fixup! stream: add diagnostics_channel event for completion

Signed-off-by: Bryan English <[email protected]>

Author: bengl

doc/api/diagnostics_channel.md

@@ -1853,6 +1853,24 @@ Emitted when [`child_process.spawn()`][] encounters an error.
 
 Emitted when [`process.execve()`][] is invoked.
 
+#### Streams
+
+> Stability: 1 - Experimental
+
+<!-- YAML
+added: REPLACEME
+-->
+
+##### Event: `'stream.web.done'`
+
+* `stream` {ReadableStream} The stream that finished.
+
+Emitted when a [`ReadableStream`][] has finished, either because all data has
+been read or because the stream was cancelled. The event fires once per stream,
+after the stream has transitioned to the `'closed'` state. It is emitted for
+both the async iterator (`for await (...)`) and the direct reader
+(`reader.read()`, including BYOB readers) consumption paths.
+
 #### Web Locks
 
 > Stability: 1 - Experimental
@@ -1917,6 +1935,7 @@ Emitted when a new thread is created.
 [TracingChannel Channels]: #tracingchannel-channels
 [`'uncaughtException'`]: process.md#event-uncaughtexception
 [`BoundedChannel`]: #class-boundedchannel
+[`ReadableStream`]: webstreams.md#class-readablestream
 [`TracingChannel`]: #class-tracingchannel
 [`asyncEnd` event]: #asyncendevent
 [`asyncStart` event]: #asyncstartevent

test/parallel/test-whatwg-webstreams-dc-events.mjs

@@ -43,3 +43,28 @@ import * as dc from 'diagnostics_channel';
 
   channel.unsubscribe(subscriber);
 }
+
+{
+  const readable = new ReadableStream({
+    type: 'bytes',
+    start(controller) {
+      controller.enqueue(new Uint8Array([1, 2, 3]));
+      controller.close();
+    },
+  });
+
+  const channel = dc.channel('stream.web.done');
+  const subscriber = common.mustCall(({ stream }) => {
+    assert.strictEqual(readable, stream);
+    assert.strictEqual(readable[util.kState].state, 'closed');
+  });
+  channel.subscribe(subscriber);
+
+  const reader = readable.getReader({ mode: 'byob' });
+  let result;
+  while (!result?.done) {
+    result = await reader.read(new Uint8Array(8));
+  }
+
+  channel.unsubscribe(subscriber);
+}