add: client MTU settings available from command line

main.go

@@ -3,10 +3,11 @@ package main
 import (
 	"flag"
 	"fmt"
-	"github.com/labstack/echo/v4"
 	"net/http"
 	"time"
 
+	"github.com/labstack/echo/v4"
+
 	rice "github.com/GeertJohan/go.rice"
 	"github.com/ngoduykhanh/wireguard-ui/emailer"
 	"github.com/ngoduykhanh/wireguard-ui/handler"
@@ -34,6 +35,7 @@ var (
 	flagEmailFrom      string
 	flagEmailFromName  string = "WireGuard UI"
 	flagSessionSecret  string
+	flagClientMTU      int
 )
 
 const (
@@ -60,6 +62,7 @@ func init() {
 	flag.StringVar(&flagEmailFrom, "email-from", util.LookupEnvOrString("EMAIL_FROM_ADDRESS", flagEmailFrom), "'From' email address.")
 	flag.StringVar(&flagEmailFromName, "email-from-name", util.LookupEnvOrString("EMAIL_FROM_NAME", flagEmailFromName), "'From' email name.")
 	flag.StringVar(&flagSessionSecret, "session-secret", util.LookupEnvOrString("SESSION_SECRET", flagSessionSecret), "The key used to encrypt session cookies.")
+	flag.IntVar(&flagClientMTU, "client-mtu", util.LookupEnvOrInt("CLIENT_MTU", flagClientMTU), "Client default MTU")
 	flag.Parse()
 
 	// update runtime config
@@ -75,6 +78,7 @@ func init() {
 	util.EmailFrom = flagEmailFrom
 	util.EmailFromName = flagEmailFromName
 	util.SessionSecret = []byte(flagSessionSecret)
+	util.ClientMTU = flagClientMTU
 
 	// print app information
 	fmt.Println("Wireguard UI")

util/config.go

@@ -16,6 +16,7 @@ var (
 	EmailSubject   string
 	EmailContent   string
 	SessionSecret  []byte
+	ClientMTU      int
 )
 
 const (

util/util.go

@@ -27,6 +27,10 @@ func BuildClientConfig(client model.Client, server model.Server, setting model.G
 	if client.UseServerDNS {
 		clientDNS = fmt.Sprintf("DNS = %s\n", strings.Join(setting.DNSServers, ","))
 	}
+	clientMTU := ""
+	if ClientMTU > 0 {
+		clientMTU = fmt.Sprintf("MTU =  %d\n", ClientMTU)
+	}
 
 	// Peer section
 	peerPublicKey := fmt.Sprintf("PublicKey = %s\n", server.KeyPair.PublicKey)
@@ -60,6 +64,7 @@ func BuildClientConfig(client model.Client, server model.Server, setting model.G
 		clientAddress +
 		clientPrivateKey +
 		clientDNS +
+		clientMTU +
 		"\n[Peer]\n" +
 		peerPublicKey +
 		peerPresharedKey +