Improve network resources doctor check (flutter#120417)

...and various other minor cleanup:

* Moved "FLUTTER_STORAGE_BASE_URL" into a constant throughout the code. There are other strings that we should do that to but this one was relevant to the code I was changing.

* Fixed the logger's handling of slow warnings. Previously it deleted too much text. Fixed the test for that to actually verify it entirely, too.

* Made the logger delete the slow warning when it's finished.

* Fixed 'Please choose one (To quit, press "q/Q")' message to be the cleaner 'Please choose one (or "q" to quit)'.

* Added a debug toString to ValidationResult for debugging purposes (not used).

* In http_host_validator:

  - Shortened constant names to be clearer (e.g. kPubDevHttpHost -> kPubDev).
  - Added GitHub as a tested host since when you run `flutter` we hit that immediately.
  - Renamed the check "Network resources".
  - Updated the `slowWarning` of the check to say which hosts are pending.
  - Removed all timeout logic. Timeouts violate our style guide.
  - Removed `int.parse(... ?? '10')`; passing a constant to `int.parse` is inefficient.
  - Replaced the `_HostValidationResult` class with `String?` for simplicity.
  - Improved the error messages to be more detailed.
  - Removed all checks that dependened on the stringification of exceptions. That's very brittle.
  - Added a warning specifically for HandshakeException that talks about the implications (MITM attacks).
  - Replaced exception-message-parsing logic with just calling `Uri.tryParse` and validating the result.
  - Replaced a lot of list-filtering logic with just a single for loop to check the results.
  - Replaced code that added a constant to a known-empty list with just returning a constant list.
  - Revamped the logic for deciding which hosts to check to just use a single chain of if/else blocks instead of getters, lists literals with `if` expressions, `??`, functions, etc spread over multiple places in the code.

packages/flutter_tools/lib/src/android/gradle.dart

@@ -16,6 +16,7 @@ import '../base/deferred_component.dart';
 import '../base/file_system.dart';
 import '../base/io.dart';
 import '../base/logger.dart';
+import '../base/net.dart';
 import '../base/platform.dart';
 import '../base/process.dart';
 import '../base/terminal.dart';
@@ -696,7 +697,7 @@ void printHowToConsumeAar({
   1. Open ${fileSystem.path.join('<host>', 'app', 'build.gradle')}
   2. Ensure you have the repositories configured, otherwise add them:
 
-      String storageUrl = System.env.FLUTTER_STORAGE_BASE_URL ?: "https://storage.googleapis.com"
+      String storageUrl = System.env.$kFlutterStorageBaseUrl ?: "https://storage.googleapis.com"
       repositories {
         maven {
             url '${repoDirectory.path}'

packages/flutter_tools/lib/src/base/logger.dart

@@ -1360,7 +1360,9 @@ class AnonymousSpinnerStatus extends Status {
     if (seemsSlow) {
       if (!timedOut) {
         timedOut = true;
-        _clear(_currentLineLength);
+        if (_currentLineLength > _lastAnimationFrameLength) {
+          _clear(_currentLineLength - _lastAnimationFrameLength);
+        }
       }
       if (_slowWarning == '' && slowWarningCallback != null) {
         _slowWarning = slowWarningCallback!();
@@ -1398,7 +1400,8 @@ class AnonymousSpinnerStatus extends Status {
     assert(timer!.isActive);
     timer?.cancel();
     timer = null;
-    _clear(_lastAnimationFrameLength);
+    _clear(_lastAnimationFrameLength + _slowWarning.length);
+    _slowWarning = '';
     _lastAnimationFrameLength = 0;
     super.finish();
   }

packages/flutter_tools/lib/src/base/net.dart

@@ -14,6 +14,7 @@ import 'logger.dart';
 import 'platform.dart';
 
 const int kNetworkProblemExitCode = 50;
+const String kFlutterStorageBaseUrl = 'FLUTTER_STORAGE_BASE_URL';
 
 typedef HttpClientFactory = HttpClient Function();
 
