akme/get-closer

package protocols

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

// UseCustomDNS set custom DNS resolver
func UseCustomDNS(dns []string) {

    resolver := net.Resolver{
        PreferGo: true,
        Dial: func(ctx context.Context, network, address string) (conn net.Conn, err error) {
            for _, addr := range dns {
                if conn, err = net.Dial("udp", addr+":53"); err != nil {
                    continue
                } else {
                    return conn, nil
                }
            }
            return
        },
    }
    net.DefaultResolver = &resolver
}

//DNSPing set timeout for DNS request
func DNSPing(host string) time.Duration {
    timeout := 5 * time.Second
    ctx, cancel := context.WithTimeout(context.TODO(), timeout)
    defer cancel() // important to avoid a resource leak
    r := net.DefaultResolver
    startTime := time.Now()
    _, err := r.LookupHost(ctx, host)
    endTime := time.Now()
    if err != nil {
        fmt.Println(err)
    }
    //fmt.Println(addrs)
    return endTime.Sub(startTime)
}