Add dns interceptor based domain route functionality (#3032)

client/internal/dns/mock_server.go

@@ -3,14 +3,30 @@ package dns
 import (
 	"fmt"
 
+	"github.com/miekg/dns"
+
 	nbdns "github.com/netbirdio/netbird/dns"
 )
 
 // MockServer is the mock instance of a dns server
 type MockServer struct {
-	InitializeFunc      func() error
-	StopFunc            func()
-	UpdateDNSServerFunc func(serial uint64, update nbdns.Config) error
+	InitializeFunc        func() error
+	StopFunc              func()
+	UpdateDNSServerFunc   func(serial uint64, update nbdns.Config) error
+	RegisterHandlerFunc   func([]string, dns.Handler, int)
+	DeregisterHandlerFunc func([]string, int)
+}
+
+func (m *MockServer) RegisterHandler(domains []string, handler dns.Handler, priority int) {
+	if m.RegisterHandlerFunc != nil {
+		m.RegisterHandlerFunc(domains, handler, priority)
+	}
+}
+
+func (m *MockServer) DeregisterHandler(domains []string, priority int) {
+	if m.DeregisterHandlerFunc != nil {
+		m.DeregisterHandlerFunc(domains, priority)
+	}
 }
 
 // Initialize mock implementation of Initialize from Server interface