micro/resolver/dns/dns.go

// Package dns resolves names to dns records
package dns

import (
	"context"
	"net"

	"github.com/miekg/dns"
	"github.com/unistack-org/micro/v3/resolver"
)

// Resolver is a DNS network resolve
type Resolver struct {
	// The resolver address to use
	Address string
}

// Resolve assumes ID is a domain name e.g micro.mu
func (r *Resolver) Resolve(name string) ([]*resolver.Record, error) {
	host, port, err := net.SplitHostPort(name)
	if err != nil {
		host = name
		port = "8085"
	}

	if len(host) == 0 {
		host = "localhost"
	}

	if len(r.Address) == 0 {
		r.Address = "1.0.0.1:53"
	}

	//nolint:prealloc
	var records []*resolver.Record

	// parsed an actual ip
	if v := net.ParseIP(host); v != nil {
		records = append(records, &resolver.Record{
			Address: net.JoinHostPort(host, port),
		})
		return records, nil
	}

	for _, q := range []uint16{dns.TypeA, dns.TypeAAAA} {
		m := new(dns.Msg)
		m.SetQuestion(dns.Fqdn(host), q)
		rec, err := dns.ExchangeContext(context.Background(), m, r.Address)
		if err != nil {
			return nil, err
		}

		var addr string
		for _, answer := range rec.Answer {
			h := answer.Header()
			// check record type matches
			switch h.Rrtype {
			case dns.TypeA:
				arec, _ := answer.(*dns.A)
				addr = arec.A.String()
			case dns.TypeAAAA:
				arec, _ := answer.(*dns.AAAA)
				addr = arec.AAAA.String()
			default:
				continue
			}

			// join resolved record with port
			address := net.JoinHostPort(addr, port)
			// append to record set
			records = append(records, &resolver.Record{
				Address: address,
			})
		}
	}

	// no records returned so just best effort it
	if len(records) == 0 {
		records = append(records, &resolver.Record{
			Address: net.JoinHostPort(host, port),
		})
	}

	return records, nil
}