Use better lints (#704)

* use `package:leancode_lint`

* fix most of lint warnings

* add CODEOWNERS file

Author: bartekpacia

.github/CODEOWNERS

@@ -0,0 +1 @@
+* @bartekpacia

README.md

@@ -249,7 +249,7 @@ following messages.
 <string name="flutter_downloader_notification_paused">Download paused</string>
 ```
 
-You can learn more about localization on Android [here][4]).
+You can learn more about localization on Android [here][4].
 
 ### Install .apk files
 
@@ -300,7 +300,7 @@ final taskId = await FlutterDownloader.enqueue(
 ### Update download progress
 
 ```dart
-FlutterDownloader.registerCallback(callback); // callback is a top-level or static function
+await FlutterDownloader.registerCallback(callback); // callback is a top-level or static function
 ```
 
 **Important**
@@ -445,16 +445,12 @@ plugin is missing some feature.
 
 Pull request are also very welcome!
 
-[fluttercommunity_badge]:
-    https://fluttercommunity.dev/_github/header/flutter_downloader
+[fluttercommunity_badge]: https://fluttercommunity.dev/_github/header/flutter_downloader
 [fluttercommunity_link]: https://github.com/fluttercommunity/community
 [pub_badge]: https://img.shields.io/pub/v/flutter_downloader.svg
 [pub_link]: https://pub.dartlang.org/packages/flutter_downloader
-[work_manager]:
-    https://developer.android.com/topic/libraries/architecture/workmanager
-[url_session_download_task]:
-    https://developer.apple.com/documentation/foundation/nsurlsessiondownloadtask?language=objc
-[android_9_cleartext_traffic]:
-    https://medium.com/@son.rommer/fix-cleartext-traffic-error-in-android-9-pie-2f4e9e2235e6
+[work_manager]: https://developer.android.com/topic/libraries/architecture/workmanager
+[url_session_download_task]: https://developer.apple.com/documentation/foundation/nsurlsessiondownloadtask?language=objc
+[android_9_cleartext_traffic]: https://medium.com/@son.rommer/fix-cleartext-traffic-error-in-android-9-pie-2f4e9e2235e6
 [3]: https://medium.com/@guerrix/info-plist-localization-ad5daaea732a
 [4]: https://developer.android.com/training/basics/supporting-devices/languages

analysis_options.yaml

@@ -1 +1 @@
-include: package:flutter_lints/flutter.yaml
+include: package:leancode_lint/analysis_options_package.yaml

lib/flutter_downloader.dart

@@ -13,4 +13,5 @@
 library flutter_downloader;
 
 export 'src/downloader.dart';
+export 'src/exceptions.dart';
 export 'src/models.dart';

lib/src/callback_dispatcher.dart

@@ -6,32 +6,31 @@ import 'package:flutter/widgets.dart';
 
 import 'models.dart';
 
-// pragma annotation is needed to avoid tree shaking in release mode
-// https://github.com/dart-lang/sdk/blob/master/runtime/docs/compiler/aot/entry_point_pragma.md
+/// Pragma annotation is needed to avoid tree shaking in release mode. See
+/// https://github.com/dart-lang/sdk/blob/master/runtime/docs/compiler/aot/entry_point_pragma.md
 @pragma('vm:entry-point')
 void callbackDispatcher() {
-  const MethodChannel backgroundChannel =
-      MethodChannel('vn.hunghd/downloader_background');
+  const backgroundChannel = MethodChannel('vn.hunghd/downloader_background');
 
   WidgetsFlutterBinding.ensureInitialized();
 
-  backgroundChannel.setMethodCallHandler((MethodCall call) async {
-    final args = call.arguments;
-    final handle = CallbackHandle.fromRawHandle(args[0]);
-    final callback = PluginUtilities.getCallbackFromHandle(handle);
-
-    if (callback == null) {
-      // ignore: avoid_print
-      print('fatal error: could not find callback');
-      exit(1);
-    }
-
-    final String id = args[1];
-    final int status = args[2];
-    final int progress = args[3];
-
-    callback(id, DownloadTaskStatus(status), progress);
-  });
-
-  backgroundChannel.invokeMethod('didInitializeDispatcher');
+  backgroundChannel
+    ..setMethodCallHandler((call) async {
+      final args = call.arguments as List<dynamic>;
+      final handle = CallbackHandle.fromRawHandle(args[0] as int);
+      final callback = PluginUtilities.getCallbackFromHandle(handle);
+
+      if (callback == null) {
+        // ignore: avoid_print
+        print('fatal error: could not find callback');
+        exit(1);
+      }
+
+      final id = args[1] as String;
+      final status = args[2] as int;
+      final progress = args[3] as int;
+
+      callback(id, DownloadTaskStatus(status), progress);
+    })
+    ..invokeMethod<void>('didInitializeDispatcher');
 }

lib/src/downloader.dart

@@ -1,9 +1,11 @@
 import 'dart:async';
+import 'dart:convert';
 import 'dart:io';
 import 'dart:ui';
 
 import 'package:flutter/services.dart';
 import 'package:flutter/widgets.dart';
+import 'package:flutter_downloader/src/exceptions.dart';
 
 import 'callback_dispatcher.dart';
 import 'models.dart';
@@ -21,9 +23,14 @@ class FlutterDownloader {
