feat: add onclose method to MessagePort (#22532)

* feat: add onclose method to MessagePort

* more scope, more good

* de-flake GC test

docs/api/message-port-main.md

@@ -45,5 +45,9 @@ Returns:
 
 Emitted when a MessagePortMain object receives a message.
 
+#### Event: 'close'
+
+Emitted when the remote end of a MessagePortMain object becomes disconnected.
+
 [`MessagePort`]: https://developer.mozilla.org/en-US/docs/Web/API/MessagePort
 [Channel Messaging API]: https://developer.mozilla.org/en-US/docs/Web/API/Channel_Messaging_API

patches/chromium/.patches

@@ -91,3 +91,4 @@ feat_enable_offscreen_rendering_with_viz_compositor.patch
 delay_lock_the_protocol_scheme_registry.patch
 gpu_notify_when_dxdiag_request_fails.patch
 feat_allow_embedders_to_add_observers_on_created_hunspell.patch
+feat_add_onclose_to_messageport.patch

patches/chromium/feat_add_onclose_to_messageport.patch

@@ -0,0 +1,51 @@
+From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
+From: Jeremy Apthorp <nornagon@nornagon.net>
+Date: Wed, 4 Mar 2020 11:18:03 -0800
+Subject: feat: add onclose to MessagePort
+
+This adds the 'onclose' event to MessagePort. This is
+[proposed](https://github.com/w3ctag/design-reviews/issues/269#issuecomment-407584290)
+in w3c and has been discussed for years without conclusion. I'd like to
+get this standardised, but in lieu of that, this makes MessagePort a
+whole bunch more useful!
+
+diff --git a/third_party/blink/renderer/core/messaging/message_port.cc b/third_party/blink/renderer/core/messaging/message_port.cc
+index e2ddbafc9ea2836a302da481702e2922949ffe78..7da7071862e384bce65ecb52996b5287891a33f9 100644
+--- a/third_party/blink/renderer/core/messaging/message_port.cc
++++ b/third_party/blink/renderer/core/messaging/message_port.cc
+@@ -156,6 +156,7 @@ void MessagePort::close() {
+     Entangle(mojo::MessagePipe().handle0);
+   }
+   closed_ = true;
++  DispatchEvent(*Event::Create(event_type_names::kClose));
+ }
+ 
+ void MessagePort::Entangle(mojo::ScopedMessagePipeHandle handle) {
+diff --git a/third_party/blink/renderer/core/messaging/message_port.h b/third_party/blink/renderer/core/messaging/message_port.h
+index 2a08335398b30671a61aee0f1ebe060222a4f1ff..874aecb9c038f19cc03641a19ce51cf2f958d80c 100644
+--- a/third_party/blink/renderer/core/messaging/message_port.h
++++ b/third_party/blink/renderer/core/messaging/message_port.h
+@@ -119,6 +119,13 @@ class CORE_EXPORT MessagePort : public EventTargetWithInlineData,
+     return GetAttributeEventListener(event_type_names::kMessageerror);
+   }
+ 
++  void setOnclose(EventListener* listener) {
++    SetAttributeEventListener(event_type_names::kClose, listener);
++  }
++  EventListener* onclose() {
++    return GetAttributeEventListener(event_type_names::kClose);
++  }
++
+   // A port starts out its life entangled, and remains entangled until it is
+   // closed or is cloned.
+   bool IsEntangled() const { return !closed_ && !IsNeutered(); }
+diff --git a/third_party/blink/renderer/core/messaging/message_port.idl b/third_party/blink/renderer/core/messaging/message_port.idl
+index 6fab27fcdf1c333739b6ffe88b3cc4eed3301ee4..3f1f181d9b8a66997136f870f55c97c08294b6eb 100644
+--- a/third_party/blink/renderer/core/messaging/message_port.idl
++++ b/third_party/blink/renderer/core/messaging/message_port.idl
+@@ -40,4 +40,5 @@
+     // event handlers
+     attribute EventHandler onmessage;
+     attribute EventHandler onmessageerror;
++    attribute EventHandler onclose;
+ };

shell/browser/api/message_port.cc

@@ -103,6 +103,12 @@ void MessagePort::Close() {
   closed_ = true;
   if (!HasPendingActivity())
     Unpin();
+
+  v8::Isolate* isolate = v8::Isolate::GetCurrent();
+  v8::HandleScope scope(isolate);
+  v8::Local<v8::Object> self;
+  if (GetWrapper(isolate).ToLocal(&self))
+    gin_helper::EmitEvent(isolate, self, "close");
 }
 
 void MessagePort::Entangle(mojo::ScopedMessagePipeHandle handle) {
@@ -196,6 +202,7 @@ void MessagePort::Pin() {
   if (!pinned_.IsEmpty())
     return;
   v8::Isolate* isolate = v8::Isolate::GetCurrent();
+  v8::HandleScope scope(isolate);
   v8::Local<v8::Value> self;
   if (GetWrapper(isolate).ToLocal(&self)) {
     pinned_.Reset(isolate, self);

spec-main/api-ipc-spec.ts

@@ -278,6 +278,57 @@ describe('ipc module', () => {
       expect(data).to.equal('a message')
     })
 
+    describe('close event', () => {
+      describe('in renderer', () => {
+        it('is emitted when the main process closes its end of the port', async () => {
+          const w = new BrowserWindow({ show: false, webPreferences: { nodeIntegration: true } })
+          w.loadURL('about:blank')
+          await w.webContents.executeJavaScript(`(${function () {
+            const { ipcRenderer } = require('electron')
+            ipcRenderer.on('port', (e) => {
+              const [port] = e.ports
+              port.start();
+              (port as any).onclose = () => {
+                ipcRenderer.send('closed')
+              }
+            })
+          }})()`)
+          const { port1, port2 } = new MessageChannelMain()
+          w.webContents.postMessage('port', null, [port2])
+          port1.close()
+          await emittedOnce(ipcMain, 'closed')
+        })
+
+        it('is emitted when the other end of a port is garbage-collected', async () => {
+          const w = new BrowserWindow({ show: false, webPreferences: { nodeIntegration: true } })
+          w.loadURL('about:blank')
+          await w.webContents.executeJavaScript(`(${async function () {
+            const { port2 } = new MessageChannel()
+            await new Promise(resolve => {
+              port2.start();
+              (port2 as any).onclose = resolve
+              process.electronBinding('v8_util').requestGarbageCollectionForTesting()
+            })
+          }})()`)
+        })
+
+        it('is emitted when the other end of a port is sent to nowhere', async () => {
+          const w = new BrowserWindow({ show: false, webPreferences: { nodeIntegration: true } })
+          w.loadURL('about:blank')
+          ipcMain.once('do-a-gc', () => v8Util.requestGarbageCollectionForTesting())
+          await w.webContents.executeJavaScript(`(${async function () {
+            const { port1, port2 } = new MessageChannel()
+            await new Promise(resolve => {
+              port2.start();
+              (port2 as any).onclose = resolve
+              require('electron').ipcRenderer.postMessage('nobody-listening', null, [port1])
+              require('electron').ipcRenderer.send('do-a-gc')
+            })
+          }})()`)
+        })
+      })
+    })
+
     describe('MessageChannelMain', () => {
       it('can be created', () => {
         const { port1, port2 } = new MessageChannelMain()