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("-l=0.0.0.0:9897 -d=127.0.0.1:1789")
        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)
        if err != nil {
            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)
        if err != nil {
            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
}