IssueTracker

- Steps to reproduce the problem (including sample code if appropriate).

1. Obtain a test device that has 1+ MP3 files on it, indexed by the MediaStore, where you have backed up the MP3 file somewhere (as depending on what you try here, it may be cleared)

2. UnZIP the attached project, import into Android Studio (tested on AS 3.4), and run it on the test device -- the Storage Access Framework (SAF) content selector will immediately appear

3. Tap on the "Audio" category in the SAF content selector, then browse to your MP3 file and select it

- What happened.

The app crashes with:

    Process: com.commonsware.android.myapplication, PID: 12798
    java.lang.RuntimeException: Failure delivering result ResultInfo{who=null, request=1337, result=-1, data=Intent { dat=content://com.android.providers.media.documents/document/audio:798 flg=0x43 }} to activity {com.commonsware.android.myapplication/com.commonsware.android.myapplication.MainActivity}: java.lang.IllegalArgumentException: Media is read-only
        at android.app.ActivityThread.deliverResults(ActivityThread.java:4398)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:4440)
        at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:49)
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108)
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68)
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816)
        at android.os.Handler.dispatchMessage(Handler.java:106)
        at android.os.Looper.loop(Looper.java:193)
        at android.app.ActivityThread.main(ActivityThread.java:6718)
        at java.lang.reflect.Method.invoke(Native Method)
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493)
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858)
     Caused by: java.lang.IllegalArgumentException: Media is read-only
        at android.database.DatabaseUtils.readExceptionFromParcel(DatabaseUtils.java:165)
        at android.database.DatabaseUtils.readExceptionWithFileNotFoundExceptionFromParcel(DatabaseUtils.java:146)
        at android.content.ContentProviderProxy.openAssetFile(ContentProviderNative.java:625)
        at android.content.ContentResolver.openAssetFileDescriptor(ContentResolver.java:1314)
        at android.content.ContentResolver.openOutputStream(ContentResolver.java:1056)
        at android.content.ContentResolver.openOutputStream(ContentResolver.java:1032)
        at com.commonsware.android.myapplication.MainActivity.onActivityResult(MainActivity.kt:29)
        at android.app.Activity.dispatchActivityResult(Activity.java:7462)
        at android.app.ActivityThread.deliverResults(ActivityThread.java:4391)
        at android.app.ActivityThread.handleSendResult(ActivityThread.java:4440) 
        at android.app.servertransaction.ActivityResultItem.execute(ActivityResultItem.java:49) 
        at android.app.servertransaction.TransactionExecutor.executeCallbacks(TransactionExecutor.java:108) 
        at android.app.servertransaction.TransactionExecutor.execute(TransactionExecutor.java:68) 
        at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1816) 
        at android.os.Handler.dispatchMessage(Handler.java:106) 
        at android.os.Looper.loop(Looper.java:193) 
        at android.app.ActivityThread.main(ActivityThread.java:6718) 
        at java.lang.reflect.Method.invoke(Native Method) 
        at com.android.internal.os.RuntimeInit$MethodAndArgsCaller.run(RuntimeInit.java:493) 
        at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:858) 

- What you think the correct behavior should be.

The MP3 file should be replaced by a 0-byte file, which is what happens if you choose the MP3 file through browsing "internal" storage. Note: if you test this, you will want to restore that MP3 file from the aforementioned backup.

This was tested on a Pixel 3 running Android 9.0. I suspect it is a much broader problem than this.

---------

The crash stems from the MediaDocumentsProvider:

2019-05-25 18:46:46.587 11706-11718/? E/DatabaseUtils: Writing exception to parcel
    java.lang.IllegalArgumentException: Media is read-only
        at com.android.providers.media.MediaDocumentsProvider.openDocument(MediaDocumentsProvider.java:712)
        at android.provider.DocumentsProvider.openAssetFile(DocumentsProvider.java:1214)
        at android.content.ContentProvider$Transport.openAssetFile(ContentProvider.java:391)
        at android.content.ContentProviderNative.onTransact(ContentProviderNative.java:251)
        at android.os.Binder.execTransact(Binder.java:731)

MediaDocumentsProvider throws that for any write access:

https://github.com/aosp-mirror/platform_packages_providers_mediaprovider/blob/android-q-preview-2.5/src/com/android/providers/media/MediaDocumentsProvider.java#L731

The app simply launches ACTION_OPEN_DOCUMENT, then attempts to open an OutputStream on the supplied Uri:

package com.commonsware.android.myapplication

import android.app.Activity
import androidx.appcompat.app.AppCompatActivity
import android.os.Bundle
import android.content.Intent

private const val REQUEST_WTF = 1337

class MainActivity : AppCompatActivity() {

  override fun onCreate(savedInstanceState: Bundle?) {
    super.onCreate(savedInstanceState)
    setContentView(R.layout.activity_main)

    val intent = Intent(Intent.ACTION_OPEN_DOCUMENT)
    intent.addCategory(Intent.CATEGORY_OPENABLE)
    intent.type = "audio/mpeg"
    startActivityForResult(intent, REQUEST_WTF)
  }

  override fun onActivityResult(
    requestCode: Int,
    resultCode: Int,
    data: Intent?
  ) {
    if (requestCode == REQUEST_WTF) {
      if (resultCode == Activity.RESULT_OK && data != null) {
        val out = contentResolver.openOutputStream(data.data!!)

        out?.close()
      }
    }
  }
}

The problem is that we have no way of specifying on the ACTION_OPEN_DOCUMENT Intent that we intend to write and therefore want to limit the user to writable locations. Given that Android Q/R are putting extra emphasis on us migrating to the Storage Access Framework, this sort of feature is needed. Otherwise, all we can do is detect that we do not have write access (e.g., DocumentFile and canWrite()), then tell the user "sorry, I can't write there", which leads to a bad user experience. Instead, the SAF UI needs to filter out unusable locations for us, such as by us passing true for an EXTRA_READ_WRITE or EXTRA_SHOW_WRITEABLE_LOCATIONS or EXTRA_CAN_I_PLZ_WRITE_K_THX_BYE extra.

Thanks for considering this!