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);
}
}
}