tshd-initiated communication for Connect

[ravicious]

teleport counterpart: gravitational/teleport#16043

The important logic is contained within ClustersService.initializeClusterEventsStream which I plan to refactor to a separate service.

That method is called from AppContext.init when the app starts.

webapps/packages/teleterm/src/ui/services/clusters/clustersService.ts

Lines 484 to 522 in 6cf40fa

	// TODO: Move this elsewhere, perhaps ClusterEventsService?
	async initializeClusterEventsStream() {
	const uid = unique(5);
	const logger = new Logger(`Cluster events ${uid}`);
	logger.info('Initializing cluster events stream');
	const clusterEventsStream = this.client.clusterEvents();
	clusterEventsStream.onNewGatewayConnectionAccepted(() => {
	logger.info('New connection accepted!');
	});
	clusterEventsStream.onError((error: Error) => {
	// TODO: Add gRPC stream interceptor in lib/teleterm/apiserver so that error codes are
	// properly propagated. Then match on AlreadyExists code rather than the error message.
	if (error.message.includes('another stream is already active')) {
	logger.error('Another cluster events stream is already open!');
	return;
	}
	logger.error(
	`Restarting cluster events stream because of an error`,
	error
	);
	this.initializeClusterEventsStream();
	});
	clusterEventsStream.onEnd(() => {
	logger.info('Cluster events stream has been closed by the server');
	});
	clusterEventsStream.onStatus(status => {
	logger.info(
	'Cluster events stream received status from the server',
	status
	);
	});
	}

webapps/packages/teleterm/src/ui/appContext.ts

Lines 85 to 92 in 6cf40fa

	async init(): Promise<void> {
	// The stream for cluster events needs to be initialized first, otherwise the code in tshd that
	// writes to it will block execution.
	// TODO: Expand the comment above.
	await this.clustersService.initializeClusterEventsStream();
	await this.clustersService.syncRootClusters();
	this.workspacesService.restorePersistedState();
	}

Updates gravitational/webapps.e#299