   static const _channel = MethodChannel('vn.hunghd/downloader');
 
   static bool _initialized = false;
+
+  /// Whether the plugin is initialized. The plugin must be initialized before
+  /// use.
   static bool get initialized => _initialized;
 
   static bool _debug = false;
+
+  /// If true, more logs are printed.
   static bool get debug => _debug;
 
   /// Initializes the plugin. This must be called before any other method.
@@ -47,10 +54,10 @@ class FlutterDownloader {
     WidgetsFlutterBinding.ensureInitialized();
 
     final callback = PluginUtilities.getCallbackHandle(callbackDispatcher)!;
-    await _channel.invokeMethod('initialize', <dynamic>[
+    await _channel.invokeMethod<void>('initialize', <dynamic>[
       callback.toRawHandle(),
-      debug ? 1 : 0,
-      ignoreSsl ? 1 : 0,
+      if (debug) 1 else 0,
+      if (ignoreSsl) 1 else 0,
     ]);
 
     _initialized = true;
@@ -87,62 +94,78 @@ class FlutterDownloader {
     required String url,
     required String savedDir,
     String? fileName,
-    Map<String, String>? headers,
+    Map<String, String> headers = const {},
     bool showNotification = true,
     bool openFileFromNotification = true,
     bool requiresStorageNotLow = true,
     bool saveInPublicStorage = false,
   }) async {
     assert(_initialized, 'plugin flutter_downloader is not initialized');
-    assert(Directory(savedDir).existsSync(), "savedDir does not exist");
-
-    StringBuffer headerBuilder = StringBuffer();
-    if (headers != null) {
-      headerBuilder.write('{');
-      headerBuilder.writeAll(
-        headers.entries.map((entry) => '"${entry.key}": "${entry.value}"'),
-        ',',
-      );
-      headerBuilder.write('}');
-    }
+    assert(Directory(savedDir).existsSync(), 'savedDir does not exist');
+
     try {
-      String? taskId = await _channel.invokeMethod('enqueue', {
+      final taskId = await _channel.invokeMethod<String>('enqueue', {
         'url': url,
         'saved_dir': savedDir,
         'file_name': fileName,
-        'headers': headerBuilder.toString(),
+        'headers': jsonEncode(headers),
         'show_notification': showNotification,
         'open_file_from_notification': openFileFromNotification,
         'requires_storage_not_low': requiresStorageNotLow,
         'save_in_public_storage': saveInPublicStorage,
       });
+
+      if (taskId == null) {
+        throw const FlutterDownloaderException(
+          message: '`enqueue` returned null taskId',
+        );
+      }
+
       return taskId;
-    } on PlatformException catch (e) {
-      _log('Download task is failed with reason(${e.message})');
-      return null;
+    } on FlutterDownloaderException catch (err) {
+      _log('Failed to enqueue. Reason: ${err.message}');
+    } on PlatformException catch (err) {
+      _log('Failed to enqueue. Reason: ${err.message}');
     }
+
+    return null;
   }
 
   /// Loads all tasks from SQLite database.
   static Future<List<DownloadTask>?> loadTasks() async {
     assert(_initialized, 'plugin flutter_downloader is not initialized');
 
     try {
-      List<dynamic> result = await _channel.invokeMethod('loadTasks');
-      return result
-          .map((item) => DownloadTask(
-              taskId: item['task_id'],
-              status: DownloadTaskStatus(item['status']),
-              progress: item['progress'],
-              url: item['url'],
-              filename: item['file_name'],
-              savedDir: item['saved_dir'],
-              timeCreated: item['time_created']))
-          .toList();
-    } on PlatformException catch (e) {
-      _log(e.message);
+      final result = await _channel.invokeMethod<List<dynamic>>('loadTasks');
+
+      if (result == null) {
+        throw const FlutterDownloaderException(
+          message: '`loadTasks` returned null',
+        );
+      }
+
+      return result.map(
+        (dynamic item) {
+          // item as Map<String, dynamic>; // throws
+
+          return DownloadTask(
+            taskId: item['task_id'] as String,
+            status: DownloadTaskStatus(item['status'] as int),
+            progress: item['progress'] as int,
+            url: item['url'] as String,
+            filename: item['file_name'] as String?,
+            savedDir: item['saved_dir'] as String,
+            timeCreated: item['time_created'] as int,
+          );
+        },
+      ).toList();
+    } on FlutterDownloaderException catch (err) {
+      _log('Failed to load tasks. Reason: ${err.message}');
+    } on PlatformException catch (err) {
+      _log(err.message);
       return null;
     }
+    return null;
   }
 
   /// Loads tasks from SQLite database using raw [query].
@@ -167,20 +190,34 @@ class FlutterDownloader {
     assert(_initialized, 'plugin flutter_downloader is not initialized');
 
     try {
