golang 实现tcp转发代理的方法

package main
 
import (
	"flag"
	"fmt"
	"io"
	"net"
	"os"
	"strings"
	"sync"
)
 
var lock sync.mutex
var truelist []string
var ip string
var list string
 
func main() {
	flag.stringvar(&ip, "l", ":9897", "-l=0.0.0.0:9897 指定服务监听的端口")
	flag.stringvar(&list, "d", "127.0.0.1:1789,127.0.0.1:1788", "-d=127.0.0.1:1789,127.0.0.1:1788 指定后端的ip和端口,多个用','隔开")
	flag.parse()
	truelist = strings.split(list, ",")
	if len(truelist) <= 0 {
		fmt.println("后端ip和端口不能空,或者无效")
		os.exit(1)
	}
	server()
}
 
func server() {
	lis, err := net.listen("tcp", ip)
	if err != nil {
		fmt.println(err)
		return
	}
	defer lis.close()
	for {
		conn, err := lis.accept()
		if err != nil {
			fmt.println("建立连接错误:%v\n", err)
			continue
		}
		fmt.println(conn.remoteaddr(), conn.localaddr())
		go handle(conn)
	}
}
 
func handle(sconn net.conn) {
	defer sconn.close()
	ip, ok := getip()
	if !ok {
		return
	}
	dconn, err := net.dial("tcp", ip)
	if err != nil {
		fmt.printf("连接%v失败:%v\n", ip, err)
		return
	}
	exitchan := make(chan bool, 1)
	go func(sconn net.conn, dconn net.conn, exit chan bool) {
		_, err := io.copy(dconn, sconn)
		fmt.printf("往%v发送数据失败:%v\n", ip, err)
		exitchan <- true
	}(sconn, dconn, exitchan)
	go func(sconn net.conn, dconn net.conn, exit chan bool) {
		_, err := io.copy(sconn, dconn)
		fmt.printf("从%v接收数据失败:%v\n", ip, err)
		exitchan <- true
	}(sconn, dconn, exitchan)
	<-exitchan
	dconn.close()
}
 
func getip() (string, bool) {
	lock.lock()
	defer lock.unlock()
 
	if len(truelist) < 1 {
		return "", false
	}
	ip := truelist[0]
	truelist = append(truelist[1:], ip)
	return ip, true
}