Refactor code structure for improved readability and maintainability

resolver/splithorizon_test.go

@@ -0,0 +1,165 @@
+package resolver_test
+
+import (
+	"context"
+	"io"
+	"testing"
+	"time"
+
+	"dns-helper/resolver"
+)
+
+// ---------------------------------------------------------------------------
+// CheckSplitHorizon tests (T015)
+// ---------------------------------------------------------------------------
+
+func TestCheckSplitHorizon_NoConflict_SameIPs(t *testing.T) {
+	qname := mustNewName("www.example.com.")
+
+	localAddr := startFakeDNSMulti(t, func(query []byte) []byte {
+		return buildAResponse(queryID(query), qname, [][4]byte{{93, 184, 216, 34}})
+	})
+
+	authIPs := []string{"93.184.216.34"}
+	result := resolver.CheckSplitHorizon(
+		context.Background(),
+		io.Discard,
+		[]string{localAddr},
+		"www.example.com",
+		authIPs,
+		"ns1.example.com",
+		2*time.Second,
+	)
+
+	if result.HasConflict {
+		t.Errorf("expected no conflict when IPs match, got conflict: local=%v auth=%v",
+			result.LocalIPs, result.AuthoritativeIPs)
+	}
+}
+
+func TestCheckSplitHorizon_Conflict_DifferentIPs(t *testing.T) {
+	qname := mustNewName("www.example.com.")
+
+	// Local resolver returns internal IP.
+	localAddr := startFakeDNSMulti(t, func(query []byte) []byte {
+		return buildAResponse(queryID(query), qname, [][4]byte{{10, 0, 5, 100}})
+	})
+
+	authIPs := []string{"203.0.113.50"} // authoritative returned a different IP
+	result := resolver.CheckSplitHorizon(
+		context.Background(),
+		io.Discard,
+		[]string{localAddr},
+		"www.example.com",
+		authIPs,
+		"ns1.example.com",
+		2*time.Second,
+	)
+
+	if !result.HasConflict {
+		t.Error("expected conflict when IPs differ")
+	}
+	if len(result.LocalIPs) == 0 {
+		t.Error("expected LocalIPs to be populated")
+	}
+	if result.LocalSource == "" {
+		t.Error("expected LocalSource to be populated")
+	}
+}
+
+func TestCheckSplitHorizon_NoConflict_LocalNXDOMAIN(t *testing.T) {
+	qname := mustNewName("www.example.com.")
+
+	localAddr := startFakeDNSMulti(t, func(query []byte) []byte {
+		return buildNXDOMAINResponse(queryID(query), qname)
+	})
+
+	authIPs := []string{"93.184.216.34"}
+	result := resolver.CheckSplitHorizon(
+		context.Background(),
+		io.Discard,
+		[]string{localAddr},
+		"www.example.com",
+		authIPs,
+		"ns1.example.com",
+		2*time.Second,
+	)
+
+	if result.HasConflict {
+		t.Error("expected no conflict when local returns NXDOMAIN")
+	}
+	if result.LocalIPs != nil {
+		t.Errorf("expected nil LocalIPs for NXDOMAIN, got %v", result.LocalIPs)
+	}
+}
+
+func TestCheckSplitHorizon_NoConflict_LocalTimeout(t *testing.T) {
+	silentAddr := startSilentDNS(t)
+
+	authIPs := []string{"93.184.216.34"}
+	result := resolver.CheckSplitHorizon(
+		context.Background(),
+		io.Discard,
+		[]string{silentAddr},
+		"www.example.com",
+		authIPs,
+		"ns1.example.com",
+		100*time.Millisecond,
+	)
+
+	if result.HasConflict {
+		t.Error("expected no conflict when local resolver times out")
+	}
+	if result.LocalIPs != nil {
+		t.Errorf("expected nil LocalIPs for timeout, got %v", result.LocalIPs)
+	}
+}
+
+func TestCheckSplitHorizon_NoConflict_OrderIndependent(t *testing.T) {
+	qname := mustNewName("www.example.com.")
+
+	// Local resolver returns IPs in different order than authoritative.
+	localAddr := startFakeDNSMulti(t, func(query []byte) []byte {
+		return buildAResponse(queryID(query), qname, [][4]byte{
+			{5, 6, 7, 8},
+			{1, 2, 3, 4},
+		})
+	})
+
+	// Authoritative had them in reverse order.
+	authIPs := []string{"1.2.3.4", "5.6.7.8"}
+	result := resolver.CheckSplitHorizon(
+		context.Background(),
+		io.Discard,
+		[]string{localAddr},
+		"www.example.com",
+		authIPs,
+		"ns1.example.com",
+		2*time.Second,
+	)
+
+	if result.HasConflict {
+		t.Errorf("expected no conflict for same IPs in different order: local=%v auth=%v",
+			result.LocalIPs, result.AuthoritativeIPs)
+	}
+}
+
+func TestCheckSplitHorizon_NoLocalResolvers(t *testing.T) {
+	authIPs := []string{"93.184.216.34"}
+	result := resolver.CheckSplitHorizon(
+		context.Background(),
+		io.Discard,
+		nil, // no local resolvers
+		"www.example.com",
+		authIPs,
+		"ns1.example.com",
+		2*time.Second,
+	)
+
+	if result.HasConflict {
+		t.Error("expected no conflict when no local resolvers provided")
+	}
+	if result.LocalIPs != nil {
+		t.Error("expected nil LocalIPs when no resolvers provided")
+	}
+}