How to write a port forwarding program using Golang

1. Background introduction

In practical applications, we often need to forward different ports in order to realize the transmission and sharing of network data. For example, in some enterprise applications, we need to forward access requests from the external network to servers on the internal network in order to access and manage internal applications. In this process, port forwarding is a technology that must be used.

Golang is an emerging programming language that is efficient, safe, and concise. Other common programming languages ​​​​can perform port forwarding by calling code written in Golang.

This article will introduce how to use Golang to write a port forwarding program and demonstrate the advantages of Golang in the field of network programming.

2. Golang implements port forwarding

1. Implementation method

Port forwarding in Golang can be operated using the net package in the standard library without the help of Additional dependent libraries.

The core implementation principle of port forwarding is to establish two network connections: one connection listens to the specified port, and the other connection handles the data forwarding operation. The received data can be processed concurrently through goroutine to achieve efficient forwarding of data.

Code example:

package main

import (
    "fmt"
    "net"
)

func main() {
    listener, err := net.Listen("tcp", ":8888")
    if err != nil {
        fmt.Println("Error: ", err)
        return
    }

    for {
        conn, err := listener.Accept()
        if err != nil {
            fmt.Println("Error: ", err)
            continue
        }

        go handleConnection(conn)
    }
}

func handleConnection(conn net.Conn) {
    remote, err := net.Dial("tcp", "localhost:9999")
    if err != nil {
        fmt.Println("Error: ", err)
        return
    }

    defer remote.Close()
    defer conn.Close()

    go func() {
        _, err := copyData(conn, remote)
        if err != nil {
            fmt.Println("Error: ", err)
            return
        }
    }()

    _, err = copyData(remote, conn)
    if err != nil {
        fmt.Println("Error: ", err)
        return
    }
}

func copyData(dst net.Conn, src net.Conn) (int, error) {
    buf := make([]byte, 256)

    n, err := src.Read(buf)
    if err != nil {
        return 0, err
    }

    n, err = dst.Write(buf[:n])
    if err != nil {
        return 0, err
    }

    return n, nil
}

Code description:

The above code provides external network services by listening to the local 8888 port. When a client connects to port 8888, a new goroutine will be created, and this goroutine will handle the data forwarding operation. When forwarding data from the client, you need to establish a network connection to the local port 9999 and forward the data to this connection.

2. Implementation effect

The effect of the above code is to listen to port 8888 locally. When a request is made to access this port, the request will be forwarded to the local port 9999. Use the telnet tool to test whether the forwarding is normal:

When connecting to the local port 8888, the system console will output a line of text prompt "New connection received", indicating successful monitoring. Then, follow the following command to connect to port 9999:

$ telnet localhost 8888

After the connection is successful, enter some data, such as "Hello World!", and then press the Enter key. We should see the same data appear on another terminal, which indicates that the data has been successfully forwarded to another port through the serial port.

3. Summary

Through the introduction of this article, I believe you have mastered how to use Golang to implement port forwarding, which is very helpful for network programming work.

In general, Golang has the advantages of efficiency, security, and simplicity, and can help you realize your network programming needs more effectively.

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