Mine

s_initialize("tftp")s_group("opcode", values=["\x00\x01","\x00\x02"])s_group("transfertype", values=["netascii","octet","mail", "abcdabcd"])if s_block_start("filerequest", group="opcode"):	# filename	s_string("ABCDABCD")	# terminator	s_static("\x00")		if s_block_start("transtype", group="transfertype"):		s_block_end("transtype")		s_static("\x00")s_block_end("filerequest")