Net::FTP#getbinaryfile

# File tmp/rubies/ruby-3.0.5/lib/net/ftp.rb, line 769
def getbinaryfile(remotefile, localfile = File.basename(remotefile),
                  blocksize = DEFAULT_BLOCKSIZE, &block) # :yield: data
  f = nil
  result = nil
  if localfile
    if @resume
      rest_offset = File.size?(localfile)
      f = File.open(localfile, "a")
    else
      rest_offset = nil
      f = File.open(localfile, "w")
    end
  elsif !block_given?
    result = String.new
  end
  begin
    f&.binmode
    retrbinary("RETR #{remotefile}", blocksize, rest_offset) do |data|
      f&.write(data)
      block&.(data)
      result&.concat(data)
    end
    return result
  ensure
    f&.close
  end
end