Allow opening files shared to android using the notification

Summary:
Since Android Nougat, the previous way to open a file shared to android did not work anymore (using `file://` urls), as marked with a TODO.

This diff implements the new way of opening files: a content provider url (`content://`) allows opening files through the KDE Connect app. As an added benefit, apps without external files permission can now open files received by KDE Connect.

Test Plan: Works for me.

Reviewers: #kde_connect, albertvaka

Reviewed By: #kde_connect, albertvaka

Subscribers: albertvaka, nicolasfella

Differential Revision: https://phabricator.kde.org/D9331

AndroidManifest.xml

@@ -198,6 +198,15 @@
                 android:name="android.service.chooser.chooser_target_service"
                 android:value="org.kde.kdeconnect.Plugins.SharePlugin.ShareChooserTargetService" />
         </activity>
+        <provider
+            android:name="android.support.v4.content.FileProvider"
+            android:authorities="org.kde.kdeconnect_tp.fileprovider"
+            android:exported="false"
+            android:grantUriPermissions="true">
+            <meta-data
+                android:name="android.support.FILE_PROVIDER_PATHS"
+                android:resource="@xml/fileprovider_paths" />
+        </provider>
         <service
             android:name="org.kde.kdeconnect.Plugins.NotificationsPlugin.NotificationReceiver"
             android:permission="android.permission.BIND_NOTIFICATION_LISTENER_SERVICE" >

res/xml/fileprovider_paths.xml

@@ -0,0 +1,4 @@
+<?xml version="1.0" encoding="utf-8"?>
+<paths xmlns:android="http://schemas.android.com/apk/res/android">
+   <external-path name="external_files" path="." />
+</paths>

src/org/kde/kdeconnect/Plugins/SharePlugin/ShareNotification.java

@@ -31,11 +31,14 @@ import android.os.Build;
 import android.preference.PreferenceManager;
 import android.support.v4.app.NotificationCompat;
 import android.support.v4.app.TaskStackBuilder;
+import android.support.v4.content.FileProvider;
 
 import org.kde.kdeconnect.Device;
 import org.kde.kdeconnect.Helpers.NotificationHelper;
 import org.kde.kdeconnect_tp.R;
 
+import java.io.File;
+
 public class ShareNotification {
 
     private final String filename;
@@ -88,11 +91,28 @@ public class ShareNotification {
     }
 
     public void setURI(Uri destinationUri, String mimeType) {
-        // Nougat requires share:// URIs instead of file:// URIs
+        /*
-        // TODO use FileProvider for >=Nougat
+         * We only support file URIs (because sending a content uri to another app does not work for security reasons).
-        if (Build.VERSION.SDK_INT < 24) {
+         * In effect, that means only the default download folder currently works.
+         *
+         * TODO: implement our own content provider (instead of support-v4's FileProvider). It should:
+         *  - Proxy to real files (in case of the default download folder)
+         *  - Proxy to the underlying content uri (in case of a custom download folder)
+         */
+        if (!"file".equals(destinationUri.getScheme())) {
+            return;
+        }
+
         Intent intent = new Intent(Intent.ACTION_VIEW);
+        if (Build.VERSION.SDK_INT >= 24) {
+            //Nougat and later require "content://" uris instead of "file://" uris
+            File file = new File(destinationUri.getPath());
+            Uri contentUri = FileProvider.getUriForFile(device.getContext(), "org.kde.kdeconnect_tp.fileprovider", file);
+            intent.setDataAndType(contentUri, mimeType);
+            intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
+        } else {
             intent.setDataAndType(destinationUri, mimeType);
+        }
         intent.addFlags(Intent.FLAG_ACTIVITY_NEW_TASK);
         TaskStackBuilder stackBuilder = TaskStackBuilder.create(device.getContext());
         stackBuilder.addNextIntent(intent);
@@ -101,4 +121,3 @@ public class ShareNotification {
                 .setContentIntent(resultPendingIntent);
     }
 }
-}