Reject channel writes if channel has been closed

src/tests/webR/webr-main.test.ts

@@ -1034,6 +1034,11 @@ test('Close webR communication channel', async () => {
   // Close the channel
   tempR.close();
   await expect(closedPromise).resolves.toEqual(true);
+
+  // Writing messages after closing the channel is an error
+  expect(() => tempR.writeConsole('foo <- 123')).toThrow(
+    "The webR communication channel has been closed"
+  );
 });
 
 test('Default and user provided REnv properties are merged', async () => {

src/webR/chan/channel-postmessage.ts

@@ -29,7 +29,10 @@ export class PostMessageChannelMain extends ChannelMain {
     const initWorker = (worker: Worker) => {
       this.#worker = worker;
       this.#handleEventsFromWorker(worker);
-      this.close = () => worker.terminate();
+      this.close = () => {
+        worker.terminate();
+        this.putClosedMessage();
+      };
       const msg = {
         type: 'init',
         data: { config, channelType: ChannelType.PostMessage },

src/webR/chan/channel.ts

@@ -7,6 +7,7 @@ import { promiseHandles, ResolveFn, RejectFn } from '../utils';
 import { AsyncQueue } from './queue';
 import { Message, newRequest, Response } from './message';
 import { WebRPayload, WebRPayloadWorker, webRPayloadAsError } from '../payload';
+import { WebRChannelError } from '../error';
 
 // The channel structure is asymmetric:
 //
@@ -34,6 +35,7 @@ export abstract class ChannelMain {
   systemQueue = new AsyncQueue<Message>();
 
   #parked = new Map<string, { resolve: ResolveFn; reject: RejectFn }>();
+  #closed = false;
 
   abstract initialised: Promise<unknown>;
   abstract close(): void;
@@ -56,6 +58,9 @@ export abstract class ChannelMain {
   }
 
   write(msg: Message): void {
+    if (this.#closed) {
+      throw new WebRChannelError("The webR communication channel has been closed.");
+    }
     this.inputQueue.put(msg);
   }
 
@@ -70,6 +75,7 @@ export abstract class ChannelMain {
   }
 
   protected putClosedMessage(): void {
+    this.#closed = true;
     this.outputQueue.put({ type: 'closed' });
   }