def get_contents_to_buf(self):
#download file by using file name(string)
#flow : download each cloud storage -> combine -> decryption -> save complete file -> flush tmp dir
#download each cloud storage
#download from s3
combiner = file_mng(self.tmp_dir)
tmp_dir = combiner.tmp_dir
print "download to s3"
self.s3_key.get_contents_to_filename(tmp_dir+"tmp1")
print "download to ssg"
self.ssg_key.get_contents_to_filename(tmp_dir+"tmp2")
#combine files
enc_buf = combiner.combine_tmp_files()
#decryption(save complete file)
dec = Encryption(self.tree.connection._cre.meta_pw)
#decrpytion(filename)
dec_buf = dec.decrypt(enc_buf)
#flush tmp dir
combiner.flush_tmp_dir()
#error시엔 에러 메시지 출력 후 finally로 무조건 tmp dir 날리기
return dec_buf
