[file_selector_platform_interface] Add platform interface for new file_selector plugin

CODEOWNERS

@@ -11,6 +11,7 @@ packages/camera/**                             @bparrishMines
 packages/connectivity/**                       @cyanglaz @matthew-carroll
 packages/device_info/**                        @matthew-carroll
 packages/espresso/**                           @collinjackson @adazh
+packages/file_selector/**                      @ditman
 packages/google_maps_flutter/**                @cyanglaz
 packages/google_sign_in/**                     @cyanglaz @mehmetf
 packages/image_picker/**                       @cyanglaz

packages/file_selector/file_selector_platform_interface/CHANGELOG.md

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+## 1.0.0
+
+* Initial release.

packages/file_selector/file_selector_platform_interface/LICENSE

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+Copyright 2020 The Flutter Authors. All rights reserved.
+
+Redistribution and use in source and binary forms, with or without modification,
+are permitted provided that the following conditions are met:
+
+    * Redistributions of source code must retain the above copyright
+      notice, this list of conditions and the following disclaimer.
+    * Redistributions in binary form must reproduce the above
+      copyright notice, this list of conditions and the following
+      disclaimer in the documentation and/or other materials provided
+      with the distribution.
+    * Neither the name of Google Inc. nor the names of its
+      contributors may be used to endorse or promote products derived
+      from this software without specific prior written permission.
+
+THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
+ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE
+DISCLAIMED. IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR
+ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
+(INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES;
+LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON
+ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
+(INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS
+SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.

packages/file_selector/file_selector_platform_interface/README.md

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+# file_selector_platform_interface
+
+A common platform interface for the `file_selector` plugin.
+
+This interface allows platform-specific implementations of the `file_selector`
+plugin, as well as the plugin itself, to ensure they are supporting the
+same interface.
+
+# Usage
+
+To implement a new platform-specific implementation of `file_selector`, extend
+[`FileSelectorPlatform`][2] with an implementation that performs the
+platform-specific behavior, and when you register your plugin, set the default
+`FileSelectorPlatform` by calling
+`FileSelectorPlatform.instance = MyPlatformFileSelector()`.
+
+# Note on breaking changes
+
+Strongly prefer non-breaking changes (such as adding a method to the interface)
+over breaking changes for this package.
+
+See https://flutter.dev/go/platform-interface-breaking-changes for a discussion
+on why a less-clean interface is preferable to a breaking change.
+
+[1]: ../file_selector
+[2]: lib/file_selector_platform_interface.dart

packages/file_selector/file_selector_platform_interface/lib/file_selector_platform_interface.dart

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+export 'src/platform_interface/file_selector_interface.dart';
+export 'src/types/types.dart';

packages/file_selector/file_selector_platform_interface/lib/src/method_channel/method_channel_file_selector.dart

