Golang retrieve one domain's TXT record via custom DNS.

txt.go

package main

import (
	"fmt"
	"time"

	"github.com/miekg/dns"
)

func queryTXT(resolve, domain string) (txt string) {
	m := new(dns.Msg)
	m.Id = dns.Id()
	m.RecursionDesired = true
	m.Question = make([]dns.Question, 0, 1)
	q := dns.Question{fmt.Sprintf("%s.", domain), dns.TypeTXT, dns.ClassINET}
	m.Question = append(m.Question, q)
	in, err := dns.Exchange(m, fmt.Sprintf("%s:53", resolve))
	if err != nil {
		fmt.Println("Error: ", err.Error())
		return ""
	}
	answers := in.Answer
	n := len(answers)
	if n < 1 {
		fmt.Println("Answer error!")
	} else {
		if t, ok := in.Answer[0].(*dns.TXT); ok {
			as := t.String()
			return fmt.Sprintf("\t%s\t\tLen:%d\t%s", resolve, len(t.Txt), as)
		}
	}
	return ""
}

func handle(list []string) {
	n := len(list)
	if n < 1 {
		return
	}

	domain := "fast.com"

	results := make(chan string, n)

	for _, addr := range list {
		go func(address string) {
			start := time.Now()
			res := queryTXT(address, domain)
			end := time.Since(start).Nanoseconds()
			results <- fmt.Sprintf("Time:%dms\t%s", (end / 1000000), res)
		}(addr)
	}

	for {
		select {
		case r := <-results:
			fmt.Println(r)
		case <-time.After(time.Millisecond * 200):
			return
		}
	}
}

func main() {
	list := []string{
		"223.5.5.5",
		"223.6.6.6",
		"119.29.29.29",
		"180.76.76.76",
		"114.114.114.114",
		"114.114.115.115",
		"101.226.4.6",
		"202.106.196.115",
	}
	handle(list)
}