtu); err != nil {