If a ZipArchive instance is created with ZipArchiveMode.Update then disposed without being used to modify the archive, the underlying stream is still modified. If that underlying stream is a FileStream, this results in the associated file's modified timestamp being updated.

void Test() {
  using var stream = new FileStream("Test.zip", FileMode.Open, FileAccess.ReadWrite);
  using (var zip = new ZipArchive(stream, ZipArchiveMode.Update))
  {
     // do nothing
  } // even though the archive was unchanged from the user's perspective, stream is still updated, which changes Test.zip's modified timestamp
}

In contrast, FileStream does not exhibit this behavior. Simply opening a modifiable FileStream does not change the underlying file's modified timestamp.

Is how ZipArchive modifies its backing stream even when the archive is unmodified by the user a bug or a feature? :-)

What would be the chances of ZipArchive's manners being improved to avoid modifying its backing stream in this case?

Thanks!

-- dotnet version: 3.1.200