Writing to SD card "java.io.FileNotFoundException: Permission denied"

There are many questions on stackoverflow, but I still couldn't find a solution to my specific problem:

I have a permission app WRITE_EXTERNAL_STORAGE

and a non-export file provider

<?xml version="1.0" encoding="utf-8"?>
<manifest xmlns:android="http://schemas.android.com/apk/res/android"
      package="com.cgogolin.library"
      ...
      <uses-permission android:name="android.permission.READ_EXTERNAL_STORAGE" />
      <uses-permission android:name="android.permission.WRITE_EXTERNAL_STORAGE" />
      <uses-sdk android:minSdkVersion="11" android:targetSdkVersion="23" />
      ...
      <provider
        android:name="android.support.v4.content.FileProvider"
        android:authorities="com.cgogolin.library.fileprovider"
        android:exported="false"
        android:grantUriPermissions="true">
        <meta-data
            android:name="android.support.FILE_PROVIDER_PATHS"
            android:resource="@xml/provider_paths"/>
      </provider>
</application>

      

        
        
        
      

    

which is further specified provider_paths.xml

as

<?xml version="1.0" encoding="utf-8"?>
<paths xmlns:android="http://schemas.android.com/apk/res/android">
  <external-path name="external_files" path="."/>
  <root-path name="external_files2" path="/storage/"/>
</paths>

      

        
        
        
      

    

and which I want to use to send files from the SD card to other applications (My application acts more or less like a file browser in this case, but not really ...).

Since I am using API level 23, I am also dynamically requesting permissions by calling

requestPermissions(new String[]{android.Manifest.permission.READ_EXTERNAL_STORAGE, android.Manifest.permission.WRITE_EXTERNAL_STORAGE}, WRITE_PERMISSION_REQUEST);

      

        
        
        
      

    

A dialog will appear and after clicking Allow (and restart the application due to the error described in Cannot write to external storage if the application does not restart after granting permission ). The app is getting the permissions correctly, which I can check by checking,

android.support.v4.content.ContextCompat.checkSelfPermission(context, android.Manifest.permission.WRITE_EXTERNAL_STORAGE) == PackageManager.PERMISSION_GRANTED

      

        
        
        
      

    

and indeed it is. I can also get the file Uri

in File

from sdcard with something like

Uri uri = android.support.v4.content.FileProvider.getUriForFile(context, "com.cgogolin.library.fileprovider", file);

      

        
        
        
      

    

I can read from this file and I can, for example, run successfully Intent.ACTION_VIEW

to open the file in an external application.

But: Despite having write permissions, I cannot write the file. All attempts to open OutputStream

or ParcelFileDescriptor

before Uri

using any of the following

context.getContentResolver().openOutputStream(uri, "wa");
context.getContentResolver().openFileDescriptor(uri, "wa");

      

        
        
        
      

    

either directly from my app, or from an app opened via Intent

will result in

java.io.FileNotFoundException: Permission denied

      

        
        
        
      

    

Where is my mistake? I thought that after checkSelfPermission()

telling me what I have WRITE_EXTERNAL_STORAGE

, I really have to do it.