@@ -106,15 +107,16 @@ class Net {
       }
       response = await request.close();
     } on ArgumentError catch (error) {
-      final String? overrideUrl = _platform.environment['FLUTTER_STORAGE_BASE_URL'];
+      final String? overrideUrl = _platform.environment[kFlutterStorageBaseUrl];
       if (overrideUrl != null && url.toString().contains(overrideUrl)) {
         _logger.printError(error.toString());
         throwToolExit(
-          'The value of FLUTTER_STORAGE_BASE_URL ($overrideUrl) could not be '
+          'The value of $kFlutterStorageBaseUrl ($overrideUrl) could not be '
           'parsed as a valid url. Please see https://flutter.dev/community/china '
           'for an example of how to use it.\n'
           'Full URL: $url',
-          exitCode: kNetworkProblemExitCode,);
+          exitCode: kNetworkProblemExitCode,
+        );
       }
       _logger.printError(error.toString());
       rethrow;

packages/flutter_tools/lib/src/base/user_messages.dart

@@ -274,7 +274,7 @@ class UserMessages {
       'Found $count devices with name or id matching $deviceId:';
   String get flutterMultipleDevicesFound => 'Multiple devices found:';
   String flutterChooseDevice(int option, String name, String deviceId) => '[$option]: $name ($deviceId)';
-  String get flutterChooseOne => 'Please choose one (To quit, press "q/Q")';
+  String get flutterChooseOne => 'Please choose one (or "q" to quit)';
   String get flutterSpecifyDeviceWithAllOption =>
       'More than one device connected; please specify a device with '
       "the '-d <deviceId>' flag, or use '-d all' to act on all devices.";

packages/flutter_tools/lib/src/cache.dart

@@ -107,8 +107,8 @@ class DevelopmentArtifact {
 ///
 /// To enable Flutter users in these environments, the Flutter tool supports
 /// custom artifact mirrors that the administrators of such environments may
-/// provide. To use an artifact mirror, the user defines the
-/// `FLUTTER_STORAGE_BASE_URL` environment variable that points to the mirror.
+/// provide. To use an artifact mirror, the user defines the [kFlutterStorageBaseUrl]
+/// (`FLUTTER_STORAGE_BASE_URL`) environment variable that points to the mirror.
 /// Flutter tool reads this variable and uses it instead of the default URLs.
 ///
 /// For more details on specific URLs used to download artifacts, see
@@ -450,23 +450,23 @@ class Cache {
   /// during the installation of the Flutter SDK.
   ///
   /// By default the base URL is https://storage.googleapis.com. However, if
-  /// `FLUTTER_STORAGE_BASE_URL` environment variable is provided, the
-  /// environment variable value is returned instead.
+  /// `FLUTTER_STORAGE_BASE_URL` environment variable ([kFlutterStorageBaseUrl])
+  /// is provided, the environment variable value is returned instead.
   ///
   /// See also:
   ///
   ///  * [cipdBaseUrl], which determines how CIPD artifacts are fetched.
   ///  * [Cache] class-level dartdocs that explain how artifact mirrors work.
   String get storageBaseUrl {
-    final String? overrideUrl = _platform.environment['FLUTTER_STORAGE_BASE_URL'];
+    final String? overrideUrl = _platform.environment[kFlutterStorageBaseUrl];
     if (overrideUrl == null) {
       return 'https://storage.googleapis.com';
     }
     // verify that this is a valid URI.
     try {
       Uri.parse(overrideUrl);
     } on FormatException catch (err) {
-      throwToolExit('"FLUTTER_STORAGE_BASE_URL" contains an invalid URI:\n$err');
+      throwToolExit('"$kFlutterStorageBaseUrl" contains an invalid URL:\n$err');
     }
     _maybeWarnAboutStorageOverride(overrideUrl);
     return overrideUrl;
@@ -479,8 +479,8 @@ class Cache {
   /// from [storageBaseUrl].
   ///
   /// By default the base URL is https://chrome-infra-packages.appspot.com/dl.
-  /// However, if `FLUTTER_STORAGE_BASE_URL` environment variable is provided,
-  /// then the following value is used:
+  /// However, if `FLUTTER_STORAGE_BASE_URL` environment variable is provided
+  /// ([kFlutterStorageBaseUrl]), then the following value is used:
   ///
   ///     FLUTTER_STORAGE_BASE_URL/flutter_infra_release/cipd
   ///
@@ -492,7 +492,7 @@ class Cache {
   ///    which contains information about CIPD.
   ///  * [Cache] class-level dartdocs that explain how artifact mirrors work.
   String get cipdBaseUrl {
-    final String? overrideUrl = _platform.environment['FLUTTER_STORAGE_BASE_URL'];
+    final String? overrideUrl = _platform.environment[kFlutterStorageBaseUrl];
     if (overrideUrl == null) {
       return 'https://chrome-infra-packages.appspot.com/dl';
     }
@@ -501,7 +501,7 @@ class Cache {
     try {
       original = Uri.parse(overrideUrl);
     } on FormatException catch (err) {
-      throwToolExit('"FLUTTER_STORAGE_BASE_URL" contains an invalid URI:\n$err');
+      throwToolExit('"$kFlutterStorageBaseUrl" contains an invalid URL:\n$err');
     }
 
