WIP on adding proper android content:// provider

android/app/src/main/AndroidManifest.xml

@@ -11,6 +11,12 @@
   <uses-sdk android:minSdkVersion="8" android:targetSdkVersion="26"/>
   
   <application android:icon="@mipmap/ccicon" android:label="ClassiCube">
+    <provider
+        android:name="com.classicube.CCFileProvider"
+        android:authorities="com.classicube.android.client.ccfiles"
+        android:exported="false"
+        android:grantUriPermissions="true" >
+    </provider>
 
     <activity android:name="com.classicube.MainActivity" android:label="ClassiCube"
               android:configChanges="orientation|screenSize|keyboard|keyboardHidden">

android/app/src/main/java/com/classicube/CCFileProvider.java

@@ -0,0 +1,111 @@
+package com.classicube;
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.io.IOException;
+import java.util.ArrayList;
+
+import android.content.ContentProvider;
+import android.content.ContentValues;
+import android.content.Context;
+import android.content.pm.ProviderInfo;
+import android.database.Cursor;
+import android.database.MatrixCursor;
+import android.net.Uri;
+import android.os.ParcelFileDescriptor;
+import android.provider.OpenableColumns;
+
+public class CCFileProvider extends ContentProvider
+{
+    final static String[] DEFAULT_COLUMNS = { OpenableColumns.DISPLAY_NAME, OpenableColumns.SIZE };
+    File root;
+
+    @Override
+    public boolean onCreate() {
+        return true;
+    }
+
+    @Override
+    public void attachInfo(Context context, ProviderInfo info) {
+        super.attachInfo(context, info);
+        root = context.getExternalFilesDir(null); // getGameDataDirectory
+    }
+
+    @Override
+    public Cursor query(Uri uri, String[] projection, String selection, String[] selectionArgs, String sortOrder) {
+        File file = getFileForUri(uri);
+        // can be null when caller is requesting all supported columns
+        if (projection == null) projection = DEFAULT_COLUMNS;
+
+        ArrayList<String> cols = new ArrayList<String>(2);
+        ArrayList<Object> vals = new ArrayList<Object>(2);
+
+        for (String column : projection) {
+            if (column.equals(OpenableColumns.DISPLAY_NAME)) {
+                cols.add(OpenableColumns.DISPLAY_NAME);
+                vals.add(file.getName());
+            } else if (column.equals(OpenableColumns.SIZE)) {
+                cols.add(OpenableColumns.SIZE);
+                vals.add(file.length());
+            }
+        }
+
+        // https://stackoverflow.com/questions/4042434/converting-arrayliststring-to-string-in-java
+        MatrixCursor cursor = new MatrixCursor(cols.toArray(new String[0]), 1);
+        cursor.addRow(vals.toArray());
+        return cursor;
+    }
+
+    @Override
+    public String getType(Uri uri) {
+        String path = uri.getEncodedPath();
+        int sepExt  = path.lastIndexOf('.');
+
+        if (sepExt >= 0) {
+            String fileExt = path.substring(sepExt);
+            if (fileExt.equals(".png")) return "image/png";
+        }
+        return "application/octet-stream";
+    }
+
+    @Override
+    public Uri insert(Uri uri, ContentValues values) {
+        throw new UnsupportedOperationException("Readonly access");
+    }
+
+    @Override
+    public int update(Uri uri, ContentValues values, String selection, String[] selectionArgs) {
+        throw new UnsupportedOperationException("Readonly access");
+    }
+
+    @Override
+    public int delete(Uri uri, String selection, String[] selectionArgs) {
+        throw new UnsupportedOperationException("Readonly access");
+    }
+
+    @Override
+    public ParcelFileDescriptor openFile(Uri uri, String mode) throws FileNotFoundException {
+        File file = getFileForUri(uri);
+        return ParcelFileDescriptor.open(file, ParcelFileDescriptor.MODE_READ_ONLY);
+    }
+
+    public static Uri getUriForFile(String path) {
+        // See AndroidManifest.xml for authority
+        return new Uri.Builder()
+                .scheme("content")
+                .authority("com.classicube.android.client.ccfiles")
+                .encodedPath(Uri.encode(path, "/"))
+                .build();
+    }
+
+    File getFileForUri(Uri uri) {
+        String path = uri.getPath();
+        File file   = new File(root, path);
+        
+        file = file.getAbsoluteFile();
+        // security validation check
+        if (!file.getPath().startsWith(root.getPath())) {
+            throw new SecurityException("Resolved path lies outside app directory:" + path);
+        }
+        return file;
+    }
+}

android/app/src/main/java/com/classicube/MainActivity.java

@@ -26,7 +26,6 @@ import android.database.Cursor;
 import android.graphics.PixelFormat;
 import android.net.Uri;
 import android.os.Bundle;
-import android.os.StrictMode;
 import android.provider.OpenableColumns;
 import android.provider.Settings.Secure;
 import android.text.Editable;
@@ -159,19 +158,6 @@ public class MainActivity extends Activity
 		runGameAsync();
 	}
 	
-	void HACK_avoidFileUriExposedErrors() {
-		// StrictMode - API level 9
-		// disableDeathOnFileUriExposure - API level 24 ?????
-		try {
-			Method m = StrictMode.class.getMethod("disableDeathOnFileUriExposure");
-			m.invoke(null);
-		}  catch (NoClassDefFoundError ex) {
-			ex.printStackTrace();
-		} catch (Exception ex) {
-			ex.printStackTrace();
-		}
-	}
-	
 	@Override
 	protected void onCreate(Bundle savedInstanceState) {
 		// requestWindowFeature - API level 1
@@ -193,9 +179,6 @@ public class MainActivity extends Activity
 		// renderOverDisplayCutouts();
 		// TODO: semaphore for destroyed and surfaceDestroyed
 
-		// avoid FileUriExposed exception when taking screenshots on recent Android versions
-		HACK_avoidFileUriExposedErrors();
-
 		if (!gameRunning) startGameAsync();
 		// TODO rethink to avoid this
 		if (gameRunning) updateInstance();
@@ -811,11 +794,11 @@ public class MainActivity extends Activity
 	
 	public String shareScreenshot(String path) {
 		try {
-			File file = new File(getGameDataDirectory() + "/screenshots/" + path);
+			Uri uri = CCFileProvider.getUriForFile("screenshots", path);
 			Intent intent = new Intent();
 			
 			intent.setAction(Intent.ACTION_SEND);
-			intent.putExtra(Intent.EXTRA_STREAM, Uri.fromFile(file));
+			intent.putExtra(Intent.EXTRA_STREAM, uri);
 			intent.setType("image/png");
 			intent.addFlags(Intent.FLAG_GRANT_READ_URI_PERMISSION);
 			startActivity(Intent.createChooser(intent, "share via"));