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+// Copyright 2020 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'package:flutter/services.dart';
+
+import 'package:file_selector_platform_interface/file_selector_platform_interface.dart';
+import 'package:meta/meta.dart';
+
+const MethodChannel _channel =
+    MethodChannel('plugins.flutter.io/file_selector');
+
+/// An implementation of [FileSelectorPlatform] that uses method channels.
+class MethodChannelFileSelector extends FileSelectorPlatform {
+  /// The MethodChannel that is being used by this implementation of the plugin.
+  @visibleForTesting
+  MethodChannel get channel => _channel;
+
+  /// Load a file from user's computer and return it as an XFile
+  @override
+  Future<XFile> openFile({
+    List<XTypeGroup> acceptedTypeGroups,
+    String initialDirectory,
+    String confirmButtonText,
+  }) async {
+    final List<String> path = await _channel.invokeListMethod<String>(
+      'openFile',
+      <String, dynamic>{
+        'acceptedTypeGroups':
+            acceptedTypeGroups?.map((group) => group.toJSON())?.toList(),
+        'initialDirectory': initialDirectory,
+        'confirmButtonText': confirmButtonText,
+        'multiple': false,
+      },
+    );
+    return path == null ? null : XFile(path?.first);
+  }
+
+  /// Load multiple files from user's computer and return it as an XFile
+  @override
+  Future<List<XFile>> openFiles({
+    List<XTypeGroup> acceptedTypeGroups,
+    String initialDirectory,
+    String confirmButtonText,
+  }) async {
+    final List<String> pathList = await _channel.invokeListMethod<String>(
+      'openFile',
+      <String, dynamic>{
+        'acceptedTypeGroups':
+            acceptedTypeGroups?.map((group) => group.toJSON())?.toList(),
+        'initialDirectory': initialDirectory,
+        'confirmButtonText': confirmButtonText,
+        'multiple': true,
+      },
+    );
+    return pathList?.map((path) => XFile(path))?.toList() ?? [];
+  }
+
+  /// Gets the path from a save dialog
+  @override
+  Future<String> getSavePath({
+    List<XTypeGroup> acceptedTypeGroups,
+    String initialDirectory,
+    String suggestedName,
+    String confirmButtonText,
+  }) async {
+    return _channel.invokeMethod<String>(
+      'getSavePath',
+      <String, dynamic>{
+        'acceptedTypeGroups':
+            acceptedTypeGroups?.map((group) => group.toJSON())?.toList(),
+        'initialDirectory': initialDirectory,
+        'suggestedName': suggestedName,
+        'confirmButtonText': confirmButtonText,
+      },
+    );
+  }
+
+  /// Gets a directory path from a dialog
+  @override
+  Future<String> getDirectoryPath({
+    String initialDirectory,
+    String confirmButtonText,
+  }) async {
+    return _channel.invokeMethod<String>(
+      'getDirectoryPath',
+      <String, dynamic>{
+        'initialDirectory': initialDirectory,
+        'confirmButtonText': confirmButtonText,
+      },
+    );
+  }
+}

packages/file_selector/file_selector_platform_interface/lib/src/platform_interface/file_selector_interface.dart

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+// Copyright 2020 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+import 'dart:async';
+
+import 'package:file_selector_platform_interface/file_selector_platform_interface.dart';
+import 'package:plugin_platform_interface/plugin_platform_interface.dart';
+
+import '../method_channel/method_channel_file_selector.dart';
+
+/// The interface that implementations of file_selector must implement.
+///
+/// Platform implementations should extend this class rather than implement it as `file_selector`
+/// does not consider newly added methods to be breaking changes. Extending this class
+/// (using `extends`) ensures that the subclass will get the default implementation, while
+/// platform implementations that `implements` this interface will be broken by newly added
+/// [FileSelectorPlatform] methods.
+abstract class FileSelectorPlatform extends PlatformInterface {
+  /// Constructs a FileSelectorPlatform.
+  FileSelectorPlatform() : super(token: _token);
+
+  static final Object _token = Object();
+
+  static FileSelectorPlatform _instance = MethodChannelFileSelector();
+
+  /// The default instance of [FileSelectorPlatform] to use.
+  ///
+  /// Defaults to [MethodChannelFileSelector].
+  static FileSelectorPlatform get instance => _instance;
+
+  /// Platform-specific plugins should set this with their own platform-specific
+  /// class that extends [FileSelectorPlatform] when they register themselves.
+  static set instance(FileSelectorPlatform instance) {
+    PlatformInterface.verifyToken(instance, _token);
+    _instance = instance;
+  }
+
+  /// Open file dialog for loading files and return a file path
+  Future<XFile> openFile({
+    List<XTypeGroup> acceptedTypeGroups,
+    String initialDirectory,
+    String confirmButtonText,
+  }) {
+    throw UnimplementedError('openFile() has not been implemented.');
+  }
+
+  /// Open file dialog for loading files and return a list of file paths
+  Future<List<XFile>> openFiles({
+    List<XTypeGroup> acceptedTypeGroups,
+    String initialDirectory,
+    String confirmButtonText,
+  }) {
+    throw UnimplementedError('openFiles() has not been implemented.');
+  }
+
+  /// Open file dialog for saving files and return a file path at which to save
+  Future<String> getSavePath({
+    List<XTypeGroup> acceptedTypeGroups,
+    String initialDirectory,
+    String suggestedName,
+    String confirmButtonText,
+  }) {
+    throw UnimplementedError('getSavePath() has not been implemented.');
+  }
+
+  /// Open file dialog for loading directories and return a directory path
+  Future<String> getDirectoryPath({
+    String initialDirectory,
+    String confirmButtonText,
+  }) {
+    throw UnimplementedError('getDirectoryPath() has not been implemented.');
+  }
+}

