Bump SSE to v3.1.1 and add server KeepAlive (#876)

* Bump sse to v3.1.1 and add server keepalive

This allows the server to accept client reconnections and present them transparently to the consuming code (see dart-lang/sse#18).

* Update CHANGELOG.md

* Disconnect any old isolate

dwds/CHANGELOG.md

@@ -18,6 +18,7 @@
   to resolve breakpoint locations.
 - Remove dependency on `package:build_daemon`.
 - Add `FrontendServerAssetReader` for use with Frontend Server builds.
+- Depend on latest `package:sse` for handling client reconnects transparently on the server.
 - Fix an issue where a failure to initiate debugging through the Dart Debug
   Extension would cause your development server to crash.
 - Fix an issue where trying to launch DevTools in a non-debug enabled Chrome

dwds/debug_extension/pubspec.yaml

@@ -14,7 +14,7 @@ dependencies:
   js: ^0.6.1+1
   pedantic: ^1.5.0
   pub_semver: ^1.3.2
-  sse: ^3.0.0
+  sse: ^3.1.1
 
 dev_dependencies:
   webdev: ^2.0.0

dwds/lib/src/handlers/dev_handler.dart

@@ -37,7 +37,8 @@ import '../services/debug_service.dart';
 /// opening DevTools.
 class DevHandler {
   StreamSubscription _sub;
-  final SseHandler _sseHandler = SseHandler(Uri.parse(r'/$sseHandler'));
+  final SseHandler _sseHandler = SseHandler(Uri.parse(r'/$sseHandler'),
+      keepAlive: const Duration(seconds: 30));
   final _injectedConnections = <SseConnection>{};
   final DevTools _devTools;
   final AssetReader _assetReader;
@@ -310,6 +311,10 @@ class DevHandler {
     var services = _servicesByAppId[message.appId];
     var connection = AppConnection(message, sseConnection);
     if (services != null && services.connectedInstanceId == null) {
+      // Disconnect any old connection (eg. those in the keep-alive waiting state
+      // when reloading the page).
+      services.chromeProxyService?.destroyIsolate();
+
       // Reconnect to existing service.
       services.connectedInstanceId = message.instanceId;
       await services.chromeProxyService.createIsolate(connection);

dwds/lib/src/servers/extension_backend.dart

@@ -11,7 +11,8 @@ import 'package:http_multi_server/http_multi_server.dart';
 import 'package:shelf/shelf_io.dart';
 import 'package:sse/server/sse_handler.dart';
 
-final _sseHandler = SseHandler(Uri.parse('/\$debug'));
+final _sseHandler =
+    SseHandler(Uri.parse('/\$debug'), keepAlive: const Duration(seconds: 30));
 
 /// A backend for the Dart Debug Extension.
 ///

dwds/pubspec.yaml

@@ -30,7 +30,7 @@ dependencies:
   shelf_static: ^0.2.8
   shelf_web_socket: ^0.2.0
   source_maps: ^0.10.0
-  sse: ^3.0.0
+  sse: ^3.1.1
   vm_service: 1.2.0
   web_socket_channel: ^1.0.0
   webkit_inspection_protocol: '>=0.4.0 <0.6.0'

webdev/pubspec.yaml

@@ -29,7 +29,7 @@ dependencies:
   shelf: ^0.7.4
   shelf_proxy: ^0.1.0+5
   shelf_static: ^0.2.8
-  sse: ^3.0.0
+  sse: ^3.1.1
   vm_service: ^1.1.0
   webkit_inspection_protocol: '>=0.4.0 <0.6.0'
   yaml: ^2.1.13