Add TLS resolver connection reusing and pooling

Also, fix caching issues and add more tests

resolver/rrcache_test.go

@@ -0,0 +1,41 @@
+package resolver
+
+import (
+	"testing"
+
+	"github.com/miekg/dns"
+)
+
+func TestCaching(t *testing.T) {
+	testDomain := "Mk35mMqOWEHXSMk11MYcbjLOjTE8PQvDiAVUxf4BvwtgR.example.com."
+	testQuestion := "A"
+
+	testNameRecord := &NameRecord{
+		Domain:   testDomain,
+		Question: testQuestion,
+	}
+
+	err := testNameRecord.Save()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rrCache, err := GetRRCache(testDomain, dns.Type(dns.TypeA))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	err = rrCache.Save()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	rrCache2, err := GetRRCache(testDomain, dns.Type(dns.TypeA))
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if rrCache2.Domain != rrCache.Domain {
+		t.Fatal("something very is wrong")
+	}
+}