chore: parse options correctly

pkg/resolvers/classic.go

@@ -13,11 +13,18 @@ type ClassicResolver struct {
 	servers []string
 }
 
+// ClassicResolverOpts holds options for setting up a Classic resolver.
+type ClassicResolverOpts struct {
+	UseIPv4 bool
+	UseIPv6 bool
+	UseTCP  bool
+}
+
 //DefaultResolvConfPath specifies path to default resolv config file on UNIX.
 const DefaultResolvConfPath = "/etc/resolv.conf"
 
 // NewClassicResolver accepts a list of nameservers and configures a DNS resolver.
-func NewClassicResolver(servers []string) (Resolver, error) {
+func NewClassicResolver(servers []string, opts ClassicResolverOpts) (Resolver, error) {
 	client := &dns.Client{}
 	var nameservers []string
 	for _, srv := range servers {
@@ -31,6 +38,13 @@ func NewClassicResolver(servers []string) (Resolver, error) {
 			nameservers = append(nameservers, fmt.Sprintf("%s:%s", host, port))
 		}
 	}
+	client.Net = "udp"
+	if opts.UseIPv4 {
+		client.Net = "udp4"
+	}
+	if opts.UseIPv6 {
+		client.Net = "udp6"
+	}
 	return &ClassicResolver{
 		client:  client,
 		servers: nameservers,
@@ -70,15 +84,8 @@ func NewResolverFromResolvFile(resolvFilePath string) (Resolver, error) {
 // It's possible to send multiple question in one message
 // but some nameservers are not able to
 func (c *ClassicResolver) Lookup(questions []dns.Question) error {
-	var messages = make([]dns.Msg, 0, len(questions))
-	for _, q := range questions {
-		msg := dns.Msg{}
-		msg.Id = dns.Id()
-		msg.RecursionDesired = true
-		// It's recommended to only send 1 question for 1 DNS message.
-		msg.Question = []dns.Question{q}
-		messages = append(messages, msg)
-	}
+	messages := prepareMessages(questions)
+
 	for _, msg := range messages {
 		for _, srv := range c.servers {
 			in, rtt, err := c.client.Exchange(&msg, srv)

pkg/resolvers/doh.go

@@ -28,15 +28,8 @@ func NewDOHResolver(servers []string) (Resolver, error) {
 }
 
 func (r *DOHResolver) Lookup(questions []dns.Question) error {
-	var messages = make([]dns.Msg, 0, len(questions))
-	for _, q := range questions {
-		msg := dns.Msg{}
-		msg.Id = dns.Id()
-		msg.RecursionDesired = true
-		// It's recommended to only send 1 question for 1 DNS message.
-		msg.Question = []dns.Question{q}
-		messages = append(messages, msg)
-	}
+	messages := prepareMessages(questions)
+
 	for _, m := range messages {
 		b, err := m.Pack()
 		if err != nil {

pkg/resolvers/utils.go

@@ -0,0 +1,18 @@
+package resolvers
+
+import "github.com/miekg/dns"
+
+// prepareMessages takes a slice fo `dns.Question`
+// and initialises `dns.Messages` for each question
+func prepareMessages(questions []dns.Question) []dns.Msg {
+	var messages = make([]dns.Msg, 0, len(questions))
+	for _, q := range questions {
+		msg := dns.Msg{}
+		msg.Id = dns.Id()
+		msg.RecursionDesired = true
+		// It's recommended to only send 1 question for 1 DNS message.
+		msg.Question = []dns.Question{q}
+		messages = append(messages, msg)
+	}
+	return messages
+}