Move the network resolver out (#1944)

resolver/dns/dns.go

@@ -0,0 +1,78 @@
+// Package dns resolves names to dns records
+package dns
+
+import (
+	"context"
+	"net"
+
+	"github.com/micro/go-micro/v3/resolver"
+	"github.com/miekg/dns"
+)
+
+// 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
+	}
+
+	m := new(dns.Msg)
+	m.SetQuestion(dns.Fqdn(host), dns.TypeA)
+	rec, err := dns.ExchangeContext(context.Background(), m, r.Address)
+	if err != nil {
+		return nil, err
+	}
+
+	for _, answer := range rec.Answer {
+		h := answer.Header()
+		// check record type matches
+		if h.Rrtype != dns.TypeA {
+			continue
+		}
+
+		arec, _ := answer.(*dns.A)
+		addr := arec.A.String()
+
+		// 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
+}