packages/file_selector/file_selector_platform_interface/lib/src/types/types.dart

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+export 'x_file/x_file.dart';
+
+export 'x_type_group/x_type_group.dart';

packages/file_selector/file_selector_platform_interface/lib/src/types/x_file/base.dart

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+import 'dart:convert';
+import 'dart:typed_data';
+
+/// The interface for a XFile.
+///
+/// A XFile is a container that wraps the path of a selected
+/// file by the user and (in some platforms, like web) the bytes
+/// with the contents of the file.
+///
+/// This class is a very limited subset of dart:io [File], so all
+/// the methods should seem familiar.
+abstract class XFileBase {
+  /// Construct a XFile
+  XFileBase(String path);
+
+  /// Save the XFile at the indicated file path.
+  void saveTo(String path) async {
+    throw UnimplementedError('saveTo has not been implemented.');
+  }
+
+  /// Get the path of the picked file.
+  ///
+  /// This should only be used as a backwards-compatibility clutch
+  /// for mobile apps, or cosmetic reasons only (to show the user
+  /// the path they've picked).
+  ///
+  /// Accessing the data contained in the picked file by its path
+  /// is platform-dependant (and won't work on web), so use the
+  /// byte getters in the XFile instance instead.
+  String get path {
+    throw UnimplementedError('.path has not been implemented.');
+  }
+
+  /// The name of the file as it was selected by the user in their device.
+  ///
+  /// Use only for cosmetic reasons, do not try to use this as a path.
+  String get name {
+    throw UnimplementedError('.name has not been implemented.');
+  }
+
+  /// For web, it may be necessary for a file to know its MIME type.
+  String get mimeType {
+    throw UnimplementedError('.mimeType has not been implemented.');
+  }
+
+  /// Get the length of the file. Returns a `Future<int>` that completes with the length in bytes.
+  Future<int> length() {
+    throw UnimplementedError('.length() has not been implemented.');
+  }
+
+  /// Synchronously read the entire file contents as a string using the given [Encoding].
+  ///
+  /// By default, `encoding` is [utf8].
+  ///
+  /// Throws Exception if the operation fails.
+  Future<String> readAsString({Encoding encoding = utf8}) {
+    throw UnimplementedError('readAsString() has not been implemented.');
+  }
+
+  /// Synchronously read the entire file contents as a list of bytes.
+  ///
+  /// Throws Exception if the operation fails.
+  Future<Uint8List> readAsBytes() {
+    throw UnimplementedError('readAsBytes() has not been implemented.');
+  }
+
+  /// Create a new independent [Stream] for the contents of this file.
+  ///
+  /// If `start` is present, the file will be read from byte-offset `start`. Otherwise from the beginning (index 0).
+  ///
+  /// If `end` is present, only up to byte-index `end` will be read. Otherwise, until end of file.
+  ///
+  /// In order to make sure that system resources are freed, the stream must be read to completion or the subscription on the stream must be cancelled.
+  Stream<Uint8List> openRead([int start, int end]) {
+    throw UnimplementedError('openRead() has not been implemented.');
+  }
+
+  /// Get the last-modified time for the XFile
+  Future<DateTime> lastModified() {
+    throw UnimplementedError('openRead() has not been implemented.');
+  }
+}