1 files changed, 62 insertions, 0 deletions
diff --git a/utils/dns_utils.go b/utils/dns_utils.go
new file mode 100644
index 0000000..4a4131d
--- /dev/null
+++ b/utils/dns_utils.go
@@ -0,0 +1,62 @@
+// dns utils
+package utils
+
+import (
+	"github.com/miekg/dns"
+)
+
+type DNSOptions struct {
+	Domain string
+	RD     bool
+	Qclass uint16
+	Qtype  uint16
+	EDNS   bool
+}
+
+// build the question section of a dns packet
+func questionMaker(domain string, qclass uint16, qtype uint16) *dns.Question {
+	return &dns.Question{Name: dns.Fqdn(domain), Qtype: qtype, Qclass: qclass}
+}
+
+// build a specific query message
+func queryMaker(domain string, rd bool, qclass uint16, qtype uint16, edns bool) *dns.Msg {
+	msg := new(dns.Msg)
+	msg.Id = dns.Id()
+	msg.RecursionDesired = rd
+	msg.Question = make([]dns.Question, 1)
+	msg.Question[0] = *questionMaker(domain, qclass, qtype)
+	if edns {
+		msg = msg.SetEdns0(1232, false)
+	}
+	return msg
+}
+
+// query and receive the response
+// addr must contain dest port
+// func DNSQuery(addr string, domain string, rd bool, qclass uint16, qtype uint16, edns bool) (*dns.Msg, error) {
+func DNSQuery(addr string, opt DNSOptions) (*dns.Msg, error) {
+	if opt.Qclass == 0 {
+		opt.Qclass = 1
+	}
+	if opt.Qtype == 0 {
+		opt.Qtype = 1
+	}
+	msg := queryMaker(opt.Domain, opt.RD, opt.Qclass, opt.Qtype, opt.EDNS)
+	res, err := dns.Exchange(msg, addr)
+	return res, err
+}
+
+func AsyncDNSQuery(addr string, domain string, rd bool, qclass uint16, qtype uint16, edns bool) error {
+	msg := queryMaker(domain, rd, qclass, qtype, edns)
+	client := dns.Client{Net: "udp"}
+	conn, err := client.Dial(addr)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+	err = conn.WriteMsg(msg)
+	if err != nil {
+		return err
+	}
+	return nil
+}