Android SAF: Uri of a folder (on disk) from DocumentsContract.getTreeDocumentId has different form, in respect to the previously authorized one

Question

I am testing the Storage Access Framework for my app.

In my app the user selects a folder as an access point to the filesystem for the app itself.

This method is used:

static public void openPickerForFolderSelection(Activity activity, int requestCode)
{
    Intent intent = new Intent(Intent.ACTION_OPEN_DOCUMENT_TREE);
    intent.addFlags(Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION);
    intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
    intent.addFlags(Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
    intent.addFlags(Intent.FLAG_GRANT_PREFIX_URI_PERMISSION); //useful?
    activity.startActivityForResult(intent, requestCode);
}

In the onActivityResult method the following code is called:

static public String takePermanentReadWritePermissions(Activity activity, Intent data)
{
int takeFlags = data.getFlags()
        &
        (Intent.FLAG_GRANT_READ_URI_PERMISSION | Intent.FLAG_GRANT_WRITE_URI_PERMISSION);
ContentResolver resolver = activity.getContentResolver();
resolver.takePersistableUriPermission(data.getData(),takeFlags);
return data.getData().toString();

}

Example, the Uri is:

content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Faccesspoint1

In fact, the Uri happens to be authorized as detected by this method:

static boolean arePermissionsGranted(Activity activity, String uriString)
{
    ContentResolver resolver = activity.getContentResolver();
    List<UriPermission> list = resolver.getPersistedUriPermissions();
    for (int i = 0; i < list.size(); i++){
    Log.d("compare",uriString+" "+Uri.decode(list.get(i).getUri().toString())+" "+String.valueOf(list.get(i).isWritePermission())+" "+String.valueOf(list.get(i).isReadPermission()));
    if(((Uri.decode(list.get(i).getUri().toString())).equals( uriString)) && list.get(i).isWritePermission()&& list.get(i).isReadPermission()){
            return true;
        }

then, when it is necessary to create a new folder in the selected folder the following method is called but there is an error before attempting to create the folder:

static public boolean createFolderInFolder(Activity activity,String parentFolderUriString,String folderName)
{
boolean result=false;
ContentResolver contentResolver;
Uri parentFolderUri=null;
String id=DocumentsContract.getTreeDocumentId(Uri.parse(parentFolderUriString));
Log.d("id ",id); 
parentFolderUri= DocumentsContract.buildTreeDocumentUri(PROVIDER_AUTHORITY,id);
try {
//error here
    DocumentsContract.createDocument(contentResolver,parentFolderUri,DocumentsContract.Document.MIME_TYPE_DIR,folderName);
            result=true;
} catch (FileNotFoundException e) {
    result =false;
}
return result;
}

I get:

java.lang.SecurityException: Permission Denial: opening provider com.google.android.apps.docs.storagebackend.StorageBackendContentProvider from ProcessRecord{1426e0c 13943:com.example.app/u0a439} (pid=13943, uid=10439) requires that you obtain access using ACTION_OPEN_DOCUMENT or related APIs

(note that using

parentFolderUri=Uri.parse(parentFolderUriString); 

directly leads to an "invalid Uri" error)

The fact is that the permissions are granted on a different Uri than the one from DocumentsContract.getTreeDocumentId(Uri.parse(parentFolderUriString));

Here's the log:

D/compare: content://com.android.providers.downloads.documents/tree/raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Faccesspoint1 content://com.android.providers.downloads.documents/tree/raw:/storage/emulated/0/Download/accesspoint1 true true

Indeed the id value is:

raw%3A%2Fstorage%2Femulated%2F0%2FDownload%2Faccesspoint1

that leads to the final Uri value

content://com.google.android.apps.docs.storage/tree/raw%253A%252Fstorage%252Femulated%252F0%252FDownload%252Faccesspoint1

So it seems that I should request permissions also on this different version of the Uri, if I want that no security exception (with permission denial) is issued? But it seems not possible to take the permissions on a different form uri.

How to solve this?

Answer 1

Offtopic: you don't need intent.addFlags() in 'openPickerForFolderSelection' method.

Now on your topic - I think you just need to use DocumentContract.buildDocumentUriUsingTree() to get the uri you need (atleast this worked for me when I tried to create file/directory this way), so it would be something like:

Uri oldParentUri = Uri.parse(parentFolderUriString);
String id = DocumentsContract.getTreeDocumentId(oldParentUri );
Uri parentFolderUri= DocumentsContract.buildChildDocumentsUriUsingTree(oldParentUri , id);

On the other hand I suggest you use DocumentFile API - it's much easier imo. your 'createFolderInFolder' would then look like this:

Uri parentFolderUri = Uri.parse(parentFolderUriString);
DocumentFile parentFolder = DocumentFile.fromTreeUri(context, parentFolderUri);
parentFolder.createDirectory(folderName);

Then you can easily get the created folder uri and do something from there.