Add support for changing save location on Android (#1520)

- Enabled the Android UI path for changing the data folder
- Added Android MANAGE_EXTERNAL_STORAGE permission
- Added an Android flow to request “All files access” before opening the folder picker
- Added code path to resume the folder selection flow after returning from Android settings
- Improved the Android write-probe error message to point users at the required permission

platforms/android/app/src/main/AndroidManifest.xml

@@ -11,6 +11,7 @@
 
     <uses-permission android:name="android.permission.VIBRATE" />
     <uses-permission android:name="android.permission.INTERNET" />
+    <uses-permission android:name="android.permission.MANAGE_EXTERNAL_STORAGE" />
 
     <application
         android:allowBackup="true"

platforms/android/app/src/main/java/com/twilitrealm/dusk/DuskActivity.java

@@ -12,6 +12,7 @@ import android.os.Bundle;
 import android.os.Environment;
 import android.provider.DocumentsContract;
 import android.provider.OpenableColumns;
+import android.provider.Settings;
 import android.util.Log;
 import android.view.View;
 import android.view.Window;
@@ -27,10 +28,12 @@ import java.util.List;
 public class DuskActivity extends SDLActivity {
     private static final String TAG = "DuskActivity";
     private static final int FOLDER_DIALOG_REQUEST_CODE = 0x4455;
+    private static final int MANAGE_STORAGE_REQUEST_CODE = 0x4456;
     private static final String EXTERNAL_STORAGE_AUTHORITY =
         "com.android.externalstorage.documents";
 
     private long folderDialogUserdata = 0;
+    private boolean awaitingManageStoragePermission = false;
 
     private static native void nativeFolderDialogResult(long userdata, String path, String error);
 
@@ -89,6 +92,9 @@ public class DuskActivity extends SDLActivity {
     protected void onResume() {
         super.onResume();
         hideSystemBars();
+        if (awaitingManageStoragePermission) {
+            resumeFolderDialogAfterPermissionGrant();
+        }
     }
 
     @Override
@@ -171,6 +177,19 @@ public class DuskActivity extends SDLActivity {
         }
 
         folderDialogUserdata = userdata;
+        if (requiresManageStoragePermission() && !hasManageStoragePermission()) {
+            if (!requestManageStoragePermission()) {
+                finishFolderDialogWithError("Unable to request Android file access permission");
+                return false;
+            }
+            return true;
+        }
+
+        openFolderDialog();
+        return true;
+    }
+
+    private void openFolderDialog() {
         runOnUiThread(() -> {
             Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
             intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION |
@@ -185,9 +204,71 @@ public class DuskActivity extends SDLActivity {
                 finishFolderDialog(Activity.RESULT_CANCELED, null);
             }
         });
+    }
+
+    private boolean requiresManageStoragePermission() {
+        return Build.VERSION.SDK_INT >= Build.VERSION_CODES.R;
+    }
+
+    private boolean hasManageStoragePermission() {
+        return !requiresManageStoragePermission() || Environment.isExternalStorageManager();
+    }
+
+    private boolean requestManageStoragePermission() {
+        if (!requiresManageStoragePermission()) {
+            return true;
+        }
+
+        awaitingManageStoragePermission = true;
+        runOnUiThread(() -> {
+            if (tryStartManageStorageIntent(
+                    new Intent(Settings.ACTION_MANAGE_APP_ALL_FILES_ACCESS_PERMISSION)
+                        .setData(Uri.parse("package:" + getPackageName()))) ||
+                tryStartManageStorageIntent(
+                    new Intent(Settings.ACTION_MANAGE_ALL_FILES_ACCESS_PERMISSION)))
+            {
+                return;
+            }
+
+            finishFolderDialogWithError("Unable to request Android file access permission");
+        });
         return true;
     }
 
+    private boolean tryStartManageStorageIntent(Intent intent) {
+        try {
+            startActivityForResult(intent, MANAGE_STORAGE_REQUEST_CODE);
+            return true;
+        } catch (ActivityNotFoundException e) {
+            Log.w(TAG, "Unable to open all-files access settings.", e);
+            return false;
+        }
+    }
+
+    private void resumeFolderDialogAfterPermissionGrant() {
+        awaitingManageStoragePermission = false;
+        if (folderDialogUserdata == 0) {
+            return;
+        }
+
+        if (hasManageStoragePermission()) {
+            openFolderDialog();
+            return;
+        }
+
+        finishFolderDialogWithError(
+            "Allow \"All files access\" for Dusklight before choosing a custom data folder");
+    }
+
+    private void finishFolderDialogWithError(String error) {
+        long userdata = folderDialogUserdata;
+        folderDialogUserdata = 0;
+        awaitingManageStoragePermission = false;
+        if (userdata != 0) {
+            nativeFolderDialogResult(userdata, null, error);
+        }
+    }
+
     private void finishFolderDialog(int resultCode, Intent data) {
         long userdata = folderDialogUserdata;
         folderDialogUserdata = 0;

src/dusk/data.cpp

@@ -525,7 +525,14 @@ bool validate_writable_data_path(const std::filesystem::path& path, std::string*
     try {
         io::FileStream::WriteAllText(probePath, "dusk");
     } catch (const std::exception& e) {
+#if defined(__ANDROID__)
+        set_error(errorOut,
+            fmt::format("{} could not write to the selected folder. On Android, allow "
+                        "\"All files access\" for Dusklight and try again.",
+                AppName));
+#else
         set_error(errorOut, fmt::format("{} could not write to the selected folder.", AppName));
+#endif
         Log.warn("Failed write probe for custom data folder '{}': {}", io::fs_path_to_string(path),
             e.what());
         return false;

src/dusk/data.hpp

@@ -15,7 +15,7 @@
 #define DUSK_CAN_OPEN_DATA_FOLDER 0
 #endif
 
-#if (defined(__APPLE__) && TARGET_OS_IOS && !TARGET_OS_MACCATALYST) || defined(__ANDROID__)
+#if (defined(__APPLE__) && TARGET_OS_IOS && !TARGET_OS_MACCATALYST)
 #define DUSK_CAN_CHANGE_DATA_FOLDER 0
 #else
 #define DUSK_CAN_CHANGE_DATA_FOLDER 1