Fix downloading/exporting when overwriting file would not truncate

app/src/main/java/org/schabi/newpipe/local/subscription/services/SubscriptionsExportService.java

@@ -76,7 +76,10 @@ public int onStartCommand(final Intent intent, final int flags, final int startI
 
         try {
             outFile = new StoredFileHelper(this, path, "application/json");
-            outputStream = new SharpOutputStream(outFile.getStream());
+            // truncate the file before writing to it, otherwise if the new content is smaller than
+            // the previous file size, the file will retain part of the previous content and be
+            // corrupted
+            outputStream = new SharpOutputStream(outFile.openAndTruncateStream());
         } catch (final IOException e) {
             handleError(e);
             return START_NOT_STICKY;

app/src/main/java/org/schabi/newpipe/settings/export/ImportExportManager.kt

@@ -24,8 +24,9 @@ class ImportExportManager(private val fileLocator: BackupFileLocator) {
      */
     @Throws(Exception::class)
     fun exportDatabase(preferences: SharedPreferences, file: StoredFileHelper) {
-        file.create()
-        ZipOutputStream(SharpOutputStream(file.stream).buffered()).use { outZip ->
+        // truncate the file before writing to it, otherwise if the new content is smaller than the
+        // previous file size, the file will retain part of the previous content and be corrupted
+        ZipOutputStream(SharpOutputStream(file.openAndTruncateStream()).buffered()).use { outZip ->
             // add the database
             ZipHelper.addFileToZip(
                 outZip,

app/src/main/java/org/schabi/newpipe/streams/io/StoredFileHelper.java

@@ -189,6 +189,19 @@ public SharpStream getStream() throws IOException {
         }
     }
 
+    public SharpStream openAndTruncateStream() throws IOException {
+        final SharpStream sharpStream = getStream();
+        try {
+            sharpStream.setLength(0);
+        } catch (final Throwable e) {
+            // we can't use try-with-resources here, since we only want to close the stream if an
+            // exception occurs, but leave it open if everything goes well
+            sharpStream.close();
+            throw e;
+        }
+        return sharpStream;
+    }
+
     /**
      * Indicates whether it's using the {@code java.io} API.
      *

app/src/test/java/org/schabi/newpipe/settings/ImportExportManagerTest.kt

@@ -55,7 +55,7 @@ class ImportExportManagerTest {
         `when`(sharedPreferences.all).thenReturn(expectedPreferences)
 
         val output = File.createTempFile("newpipe_", "")
-        `when`(storedFileHelper.stream).thenReturn(FileStream(output))
+        `when`(storedFileHelper.openAndTruncateStream()).thenReturn(FileStream(output))
         ImportExportManager(fileLocator).exportDatabase(sharedPreferences, storedFileHelper)
 
         val zipFile = ZipFile(output)