throw error if parent is destroyed already when creating sub streams

.nvmrc

@@ -1 +1 @@
-v12
+v12

src/ObjectMultiplex.ts

@@ -23,6 +23,16 @@ export class ObjectMultiplex extends Duplex {
   }
 
   createStream(name: string): Substream {
+    // guard stream against destroyed already
+    if (this.destroyed) {
+      throw new Error('ObjectMultiplex - parent stream already destroyed');
+    }
+
+    // guard stream against ended already
+    if (this._readableState.ended || this._writableState.ended) {
+      throw new Error('ObjectMultiplex - parent stream already ended');
+    }
+
     // validate name
     if (!name) {
       throw new Error('ObjectMultiplex - name must not be empty');

test/index.js

@@ -79,6 +79,28 @@ test('roundtrip', (t) => {
   setTimeout(() => outTransport.destroy(), 100);
 });
 
+test('error on createStream if destroyed', (t) => {
+  const stream = new ObjMultiplex();
+  stream.destroy();
+  try {
+    stream.createStream('controller');
+  } catch (e) {
+    t.assert(e.message.includes('already destroyed'), true);
+    t.end();
+  }
+});
+
+test('error on createStream if ended', (t) => {
+  const stream = new ObjMultiplex();
+  stream.end();
+  try {
+    stream.createStream('controller');
+  } catch (e) {
+    t.assert(e.message.includes('already ended'), true);
+    t.end();
+  }
+});
+
 // util
 
 function basicTestSetup() {