def build_ip_packet(pkt_len, protocol, saddr, daddr, message, pkt_id=1, flags_df=0, flags_mf=0, offset=0):
"""创建IP数据包
:param pkt_len:包长度
:param saddr: bytes类型的源地址
:param daddr: bytes类型的目的地址
:param message:消息内容
:param pkt_id: 包ID
:param flags_df: 分段df位
:param flags_mf:分段mf位
:param offset:包偏移
:return ip_pkt:
"""
if pkt_len < __IP_HDR_SIZE: raise ValueError("the value of pkt_len must be less than 20")
if protocol < 0 or protocol > 255: raise ValueError("the value of protocol is wrong")
tpl = b'E\x00\x00\x14\x00\x01\x00\x00@\x00z\xea\x00\x00\x00\x00\x00\x00\x00\x00'
L = list(tpl)
# 修改地址
csum = (L[10] << 8) | L[11]
csum = checksum.calc_checksum_for_ip_change(tpl[12:16], saddr, csum)
csum = checksum.calc_checksum_for_ip_change(tpl[16:20], daddr, csum)
L[12:16] = saddr
L[16:20] = daddr
# 修改包长度
old_v = (L[2] << 8) | L[3]
new_v = pkt_len
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[2:4] = ((pkt_len & 0xff00) >> 8, pkt_len & 0x00ff,)
# 修改包ID
old_v = (L[4] << 8) | L[5]
new_v = pkt_id
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[4:6] = ((pkt_id & 0xff00) >> 8, pkt_id & 0x00ff,)
# 修改flags以及offset
old_v = (L[6] << 8) | L[7]
new_v = (flags_df << 14) | (flags_mf << 13) | offset
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[6:8] = ((new_v & 0xff00) >> 8, new_v & 0x00ff,)
# 修改协议
old_v = L[9]
new_v = protocol
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[9] = protocol
# 修改校检和
# L[10:12] = (0, 0,)
# csum = fn_utils.calc_csum(bytes(L), 20)
L[10:12] = ((csum & 0xff00) >> 8, csum & 0x00ff,)
return b"".join((bytes(L), message,))
def __modify_src_address(self, new_ip_pkt, pkt_list):
"""修改源地址"""
old_checsum = (pkt_list[10] << 8) | pkt_list[11]
new_csum = checksum.calc_checksum_for_ip_change(
bytes(pkt_list[12:16]), new_ip_pkt, old_checsum
)
pkt_list[10:12] = ((new_csum & 0xff00) >> 8, new_csum & 0x00ff,)
pkt_list[12:16] = new_ip_pkt
def build_ip_packet(pkt_len,
protocol,
saddr,
daddr,
message,
pkt_id=1,
flags_df=0,
flags_mf=0,
offset=0):
"""创建IP数据包
:param pkt_len:包长度
:param saddr: bytes类型的源地址
:param daddr: bytes类型的目的地址
:param message:消息内容
:param pkt_id: 包ID
:param flags_df: 分段df位
:param flags_mf:分段mf位
:param offset:包偏移
:return ip_pkt:
"""
if pkt_len < __IP_HDR_SIZE:
raise ValueError("the value of pkt_len must be less than 20")
if protocol < 0 or protocol > 255:
raise ValueError("the value of protocol is wrong")
tpl = b'E\x00\x00\x14\x00\x01\x00\x00@\x00z\xea\x00\x00\x00\x00\x00\x00\x00\x00'
L = list(tpl)
# 修改地址
csum = (L[10] << 8) | L[11]
csum = checksum.calc_checksum_for_ip_change(tpl[12:16], saddr, csum)
csum = checksum.calc_checksum_for_ip_change(tpl[16:20], daddr, csum)
L[12:16] = saddr
L[16:20] = daddr
# 修改包长度
old_v = (L[2] << 8) | L[3]
new_v = pkt_len
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[2:4] = (
(pkt_len & 0xff00) >> 8,
pkt_len & 0x00ff,
)
# 修改包ID
old_v = (L[4] << 8) | L[5]
new_v = pkt_id
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[4:6] = (
(pkt_id & 0xff00) >> 8,
pkt_id & 0x00ff,
)
# 修改flags以及offset
old_v = (L[6] << 8) | L[7]
new_v = (flags_df << 14) | (flags_mf << 13) | offset
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[6:8] = (
(new_v & 0xff00) >> 8,
new_v & 0x00ff,
)
# 修改协议
old_v = L[9]
new_v = protocol
csum = fn_utils.calc_incre_csum(csum, old_v, new_v)
L[9] = protocol
# 修改校检和
# L[10:12] = (0, 0,)
# csum = fn_utils.calc_csum(bytes(L), 20)
L[10:12] = (
(csum & 0xff00) >> 8,
csum & 0x00ff,
)
return b"".join((
bytes(L),
message,
))
