使用golang网络编程实现一个简单的TCP代理（不支持HTTP）

package mainimport (    "flag"    "github.com/rs/zerolog"    "net"    "os")var logger = zerolog.New(os.Stdout).With().Timestamp().Logger()func main() {    help := flag.Bool("help", false, "print usage")    bind := flag.String("bind", "127.0.0.1:6000", "The address to bind to")    backend := flag.String("backend", "", "The backend server address")    flag.Parse()    logger.Level(zerolog.DebugLevel)    if *help {        flag.Usage()        return    }    if *backend == "" {        flag.Usage()        return    }    if *bind == "" {        //use default bind        logger.Info().Str("bind", *bind).Msg("use default bind")    }    success, err := RunProxy(*bind, *backend)    if !success {        logger.Error().Err(err).Send()        os.Exit(1)    }}func RunProxy(bind, backend string) (bool, error) {    listener, err := net.Listen("tcp", bind)    if err != nil {        return false, err    }    defer listener.Close()    logger.Info().Str("bind", bind).Str("backend", backend).Msg("tcp-proxy started.")    for {        conn, err := listener.Accept()        if err != nil {            logger.Error().Err(err).Send()        } else {            go ConnectionHandler(conn, backend)        }    }}func ConnectionHandler(conn net.Conn, backend string) {    logger.Info().Str("conn", conn.RemoteAddr().String()).Msg("client connected.")    target, err := net.Dial("tcp", backend)    defer conn.Close()    if err != nil {        logger.Error().Err(err).Send()    } else {        defer target.Close()        logger.Info().Str("conn", conn.RemoteAddr().String()).Str("backend", target.LocalAddr().String()).Msg("backend connected.")        closed := make(chan bool, 2)        go Proxy(conn, target, closed)        go Proxy(target, conn, closed)        <-closed        logger.Info().Str("conn", conn.RemoteAddr().String()).Msg("Connection closed.")    }}func Proxy(from net.Conn, to net.Conn, closed chan bool) {    buffer := make([]byte, 4096)    for {        n1, err := from.Read(buffer)        if err != nil {            closed <- true            return        }        n2, err := to.Write(buffer[:n1])        logger.Debug().Str("from", from.RemoteAddr().String()).Int("recv", n1).Str("to", to.RemoteAddr().String()).Int("send", n2).Send()        if err != nil {            closed <- true            return        }    }}

使用方式

代理监听9000端口，代理后端服务的8000端口

tcp-proxy --bind 0.0.0.0:9000 --backend 127.0.0.1:8000

源码解析

这个简单的小程序主要由三个函数构成
1.RunProxy 启动代理服务，监听bind参数指定的端口，接收客户端请求
2.ConnectionHandler 客户端请求处理，连接backend服务
3.Proxy 数据传输代理，将客户端数据发送到backend服务，将backend数据发送给客户端

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