shorten UTF-8 character string to fit bytes which length you want.　

shorten_UTF8_to_byte_you_want.rb

original_file_extension = File.extname(@original_filename)
#@original_filename = File.basename(@original_filename)

@original_filename.force_encoding("ascii-8bit")

pp "ascii"
pp @original_filename

@original_filename = @original_filename[0, (configatron.uploadfilename.bytesize - original_file_extension.bytesize)]

pp "slice"
pp @original_filename

@original_filename.encode!("UTF-16BE", "UTF-8", :invalid => :replace, :undef => :replace, :replace => '')
@original_filename.encode!("UTF-8")

pp "utf-8"
pp @original_filename

@original_filename += original_file_extension

pp "bytesize"
pp @original_filename.bytesize