feat: Simplify resolvers

pkg/resolvers/classic.go

@@ -0,0 +1,77 @@
+package resolvers
+
+import (
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+// ClassicResolver represents the config options for setting up a Resolver.
+type ClassicResolver struct {
+	client *dns.Client
+	server string
+}
+
+// ClassicResolverOpts holds options for setting up a Classic resolver.
+type ClassicResolverOpts struct {
+	IPv4Only bool
+	IPv6Only bool
+	Timeout  time.Duration
+	UseTLS   bool
+	UseTCP   bool
+}
+
+// NewClassicResolver accepts a list of nameservers and configures a DNS resolver.
+func NewClassicResolver(server string, opts ClassicResolverOpts) (Resolver, error) {
+	net := "udp"
+	client := &dns.Client{
+		Timeout: opts.Timeout,
+		Net:     "udp",
+	}
+
+	if opts.UseTCP {
+		net = "tcp"
+	}
+
+	if opts.IPv4Only {
+		net = net + "4"
+	}
+	if opts.IPv6Only {
+		net = net + "6"
+	}
+
+	if opts.UseTLS {
+		net = net + "-tls"
+	}
+
+	client.Net = net
+
+	return &ClassicResolver{
+		client: client,
+		server: server,
+	}, nil
+}
+
+// Lookup prepare a list of DNS messages to be sent to the server.
+// It's possible to send multiple question in one message
+// but some nameservers are not able to
+func (r *ClassicResolver) Lookup(questions []dns.Question) ([]Response, error) {
+	var (
+		messages  = prepareMessages(questions)
+		responses []Response
+	)
+
+	for _, msg := range messages {
+		in, rtt, err := r.client.Exchange(&msg, r.server)
+		if err != nil {
+			return nil, err
+		}
+		rsp := Response{
+			Message:    *in,
+			RTT:        rtt,
+			Nameserver: r.server,
+		}
+		responses = append(responses, rsp)
+	}
+	return responses, nil
+}