golang官方dns解析与只解析a记录的差距

arecord.go

package main

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

	"github.com/miekg/dns"
)

func main() {
	domain := "hacktech.cn"
	start1 := time.Now().UnixNano()
	aLookupHost(domain)
	end1 := time.Now().UnixNano()
	fmt.Println((end1-start1)/1e6, "ms")
	start2 := time.Now().UnixNano()
	goLookupHost(domain)
	end2 := time.Now().UnixNano()
	fmt.Println((end2-start2)/1e6, "ms")
}

func goLookupHost(domain string) {
	resolver := &net.Resolver{
		PreferGo: true,
		Dial: func(ctx context.Context, network string, address string) (net.Conn, error) {
			d := net.Dialer{}
			return d.DialContext(ctx, "udp", "223.5.5.5:53")
		},
	}
	fmt.Println(resolver.LookupHost(context.Background(), domain))
}

func aLookupHost(domain string) {
	c := new(dns.Client)
	m := new(dns.Msg)
	m.SetQuestion(domain+".", dns.TypeA)
	m.RecursionDesired = true
	r, _, err := c.Exchange(m, "223.5.5.5:53")
	if err != nil {
		return
	}
	if r.Rcode != dns.RcodeSuccess {
		return
	}
	for _, a := range r.Answer {
		if arecord, ok := a.(*dns.A); ok {
			fmt.Printf("%s\n", arecord.A.String())
		}
	}
}

// Output
// > arecord.exe
// 185.199.111.153
// 185.199.108.153
// 185.199.110.153
// 185.199.109.153
// 9 ms
// [185.199.111.153 185.199.109.153 185.199.108.153 185.199.110.153 185.199.111.153 185.199.109.153 185.199.108.153 185.199.110.153] <nil>
// 16133 ms