Add a flag for using WS for debug backend (#61359)

packages/flutter_tools/lib/src/build_runner/devfs_web.dart

@@ -42,6 +42,7 @@ typedef DwdsLauncher = Future<Dwds> Function({
   bool enableDebugExtension,
   String hostname,
   bool useSseForDebugProxy,
+  bool useSseForDebugBackend,
   bool serveDevTools,
   void Function(Level, String) logWriter,
   bool verbose,
@@ -142,6 +143,7 @@ class WebAssetServer implements AssetReader {
     int port,
     UrlTunneller urlTunneller,
     bool useSseForDebugProxy,
+    bool useSseForDebugBackend,
     BuildInfo buildInfo,
     bool enableDwds,
     Uri entrypoint,
@@ -235,6 +237,7 @@ class WebAssetServer implements AssetReader {
         urlEncoder: urlTunneller,
         enableDebugging: true,
         useSseForDebugProxy: useSseForDebugProxy,
+        useSseForDebugBackend: useSseForDebugBackend,
         serveDevTools: false,
         logWriter: (Level logLevel, String message) => globals.printTrace(message),
         loadStrategy: RequireStrategy(
@@ -627,6 +630,7 @@ class WebDevFS implements DevFS {
     @required this.packagesFilePath,
     @required this.urlTunneller,
     @required this.useSseForDebugProxy,
+    @required this.useSseForDebugBackend,
     @required this.buildInfo,
     @required this.enableDwds,
     @required this.entrypoint,
@@ -641,6 +645,7 @@ class WebDevFS implements DevFS {
   final String packagesFilePath;
   final UrlTunneller urlTunneller;
   final bool useSseForDebugProxy;
+  final bool useSseForDebugBackend;
   final BuildInfo buildInfo;
   final bool enableDwds;
   final bool testMode;
@@ -708,6 +713,7 @@ class WebDevFS implements DevFS {
       port,
       urlTunneller,
       useSseForDebugProxy,
+      useSseForDebugBackend,
       buildInfo,
       enableDwds,
       entrypoint,

packages/flutter_tools/lib/src/build_runner/resident_web_runner.dart

@@ -448,6 +448,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
           packagesFilePath: packagesFilePath,
           urlTunneller: urlTunneller,
           useSseForDebugProxy: debuggingOptions.webUseSseForDebugProxy,
+          useSseForDebugBackend: debuggingOptions.webUseSseForDebugBackend,
           buildInfo: debuggingOptions.buildInfo,
           enableDwds: _enableDwds,
           entrypoint: globals.fs.file(target).uri,

packages/flutter_tools/lib/src/commands/run.dart

@@ -374,6 +374,7 @@ class RunCommand extends RunCommandBase {
         hostname: featureFlags.isWebEnabled ? stringArg('web-hostname') : '',
         port: featureFlags.isWebEnabled ? stringArg('web-port') : '',
         webUseSseForDebugProxy: featureFlags.isWebEnabled && stringArg('web-server-debug-protocol') == 'sse',
+        webUseSseForDebugBackend: featureFlags.isWebEnabled && stringArg('web-server-debug-backend-protocol') == 'sse',
         webEnableExposeUrl: featureFlags.isWebEnabled && boolArg('web-allow-expose-url'),
         webRunHeadless: featureFlags.isWebEnabled && boolArg('web-run-headless'),
         webBrowserDebugPort: browserDebugPort,
@@ -400,6 +401,7 @@ class RunCommand extends RunCommandBase {
         hostname: featureFlags.isWebEnabled ? stringArg('web-hostname') : '',
         port: featureFlags.isWebEnabled ? stringArg('web-port') : '',
         webUseSseForDebugProxy: featureFlags.isWebEnabled && stringArg('web-server-debug-protocol') == 'sse',
+        webUseSseForDebugBackend: featureFlags.isWebEnabled && stringArg('web-server-debug-backend-protocol') == 'sse',
         webEnableExposeUrl: featureFlags.isWebEnabled && boolArg('web-allow-expose-url'),
         webRunHeadless: featureFlags.isWebEnabled && boolArg('web-run-headless'),
         webBrowserDebugPort: browserDebugPort,

packages/flutter_tools/lib/src/device.dart

@@ -738,6 +738,7 @@ class DebuggingOptions {
     this.port,
     this.webEnableExposeUrl,
     this.webUseSseForDebugProxy = true,
+    this.webUseSseForDebugBackend = true,
     this.webRunHeadless = false,
     this.webBrowserDebugPort,
     this.webEnableExpressionEvaluation = false,
@@ -751,6 +752,7 @@ class DebuggingOptions {
       this.hostname,
       this.webEnableExposeUrl,
       this.webUseSseForDebugProxy = true,
+      this.webUseSseForDebugBackend = true,
       this.webRunHeadless = false,
       this.webBrowserDebugPort,
       this.cacheSkSL = false,
@@ -797,6 +799,7 @@ class DebuggingOptions {
   final String hostname;
   final bool webEnableExposeUrl;
   final bool webUseSseForDebugProxy;
+  final bool webUseSseForDebugBackend;
 
   /// Whether to run the browser in headless mode.
   ///

packages/flutter_tools/lib/src/runner/flutter_command.dart

@@ -184,11 +184,20 @@ abstract class FlutterCommand extends Command<void> {
       allowed: <String>['sse', 'ws'],
       defaultsTo: 'sse',
       help: 'The protocol (SSE or WebSockets) to use for the debug service proxy '
-      'when using the Web Server device and Dart Debugger extension. '
+      'when using the Web Server device and Dart Debug extension. '
       'This is useful for editors/debug adapters that do not support debugging '
       'over SSE (the default protocol for Web Server/Dart Debugger extension).',
       hide: hide,
     );
+    argParser.addOption('web-server-debug-backend-protocol',
+      allowed: <String>['sse', 'ws'],
+      defaultsTo: 'sse',
+      help: 'The protocol (SSE or WebSockets) to use for the Dart Debug Extension '
+      'backend service when using the Web Server device. '
+      'Using WebSockets can improve performance but may fail when connecting through '
+      'some proxy servers.',
+      hide: hide,
+    );
     argParser.addFlag('web-allow-expose-url',
       defaultsTo: false,
       help: 'Enables daemon-to-editor requests (app.exposeUrl) for exposing URLs '

packages/flutter_tools/test/general.shard/web/devfs_web_test.dart

@@ -461,6 +461,7 @@ void main() {
       packagesFilePath: '.packages',
       urlTunneller: null,
       useSseForDebugProxy: true,
+      useSseForDebugBackend: true,
       buildInfo: const BuildInfo(
         BuildMode.debug,
         '',
@@ -572,6 +573,7 @@ void main() {
       packagesFilePath: '.packages',
       urlTunneller: null,
       useSseForDebugProxy: true,
+      useSseForDebugBackend: true,
       buildInfo: const BuildInfo(
         BuildMode.debug,
         '',
@@ -680,6 +682,7 @@ void main() {
       packagesFilePath: '.packages',
       urlTunneller: null,
       useSseForDebugProxy: true,
+      useSseForDebugBackend: true,
       buildInfo: BuildInfo.debug,
       enableDwds: false,
       entrypoint: Uri.base,
@@ -721,6 +724,7 @@ void main() {
       packagesFilePath: '.packages',
       urlTunneller: null,
       useSseForDebugProxy: true,
+      useSseForDebugBackend: true,
       buildInfo: const BuildInfo(
         BuildMode.debug,
         '',