Switch isDevToolsServerAvailable to not depend on the SSE connection (#9024)

* Switch isDevToolsServerAvailable to not depend on the SSE connection

My recent change to disable the SSE connection when running embedded had an unintended side-effect. There's a number of places that check `isDevToolsServerAvailable` to see if they can call the HTTP API (and to set up server-side storage), however this was checking whether the SSE connection was made, not only that the server was available.

This change moves the server API check out of `DevToolsServerConnection` (which is basically the SSE API) and sets the storage (and therefore `isDevToolsServerAvailable`) based on just the HTTP API regardless of SSE, and then only attempts to connect SSE after.

Fixes #9023

* Remove unused import

Author: DanTup

packages/devtools_app/lib/src/shared/config_specific/framework_initialize/_framework_initialize_web.dart

@@ -6,6 +6,7 @@ import 'dart:js_interop';
 
 import 'package:devtools_app_shared/utils.dart';
 import 'package:devtools_app_shared/web_utils.dart';
+import 'package:logging/logging.dart';
 import 'package:web/web.dart' hide Storage;
 
 import '../../../service/service_manager.dart';
@@ -14,6 +15,8 @@ import '../../primitives/storage.dart';
 import '../../server/server.dart' as server;
 import '../../server/server_api_client.dart';
 
+final _log = Logger('framework_initialize');
+
 /// Return the url the application is launched from.
 Future<String> initializePlatform() async {
   // Clear out the unneeded HTML from index.html.
@@ -27,20 +30,28 @@ Future<String> initializePlatform() async {
         }.toJS,
       );
 
-  // TODO(kenz): this server connection initialized listeners that are never
-  //  disposed, so this is likely leaking resources.
-  // Here, we try and initialize the connection between the DevTools web app and
-  // its local server. DevTools can be launched without the server however, so
-  // establishing this connection is a best-effort.
-  // TODO(kenz): investigate if we can remove the DevToolsServerConnection
-  //  code in general - it is currently only used for non-embedded pages to
-  //  support some functionality like having VS Code reuse existing browser tabs
-  //  and showing notifications if you try to launch when you already have one
-  //  open.
-  final connection = await DevToolsServerConnection.connect();
-  if (connection != null) {
+  // Check if the server API is available.
+  if (await server.checkServerHttpApiAvailable()) {
+    _log.info('Server HTTP API is available, using server for storage.');
     setGlobal(Storage, server.ServerConnectionStorage());
+
+    // And also connect the legacy SSE API if necessary
+    // (`DevToolsServerConnection.connect`) may short-circuit in some cases,
+    // such as when embedded.
+
+    // TODO(kenz): this server connection initialized listeners that are never
+    //  disposed, so this is likely leaking resources.
+    // Here, we try and initialize the connection between the DevTools web app and
+    // its local server. DevTools can be launched without the server however, so
+    // establishing this connection is a best-effort.
+    // TODO(kenz): investigate if we can remove the DevToolsServerConnection
+    //  code in general - it is currently only used for non-embedded pages to
+    //  support some functionality like having VS Code reuse existing browser tabs
+    //  and showing notifications if you try to launch when you already have one
+    //  open.
+    await DevToolsServerConnection.connect();
   } else {
+    _log.info('Server HTTP API is not available, using browser for storage.');
     setGlobal(Storage, BrowserStorage());
   }
 

packages/devtools_app/lib/src/shared/server/_server_api.dart

@@ -0,0 +1,31 @@
+// Copyright 2025 The Flutter Authors
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file or at https://developers.google.com/open-source/licenses/bsd.
+
+part of 'server.dart';
+
+/// Checks whether the server HTTP API is available.
+Future<bool> checkServerHttpApiAvailable() async {
+  try {
+    // Unlike other parts of this API, the ping request is handled directly
+    // in the server in the SDK (see `pkg\dds\lib\src\devtools\handler.dart`)
+    // and not delegated back to DevTools shared code.
+    final response = await get(
+      Uri.parse('${apiPrefix}ping'),
+    ).timeout(const Duration(seconds: 5));
+    // When running with the local dev server Flutter may serve its index page
+    // for missing files to support the hashless url strategy. Check the response
+    // content to confirm it came from our server.
+    // See https://github.com/flutter/flutter/issues/67053
+    if (response.statusCode != 200 || response.body != 'OK') {
+      _log.info('DevTools server not available (${response.statusCode})');
+      return false;
+    }
+  } catch (e) {
+    // unable to locate dev server
+    _log.info('DevTools server not available ($e)');
+    return false;
+  }
+
+  return true;
+}

packages/devtools_app/lib/src/shared/server/server.dart

@@ -25,15 +25,22 @@ part '_dtd_api.dart';
 part '_extensions_api.dart';
 part '_preferences_api.dart';
 part '_release_notes_api.dart';
+part '_server_api.dart';
 part '_survey_api.dart';
 
 final _log = Logger('devtools_server_client');
 
-/// Whether the DevTools server is available.
+/// Whether the DevTools server is available so that the HTTP API can be used.
+///
+/// A value of `true` here does not necessarily mean the legacy SSE API is
+/// available.
 ///
 /// Since the DevTools server is a web server, it is only available for the
 /// web platform.
 ///
+/// TODO(dantup): Since this relates only to non-SSE API, it could be available
+///  for non-web?
+///
 /// In `framework_initialize_web.dart`, we test the DevTools server connection
 /// by pinging the server and checking the response. If this is successful, we
 /// set the [storage] global to an instance of [ServerConnectionStorage].

packages/devtools_app/lib/src/shared/server/server_api_client.dart

@@ -8,7 +8,6 @@ import 'dart:convert';
 import 'package:devtools_app_shared/ui.dart' show isEmbedded;
 import 'package:devtools_shared/devtools_shared.dart';
 import 'package:flutter/foundation.dart';
-import 'package:http/http.dart' as http;
 import 'package:logging/logging.dart';
 
 import '../config_specific/notifications/notifications.dart';
@@ -47,6 +46,11 @@ class DevToolsServerConnection {
           ? baseUri.resolve('devtools/api/')
           : baseUri.resolve('api/');
 
+  /// Connects to the legacy SSE API.
+  ///
+  /// Callers should first ensure the DevTools server is available (for example
+  /// by calling [checkServerHttpApiAvailable] or verifying that it was
+  /// successfull by using [isDevToolsServerAvailable])
   static Future<DevToolsServerConnection?> connect() async {
     // Don't connect SSE when running embedded because the API does not provide
     // anything that is used when embedded but it ties up one of the limited
@@ -58,27 +62,6 @@ class DevToolsServerConnection {
 
     final serverUri = Uri.parse(devToolsServerUriAsString);
     final apiUri = apiUriFor(serverUri);
-    final pingUri = apiUri.resolve('ping');
-
-    try {
-      final response = await http
-          .get(pingUri)
-          .timeout(const Duration(seconds: 5));
-      // When running with the local dev server Flutter may serve its index page
-      // for missing files to support the hashless url strategy. Check the response
-      // content to confirm it came from our server.
-      // See https://github.com/flutter/flutter/issues/67053
-      if (response.statusCode != 200 || response.body != 'OK') {
-        // unable to locate dev server
-        _log.info('devtools server not available (${response.statusCode})');
-        return null;
-      }
-    } catch (e) {
-      // unable to locate dev server
-      _log.info('devtools server not available ($e)');
-      return null;
-    }
-
     final sseUri = apiUri.resolve('sse');
     final client = SseClient(sseUri.toString(), debugKey: 'DevToolsServer');
     return DevToolsServerConnection._(client);