[https://github.com/SSPkrolik/nimongo/pull/81](https://github.com/SSPkrolik/nimongo/pull/81) there, added for limited elementary functionalities for GridFS.
Unfortunately I never intensively used mongo except for simplest CRUD and those GridFS features only tested on Windows, very likely you need to test for Linux and/or Bsd variants. My Mongodb version is 4.0.5
