private void EnsureManifest() { using (Stream stream = _streamFactory()) { var package = new ZipArchive(stream); ZipArchiveEntry manifestPart = package.GetManifest(); if (manifestPart == null) { throw new InvalidOperationException(NuGetResources.PackageDoesNotContainManifest); } using (Stream manifestStream = manifestPart.Open()) { ReadManifest(manifestStream); } } }