Send an event notifying DWDS when the debugger is detached (#1595)

Author: elliette

dwds/CHANGELOG.md

@@ -10,6 +10,7 @@
   - Remove clearing all scripts on page load for extension debugger.
 - Fix breakpoints not hitting after changing a base in index.html.
 - Find best locations for call frames, breakpoints, or expression evaluation.
+- Close the SSE connection when a DebugExtension.detached event is received.
 
 **Breaking changes:**
 - Add `basePath` parameter to `FrontendServerRequireStrategy`.

dwds/debug_extension/CHANGELOG.md

@@ -2,6 +2,7 @@
 
 - Notify the debugger and inspector panels when the debug session is disconnected.
 - Provide a detailed error message when the debugger fails to connect.
+- Send an event to the server when the debugger is detached.
 
 ## 1.28
 

dwds/debug_extension/web/background.dart

@@ -295,6 +295,14 @@ int _removeDebugSessionForTab(int tabId) {
       (session) => session.appTabId == tabId || session.devtoolsTabId == tabId,
       orElse: () => null);
   if (session != null) {
+    // Note: package:sse will try to keep the connection alive, even after the
+    // client has been closed. Therefore the extension sends an event to notify
+    // DWDS that we should close the connection, instead of relying on the done
+    // event sent when the client is closed. See details:
+    // https://github.com/dart-lang/webdev/pull/1595#issuecomment-1116773378
+    final event =
+        _extensionEventFor('DebugExtension.detached', js_util.jsify({}));
+    session.socketClient.sink.add(jsonEncode(serializers.serialize(event)));
     session.socketClient.close();
     _debugSessions.remove(session);