Trying to takePersistableUriPermission() fails for custom DocumentsProvider via ACTION_OPEN_DOCUMENT

Question

I am trying to write a custom DocumentsProvider that allows other apps to take persistable permissions to the Uris it provides

I have a DocumentsProvider that I declare in my AndroidManufest.xml as follows

<provider
   android:name="com.cgogolin.myapp.MyContentProvider"
   android:authorities="com.cgogolin.myapp.MyContentProvider"
   android:grantUriPermissions="true"
   android:exported="true"
   android:permission="android.permission.MANAGE_DOCUMENTS"
   android:enabled="@bool/atLeastKitKat">
  <intent-filter>
    <action android:name="android.content.action.DOCUMENTS_PROVIDER" />
  </intent-filter>
</provider>

and my app has the MANAGE_DOCUMENTS permission set

<uses-permission android:name="android.permission.MANAGE_DOCUMENTS" />

(apparently this is not necessary but adding/removing it also doesn't matter). I can then see my provider when I open the ACTION_OPEN_DOCUMENT picker UI with

Intent openDocumentIntent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
openDocumentIntent.addCategory(Intent.CATEGORY_OPENABLE);
openDocumentIntent.setType("application/pdf");
openDocumentIntent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION|Intent.FLAG_GRANT_WRITE_URI_PERMISSION|Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION);
startActivityForResult(openDocumentIntent, EDIT_REQUEST);

and, after picking a file from my provider there, in the onActivityResult() method of my App I can then successfully open the file provided by my DocumentsProvider via the Uri I get from intent.getData().

However, trying to persist read or write permissions with

getContentResolver().takePersistableUriPermission(uri, Intent.FLAG_GRANT_READ_URI_PERMISSION);

or

getContentResolver().takePersistableUriPermission(uri, Intent.FLAG_GRANT_WRITE_URI_PERMISSION);

always fails with an exception like

No permission grant found for UID 10210 and Uri content://com.cgogolin.myapp.MyContentProvider/document/tshjhczf.pdf

If I pick a file from the google drive or downloads provider in the picker UI taking permissions in this way works. So I think the problem is in my provider.

Why is there no permission grant created despite me specifying android:grantUriPermissions="true"?

How can I convince Android to create such a permission grant for me?

After all I don't think I can do it myself, as I cannot know the UID of the process that opened the picker UI, or at least not that I knew how.

Answer 1

EDIT:

My previous answer wasn't good. You are suppose to use "android.permission.MANAGE_DOCUMENTS" for security reasons.
Only System UI picker will be able to list your documents.

But you don't need this permission in the manifest of the application that opens documents.
Actually you should not to be able to gain this permission as it is system permission.

I've just tested it and call to takePersistableUriPermission form onActivityResult was successful.

I used DocumentProvider with mock data (one root, 3 txt documents).
If it still doesn't work for you there could be some issue with your document provider.

EDIT2:

Sample code

package com.example.test;

import android.database.Cursor;
import android.database.MatrixCursor;
import android.os.CancellationSignal;
import android.os.ParcelFileDescriptor;
import android.provider.DocumentsProvider;

import java.io.FileNotFoundException;

public class MyContentProvider extends DocumentsProvider {

    private final static String[] rootColumns = new String[]{
            "_id", "root_id", "title", "icon"
    };
    private final static String[] docColumns = new String[]{
            "_id", "document_id", "_display_name", "mime_type", "icon"
    };

    MatrixCursor matrixCursor;
    MatrixCursor matrixRootCursor;

    @Override
    public boolean onCreate() {

        matrixRootCursor = new MatrixCursor(rootColumns);
        matrixRootCursor.addRow(new Object[]{1, 1, "TEST", R.mipmap.ic_launcher});

        matrixCursor = new MatrixCursor(docColumns);
        matrixCursor.addRow(new Object[]{1, 1, "a.txt", "text/plain", R.mipmap.ic_launcher});
        matrixCursor.addRow(new Object[]{2, 2, "b.txt", "text/plain", R.mipmap.ic_launcher});
        matrixCursor.addRow(new Object[]{3, 3, "c.txt", "text/plain", R.mipmap.ic_launcher});

        return true;
    }

    @Override
    public Cursor queryRoots(String[] projection) throws FileNotFoundException {
        return matrixRootCursor;
    }

