How do I determine if Tempfile is a stream or not?

Question

I have a problem with roo gem. When I upload the file using my Rails app it ends up as a Tempfile on the file system, because I do not want to keep the file but import the spreadsheet data from it.

https://github.com/roo-rb/roo/blob/3ed05e1caef0ce3c5db5c19f1fa14e6f74193079/lib/roo/base.rb#L374

The above line checks if my object responds to seek. And that leads to a problem.

(byebug) filename_or_stream.class
Tempfile

(byebug) filename_or_stream.methods.include? :seek
true

How do you suggest I should go round this problem?

I have tried to suppress the error

https://github.com/bigos/roo/commit/55ec3325ec3131fa34c3e0f5e647160cb17ef114

and was able to continue with my work, but the question still remains, How did the Tempfile get the seek method?

Looking for seek leads to this line

https://github.com/roo-rb/roo/blob/3ed05e1caef0ce3c5db5c19f1fa14e6f74193079/lib/roo/open_office.rb#L372

which makes no sense to me and I still do not know why Tempfile responds to seek if the documentation does not say anything about it.

application illustrating the problem

https://github.com/bigos/open_example/blob/master/spec/models/open_sheet_spec.rb

possible simple solution

if file.is_a? Tempfile
  @workbook = Roo::OpenOffice.new(file.path)
else
  @workbook = Roo::OpenOffice.new(file)
end

But why it was only a problem with Opensheet part of the roo gem? I did not notice the problem in other spreadsheets.