Feature/dns-server (#537)

Adding DNS server for client

Updated the API with new fields

Added custom zone object for peer's DNS resolution

client/internal/dns/upstream_test.go

@@ -0,0 +1,110 @@
+package dns
+
+import (
+	"context"
+	"github.com/miekg/dns"
+	"strings"
+	"testing"
+	"time"
+)
+
+func TestUpstreamResolver_ServeDNS(t *testing.T) {
+
+	testCases := []struct {
+		name                string
+		inputMSG            *dns.Msg
+		responseShouldBeNil bool
+		InputServers        []string
+		timeout             time.Duration
+		cancelCTX           bool
+		expectedAnswer      string
+	}{
+		{
+			name:           "Should Resolve A Record",
+			inputMSG:       new(dns.Msg).SetQuestion("one.one.one.one.", dns.TypeA),
+			InputServers:   []string{"8.8.8.8:53", "8.8.4.4:53"},
+			timeout:        defaultUpstreamTimeout,
+			expectedAnswer: "1.1.1.1",
+		},
+		{
+			name:           "Should Resolve If First Upstream Times Out",
+			inputMSG:       new(dns.Msg).SetQuestion("one.one.one.one.", dns.TypeA),
+			InputServers:   []string{"8.0.0.0:53", "8.8.4.4:53"},
+			timeout:        2 * time.Second,
+			expectedAnswer: "1.1.1.1",
+		},
+		{
+			name:                "Should Not Resolve If Can't Connect To Both Servers",
+			inputMSG:            new(dns.Msg).SetQuestion("one.one.one.one.", dns.TypeA),
+			InputServers:        []string{"8.0.0.0:53", "8.0.0.1:53"},
+			timeout:             200 * time.Millisecond,
+			responseShouldBeNil: true,
+		},
+		{
+			name:                "Should Not Resolve If Parent Context Is Canceled",
+			inputMSG:            new(dns.Msg).SetQuestion("one.one.one.one.", dns.TypeA),
+			InputServers:        []string{"8.0.0.0:53", "8.8.4.4:53"},
+			cancelCTX:           true,
+			timeout:             defaultUpstreamTimeout,
+			responseShouldBeNil: true,
+		},
+		//{
+		//	name:        "Should Resolve CNAME Record",
+		//	inputMSG:    new(dns.Msg).SetQuestion("one.one.one.one", dns.TypeCNAME),
+		//},
+		//{
+		//	name:                "Should Not Write When Not Found A Record",
+		//	inputMSG:            new(dns.Msg).SetQuestion("not.found.com", dns.TypeA),
+		//	responseShouldBeNil: true,
+		//},
+	}
+	// should resolve if first upstream times out
+	// should not write when both fails
+	// should not resolve if parent context is canceled
+
+	for _, testCase := range testCases {
+		t.Run(testCase.name, func(t *testing.T) {
+			ctx, cancel := context.WithCancel(context.TODO())
+			resolver := &upstreamResolver{
+				parentCTX:       ctx,
+				upstreamClient:  &dns.Client{},
+				upstreamServers: testCase.InputServers,
+				upstreamTimeout: testCase.timeout,
+			}
+			if testCase.cancelCTX {
+				cancel()
+			} else {
+				defer cancel()
+			}
+
+			var responseMSG *dns.Msg
+			responseWriter := &mockResponseWriter{
+				WriteMsgFunc: func(m *dns.Msg) error {
+					responseMSG = m
+					return nil
+				},
+			}
+
+			resolver.ServeDNS(responseWriter, testCase.inputMSG)
+
+			if responseMSG == nil {
+				if testCase.responseShouldBeNil {
+					return
+				}
+				t.Fatalf("should write a response message")
+			}
+
+			foundAnswer := false
+			for _, answer := range responseMSG.Answer {
+				if strings.Contains(answer.String(), testCase.expectedAnswer) {
+					foundAnswer = true
+					break
+				}
+			}
+
+			if !foundAnswer {
+				t.Errorf("couldn't find the required answer, %s, in the dns response", testCase.expectedAnswer)
+			}
+		})
+	}
+}