How can I send a notification/event from a JDTLS extension to the RedHat VS Code extension for broadcasting to another VS Code extension?

[guw]

Here is my use case:

I have a JDTLS extension bundle jar, which gets plugged into JDTLS by the RedHat Java extension during JDTL initialization.
I now want to send an event from that extension via JDTLS back to VS Code. In VS Code I want to receive and process the event by some other extension, i.e. not within the RedHat Java extension.

Any ideas?

[rgrunber]

I had to look through this myself because I thought it was definitely possible, but we're just missing a small piece.

From your JDT-LS extension bundle
Use JavaLanguageServerPlugin.getInstance().getClientConnection(). It'll return you a JavaClientConnection which should contain all the method calls that go from server -> client. In particular the one you want is : sendEventNotification(EventNotification notification)

That notification will travel from server to client.

From your own VS Code extension

vscode-java exposes its own api manager. See

vscode-java/src/apiManager.ts

Lines 15 to 81 in b041ca4

	class ApiManager {
	private api: ExtensionAPI;
	private onDidClasspathUpdateEmitter: Emitter<Uri> = new Emitter<Uri>();
	private onDidServerModeChangeEmitter: Emitter<ServerMode> = new Emitter<ServerMode>();
	private onDidProjectsImportEmitter: Emitter<Uri[]> = new Emitter<Uri[]>();
	private onDidProjectsDeleteEmitter: Emitter<Uri[]> = new Emitter<Uri[]>();
	private traceEventEmitter: Emitter<any> = new Emitter<any>();
	private sourceInvalidatedEventEmitter: Emitter<SourceInvalidatedEvent> = new Emitter<SourceInvalidatedEvent>();
	private serverReadyPromiseResolve: (result: boolean) => void;
	public initialize(requirements: RequirementsData, serverMode: ServerMode): void {
	// if it's manual import mode, set the server mode to lightwight, so that the
	// project explorer won't spinning until import project is triggered.
	if (getJavaConfiguration().get<string>("import.projectSelection") === "manual") {
	serverMode = ServerMode.lightWeight;
	}
	const getDocumentSymbols: GetDocumentSymbolsCommand = getDocumentSymbolsProvider();
	const goToDefinition: GoToDefinitionCommand = goToDefinitionProvider();
	const getProjectSettings = async (uri: string, settingKeys: string[]) => {
	return await commands.executeCommand<Object>(Commands.EXECUTE_WORKSPACE_COMMAND, Commands.GET_PROJECT_SETTINGS, uri, settingKeys);
	};
	const getClasspaths = async (uri: string, options: ClasspathQueryOptions) => {
	return await commands.executeCommand<ClasspathResult>(Commands.EXECUTE_WORKSPACE_COMMAND, Commands.GET_CLASSPATHS, uri, JSON.stringify(options));
	};
	const isTestFile = async (uri: string) => {
	return await commands.executeCommand<boolean>(Commands.EXECUTE_WORKSPACE_COMMAND, Commands.IS_TEST_FILE, uri);
	};
	const onDidClasspathUpdate = this.onDidClasspathUpdateEmitter.event;
	const onDidServerModeChange = this.onDidServerModeChangeEmitter.event;
	const onDidProjectsImport = this.onDidProjectsImportEmitter.event;
	const onDidProjectsDelete = this.onDidProjectsDeleteEmitter.event;
	const traceEvent = this.traceEventEmitter.event;
	const serverReadyPromise: Promise<boolean> = new Promise<boolean>((resolve) => {
	this.serverReadyPromiseResolve = resolve;
	});
	const serverReady = async () => {
	return serverReadyPromise;
	};
	this.api = {
	apiVersion: extensionApiVersion,
	javaRequirement: requirements,
	status: ClientStatus.starting,
	registerHoverCommand: registerHoverCommand,
	getDocumentSymbols,
	goToDefinition,
	getProjectSettings,
	getClasspaths,
	isTestFile,
	onDidClasspathUpdate,
	serverMode,
	onDidServerModeChange,
	onDidProjectsImport,
	onDidProjectsDelete,
	serverReady,
	onWillRequestStart,
	onDidRequestEnd,
	trackEvent: traceEvent,
	onDidSourceInvalidate: this.sourceInvalidatedEventEmitter.event,
	};
	}

I describe in #3102 (comment) how to access it, and there's quite a few extension that do it this way. Basically, the return value of activating the vscode-java extension is the API defined above.

const vscodeJava = extensions.getExtension('redhat.java');
const api = await vscodeJava.activate();

The problem is, we don't expose an emitter for any notification. Just some specific ones we care about, like errors. We could open this up. If you wanted a hack that might work immediately :

Instead of sending sendEventNotification like I described above, use telemetryEvent instead. A telemetry event is like any other notification except it gets its own endpoint.

Our vscode-java extension will receive the telemetry event from the server and expose it to the API through :

vscode-java/src/standardLanguageClient.ts

Lines 337 to 338 in b041ca4

	this.languageClient.onTelemetry(async (e: TelemetryEvent) => {
	apiManager.fireTraceEvent(e);

.

Then just :

api.trackEvent((event: any) => {
...
...
});

I think this should work but haven't tried it myself. Otherwise, we should probably create an api event emitter for generic notifications.

[guw]

Would it be possible to expose the notifications in a similar way? We do have telemetry collection disabled in the preferences because we don't have approval for sending data to external systems.

Or alternatively, can we prevent vscode-java from sending events externally but sill have telemetry enabled?

[rgrunber]

I think so. I see it as the reasonable way forward. We should create a separate event transmitter for notifications from the server, and fire off the event to the api manager for all/most languageclient.onNotification(..) callbacks. @testforstephen , let me know if that seems reasonable, or if I've missed some existing way to get notifications through the api manager.

[testforstephen]

@guw You can use JavaLanguageServerPlugin.getInstance().getClientConnection().sendNotification(clientCommandId, clientCommandParams) to trigger a command on client side from server side. The clientCommandId is the vscode command you registered on your own extension, where you can either forward it to another extension or perform an action directly.

Here is the vscode-java side to handle such notification.

vscode-java/src/standardLanguageClient.ts

Lines 313 to 314 in 7f89deb

	this.languageClient.onNotification(ServerNotification.type, (params) => {
	commands.executeCommand(params.command, ...params.arguments);