fix(share_plus): Fix url encoding for web, Linux and Windows

packages/share_plus_linux/lib/share_plus_linux.dart

@@ -14,9 +14,22 @@ class ShareLinux extends SharePlatform {
     String text, {
     String? subject,
     Rect? sharePositionOrigin,
-  }) {
-    final uri = Uri.encodeFull('mailto:?subject=$subject&body=$text');
-    return launch(uri);
+  }) async {
+    final queryParameters = {
+      if (subject != null) 'subject': subject,
+      'body': text,
+    };
+
+    final uri = Uri(
+      scheme: 'mailto',
+      queryParameters: queryParameters,
+    );
+
+    if (await canLaunch(uri.toString())) {
+      await launch(uri.toString());
+    } else {
+      throw Exception('Unable to share on linux');
+    }
   }
 
   /// Share files.

packages/share_plus_linux/test/share_plus_linux_test.dart

@@ -0,0 +1,51 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:share_plus_linux/share_plus_linux.dart';
+import 'package:url_launcher_platform_interface/url_launcher_platform_interface.dart';
+import 'package:url_launcher_platform_interface/link.dart';
+
+void main() {
+  test('url encoding is correct', () {
+    final mock = MockUrlLauncherPlatform();
+    UrlLauncherPlatform.instance = mock;
+
+    ShareLinux().share('foo&bar', subject: 'bar&foo');
+
+    expect(mock.url, 'mailto:?subject=bar%26foo&body=foo%26bar');
+  });
+
+  test('throws when url_launcher can\'t launch uri', () async {
+    final mock = MockUrlLauncherPlatform();
+    mock.canLaunchMockValue = false;
+    UrlLauncherPlatform.instance = mock;
+
+    expect(() async => await ShareLinux().share('foo bar'), throwsException);
+  });
+}
+
+class MockUrlLauncherPlatform extends UrlLauncherPlatform {
+  String? url;
+  bool canLaunchMockValue = true;
+
+  @override
+  LinkDelegate? get linkDelegate => throw UnimplementedError();
+
+  @override
+  Future<bool> canLaunch(String url) async {
+    return canLaunchMockValue;
+  }
+
+  @override
+  Future<bool> launch(
+    String url, {
+    required bool useSafariVC,
+    required bool useWebView,
+    required bool enableJavaScript,
+    required bool enableDomStorage,
+    required bool universalLinksOnly,
+    required Map<String, String> headers,
+    String? webOnlyWindowName,
+  }) async {
+    this.url = url;
+    return true;
+  }
+}

packages/share_plus_web/lib/share_plus_web.dart

@@ -19,9 +19,8 @@ class SharePlusPlugin extends SharePlatform {
   SharePlusPlugin({@visibleForTesting html.Navigator? debugNavigator})
       : _navigator = debugNavigator ?? html.window.navigator;
 
-  @override
-
   /// Share text
+  @override
   Future<void> share(
     String text, {
     String? subject,
@@ -31,14 +30,26 @@ class SharePlusPlugin extends SharePlatform {
       await _navigator.share({'title': subject, 'text': text});
     } catch (e) {
       //Navigator is not available or the webPage is not served on https
-      final uri = Uri.encodeFull('mailto:?subject=$subject&body=$text');
-      await launch(uri);
+      final queryParameters = {
+        if (subject != null) 'subject': subject,
+        'body': text,
+      };
+
+      final uri = Uri(
+        scheme: 'mailto',
+        queryParameters: queryParameters,
+      );
+
+      if (await canLaunch(uri.toString())) {
+        await launch(uri.toString());
+      } else {
+        throw Exception('Unable to share on web');
+      }
     }
   }
 
-  @override
-
   /// Share files
+  @override
   Future<void> shareFiles(
     List<String> paths, {
     List<String>? mimeTypes,

packages/share_plus_windows/lib/share_plus_windows.dart

@@ -14,9 +14,22 @@ class ShareWindows extends SharePlatform {
     String text, {
     String? subject,
     Rect? sharePositionOrigin,
-  }) {
-    final uri = Uri.encodeFull('mailto:?subject=$subject&body=$text');
-    return launch(uri);
+  }) async {
+    final queryParameters = {
+      if (subject != null) 'subject': subject,
+      'body': text,
+    };
+
+    final uri = Uri(
+      scheme: 'mailto',
+      queryParameters: queryParameters,
+    );
+
+    if (await canLaunch(uri.toString())) {
+      await launch(uri.toString());
+    } else {
+      throw Exception('Unable to share on windows');
+    }
   }
 
   /// Share files.

packages/share_plus_windows/test/share_plus_windows_test.dart

@@ -0,0 +1,51 @@
+import 'package:flutter_test/flutter_test.dart';
+import 'package:share_plus_windows/share_plus_windows.dart';
+import 'package:url_launcher_platform_interface/url_launcher_platform_interface.dart';
+import 'package:url_launcher_platform_interface/link.dart';
+
+void main() {
+  test('url encoding is correct', () {
+    final mock = MockUrlLauncherPlatform();
+    UrlLauncherPlatform.instance = mock;
+
+    ShareWindows().share('foo&bar', subject: 'bar&foo');
+
+    expect(mock.url, 'mailto:?subject=bar%26foo&body=foo%26bar');
+  });
+
+  test('throws when url_launcher can\'t launch uri', () async {
+    final mock = MockUrlLauncherPlatform();
+    mock.canLaunchMockValue = false;
+    UrlLauncherPlatform.instance = mock;
+
+    expect(() async => await ShareWindows().share('foo bar'), throwsException);
+  });
+}
+
+class MockUrlLauncherPlatform extends UrlLauncherPlatform {
+  String? url;
+  bool canLaunchMockValue = true;
+
+  @override
+  LinkDelegate? get linkDelegate => throw UnimplementedError();
+
+  @override
+  Future<bool> canLaunch(String url) async {
+    return canLaunchMockValue;
+  }
+
+  @override
+  Future<bool> launch(
+    String url, {
+    required bool useSafariVC,
+    required bool useWebView,
+    required bool enableJavaScript,
+    required bool enableDomStorage,
+    required bool universalLinksOnly,
+    required Map<String, String> headers,
+    String? webOnlyWindowName,
+  }) async {
+    this.url = url;
+    return true;
+  }
+}