feat: implement DERP streaming on tailnet Client API (#11302)

Implements DERPMap streaming from client API.

In a subsequent PR I plan to remove the implementation in coderd/agentapi in favor of the tailnet one

coderd/coderd.go

@@ -479,7 +479,11 @@ func New(options *Options) *API {
 		}
 	}
 	api.TailnetClientService, err = tailnet.NewClientService(
-		api.Logger.Named("tailnetclient"), &api.TailnetCoordinator)
+		api.Logger.Named("tailnetclient"),
+		&api.TailnetCoordinator,
+		api.Options.DERPMapUpdateFrequency,
+		api.DERPMap,
+	)
 	if err != nil {
 		api.Logger.Fatal(api.ctx, "failed to initialize tailnet client service", slog.Error(err))
 	}

tailnet/service.go

@@ -7,11 +7,13 @@ import (
 	"strconv"
 	"strings"
 	"sync/atomic"
+	"time"
 
 	"github.com/google/uuid"
 	"github.com/hashicorp/yamux"
 	"storj.io/drpc/drpcmux"
 	"storj.io/drpc/drpcserver"
+	"tailscale.com/tailcfg"
 
 	"cdr.dev/slog"
 	"github.com/coder/coder/v2/tailnet/proto"
@@ -92,10 +94,22 @@ type ClientService struct {
 
 // NewClientService returns a ClientService based on the given Coordinator pointer.  The pointer is
 // loaded on each processed connection.
-func NewClientService(logger slog.Logger, coordPtr *atomic.Pointer[Coordinator]) (*ClientService, error) {
+func NewClientService(
+	logger slog.Logger,
+	coordPtr *atomic.Pointer[Coordinator],
+	derpMapUpdateFrequency time.Duration,
+	derpMapFn func() *tailcfg.DERPMap,
+) (
+	*ClientService, error,
+) {
 	s := &ClientService{logger: logger, coordPtr: coordPtr}
 	mux := drpcmux.New()
-	drpcService := NewDRPCService(logger, coordPtr)
+	drpcService := &DRPCService{
+		CoordPtr:               coordPtr,
+		Logger:                 logger,
+		DerpMapUpdateFrequency: derpMapUpdateFrequency,
+		DerpMapFn:              derpMapFn,
+	}
 	err := proto.DRPCRegisterClient(mux, drpcService)
 	if err != nil {
 		return nil, xerrors.Errorf("register DRPC service: %w", err)
@@ -145,22 +159,39 @@ func (s *ClientService) ServeClient(ctx context.Context, version string, conn ne
 
 // DRPCService is the dRPC-based, version 2.x of the tailnet API and implements proto.DRPCClientServer
 type DRPCService struct {
-	coordPtr *atomic.Pointer[Coordinator]
-	logger   slog.Logger
+	CoordPtr               *atomic.Pointer[Coordinator]
+	Logger                 slog.Logger
+	DerpMapUpdateFrequency time.Duration
+	DerpMapFn              func() *tailcfg.DERPMap
 }
 
-func NewDRPCService(logger slog.Logger, coordPtr *atomic.Pointer[Coordinator]) *DRPCService {
-	return &DRPCService{
-		coordPtr: coordPtr,
-		logger:   logger,
+func (s *DRPCService) StreamDERPMaps(_ *proto.StreamDERPMapsRequest, stream proto.DRPCClient_StreamDERPMapsStream) error {
+	defer stream.Close()
+
+	ticker := time.NewTicker(s.DerpMapUpdateFrequency)
+	defer ticker.Stop()
+
+	var lastDERPMap *tailcfg.DERPMap
+	for {
+		derpMap := s.DerpMapFn()
+		if lastDERPMap == nil || !CompareDERPMaps(lastDERPMap, derpMap) {
+			protoDERPMap := DERPMapToProto(derpMap)
+			err := stream.Send(protoDERPMap)
+			if err != nil {
+				return xerrors.Errorf("send derp map: %w", err)
+			}
+			lastDERPMap = derpMap
+		}
+
+		ticker.Reset(s.DerpMapUpdateFrequency)
+		select {
+		case <-stream.Context().Done():
+			return nil
+		case <-ticker.C:
+		}
 	}
 }
 
