golang sets temporary dns

During development and testing, we may need to deploy our application into a virtual machine and simulate some specific network settings in the virtual machine.

Sometimes we need to set up a specific dns server in the virtual machine so that we can simulate the application behavior under certain network conditions. This article will introduce how to set up a temporary dns server in golang application.

Step 1: Import the net package
First, we need to import the net package in our code so that we can use the net.Dial() method to test the network connection.

The code is as follows:

import "net"

Step 2: Set up dns server
We need to use net.Resolver to set up dns server. In this example, we will use the DNS server named "8.8.8.8". You can change the address of this server if necessary.

The code is as follows:

resolver := &net.Resolver{
    Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
        d := net.Dialer{
            Timeout:   time.Millisecond * 500,
            KeepAlive: time.Millisecond * 500,
        }
        return d.DialContext(ctx, "udp", "8.8.8.8:53")
    },
}

In the above code, we use an anonymous function that returns a type that implements the Dial() method. We use this Dial() method to connect to the dns server we set.

Setting the timeout and keepalive parameters can prevent our program from crashing due to timeout when connecting to the dns server.

Step 3: Test the network connection using the new dns server
Now that we have set up our dns server, let’s test the network connection. In this example we will check if we can connect to www.google.com.

The code is as follows:

ips, err := resolver.LookupIP(context.Background(), "ip", "www.google.com")
if err != nil {
    fmt.Printf("Error: %s", err.Error())
    return
}
for _, ip := range ips {
    fmt.Printf("IP: %s
", ip.String())
}

In the above code, we use the resolver.LookupIP() method to find the IP address of www.google.com. We also pass the "ip" parameter in the second parameter to indicate that we want to find an IPv4 address.

If we successfully find the IP address of www.google.com, then we print these IP addresses in a loop.

Full Code Example

The following is a complete example program for setting up a temporary dns server and finding the IP address of www.google.com.

package main

import (
    "context"
    "fmt"
    "net"
    "time"
)

func main() {
    resolver := &net.Resolver{
        Dial: func(ctx context.Context, network, address string) (net.Conn, error) {
            d := net.Dialer{
                Timeout:   time.Millisecond * 500,
                KeepAlive: time.Millisecond * 500,
            }
            return d.DialContext(ctx, "udp", "8.8.8.8:53")
        },
    }

    ips, err := resolver.LookupIP(context.Background(), "ip", "www.google.com")
    if err != nil {
        fmt.Printf("Error: %s", err.Error())
        return
    }
    for _, ip := range ips {
        fmt.Printf("IP: %s
", ip.String())
    }
}

It should be noted that the above sample code is just a simple example and is only used to demonstrate how to set up a temporary dns server in a golang application. In an actual production environment, we need to configure the dns server and network connection in more detail.

The above is the detailed content of golang sets temporary dns. For more information, please follow other related articles on the PHP Chinese website!