1 files changed, 63 insertions, 0 deletions
diff --git a/dnsutil/dnsutil.go b/dnsutil/dnsutil.go
new file mode 100644
index 0000000..6f791ef
--- /dev/null
+++ b/dnsutil/dnsutil.go
@@ -0,0 +1,63 @@
+package dnsutil
+
+import (
+	"time"
+
+	"github.com/miekg/dns"
+)
+
+var (
+	// TypeToString contains a mapping of DNS request type to string.
+	TypeToString = dns.TypeToString
+
+	// RcodeToString contains a mapping of Mapping DNS response code to string.
+	RcodeToString = dns.RcodeToString
+)
+
+// Answers returns all values in the answer section of DNS message msg.
+func Answers(msg *dns.Msg) []string {
+	var answers []string
+	for _, answer := range msg.Answer {
+		switch v := answer.(type) {
+		case *dns.A:
+			answers = append(answers, v.A.String())
+		case *dns.AAAA:
+			answers = append(answers, v.AAAA.String())
+		case *dns.MX:
+			answers = append(answers, v.Mx)
+		case *dns.PTR:
+			answers = append(answers, v.Ptr)
+		case *dns.NS:
+			answers = append(answers, v.Ns)
+		case *dns.CNAME:
+			answers = append(answers, v.Target)
+		}
+	}
+	return answers
+}
+
+// MinTTL returns the lowest TTL of of answer, authority and additional sections.
+func MinTTL(msg *dns.Msg) time.Duration {
+	var ttl uint32 = (1 << 31) - 1 // Maximum TTL from RFC 2181
+	for _, answer := range msg.Answer {
+		ttl = min(answer.Header().Ttl, ttl)
+	}
+	for _, ns := range msg.Ns {
+		ttl = min(ns.Header().Ttl, ttl)
+	}
+	for _, extra := range msg.Extra {
+		// OPT (EDNS) is a pseudo record which uses TTL field for extended RCODE and flags
+		if extra.Header().Rrtype == dns.TypeOPT {
+			continue
+		}
+		ttl = min(extra.Header().Ttl, ttl)
+	}
+	return time.Duration(ttl) * time.Second
+}
+
+func min(x, y uint32) uint32 {
+	if x < y {
+		return x
+	}
+	return y
+}