Feature: support pre&post-up exec (#233)

* Add tun pre/post script
* Improve: pre & post tun

---------

Co-authored-by: xjasonlyu <xjasonlyu@gmail.com>

engine/engine.go

@@ -3,6 +3,8 @@ package engine
 import (
 	"errors"
 	"net"
+	"os/exec"
+	"strings"
 	"sync"
 	"time"
 
@@ -90,6 +92,15 @@ func stop() (err error) {
 	return err
 }
 
+func execCommand(cmd string) error {
+	parts := strings.Fields(cmd)
+	if len(parts) == 0 {
+		return errors.New("empty command")
+	}
+	_, err := exec.Command(parts[0], parts[1:]...).Output()
+	return err
+}
+
 func general(k *Key) error {
 	level, err := log.ParseLevel(k.LogLevel)
 	if err != nil {
@@ -158,6 +169,21 @@ func netstack(k *Key) (err error) {
 		return errors.New("empty device")
 	}
 
+	if k.TUNPreUp != "" {
+		if preUpErr := execCommand(k.TUNPreUp); preUpErr != nil {
+			log.Warnf("[TUN] failed to pre-execute: %s: %v", k.TUNPreUp, preUpErr)
+		}
+	}
+
+	defer func() {
+		if k.TUNPostUp == "" || err != nil {
+			return
+		}
+		if postUpErr := execCommand(k.TUNPostUp); postUpErr != nil {
+			log.Warnf("[TUN] failed to post-execute: %s: %v", k.TUNPostUp, postUpErr)
+		}
+	}()
+
 	if _defaultProxy, err = parseProxy(k.Proxy); err != nil {
 		return
 	}

engine/key.go

@@ -13,5 +13,7 @@ type Key struct {
 	TCPModerateReceiveBuffer bool          `yaml:"tcp-moderate-receive-buffer"`
 	TCPSendBufferSize        string        `yaml:"tcp-send-buffer-size"`
 	TCPReceiveBufferSize     string        `yaml:"tcp-receive-buffer-size"`
+	TUNPreUp                 string        `yaml:"tun-pre-up"`
+	TUNPostUp                string        `yaml:"tun-post-up"`
 	UDPTimeout               time.Duration `yaml:"udp-timeout"`
 }

main.go

@@ -36,6 +36,8 @@ func init() {
 	flag.StringVar(&key.TCPSendBufferSize, "tcp-sndbuf", "", "Set TCP send buffer size for netstack")
 	flag.StringVar(&key.TCPReceiveBufferSize, "tcp-rcvbuf", "", "Set TCP receive buffer size for netstack")
 	flag.BoolVar(&key.TCPModerateReceiveBuffer, "tcp-auto-tuning", false, "Enable TCP receive buffer auto-tuning")
+	flag.StringVar(&key.TUNPreUp, "tun-pre-up", "", "Execute a command before TUN device setup")
+	flag.StringVar(&key.TUNPostUp, "tun-post-up", "", "Execute a command after TUN device setup")
 	flag.BoolVar(&versionFlag, "version", false, "Show version and then quit")
 	flag.Parse()
 }