Add another attempt to check write permissions on a folder (fixes #1971)

app/src/main/java/com/nutomic/syncthingandroid/activities/FolderActivity.java

@@ -9,6 +9,8 @@
 import android.os.Build;
 import android.os.Bundle;
 import androidx.documentfile.provider.DocumentFile;
+
+import android.os.Environment;
 import android.text.Editable;
 import android.text.TextUtils;
 import android.text.TextWatcher;
@@ -537,6 +539,10 @@ private void checkWriteAndUpdateUI() {
          * Access level readwrite: folder can be configured "sendonly" or "sendreceive".
          */
         mCanWriteToPath = Util.nativeBinaryCanWriteToPath(FolderActivity.this, mFolder.path);
+        if(!mCanWriteToPath){
+           final File externalStorageDirectory = Environment.getExternalStorageDirectory();
+           mCanWriteToPath = Util.nativeBinaryCanWriteToPath2(externalStorageDirectory, mFolder.path);
+        }
         if (mCanWriteToPath) {
             binding.accessExplanationView.setText(R.string.folder_path_readwrite);
             binding.folderType.setEnabled(true);

app/src/main/java/com/nutomic/syncthingandroid/util/Util.java

@@ -7,7 +7,6 @@
 import android.content.Context;
 import android.content.pm.ApplicationInfo;
 import android.content.pm.PackageManager.NameNotFoundException;
-import android.os.Build;
 import android.preference.PreferenceManager;
 import androidx.appcompat.app.AlertDialog;
 import android.util.Log;
@@ -172,6 +171,38 @@ public static boolean nativeBinaryCanWriteToPath(Context context, String absolut
         return true;
     }
 
+    /**
+     * Returns if the syncthing binary would be able to write a file into
+     * the given folder given the configured access level.
+     *
+     * This uses the Android-native File API
+     */
+    public static Boolean nativeBinaryCanWriteToPath2(File externalStorageDir, String absoluteFolderPath) {
+        final String TOUCH_FILE_NAME = ".stwritetest";
+
+        // normalize path replacing ~ with external storage directory
+        // this is consistent with what $HOME is set to in SyncthingRunnable
+        final String normalizedPath = absoluteFolderPath.replaceFirst("^~", externalStorageDir.getAbsolutePath());
+
+        // Write permission test file
+        File touchFile = new File(normalizedPath, TOUCH_FILE_NAME);
+        final String touchFilePath = touchFile.getAbsolutePath();
+        try{
+            Boolean fileCreated = touchFile.createNewFile();
+            Log.d(TAG, String.format("%s createNewFile result %b", touchFilePath, fileCreated));
+            Boolean fileDeleted = touchFile.delete();
+            Log.d(TAG, String.format("%s delete result %b", touchFilePath, fileDeleted));
+        } catch (IOException e) {
+            Log.e(TAG, String.format("Failed to write test file '%s'", touchFilePath), e);
+            return false;
+        }
+
+        // Detected we have write permission.
+        Log.i(TAG, String.format("Successfully wrote test file '%s'", touchFile));
+
+        return true;
+    }
+
     /**
      * Run command in a shell and return the exit code.
      */
@@ -241,4 +272,5 @@ public static AlertDialog.Builder getAlertDialogBuilder(Context context)
     {
         return new MaterialAlertDialogBuilder(context);
     }
+
 }