How to use Golang to change the gateway (A brief analysis of the method)

Golang is a very popular programming language with features such as efficiency, simplicity, and security. It has a wide range of applications, such as network development. In network development, we often encounter situations where we need to change the gateway. This article will introduce how to use Golang to change the gateway.

1. What is a gateway

In a computer network, a gateway is a device or program that transmits data between different networks. A gateway is actually a door that connects two different networks so that they can communicate with each other. For example, if we connect to another machine locally, we need to obtain data through the gateway. If we want to modify the gateway address of this machine, we need to use the relevant API provided by Golang to set it up.

2. How to use Golang to change the gateway

In Golang, we can use the relevant API provided by the net package to change the gateway. Below we will introduce in detail how to use Golang to change the gateway.

1. Get the current local network information

We can get the current local network information through the relevant API in Golang's net package, including the local IP address, MAC address, Subnet mask, gateway address, etc. The specific code is as follows:

package main

import (
    "fmt"
    "net"
)

func main() {
    i, err := net.InterfaceByName("en0") // en0 表示当前网络接口
    if err != nil {
        fmt.Println(err)
        return
    }
    addrs, err := i.Addrs()
    if err != nil {
        fmt.Println(err)
        return
    }
    for _, addr := range addrs {
        if ipnet, ok := addr.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
            if ipnet.IP.To4() != nil {
                fmt.Println("IP地址:", ipnet.IP.String())
            }
        }
    }
    addrs2, _ := i.Addrs()
    for _, addr := range addrs2 {
        fmt.Println("地址:", addr)
    }
    fmt.Println("MAC地址:", i.HardwareAddr)
    fmt.Println("子网掩码:", net.IPv4Mask(255, 255, 255, 0).String())
    fmt.Println("网关地址:", i.Addrs()[0].(*net.IPNet).IP)
}

2. Get gateway address information

To get the gateway address information of the current network, you can use the RouteTable method in the net package. The code is as follows:

package main

import (
    "fmt"
    "net"
)
func getGatewayAddr() (string, error) {
    var gateway string
    routes, err := net.InterfaceAddrs()
    if err != nil {
        return "", err
    }
    for _, route := range routes {
        if ipnet, ok := route.(*net.IPNet); ok && !ipnet.IP.IsLoopback() {
            if ipnet.IP.To4() != nil {
                if ipnet.Mask.String() != "ffffffff" {
                    addrs, err := net.InterfaceAddrs()
                    if err != nil {
                        fmt.Println(err)
                        os.Exit(1)
                    }
                    for _, addr := range addrs {
                        if ip, ok := addr.(*net.IPNet); ok && !ip.IP.IsLoopback() {
                            if ip.Mask.String() != "ffffffff" && ip.IP.To4() != nil {
                                ipoff := binary.BigEndian.Uint32(ip.IP.To4()) & binary.BigEndian.Uint32(ip.Mask)
                                gateoff := binary.BigEndian.Uint32(ipnet.IP.To4()) & binary.BigEndian.Uint32(ipnet.Mask)
                                if ipoff == gateoff {
                                    gateway = ipnet.IP.String()
                                }
                            }
                        }
                    }
                }
            }
        }
    }
    if gateway == "" {
        return "", errors.New("no gateway found")
    }
    return gateway, nil
}

3. Use Golang to modify the gateway address

After obtaining the local network information and gateway address information, we can use the net package provided by Golang to modify the gateway address. The specific code is as follows ：

package main

import (
    "fmt"
    "net"
)

func main() {
    if err := SetDefaultGateway(net.ParseIP("192.168.1.1")); err != nil {
        fmt.Println(err)
    }
}

func SetDefaultGateway(gateway net.IP) error {
    r, err := netlink.RouteGet(net.IPv4(1, 0, 0, 0))
    if err != nil {
        return err
    }
    r[0].Gw = gateway
    return netlink.RouteReplace(r[0])
}

In the above code, we call the netlink.RouteGet method to obtain the default routing information, then change the gateway address, and finally use the netlink.RouteReplace method to update the routing information.

3. Summary

The above is the method of using Golang to change the gateway introduced in this article. We can obtain the current local network information and gateway address information through the API provided by the net package, and then use the netlink package API to modify the gateway address to meet our need to change the gateway. The teacher believes that through the introduction of this article, you have mastered the method of changing the gateway in Golang. I hope it will be helpful to you in network development.

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