Multiuser support for Android

android/app/src/main/kotlin/com/leastauthority/destiny/MainActivity.kt

@@ -7,6 +7,7 @@ import android.net.Uri
 import android.os.Bundle
 import android.os.Handler
 import android.os.Looper
+import android.os.UserManager
 import android.util.Log
 import androidx.core.app.ActivityCompat
 import androidx.core.content.ContextCompat
@@ -19,6 +20,7 @@ class MainActivity : FlutterActivity() {
     private val FILE_SELECTOR_CHANNEL_NAME = "destiny.android/file_selector"
     private val SHARE_FILE_CHANNEL_NAME = "destiny.androids/share_file"
     private val SAVE_AS_CHANNEL_NAME = "destiny.android/save_as"
+    private val USER_ID_CHANNEL_NAME = "destiny.android/user_id"
 
     private var SHARE_FILE_CHANNEL: MethodChannel? = null
 
@@ -44,6 +46,14 @@ class MainActivity : FlutterActivity() {
         }
     }
 
+    // Get emphmeral user id to be used in accessing a directory name
+    private fun getUserID(call: MethodCall, result: MethodChannel.Result) {
+        val userManager = getContext().getSystemService(UserManager::class.java)
+
+        val ephemeralUserId = userManager!!.getSerialNumberForUser(android.os.Process.myUserHandle())
+        result.success(ephemeralUserId);
+    }
+
     private fun sendFileFromIntent(intent: Intent) {
         val uri = intent.getParcelableExtra<Uri>(Intent.EXTRA_STREAM) as Uri
         if (SHARE_FILE_CHANNEL != null) {
@@ -101,6 +111,20 @@ class MainActivity : FlutterActivity() {
             }
         }
 
+        MethodChannel(
+            flutterEngine.dartExecutor.binaryMessenger, 
+            USER_ID_CHANNEL_NAME
+        ).setMethodCallHandler { call, result -> 
+            when (call.method) {
+                "getUserID" -> getUserID(call, result)
+                else -> result.error(
+                    UNKNOWN_METHOD,
+                    "Unknown method called on save as channel: ${call.method}",
+                    ""
+                )
+            }
+        }
+
         SHARE_FILE_CHANNEL =
             MethodChannel(flutterEngine.dartExecutor.binaryMessenger, SHARE_FILE_CHANNEL_NAME)
 

lib/constants/app_constants.dart

@@ -179,7 +179,9 @@ const String SETTINGS_SCREEN_SELECT_A_FOLDER_BUTTON =
     'SETTINGS_SCREEN_SELECT_A_FOLDER_BUTTON';
 const String SETTINGS_SCREEN_BOTTOM_SPACE_PLACEHOLDER =
     'SETTINGS_SCREEN_BOTTOM_SPACE_PLACEHOLDER';
-const String ANDROID_DOWNLOADS_FOLDER_PATH = '/storage/emulated/0/Download';
+const String ANDROID_DOWNLOADS_PATH = '/storage/emulated/';
+const String ANDROID_DOWNLOADS_FOLDER = '/Download';
+const int DEFAULT_ANDROID_USER = 0;
 
 const String WINDOW_TITLE = "Destiny";
 

lib/main.dart

@@ -19,18 +19,21 @@ import 'locator.dart';
 // This is our global ServiceLocator
 GetIt getIt = GetIt.instance;
 
-void startApp(Config c) {
+void startApp(Config c) async {
   WidgetsFlutterBinding.ensureInitialized();
   SystemChrome.setPreferredOrientations(
       [DeviceOrientation.portraitUp, DeviceOrientation.portraitDown]);
 
   register(getIt, c);
+  // Wait for all preferences to be loaded. Getting UserID leads to a crash if
+  await getIt.allReady();
 
   if (Platform.isWindows || Platform.isLinux || Platform.isMacOS) {
     setWindowMinSize(const Size(900, 800));
     setWindowMaxSize(const Size(1600, 1200));
     setWindowFrame(Rect.fromLTWH(0, 0, 900, 800));
   }
+
   runApp(MultiProvider(providers: [
     ChangeNotifierProvider(create: (context) => SendSharedState()),
     ChangeNotifierProvider(create: (context) => ReceiveSharedState())

lib/views/shared/file_picker.dart

@@ -161,19 +161,29 @@ FilePicker getMediaPicker() {
 
 Future<String> getDownloadPath() async {
   Directory? directory;
+
   try {
     if (Platform.isIOS) {
       directory = await getApplicationDocumentsDirectory();
     } else if (Platform.isAndroid) {
-      directory = Directory(ANDROID_DOWNLOADS_FOLDER_PATH);
+      final userData = MethodChannel('destiny.android/user_id');
+      int userId = DEFAULT_ANDROID_USER;
+
+      // try determinate emphemeral user id, to select download folder for multiple users
+      userId = await userData.invokeMethod("getUserID");
+
+      directory = Directory(ANDROID_DOWNLOADS_PATH +
+          userId.toString() +
+          ANDROID_DOWNLOADS_FOLDER);
+
       if (!await directory.exists()) {
         directory = await getExternalStorageDirectory();
       }
     } else {
       directory = await getDownloadsDirectory();
     }
   } catch (err) {
-    print("Cannot get download folder path");
+    print("Cannot get download folder path" + err.toString());
   }
   return directory!.path;
 }

lib/views/shared/receive.dart

@@ -11,7 +11,6 @@ import 'package:dart_wormhole_william/client/native_client.dart';
 import 'package:flutter/material.dart';
 import 'package:file_picker/file_picker.dart' as f;
 import 'package:flutter/services.dart';
-import 'package:path_provider/path_provider.dart';
 import 'package:shared_preferences/shared_preferences.dart';
 import 'package:wakelock/wakelock.dart';
 
@@ -102,21 +101,11 @@ class ReceiveSharedState extends ChangeNotifier {
       this.prefs = prefs;
     });
 
-    if (dartIO.Platform.isAndroid) {
-      defaultPathForPlatform = ANDROID_DOWNLOADS_FOLDER_PATH;
-    } else if (dartIO.Platform.isIOS) {
-      getApplicationDocumentsDirectory().then((downloadsDir) {
-        setState(() {
-          defaultPathForPlatform = downloadsDir.path;
-        });
-      });
-    } else {
-      getDownloadsDirectory().then((downloadsDir) {
-        setState(() {
-          defaultPathForPlatform = downloadsDir?.path;
-        });
+    getDownloadPath().then((downloadPath) {
+      setState(() {
+        defaultPathForPlatform = downloadPath;
       });
-    }
+    });
   }
 
   late ProgressSharedState progress = ProgressSharedState(setState, () {

lib/views/shared/send.dart

@@ -33,8 +33,6 @@ class SendSharedState extends ChangeNotifier {
 
   SendScreenStates currentState = SendScreenStates.Initial;
 
-  final appSettings = getIt<AppSettings>();
-
   CancelFunc cancelFunc = () {
     print("No cancel function assigned. Doing nothing");
   };
@@ -179,6 +177,8 @@ class SendSharedState extends ChangeNotifier {
     }, onError: defaultErrorHandler);
   }
 
+  final appSettings = getIt<AppSettings>();
+
   Client createClient() => Client(appSettings.config());
 
   Widget widgetByState(