go语言实现udp端口转发

直接上代码, 功能同 socat UDP6-LISTEN:1781,fork UDP4:127.0.0.1:1701

package main

import (
    "errors"
    "fmt"
    "log"
    "net"
    "os"
    "strings"
    "time"
)

var (
    timeOut = time.Second * 60 * 5
)

func main() {
    println("入参监听地址和转发地址: " + strings.Join(os.Args[1:], " "))
    listenerAddress := ":1701"
    forwardAddress := "[fe80::542b:6dc7:f5de:261e]:1781"
    if len(os.Args) == 3 {
        listenerAddress = os.Args[1]
        forwardAddress = os.Args[2]
    }
    log.SetFlags(log.LstdFlags | log.Lshortfile)

    udpForwardBean := Start(listenerAddress, forwardAddress)
    if udpForwardBean != nil {
        for {
            println(udpForwardBean.String())
            println()
            time.Sleep(time.Second * 60)
        }
    }
}

func Start(listenerAddress string, forwardAddress string) *UdpForwardBean {
    message := "Udp监听地址: " + listenerAddress + "    转发地址: " + forwardAddress
    log.Println(message)

    listenerAddr, err := net.ResolveUDPAddr("udp", listenerAddress)
    if err != nil {
        log.Println(err)
        return nil
    }
    network := "udp"
    if listenerAddr.IP.To4() != nil {
        network = "udp4"
    } else if listenerAddr.IP.To16() != nil {
        network = "udp6"
    }
    listenerConn, err := net.ListenUDP(network, listenerAddr)
    if err != nil {
        log.Println(err)
        return nil
    }
    forwardMap := map[string]*net.UDPConn{}
    udpForwardBean := &UdpForwardBean{isClosed: false, listenerAddress: listenerAddress,
        forwardAddress: forwardAddress, listenerConn: listenerConn, forwardMap: forwardMap}
    buffer := make([]byte, 1024*64)
    go func() {
        defer listenerConn.Close()
        for {
            len, clientAddr, err := listenerConn.ReadFromUDP(buffer)
            if err != nil {
                if errors.Is(err, net.ErrClosed) {
                    break
                }
                log.Println(err)
                time.Sleep(time.Second)
                continue
            }
            data := make([]byte, len)
            copy(data, buffer)
            handleClientRequest(clientAddr, data, listenerConn, forwardAddress, forwardMap)
        }
        udpForwardBean.isClosed = true
    }()
    return udpForwardBean
}

func handleClientRequest(clientAddr *net.UDPAddr, clientData []byte, listenerConn *net.UDPConn,
    forwardAddress string, forwardMap map[string]*net.UDPConn) {
    if clientAddr == nil {
        return
    }
    forwardConn := forwardMap[clientAddr.String()]
    if forwardConn == nil {
        log.Println("添加udp转发", clientAddr, forwardAddress)
        forwardAddr, err := net.ResolveUDPAddr("udp", forwardAddress)
        if err != nil {
            log.Println(err)
            return
        }
        forwardConn, err = net.DialUDP("udp", nil, forwardAddr)
        if err != nil {
            log.Println(err)
            return
        }
        forwardMap[clientAddr.String()] = forwardConn
        buffer := make([]byte, 1024*64)
        go func() {
            defer forwardConn.Close()
            for {
                forwardConn.SetReadDeadline(time.Now().Add(timeOut))
                len, serverAddr, err := forwardConn.ReadFromUDP(buffer)
                if err != nil {
                    if errors.Is(err, net.ErrClosed) {
                        break
                    }
                    if nerr, ok := err.(net.Error); ok && nerr.Timeout() {
                        break
                    }
                    log.Println(err)
                    time.Sleep(time.Second)
                    continue
                }
                if serverAddr.Port != forwardAddr.Port || serverAddr.IP.String() != forwardAddr.IP.String() {
                    log.Println("异常消息:", serverAddr.String(), forwardAddr.String())
                    continue
                }
                // log.Println("服务端消息:", serverAddr.String(), len, clientAddr.String())
                data := make([]byte, len)
                copy(data, buffer)
                listenerConn.WriteToUDP(data, clientAddr)
            }
            log.Println("移除", clientAddr, forwardAddress)
            delete(forwardMap, clientAddr.String())
        }()
    }
    // log.Println("客户端消息:", clientAddr.String(), len(clientData))
    forwardConn.Write(clientData)
    forwardConn.SetReadDeadline(time.Now().Add(timeOut))
}

type UdpForwardBean struct {
    isClosed        bool
    listenerAddress string
    forwardAddress  string
    listenerConn    *net.UDPConn
    forwardMap      map[string]*net.UDPConn
}

func (bean *UdpForwardBean) String() string {
    var keys []string
    for key := range bean.forwardMap {
        keys = append(keys, key)
    }
    return fmt.Sprintf("udp转发中: %s %s %t %s", bean.listenerAddress, bean.forwardAddress, bean.isClosed, keys)
}

func (bean *UdpForwardBean) Close() {
    bean.listenerConn.Close()
    for _, v := range bean.forwardMap {
        v.Close()
    }
}