Shared channels plugin APIs for MS Teams plugin (#25805)

New plugin APIs and hooks for accessing Shared Channels service via plugin. 

- RegisterPluginForSharedChannels(opts model.RegisterPluginOpts) (remoteID string, err error)
- UnregisterPluginForSharedChannels(pluginID string) error
- ShareChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
- UpdateSharedChannel(sc *model.SharedChannel) (*model.SharedChannel, error)
- UnshareChannel(channelID string) (unshared bool, err error)
- UpdateSharedChannelCursor(channelID, remoteID string, cusror model.GetPostsSinceForSyncCursor) error
- SyncSharedChannel(channelID string) error
- InviteRemoteToChannel(channelID string, remoteID string, userID string) error
- UninviteRemoteFromChannel(channelID string, remoteID string) error

Hooks
- OnSharedChannelsSyncMsg(msg *model.SyncMsg, rc *model.RemoteCluster) (model.SyncResponse, error)
- OnSharedChannelsPing(rc *model.RemoteCluster) bool

server/platform/services/sharedchannel/mock_AppIface_test.go

@@ -314,6 +314,30 @@ func (_m *MockAppIface) NotifySharedChannelUserUpdate(user *model.User) {
 	_m.Called(user)
 }
 
+// OnSharedChannelsSyncMsg provides a mock function with given fields: msg, rc
+func (_m *MockAppIface) OnSharedChannelsSyncMsg(msg *model.SyncMsg, rc *model.RemoteCluster) (model.SyncResponse, error) {
+	ret := _m.Called(msg, rc)
+
+	var r0 model.SyncResponse
+	var r1 error
+	if rf, ok := ret.Get(0).(func(*model.SyncMsg, *model.RemoteCluster) (model.SyncResponse, error)); ok {
+		return rf(msg, rc)
+	}
+	if rf, ok := ret.Get(0).(func(*model.SyncMsg, *model.RemoteCluster) model.SyncResponse); ok {
+		r0 = rf(msg, rc)
+	} else {
+		r0 = ret.Get(0).(model.SyncResponse)
+	}
+
+	if rf, ok := ret.Get(1).(func(*model.SyncMsg, *model.RemoteCluster) error); ok {
+		r1 = rf(msg, rc)
+	} else {
+		r1 = ret.Error(1)
+	}
+
+	return r0, r1
+}
+
 // PatchChannelModerationsForChannel provides a mock function with given fields: c, channel, channelModerationsPatch
 func (_m *MockAppIface) PatchChannelModerationsForChannel(c request.CTX, channel *model.Channel, channelModerationsPatch []*model.ChannelModerationPatch) ([]*model.ChannelModeration, *model.AppError) {
 	ret := _m.Called(c, channel, channelModerationsPatch)

server/platform/services/sharedchannel/service.go

@@ -63,6 +63,7 @@ type AppIface interface {
 	GetProfileImage(user *model.User) ([]byte, bool, *model.AppError)
 	InvalidateCacheForUser(userID string)
 	NotifySharedChannelUserUpdate(user *model.User)
+	OnSharedChannelsSyncMsg(msg *model.SyncMsg, rc *model.RemoteCluster) (model.SyncResponse, error)
 }
 
 // errNotFound allows checking against Store.ErrNotFound errors without making Store a dependency.
@@ -108,7 +109,7 @@ func NewSharedChannelService(server ServerIface, app AppIface) (*Service, error)
 // Start is called by the server on server start-up.
 func (scs *Service) Start() error {
 	rcs := scs.server.GetRemoteClusterService()
-	if rcs == nil {
+	if rcs == nil || !rcs.Active() {
 		return errors.New("Shared Channel Service cannot activate: requires Remote Cluster Service")
 	}
 
@@ -128,7 +129,7 @@ func (scs *Service) Start() error {
 // Shutdown is called by the server on server shutdown.
 func (scs *Service) Shutdown() error {
 	rcs := scs.server.GetRemoteClusterService()
-	if rcs == nil {
+	if rcs == nil || !rcs.Active() {
 		return errors.New("Shared Channel Service cannot shutdown: requires Remote Cluster Service")
 	}
 

server/platform/services/sharedchannel/sync_send_remote.go

@@ -527,13 +527,17 @@ func (scs *Service) sendProfileImageSyncData(sd *syncData) {
 	}
 }
 
-// sendSyncMsgToRemote synchronously sends the sync message to the remote cluster.
+// sendSyncMsgToRemote synchronously sends the sync message to the remote cluster (or plugin).
 func (scs *Service) sendSyncMsgToRemote(msg *model.SyncMsg, rc *model.RemoteCluster, f sendSyncMsgResultFunc) error {
 	rcs := scs.server.GetRemoteClusterService()
 	if rcs == nil {
 		return fmt.Errorf("cannot update remote cluster %s for channel id %s; Remote Cluster Service not enabled", rc.Name, msg.ChannelId)
 	}
 
+	if rc.PluginID != "" {
+		return scs.sendSyncMsgToPlugin(msg, rc, f)
+	}
+
 	b, err := json.Marshal(msg)
 	if err != nil {
 		return err
@@ -568,6 +572,17 @@ func (scs *Service) sendSyncMsgToRemote(msg *model.SyncMsg, rc *model.RemoteClus
 	return err
 }
 
+// sendSyncMsgToRemote synchronously sends the sync message to a plugin.
+func (scs *Service) sendSyncMsgToPlugin(msg *model.SyncMsg, rc *model.RemoteCluster, f sendSyncMsgResultFunc) error {
+	syncResp, errResp := scs.app.OnSharedChannelsSyncMsg(msg, rc)
+
+	if f != nil {
+		f(syncResp, errResp)
+	}
+
+	return errResp
+}
+
 func sanitizeSyncData(sd *syncData) {
 	for id, user := range sd.users {
 		sd.users[id] = sanitizeUserForSync(user)