LanguageClient.sendNotification fails due to change in state due to stopping client.

[mmahrouss]

We are working on an LS for Odoo, and we have encountered an error that happens due to change in state.

Let me describe the scenario:

• We have a listener on onDidChangeConfiguration that based on some condition closes the client with await client.stop(15000).
• In the Client base code you also have a listener to sendNotification with the didChangeConfiguration Notification to be sent to the server.
• Since we stop the client the state is updated, but it is updated after the check you have at the top of the function Here:

  vscode-languageserver-node/client/src/common/client.ts

  Lines 984 to 987 in d810d51

  	public async sendNotification<P>(type: string | MessageSignature, params?: P): Promise<void> {
  	if (this.$state === ClientState.StartFailed || this.$state === ClientState.Stopping || this.$state === ClientState.Stopped) {
  	return Promise.reject(new ResponseError(ErrorCodes.ConnectionInactive, `Client is not running`));
  	}

• At that point the state is still running, so it goes forward until it calls $start here:

  vscode-languageserver-node/client/src/common/client.ts

  Lines 999 to 1000 in d810d51

  	// Ensure we have a connection before we force the document sync.
  	const connection = await this.$start();

• Then while it awaits this.start() which is probably already a resolved promise, the code is interrupted, and the stop function is called, so the state changes to stopping.
  

  vscode-languageserver-node/client/src/common/client.ts

  Lines 1755 to 1765 in d810d51

  	private async $start(): Promise<Connection> {
  	if (this.$state === ClientState.StartFailed) {
  	throw new Error(`Previous start failed. Can't restart server.`);
  	}
  	await this.start();
  	const connection = this.activeConnection();
  	if (connection === undefined) {
  	throw new Error(`Starting server failed`);
  	}
  	return connection;
  	}

• Then of course when it goes to this.activeConnection() it returns undefined, which then throws an error.
  

  vscode-languageserver-node/client/src/common/client.ts

  Lines 1232 to 1234 in d810d51

  	private activeConnection(): Connection | undefined {
  	return this.$state === ClientState.Running && this._connection !== undefined ? this._connection : undefined;
  	}

• However in this case from our POV, it is not an error, because it was trying to send a notification while the server is stopping, and the state was stopping/stopped. I think maybe there should be a guard to check the state before raising the error so that the state is up to date.

[dbaeumer]

Thanks for the analysis. Needs some thinking...