[management, reverse proxy] Add reverse proxy feature (#5291)

* implement reverse proxy


---------

Co-authored-by: Alisdair MacLeod <git@alisdairmacleod.co.uk>
Co-authored-by: mlsmaycon <mlsmaycon@gmail.com>
Co-authored-by: Eduard Gert <kontakt@eduardgert.de>
Co-authored-by: Viktor Liu <viktor@netbird.io>
Co-authored-by: Diego Noguês <diego.sure@gmail.com>
Co-authored-by: Diego Noguês <49420+diegocn@users.noreply.github.com>
Co-authored-by: Bethuel Mmbaga <bethuelmbaga12@gmail.com>
Co-authored-by: Zoltan Papp <zoltan.pmail@gmail.com>
Co-authored-by: Ashley Mensah <ashleyamo982@gmail.com>

proxy/handle_mapping_stream_test.go

@@ -0,0 +1,94 @@
+package proxy
+
+import (
+	"context"
+	"io"
+	"testing"
+
+	log "github.com/sirupsen/logrus"
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/grpc"
+	"google.golang.org/grpc/metadata"
+
+	"github.com/netbirdio/netbird/proxy/internal/health"
+	"github.com/netbirdio/netbird/shared/management/proto"
+)
+
+type mockMappingStream struct {
+	grpc.ClientStream
+	messages []*proto.GetMappingUpdateResponse
+	idx      int
+}
+
+func (m *mockMappingStream) Recv() (*proto.GetMappingUpdateResponse, error) {
+	if m.idx >= len(m.messages) {
+		return nil, io.EOF
+	}
+	msg := m.messages[m.idx]
+	m.idx++
+	return msg, nil
+}
+
+func (m *mockMappingStream) Header() (metadata.MD, error) {
+	return nil, nil //nolint:nilnil
+}
+func (m *mockMappingStream) Trailer() metadata.MD     { return nil }
+func (m *mockMappingStream) CloseSend() error         { return nil }
+func (m *mockMappingStream) Context() context.Context { return context.Background() }
+func (m *mockMappingStream) SendMsg(any) error        { return nil }
+func (m *mockMappingStream) RecvMsg(any) error        { return nil }
+
+func TestHandleMappingStream_SyncCompleteFlag(t *testing.T) {
+	checker := health.NewChecker(nil, nil)
+	s := &Server{
+		Logger:        log.StandardLogger(),
+		healthChecker: checker,
+	}
+
+	stream := &mockMappingStream{
+		messages: []*proto.GetMappingUpdateResponse{
+			{InitialSyncComplete: true},
+		},
+	}
+
+	syncDone := false
+	err := s.handleMappingStream(context.Background(), stream, &syncDone)
+	assert.NoError(t, err)
+	assert.True(t, syncDone, "initial sync should be marked done when flag is set")
+}
+
+func TestHandleMappingStream_NoSyncFlagDoesNotMarkDone(t *testing.T) {
+	checker := health.NewChecker(nil, nil)
+	s := &Server{
+		Logger:        log.StandardLogger(),
+		healthChecker: checker,
+	}
+
+	stream := &mockMappingStream{
+		messages: []*proto.GetMappingUpdateResponse{
+			{}, // no sync flag
+		},
+	}
+
+	syncDone := false
+	err := s.handleMappingStream(context.Background(), stream, &syncDone)
+	assert.NoError(t, err)
+	assert.False(t, syncDone, "initial sync should not be marked done without flag")
+}
+
+func TestHandleMappingStream_NilHealthChecker(t *testing.T) {
+	s := &Server{
+		Logger: log.StandardLogger(),
+	}
+
+	stream := &mockMappingStream{
+		messages: []*proto.GetMappingUpdateResponse{
+			{InitialSyncComplete: true},
+		},
+	}
+
+	syncDone := false
+	err := s.handleMappingStream(context.Background(), stream, &syncDone)
+	assert.NoError(t, err)
+	assert.True(t, syncDone, "sync done flag should be set even without health checker")
+}