To add extension to a Ruby tempfile, I figured that tempfile module needs to be modified a little.

​

Make a class like this:

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require 'tempfile'

​

class CustomTempfle < Tempfile

  def initialize(filename, temp_dir = nil)

    temp_dir ||= Dir.tmpdir

    extension = File.extname(filename)

    basename = File.basename(filename, extension)

    super([basename, extension], temp_dir)

  end

end

And then you can call the class and provide the filename with the extensio and write to the file like so.

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CustomTempfle.open('filename.pdf', nil) do |tmp|

  File.open(tmp, 'wb') { |f| f << 'content_of_the_file' }

end