[cryptography_flutter] Fix platform conditions

cryptography_flutter/lib/src/_internal.dart

@@ -18,18 +18,13 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 
 import '../cryptography_flutter.dart';
-import '_internal_impl_non_browser.dart'
-    if (dart.library.html) '_internal_impl_browser.dart';
-
-export '_internal_impl_non_browser.dart'
-    if (dart.library.html) '_internal_impl_browser.dart';
 
 const MethodChannel _methodChannel = MethodChannel('cryptography_flutter');
 
-bool hasSeenMissingPluginException = false;
+bool get isAndroid => defaultTargetPlatform == TargetPlatform.android;
 
-/// True if the platform is iOS and Mac OS X.
-bool get isCupertino => isIOS || isMacOS;
+bool get isCupertino => (defaultTargetPlatform == TargetPlatform.iOS ||
+    defaultTargetPlatform == TargetPlatform.macOS);
 
 /// Returns the bytes as [Uint8List].
 Uint8List asUint8List(List<int> bytes) {
@@ -40,18 +35,6 @@ Uint8List asUint8List(List<int> bytes) {
       : Uint8List.fromList(bytes);
 }
 
-final Future<bool> _isPluginAvailable = () async {
-  try {
-    await _methodChannel.invokeMethod('encrypt', {});
-    return true;
-  } on MissingPluginException {
-    hasSeenMissingPluginException = true;
-    return false;
-  } catch (e) {
-    return true;
-  }
-}();
-
 /// Invokes plugin method.
 ///
 /// Throws [CryptographyUnsupportedError] if the platform is web or plugin is
@@ -61,7 +44,7 @@ Future<Map> invokeMethod(String name, Map<String, Object?> arguments,
   if (kIsWeb) {
     throw UnsupportedError('Running in a browser.');
   }
-  final isPluginAvailable = await _isPluginAvailable;
+  final isPluginAvailable = FlutterCryptography.isPluginPresent;
   if (!isPluginAvailable) {
     throw UnsupportedError('Unsupported platform.');
   }
@@ -78,10 +61,6 @@ Future<Map> invokeMethod(String name, Map<String, Object?> arguments,
   }
   try {
     return await _methodChannel.invokeMethod(name, arguments) as Map;
-  } on MissingPluginException catch (error, stackTrace) {
-    // Update the top-level variable
-    hasSeenMissingPluginException = true;
-    throw UnsupportedError('Caught: $error\n$stackTrace');
   } on PlatformException catch (error) {
     if (error.code == 'UNSUPPORTED_ALGORITHM') {
       throw UnsupportedError(

cryptography_flutter/lib/src/flutter/flutter_ecdh.dart

@@ -16,6 +16,7 @@ import 'package:cryptography/cryptography.dart';
 import 'package:flutter/foundation.dart';
 import 'package:flutter/services.dart';
 
+import '../../cryptography_flutter.dart';
 import '../_flutter_cryptography_implementation.dart';
 import '../_internal.dart';
 
@@ -57,8 +58,8 @@ class FlutterEcdh extends Ecdh implements PlatformCryptographicAlgorithm {
         super.constructor();
 
   @override
-  bool get isSupportedPlatform => isAndroid || isCupertino;
   bool get isSupportedPlatform => FlutterCryptography.isPluginPresent && (isAndroid || isCupertino);
+
   String get _curveName {
     switch (keyPairType) {
       case KeyPairType.p256:

cryptography_flutter/lib/src/flutter_cryptography.dart

@@ -20,7 +20,6 @@ import 'package:cryptography_flutter/src/flutter/flutter_hmac.dart';
 import 'package:flutter/foundation.dart';
 
 import '../cryptography_flutter.dart';
-import '_internal.dart';
 
 /// An implementation [Cryptography] that uses native operating system APIs.
 ///
@@ -41,14 +40,14 @@ import '_internal.dart';
 class FlutterCryptography extends BrowserCryptography {
   /// Either [FlutterCryptography] or [BrowserCryptography] depending on
   /// [FlutterCryptography.isPluginPresent].
-  static final Cryptography defaultInstance =
-      kIsWeb ? BrowserCryptography.defaultInstance : FlutterCryptography();
+  static final Cryptography defaultInstance = isPluginPresent
+      ? FlutterCryptography()
+      : BrowserCryptography.defaultInstance;
 
-  /// Tells whether the current platform has a plugin.
-  ///
-  /// Only Android, iOS, and Mac OS X are supported at the moment.
-  static bool get isPluginPresent =>
-      !kIsWeb && !hasSeenMissingPluginException && (isAndroid || isCupertino);
+  static bool _hasInitializedPlugin = false;
+
+  /// Tells whether registerWith() has been called.
+  static bool get isPluginPresent => !kIsWeb && _hasInitializedPlugin;
 
   Chacha20? _chacha20Poly1305Aead;
   Ed25519? _ed25519;
@@ -125,15 +124,6 @@ class FlutterCryptography extends BrowserCryptography {
     return super.ecdsaP256(hashAlgorithm);
   }
 
-  @override
-  Hmac hmac(HashAlgorithm hashAlgorithm) {
-    final impl = FlutterHmac(hashAlgorithm);
-    if (impl.isSupportedPlatform) {
-      return impl;
-    }
-    return super.hmac(hashAlgorithm);
-  }
-
   @override
   Ecdsa ecdsaP384(HashAlgorithm hashAlgorithm) {
     final impl = FlutterEcdsa.p384(hashAlgorithm);
@@ -160,6 +150,15 @@ class FlutterCryptography extends BrowserCryptography {
     return _ed25519 ??= _chooseEd25519();
   }
 
+  @override
+  Hmac hmac(HashAlgorithm hashAlgorithm) {
+    final impl = FlutterHmac(hashAlgorithm);
+    if (impl.isSupportedPlatform) {
+      return impl;
+    }
+    return super.hmac(hashAlgorithm);
+  }
+
   @override
   Pbkdf2 pbkdf2({
     required MacAlgorithm macAlgorithm,
@@ -247,6 +246,7 @@ class FlutterCryptography extends BrowserCryptography {
 
   /// Called by Flutter when the plugin is registered.
   static void registerWith() {
+    _hasInitializedPlugin = true;
     Cryptography.instance = defaultInstance;
   }
 }

cryptography_flutter/pubspec.yaml

@@ -42,10 +42,6 @@ flutter:
       ios:
         pluginClass: CryptographyFlutterPlugin
         dartPluginClass: FlutterCryptography
-      linux:
-        dartPluginClass: FlutterCryptography
       macos:
         pluginClass: CryptographyFlutterPlugin
         dartPluginClass: FlutterCryptography
-      windows:
-        dartPluginClass: FlutterCryptography