How to use the pypacker.structcbs.unpack_H function in pypacker

def _dissect(self, buf):
		# update dynamic header parts. buf: 1010???? -clear reserved-> 1010 -> *4
		ol = ((buf[12] >> 4) << 2) - 20	 # dataoffset - TCP-standard length

		if ol > 0:
			# parse options, add offset-length to standard-length
			opts_bytes = buf[20: 20 + ol]
			self._init_triggerlist("opts", opts_bytes, self._parse_opts)
		elif ol < 0:
			raise Exception("invalid header length")

		ports = [unpack_H(buf[0:2])[0], unpack_H(buf[2:4])[0]]

		try:
			# source or destination port should match
			# logger.debug("TCP handler: %r" % self._id_handlerclass_dct[TCP])
			htype = [x for x in ports if x in self._id_handlerclass_dct[TCP]][0]
			#logger.debug("TCP: trying to set handler, type: %d = %s" %
			#(type, self._id_handlerclass_dct[TCP][type]))
			self._init_handler(htype, buf[20 + ol:])
		except:
			# no type found
			pass
		return 20 + ol

def fletcher32(data_to_checksum, amount_words):
	# 1 word = 2 Bytes
	sum1 = 0xFFFF
	sum2 = 0xFFFF
	datapos = 0

	while amount_words > 0:
		tlen = 359 if amount_words > 359 else amount_words
		amount_words -= tlen

		while tlen > 0:
			# sum1 += unpack_word_be(data_to_checksum[datapos:datapos+2])[0]
			# print("%d" % sum1)
			sum1 += unpack_H(data_to_checksum[datapos: datapos + 2])[0]
			datapos += 2
			sum2 += sum1
			# print("%d" % sum1)
			# print("%d" % sum2)
			# print("--")
			tlen -= 1
		sum1 = (sum1 & 0xFFFF) + (sum1 >> 16)
		sum2 = (sum2 & 0xFFFF) + (sum2 >> 16)
	# Second reduction step to reduce sums to 16 bits
	sum1 = (sum1 & 0xFFFF) + (sum1 >> 16)
	sum2 = (sum2 & 0xFFFF) + (sum2 >> 16)
	return (sum2 << 16) | sum1

def _dissect(self, buf):
		ports = [unpack_H(buf[0:2])[0], unpack_H(buf[2:4])[0]]

		try:
			# source or destination port should match
			htype = [x for x in ports if x in pypacker.Packet._id_handlerclass_dct[UDP]][0]
			self._init_handler(htype, buf[8:])
		except:
			# no type found
			# logger.debug("could not parse type: %d because: %s" % (type, e))
			pass
		return 8

def _parse_icmp6opt(buf):
		# TODO: create generic TLV-parser
		opts = []
		off = 0

		while off < len(buf):
			optlen = unpack_H(buf[1:3])[0] * 8
			opt = ICMP6.ICMPv6Opt(buf[off: off + optlen])
			opts.append(opt)
			off += optlen
		return opts

def count_and_dissect_tlvs(buf):
	"""
	Count and dissect TLVs. Return length of LLDP layer

	buf -- buffer to dissect
	return -- parsed_bytes_total, [(clz, bts), ...]
	"""
	shift = 0
	tlv_type, tlv_len = 1, 1
	clz_bts_list = []

	while (tlv_type | tlv_len) != 0:
		type_and_len = unpack_H(buf[shift:shift + TLV_HEADER_LEN])[0]
		# get tlv length and type
		tlv_type = (type_and_len & TYPE_MASK) >> LENGTH_FIELD_BITS
		tlv_len = type_and_len & LENGTH_MASK

		if tlv_type != ORG_SPEC_TYPE:
			clz = LLDP_TLV_CLS.get(tlv_type, LLDPGeneric)
		else:
			oui_subtype = unpack_I(buf[shift + TLV_HEADER_LEN:shift + ORG_SPEC_HEADER_LEN + TLV_HEADER_LEN])[0]
			oui = (oui_subtype & OUI_MASK) >> SUBTYPE_LEN_BITS
			subtype = oui_subtype & SUBTYPE_MASK
			clz = LLDP_ORG_SPEC_TLV_CLS.get((oui, subtype), LLDPOrgSpecGeneric)
		# get body bytes
		tlv_body = buf[shift: tlv_len + shift + TLV_HEADER_LEN]
		# update shift to begin of next TLV (TLV_HEADER_LEN:2 + content:x)
		shift += TLV_HEADER_LEN + tlv_len
		clz_bts_list.append((clz, tlv_body))

def _dissect(self, buf):
		htype = unpack_H(buf[14: 16])[0]
		# logger.debug("type: %X" % type)
		self._init_handler(htype, buf[16:])
		return 16

def __get_time(self):
			return [unpack_H(x)[0] for x in self.time]

def _dissect(self, buf):
		hlen = 2
		opcode = unpack_H(buf[: 2])
		# logger.debug("opcode: %d" % opcode)

		if opcode in OPCODES_DATA_ACK:
			pass
		elif opcode in OPCODES_READ_WRITE:
			self.block = None
			file, ttype = split_nullbyte(buf[2:], maxsplit=2)
			# logger.debug("file/ttype = %r / %r" % (file, ttype))
			self.file = file + b"\x00"
			self.ttype = ttype + b"\x00"
			hlen = 2 + len(self.file) + len(self.ttype)
		elif opcode == OP_ERR:
			# TODO: update
			pass
		return hlen

def __parse_attrs(buf):
		attributes = []
		off = 0

		# t:2 l:2 v:x
		while off < len(buf):
			l_content = unpack_H(buf[off + 2: off + 4])[0]
			padding = (4 - (l_content % 4)) % 4
			l_total = l_content + padding + 2 + 2
			#logger.debug("STUN attr l_content: %d, padding: %d, value: %s" %
			#	 (l_content, padding, buf[off : off + l_total]))
			attributes.append(StunAttr(buf[off: off + l_total]))
			off += l_total
		return attributes

def _dissect(self, buf):
			# withdrawn Routes
			off = 4
			off_end = off + unpack_H(buf[:2])[0]

			while off < off_end:
				rlen = 3 + 0
				route = Route(buf[off:])
				self.wroutes.append(route)
				off += rlen

			# path attributes
			off_end = off + unpack_H(buf[2:4])[0]
			#logger.debug("unpacking attributes")

			while off < off_end:
				alen = 3 + buf[off + 2]
				#logger.debug("bytes for attribute: %r" % buf[off: off + alen])
				attr = BGP.Update.Attribute(buf[off: off + alen])
				self.pathattrs.append(attr)
				off += alen

			# announced routes
			off_end = len(buf)
			#logger.debug("unpacking routes")

			while off < off_end:
				rlen = 3 + 0
				#logger.debug("bytes for route: %r" % buf[off:off + rlen])