     final String cipdOverride = original.replace(
@@ -1065,11 +1065,11 @@ class ArtifactUpdater {
         }
         continue;
       } on ArgumentError catch (error) {
-        final String? overrideUrl = _platform.environment['FLUTTER_STORAGE_BASE_URL'];
+        final String? overrideUrl = _platform.environment[kFlutterStorageBaseUrl];
         if (overrideUrl != null && url.toString().contains(overrideUrl)) {
           _logger.printError(error.toString());
           throwToolExit(
-            'The value of FLUTTER_STORAGE_BASE_URL ($overrideUrl) could not be '
+            'The value of $kFlutterStorageBaseUrl ($overrideUrl) could not be '
             'parsed as a valid url. Please see https://flutter.dev/community/china '
             'for an example of how to use it.\n'
             'Full URL: $url',

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

@@ -136,7 +136,7 @@ class UpdatePackagesCommand extends FlutterCommand {
   );
 
   Future<void> _downloadCoverageData() async {
-    final String urlBase = globals.platform.environment['FLUTTER_STORAGE_BASE_URL'] ?? 'https://storage.googleapis.com';
+    final String urlBase = globals.platform.environment[kFlutterStorageBaseUrl] ?? 'https://storage.googleapis.com';
     final Uri coverageUri = Uri.parse('$urlBase/flutter_infra_release/flutter/coverage/lcov.info');
     final List<int>? data = await _net.fetchUrl(
       coverageUri,

packages/flutter_tools/lib/src/doctor.dart

@@ -15,6 +15,7 @@ import 'base/context.dart';
 import 'base/file_system.dart';
 import 'base/io.dart';
 import 'base/logger.dart';
+import 'base/net.dart';
 import 'base/os.dart';
 import 'base/platform.dart';
 import 'base/terminal.dart';
@@ -528,11 +529,11 @@ class FlutterValidator extends DoctorValidator {
       messages.add(ValidationMessage(_userMessages.engineRevision(version.engineRevisionShort)));
       messages.add(ValidationMessage(_userMessages.dartRevision(version.dartSdkVersion)));
       messages.add(ValidationMessage(_userMessages.devToolsVersion(_devToolsVersion())));
-      final String? pubUrl = _platform.environment['PUB_HOSTED_URL'];
+      final String? pubUrl = _platform.environment[kPubDevOverride];
       if (pubUrl != null) {
         messages.add(ValidationMessage(_userMessages.pubMirrorURL(pubUrl)));
       }
-      final String? storageBaseUrl = _platform.environment['FLUTTER_STORAGE_BASE_URL'];
+      final String? storageBaseUrl = _platform.environment[kFlutterStorageBaseUrl];
       if (storageBaseUrl != null) {
         messages.add(ValidationMessage(_userMessages.flutterMirrorURL(storageBaseUrl)));
       }

packages/flutter_tools/lib/src/doctor_validator.dart

@@ -207,6 +207,11 @@ class ValidationResult {
         return 'partial';
     }
   }
+
+  @override
+  String toString() {
+    return '$runtimeType($type, $messages, $statusInfo)';
+  }
 }
 
 /// A status line for the flutter doctor validation to display.