-func (*DRPCService) StreamDERPMaps(*proto.StreamDERPMapsRequest, proto.DRPCClient_StreamDERPMapsStream) error {
-	// TODO integrate with Dean's PR implementation
-	return xerrors.New("unimplemented")
-}
-
 func (s *DRPCService) CoordinateTailnet(stream proto.DRPCClient_CoordinateTailnetStream) error {
 	ctx := stream.Context()
 	streamID, ok := ctx.Value(streamIDContextKey{}).(StreamID)
@@ -168,9 +199,9 @@ func (s *DRPCService) CoordinateTailnet(stream proto.DRPCClient_CoordinateTailne
 		_ = stream.Close()
 		return xerrors.New("no Stream ID")
 	}
-	logger := s.logger.With(slog.F("peer_id", streamID), slog.F("name", streamID.Name))
+	logger := s.Logger.With(slog.F("peer_id", streamID), slog.F("name", streamID.Name))
 	logger.Debug(ctx, "starting tailnet Coordinate")
-	coord := *(s.coordPtr.Load())
+	coord := *(s.CoordPtr.Load())
 	reqs, resps := coord.Coordinate(ctx, streamID.ID, streamID.Name, streamID.Auth)
 	c := communicator{
 		logger: logger,

tailnet/service_test.go

@@ -8,8 +8,10 @@ import (
 	"net/http"
 	"sync/atomic"
 	"testing"
+	"time"
 
 	"golang.org/x/xerrors"
+	"tailscale.com/tailcfg"
 
 	"github.com/google/uuid"
 
@@ -94,7 +96,11 @@ func TestClientService_ServeClient_V2(t *testing.T) {
 	coordPtr := atomic.Pointer[tailnet.Coordinator]{}
 	coordPtr.Store(&coord)
 	logger := slogtest.Make(t, nil).Leveled(slog.LevelDebug)
-	uut, err := tailnet.NewClientService(logger, &coordPtr)
+	derpMap := &tailcfg.DERPMap{Regions: map[int]*tailcfg.DERPRegion{999: {RegionCode: "test"}}}
+	uut, err := tailnet.NewClientService(
+		logger, &coordPtr,
+		time.Millisecond, func() *tailcfg.DERPMap { return derpMap },
+	)
 	require.NoError(t, err)
 
 	ctx := testutil.Context(t, testutil.WaitShort)
@@ -112,6 +118,8 @@ func TestClientService_ServeClient_V2(t *testing.T) {
 
 	client, err := tailnet.NewDRPCClient(c)
 	require.NoError(t, err)
+
+	// Coordinate
 	stream, err := client.CoordinateTailnet(ctx)
 	require.NoError(t, err)
 	defer stream.Close()
@@ -145,7 +153,17 @@ func TestClientService_ServeClient_V2(t *testing.T) {
 	err = stream.Close()
 	require.NoError(t, err)
 
-	// stream ^^ is just one RPC; we need to close the Conn to end the session.
+	// DERP Map
+	dms, err := client.StreamDERPMaps(ctx, &proto.StreamDERPMapsRequest{})
+	require.NoError(t, err)
+
+	gotDermMap, err := dms.Recv()
+	require.NoError(t, err)
+	require.Equal(t, "test", gotDermMap.GetRegions()[999].GetRegionCode())
+	err = dms.Close()
+	require.NoError(t, err)
+
+	// RPCs closed; we need to close the Conn to end the session.
 	err = c.Close()
 	require.NoError(t, err)
 	err = testutil.RequireRecvCtx(ctx, t, errCh)
@@ -159,7 +177,7 @@ func TestClientService_ServeClient_V1(t *testing.T) {
 	coordPtr := atomic.Pointer[tailnet.Coordinator]{}
 	coordPtr.Store(&coord)
 	logger := slogtest.Make(t, nil).Leveled(slog.LevelDebug)
-	uut, err := tailnet.NewClientService(logger, &coordPtr)
+	uut, err := tailnet.NewClientService(logger, &coordPtr, 0, nil)
 	require.NoError(t, err)
 
 	ctx := testutil.Context(t, testutil.WaitShort)