[flutter_tools] retry sever socket setup (and port selection if port is unspecified) (#69351)

Fixes #69348

If the web development server fails to bind, then retry up to 5 times. If a port was not provided, select a new free port each time.

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

@@ -136,6 +136,8 @@ class WebAssetServer implements AssetReader {
   final Map<String, String> _modules;
   final Map<String, String> _digests;
 
+  int get selectedPort => _httpServer.port;
+
   void performRestart(List<String> modules) {
     for (final String module in modules) {
       // We skip computing the digest by using the hashCode of the underlying buffer.
@@ -171,14 +173,27 @@ class WebAssetServer implements AssetReader {
     bool testMode = false,
     DwdsLauncher dwdsLauncher = Dwds.start,
   }) async {
-    try {
     InternetAddress address;
     if (hostname == 'any') {
       address = InternetAddress.anyIPv4;
     } else {
       address = (await InternetAddress.lookup(hostname)).first;
     }
-      final HttpServer httpServer = await HttpServer.bind(address, port);
+    HttpServer httpServer;
+    dynamic lastError;
+    for (int i = 0; i < 5; i += 1) {
+      try {
+        httpServer = await HttpServer.bind(address, port ?? await globals.os.findFreePort());
+        break;
+      } on SocketException catch (error) {
+        lastError = error;
+        await Future<void>.delayed(const Duration(milliseconds: 100));
+      }
+    }
+    if (httpServer == null) {
+      throwToolExit('Failed to bind web development server:\n$lastError');
+    }
+
     // Allow rendering in a iframe.
     httpServer.defaultResponseHeaders.remove('x-frame-options', 'SAMEORIGIN');
 
@@ -257,10 +272,13 @@ class WebAssetServer implements AssetReader {
       useSseForDebugBackend: useSseForDebugBackend,
       serveDevTools: false,
       loadStrategy: FrontendServerRequireStrategyProvider(
-                  ReloadConfiguration.none, server, _digestProvider)
+        ReloadConfiguration.none,
-              .strategy,
+        server,
+        _digestProvider,
+      ).strategy,
       expressionCompiler: expressionCompiler,
-          spawnDds: true);
+      spawnDds: true,
+    );
     shelf.Pipeline pipeline = const shelf.Pipeline();
     if (enableDwds) {
       pipeline = pipeline.addMiddleware(middleware);
@@ -273,11 +291,6 @@ class WebAssetServer implements AssetReader {
     shelf.serveRequests(httpServer, cascade.handler);
     server.dwds = dwds;
     return server;
-    } on SocketException catch (err) {
-      throwToolExit('Failed to bind web development server:\n$err');
-    }
-    assert(false);
-    return null;
   }
 
   final BuildInfo _buildInfo;
@@ -709,7 +722,7 @@ class WebDevFS implements DevFS {
   /// server.
   WebDevFS({
     @required this.hostname,
-    @required this.port,
+    @required int port,
     @required this.packagesFilePath,
     @required this.urlTunneller,
     @required this.useSseForDebugProxy,
@@ -721,11 +734,10 @@ class WebDevFS implements DevFS {
     @required this.chromiumLauncher,
     @required this.nullAssertions,
     this.testMode = false,
-  });
+  }) : _port = port;
 
   final Uri entrypoint;
   final String hostname;
-  final int port;
   final String packagesFilePath;
   final UrlTunneller urlTunneller;
   final bool useSseForDebugProxy;
@@ -736,6 +748,7 @@ class WebDevFS implements DevFS {
   final ExpressionCompiler expressionCompiler;
   final ChromiumLauncher chromiumLauncher;
   final bool nullAssertions;
+  final int _port;
 
   WebAssetServer webAssetServer;
 
@@ -800,7 +813,7 @@ class WebDevFS implements DevFS {
     webAssetServer = await WebAssetServer.start(
       chromiumLauncher,
       hostname,
-      port,
+      _port,
       urlTunneller,
       useSseForDebugProxy,
       useSseForDebugBackend,
@@ -810,15 +823,16 @@ class WebDevFS implements DevFS {
       expressionCompiler,
       testMode: testMode,
     );
+    final int selectedPort = webAssetServer.selectedPort;
     if (buildInfo.dartDefines.contains('FLUTTER_WEB_AUTO_DETECT=true')) {
       webAssetServer.webRenderer = WebRendererMode.autoDetect;
     } else if (buildInfo.dartDefines.contains('FLUTTER_WEB_USE_SKIA=true')) {
       webAssetServer.webRenderer = WebRendererMode.canvaskit;
     }
     if (hostname == 'any') {
-      _baseUri = Uri.http('localhost:$port', '');
+      _baseUri = Uri.http('localhost:$selectedPort', '');
     } else {
-      _baseUri = Uri.http('$hostname:$port', '');
+      _baseUri = Uri.http('$hostname:$selectedPort', '');
     }
     return _baseUri;
   }

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

@@ -483,11 +483,6 @@ class _ResidentWebRunner extends ResidentWebRunner {
       'Launching ${globals.fsUtils.getDisplayPath(target)} '
       'on ${device.device.name} in $modeName mode...',
     );
-    final String effectiveHostname = debuggingOptions.hostname ?? 'localhost';
-    final int hostPort = debuggingOptions.port == null
-        ? await globals.os.findFreePort()
-        : int.tryParse(debuggingOptions.port);
-
     if (device.device is ChromiumDevice) {
       _chromiumLauncher = (device.device as ChromiumDevice).chromeLauncher;
     }
@@ -498,10 +493,11 @@ class _ResidentWebRunner extends ResidentWebRunner {
           debuggingOptions.webEnableExpressionEvaluation
               ? WebExpressionCompiler(device.generator)
               : null;
-
         device.devFS = WebDevFS(
-          hostname: effectiveHostname,
+          hostname: debuggingOptions.hostname ?? 'localhost',
-          port: hostPort,
+          port: debuggingOptions.port != null
+            ? int.tryParse(debuggingOptions.port)
+            : null,
           packagesFilePath: packagesFilePath,
           urlTunneller: urlTunneller,
           useSseForDebugProxy: debuggingOptions.webUseSseForDebugProxy,

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

@@ -699,7 +699,7 @@ void main() {
       contains('GENERATED'));
 
     // served on localhost
-    expect(uri, Uri.http('localhost:0', ''));
+    expect(uri.host, 'localhost');
 
     await webDevFS.destroy();
   }, overrides: <Type, Generator>{
@@ -813,7 +813,7 @@ void main() {
       contains('GENERATED'));
 
     // served on localhost
-    expect(uri, Uri.http('localhost:0', ''));
+    expect(uri.host, 'localhost');
 
     await webDevFS.destroy();
   }, overrides: <Type, Generator>{
@@ -859,7 +859,7 @@ void main() {
 
     final Uri uri = await webDevFS.create();
 
-    expect(uri, Uri.http('localhost:0', ''));
+    expect(uri.host, 'localhost');
     await webDevFS.destroy();
   }));