-      List<dynamic> result = await _channel
-          .invokeMethod('loadTasksWithRawQuery', {'query': query});
-      return result
-          .map((item) => DownloadTask(
-              taskId: item['task_id'],
-              status: DownloadTaskStatus(item['status']),
-              progress: item['progress'],
-              url: item['url'],
-              filename: item['file_name'],
-              savedDir: item['saved_dir'],
-              timeCreated: item['time_created']))
-          .toList();
-    } on PlatformException catch (e) {
-      _log(e.message);
+      final result = await _channel.invokeMethod<List<dynamic>>(
+        'loadTasksWithRawQuery',
+        {'query': query},
+      );
+
+      if (result == null) {
+        throw const FlutterDownloaderException(
+          message: '`loadTasksWithRawQuery` returned null',
+        );
+      }
+
+      return result.map(
+        (dynamic item) {
+          // item as Map<String, dynamic>; // throws
+
+          return DownloadTask(
+            taskId: item['task_id'] as String,
+            status: DownloadTaskStatus(item['status'] as int),
+            progress: item['progress'] as int,
+            url: item['url'] as String,
+            filename: item['file_name'] as String?,
+            savedDir: item['saved_dir'] as String,
+            timeCreated: item['time_created'] as int,
+          );
+        },
+      ).toList();
+    } on PlatformException catch (err) {
+      _log('Failed to loadTasksWithRawQuery. Reason: ${err.message}');
       return null;
     }
   }
@@ -190,9 +227,9 @@ class FlutterDownloader {
     assert(_initialized, 'plugin flutter_downloader is not initialized');
 
     try {
-      return await _channel.invokeMethod('cancel', {'task_id': taskId});
-    } on PlatformException catch (e) {
-      _log(e.message);
+      await _channel.invokeMethod<void>('cancel', {'task_id': taskId});
+    } on PlatformException catch (err) {
+      _log(err.message);
     }
   }
 
@@ -202,8 +239,8 @@ class FlutterDownloader {
 
     try {
       return await _channel.invokeMethod('cancelAll');
-    } on PlatformException catch (e) {
-      _log(e.message);
+    } on PlatformException catch (err) {
+      _log(err.message);
     }
   }
 
@@ -292,23 +329,32 @@ class FlutterDownloader {
     }
   }
 
-  /// Opens the downloaded file with [taskId]. Returns true if the downloaded
-  /// file can be opened, false otherwise.
+  /// Opens the file downloaded by download task with [taskId]. Returns true if
+  /// the downloaded file can be opened, false otherwise.
   ///
   /// On Android, there are two requirements for opening the file:
   /// - The file must be saved in external storage where other applications have
   ///   permission to read the file
-  /// - There is at least 1 application that can read the files of type of the
-  ///   file.
+  /// - There must be at least 1 application that can read the files of type of
+  ///   the file.
   static Future<bool> open({required String taskId}) async {
     assert(_initialized, 'plugin flutter_downloader is not initialized');
 
     try {
-      return await _channel.invokeMethod('open', {'task_id': taskId});
-    } on PlatformException catch (e) {
-      _log(e.message);
+      final result = await _channel.invokeMethod<bool>(
+        'open',
+        {'task_id': taskId},
+      );
+
+      if (result == null) {
+        throw const FlutterDownloaderException(message: '`open` returned null');
+      }
+    } on PlatformException catch (err) {
+      _log('Failed to open downloaded file. Reason: ${err.message}');
       return false;
     }
+
+    return false;
   }
 
   /// Registers a [callback] to track the status and progress of a download
@@ -354,7 +400,10 @@ class FlutterDownloader {
   ///  send.send([id, status, progress]);
   ///}
   ///```
-  static registerCallback(DownloadCallback callback, {int step = 10}) {
+  static Future<void> registerCallback(
+    DownloadCallback callback, {
+    int step = 10,
+  }) async {
     assert(_initialized, 'plugin flutter_downloader is not initialized');
 
     final callbackHandle = PluginUtilities.getCallbackHandle(callback);
@@ -368,7 +417,7 @@ class FlutterDownloader {
       'step size is not in the inclusive <0;100> range',
     );
 
-    _channel.invokeMethod(
+    await _channel.invokeMethod<void>(
       'registerCallback',
       <dynamic>[callbackHandle!.toRawHandle(), step],
     );

lib/src/exceptions.dart

@@ -0,0 +1,9 @@
+/// Thrown when something bad happens on the Dart side of the flutter_downloader
+/// plugin.
+class FlutterDownloaderException implements Exception {
+  /// Creates a new [FlutterDownloaderException].
+  const FlutterDownloaderException({required this.message});
+
+  /// Description of the problem.
+  final String message;
+}