Add a switch to use WebSockets for web debug proxy (#54083)

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

@@ -131,6 +131,7 @@ class WebAssetServer implements AssetReader {
     String hostname,
     int port,
     UrlTunneller urlTunneller,
+    bool useSseForDebugProxy,
     BuildMode buildMode,
     bool enableDwds,
     Uri entrypoint,
@@ -210,6 +211,7 @@ class WebAssetServer implements AssetReader {
         },
         urlEncoder: urlTunneller,
         enableDebugging: true,
+        useSseForDebugProxy: useSseForDebugProxy,
         serveDevTools: false,
         logWriter: (Level logLevel, String message) => globals.printTrace(message),
         loadStrategy: RequireStrategy(
@@ -550,6 +552,7 @@ class WebDevFS implements DevFS {
     @required this.port,
     @required this.packagesFilePath,
     @required this.urlTunneller,
+    @required this.useSseForDebugProxy,
     @required this.buildMode,
     @required this.enableDwds,
     @required this.entrypoint,
@@ -562,6 +565,7 @@ class WebDevFS implements DevFS {
   final int port;
   final String packagesFilePath;
   final UrlTunneller urlTunneller;
+  final bool useSseForDebugProxy;
   final BuildMode buildMode;
   final bool enableDwds;
   final bool testMode;
@@ -623,6 +627,7 @@ class WebDevFS implements DevFS {
       hostname,
       port,
       urlTunneller,
+      useSseForDebugProxy,
       buildMode,
       enableDwds,
       entrypoint,

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

@@ -423,6 +423,7 @@ class _ResidentWebRunner extends ResidentWebRunner {
           port: hostPort,
           packagesFilePath: packagesFilePath,
           urlTunneller: urlTunneller,
+          useSseForDebugProxy: debuggingOptions.webUseSseForDebugProxy,
           buildMode: debuggingOptions.buildInfo.mode,
           enableDwds: _enableDwds,
           entrypoint: globals.fs.file(target).uri,

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

@@ -351,6 +351,7 @@ class RunCommand extends RunCommandBase {
         initializePlatform: boolArg('web-initialize-platform'),
         hostname: featureFlags.isWebEnabled ? stringArg('web-hostname') : '',
         port: featureFlags.isWebEnabled ? stringArg('web-port') : '',
+        webUseSseForDebugProxy: featureFlags.isWebEnabled && stringArg('web-server-debug-protocol') == 'sse',
         webEnableExposeUrl: featureFlags.isWebEnabled && boolArg('web-allow-expose-url'),
         webRunHeadless: featureFlags.isWebEnabled && boolArg('web-run-headless'),
         webBrowserDebugPort: browserDebugPort,
@@ -376,6 +377,7 @@ class RunCommand extends RunCommandBase {
         initializePlatform: boolArg('web-initialize-platform'),
         hostname: featureFlags.isWebEnabled ? stringArg('web-hostname') : '',
         port: featureFlags.isWebEnabled ? stringArg('web-port') : '',
+        webUseSseForDebugProxy: featureFlags.isWebEnabled && stringArg('web-server-debug-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

@@ -585,6 +585,7 @@ class DebuggingOptions {
     this.hostname,
     this.port,
     this.webEnableExposeUrl,
+    this.webUseSseForDebugProxy = true,
     this.webRunHeadless = false,
     this.webBrowserDebugPort,
     this.vmserviceOutFile,
@@ -596,6 +597,7 @@ class DebuggingOptions {
       this.port,
       this.hostname,
       this.webEnableExposeUrl,
+      this.webUseSseForDebugProxy = true,
       this.webRunHeadless = false,
       this.webBrowserDebugPort,
       this.cacheSkSL = false,
@@ -640,6 +642,7 @@ class DebuggingOptions {
   final String port;
   final String hostname;
   final bool webEnableExposeUrl;
+  final bool webUseSseForDebugProxy;
 
   /// Whether to run the browser in headless mode.
   ///

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

@@ -168,6 +168,15 @@ abstract class FlutterCommand extends Command<void> {
         'will select a random open port on the host.',
       hide: hide,
     );
+    argParser.addOption('web-server-debug-protocol',
+      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. '
+      '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.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

@@ -376,6 +376,7 @@ void main() {
       port: 0,
       packagesFilePath: '.packages',
       urlTunneller: null,
+      useSseForDebugProxy: true,
       buildMode: BuildMode.debug,
       enableDwds: false,
       entrypoint: Uri.base,
@@ -445,6 +446,7 @@ void main() {
       'localhost',
       8123,
       (String url) => null,
+      true,
       BuildMode.debug,
       true,
       Uri.file('test.dart'),
@@ -468,11 +470,12 @@ void main() {
         expect(verbose, null);
         expect(enableDebugging, true);
         expect(enableDebugExtension, true);
+        expect(useSseForDebugProxy, true);
 
         return MockDwds();
       });
 
-      await server.dispose();
+    await server.dispose();
   }));
 }