DNS Server

Last modified: 19 December 2024

To create a DNS server program in Go, you need to create a few files: main.go for the main logic and optionally, a dnsserver.go file for the DNS server functionality. Here is a step-by-step guide:

Step 1: Initialize the Go Module

First, create a new directory for your project and initialize the Go module.

mkdir dnsserver
cd dnsserver
go mod init github.com/username/dnsserver

Step 2: Install Dependencies

You will need the miekg/dns library for DNS server functionality.

go get github.com/miekg/dns

Step 3: Create the dnsserver.go File

Create a dnsserver.go file to handle the DNS server functionality.

// dnsserver.go
package main

import (
    "github.com/miekg/dns"
    "log"
    "net"
)

// handleDNSRequest handles incoming DNS requests.
func handleDNSRequest(w dns.ResponseWriter, r *dns.Msg) {
    msg := dns.Msg{}
    msg.SetReply(r)
    msg.Authoritative = true

    switch r.Opcode {
    case dns.OpcodeQuery:
        for _, q := range r.Question {
            switch q.Qtype {
            case dns.TypeA:
                ip := net.ParseIP("127.0.0.1")
                rr := &dns.A{
                    Hdr: dns.RR_Header{
                        Name:   q.Name,
                        Rrtype: dns.TypeA,
                        Class:  dns.ClassINET,
                        Ttl:    0,
                    },
                    A: ip,
                }
                msg.Answer = append(msg.Answer, rr)
            }
        }
    }

    w.WriteMsg(&msg)
}

// StartDNSServer starts the DNS server on the specified port.
func StartDNSServer(port string) {
    server := &dns.Server{Addr: ":" + port, Net: "udp"}
    dns.HandleFunc(".", handleDNSRequest)
    log.Printf("Starting DNS server on port %s", port)
    err := server.ListenAndServe()
    if err != nil {
        log.Fatalf("Failed to start DNS server: %v", err)
    }
}

Step 4: Create the main.go File

Create a main.go file to use the DNS server functionality.

// main.go
package main

import (
    "fmt"
    "log"
    "os"
)

func main() {
    if len(os.Args) != 2 {
        fmt.Println("Usage: dnsserver <port>")
        os.Exit(1)
    }

    port := os.Args[1]

    fmt.Printf("Starting DNS server on port %s...\n", port)
    StartDNSServer(port)
}

Step 5: Run the Program

Run the program using the go run command.

go run main.go 53

This will start the DNS server on port 53. The server will respond to DNS queries with a fixed IP address (127.0.0.1).