    @Override
    public Cursor queryDocument(String documentId, String[] projection)
            throws FileNotFoundException {

        return matrixCursor;
    }

    @Override
    public Cursor queryChildDocuments(String parentDocumentId, String[] projection,
                                      String sortOrder)
            throws FileNotFoundException {

        return matrixCursor;
    }

    @Override
    public ParcelFileDescriptor openDocument(String documentId, String mode,
                                             CancellationSignal signal)
            throws FileNotFoundException {

        int id;
        try {
            id = Integer.valueOf(documentId);
        } catch (NumberFormatException e) {
            throw new FileNotFoundException("Incorrect document ID " + documentId);
        }

        String filename = "/sdcard/";

        switch (id) {
            case 1:
                filename += "a.txt";
                break;
            case 2:
                filename += "b.txt";
                break;
            case 3:
                filename += "c.txt";
                break;
            default:
                throw new FileNotFoundException("Unknown document ID " + documentId);
        }

        return ParcelFileDescriptor.open(new File(filename),
                ParcelFileDescriptor.MODE_READ_WRITE);
    }
}

Note:
You can use constants from DocumentsContract.Document and DocumentsContract.Root.
I'm not sure whether "_id" is required.

EDIT3:

Updated sample code to open documents from /sdcard.
Added read/write external storage permissions.

AndroidManifest.xml

<?xml version="1.0" encoding="utf-8"?>
<manifest
    package="com.example.test"
    xmlns:android="http://schemas.android.com/apk/res/android">

    <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE"/>
    <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE"/>

    <application
        android:icon="@mipmap/ic_launcher"
        android:label="@string/app_name">

        <provider
            android:name="com.example.test.MyContentProvider"
            android:authorities="com.example.test.document"
            android:enabled="true"
            android:exported="@bool/atLeastKitKat"
            android:grantUriPermissions="true"
            android:permission="android.permission.MANAGE_DOCUMENTS">
            <intent-filter>
                <action android:name="android.content.action.DOCUMENTS_PROVIDER"/>
            </intent-filter>
        </provider>
    </application>

</manifest>

Client app

New project with an empty activity, no permission added.

Open document

Intent openDocumentIntent = new Intent(Intent.ACTION_OPEN_DOCUMENT);
openDocumentIntent.addCategory(Intent.CATEGORY_OPENABLE);
openDocumentIntent.setType("text/plain");
openDocumentIntent.setFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION
                    | Intent.FLAG_GRANT_WRITE_URI_PERMISSION
                    | Intent.FLAG_GRANT_PERSISTABLE_URI_PERMISSION);
startActivityForResult(openDocumentIntent, 1);

onActivityResult

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    switch (requestCode) {
        case 1: // TODO: Use constant
            if (resultCode == RESULT_OK) {
                if (data == null) return; // TODO: Show error
                Uri uri = data.getData();
                if (uri == null) return; // TODO: Show error
                getContentResolver().takePersistableUriPermission(uri,
                        Intent.FLAG_GRANT_READ_URI_PERMISSION);

                InputStream is = null;
                try {
                    is = getContentResolver().openInputStream(uri);

                    // Just for quick sample (I know what I will read)
                    byte[] buffer = new byte[1024];
                    int read = is.read(buffer);
                    String text = new String(buffer, 0, read);

                    ((TextView) findViewById(R.id.text)).setText(text);
                } catch (IOException e) {
                    e.printStackTrace();
                } finally {
                    if (is != null) try {
                        is.close();
                    } catch (IOException e) {
                        e.printStackTrace();
                    }
                }
            }
            break;
    }
}

Answer 2

When working with SAF, the expected behavior on API 19-25 is that a SecurityException is thrown for URIs from your own DocumentProvider.

This has changed on API 26 and above which now allows persistable URI permission for URIs even from your own process (no official docs but an observation through testing)

But even if you get a SecurityException while trying to take persistable URI permission you'd still always have access to URIs exposed from your own DocumentsProvider.

Thus it'd be a good idea to catch and ignore the SecurityException when the content authority is from your own process.

Note: If your app contains a DocumentsProvider and also persists URIs returned from ACTION_OPEN_DOCUMENT, ACTION_OPEN_DOCUMENT_TREE, or ACTION_CREATE_DOCUMENT, be aware that you won’t be able to persist access to your own URIs via takePersistableUriPermission() — despite it failing with a SecurityException, you’ll always have access to URIs from your own app. You can add the boolean EXTRA_EXCLUDE_SELF to your Intents if you want to hide your own DocumentsProvider(s) on API 23+ devices for any of these actions.

Here's a note from official Android Developers blog that confirms this behavior - https://medium.com/androiddevelopers/building-a-documentsprovider-f7f2fb38e86a