Тell me please, is there a potential for progess download for Android client. thx.
No there's no partial progress events fired/available during Service Client requests.
well, I'll try to implement the required functionality differently, but now I've come across another problem, the service on Linux does not return Content-Length, as I understand from the written length is set automatically: https://github.com/ServiceStack/Issues/issues/104#issuecomment-46983416
what could be my problem?
You can't rely on Content-Length being always available as HTTP Responses can return chunked transfer encoding responses which wont contain a Content-Length. Which is what the nginx reverse proxy would be doing when streaming back the HTTP Response. This answer contains some info on configuring nginx proxying behavior.