Retry when safaridriver fails (#48791)

Starting `safaridriver` is flakey sometimes on macOS 13. It will occasionally error with "Operation not permitted". As a workaround, if it fails with that message, retry starting `safaridriver`.

Fixes flutter/flutter#136972.

Example of fix on macOS 13 bot: https://ci.chromium.org/ui/p/flutter/builders/try/Mac%20Engine%20Drone/564967/overview
Note: The test is still failing due to flutter/flutter#136279, but you can see it first has error "Operation not permitted" and retries and connects on second attempt.

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: vashworth

lib/web_ui/dev/safari_macos.dart

@@ -3,6 +3,7 @@
 // found in the LICENSE file.
 
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
 
 import 'package:test_api/src/backend/runtime.dart';
@@ -23,6 +24,58 @@ class SafariMacOsEnvironment extends WebDriverBrowserEnvironment {
   @override
   Uri get driverUri => Uri(scheme: 'http', host: 'localhost', port: portNumber);
 
+  late Process _driverProcess;
+  int _retryCount = 0;
+  static const int _waitBetweenRetryInSeconds = 1;
+  static const int _maxRetryCount = 10;
+
   @override
   Future<Process> spawnDriverProcess() => Process.start('safaridriver', <String>['-p', portNumber.toString()]);
+
+  @override
+  Future<void> prepare() async {
+    await _startDriverProcess();
+  }
+
+  /// Pick an unused port and start `safaridriver` using that port.
+  ///
+  /// On macOS 13, starting `safaridriver` can be flaky so if it returns an
+  /// "Operation not permitted" error, kill the `safaridriver` process and try
+  /// again with a different port. Wait [_waitBetweenRetryInSeconds] seconds
+  /// between retries. Try up to [_maxRetryCount] times.
+  Future<void> _startDriverProcess() async {
+    _retryCount += 1;
+    if (_retryCount > 1) {
+      await Future<void>.delayed(const Duration(seconds: _waitBetweenRetryInSeconds));
+    }
+    portNumber = await pickUnusedPort();
+
+    print('Attempt $_retryCount to start safaridriver on port $portNumber');
+
+    _driverProcess = await spawnDriverProcess();
+
+    _driverProcess.stderr
+        .transform(utf8.decoder)
+        .transform(const LineSplitter())
+        .listen((String error) {
+      print('[Webdriver][Error] $error');
+      if (_retryCount > _maxRetryCount) {
+        print('[Webdriver][Error] Failed to start after $_maxRetryCount tries.');
+      } else if (error.contains('Operation not permitted')) {
+        _driverProcess.kill();
+        _startDriverProcess();
+      }
+    });
+    _driverProcess.stdout
+        .transform(utf8.decoder)
+        .transform(const LineSplitter())
+        .listen((String log) {
+      print('[Webdriver] $log');
+    });
+  }
+
+  @override
+  Future<void> cleanup() async {
+    _driverProcess.kill();
+  }
 }

lib/web_ui/dev/webdriver_browser.dart

@@ -13,14 +13,14 @@ import 'package:webdriver/async_io.dart' show WebDriver, createDriver;
 import 'browser.dart';
 
 abstract class WebDriverBrowserEnvironment extends BrowserEnvironment {
-  late final int portNumber;
+  late int portNumber;
   late final Process _driverProcess;
 
   Future<Process> spawnDriverProcess();
   Uri get driverUri;
 
   /// Finds and returns an unused port on the test host in the local port range.
-  Future<int> _pickUnusedPort() async {
+  Future<int> pickUnusedPort() async {
     // Use bind to allocate an unused port, then unbind from that port to
     // make it available for use.
     final ServerSocket socket = await ServerSocket.bind('localhost', 0);
@@ -33,7 +33,7 @@ abstract class WebDriverBrowserEnvironment extends BrowserEnvironment {
 
   @override
   Future<void> prepare() async {
-    portNumber = await _pickUnusedPort();
+    portNumber = await pickUnusedPort();
 
     _driverProcess = await spawnDriverProcess();