我通过COM端口与分配器进行通信。
发送ACK。如果2字节CRC不同，则使用0x11 0x31进行响应，否则使用0x31 0x10进行响应。到现在为止还挺好。但是如果缺少2字节CRC中的字节会怎样。那我该怎么办？它也包含两个字节。
例如，预期CRC为DLE-STX-DATA-DLE-ETX-CRC，但它返回NAK（其中0x10已经尝试返回DLE-STX-DATA-DLE-ETX-CRC1-CRC2的一部分，即使我没有发送NAK！）
如何在CRC本身中丢失字节？
如何恢复？
预期行为：
DLE-STX-DATA-DLE-ETX-CRC1-CRC2 DLE-STX-DATA-DLE-ETX-(missing byte)-CRC2-DLE NAK 实际行为：
STX-DATA-DLE-ETX-CRC1-CRC2 "Process finished with exit code 0"
import socket
from struct import *
import datetime
import pcapy
import sys
def main(argv):
devices = pcapy.findalldevs()
print (devices)
for d in devices:
print "Available devices are ", d
#Device to be sniffed
input_dev = raw_input("Enter deice name to sniff")
print "Following device would be printed", input_dev
#open
#device
# Arguments here are:
# device
# snaplen (maximum number of bytes to capture _per_packet_)
# promiscious mode (1 for true)
# timeout (in milliseconds)
cap = pcapy.open_live(input_dev,65536,1,0)
#Interating all packets captured in to a variable
while(1):
(header, packet) = cap.next()
parse_packet(packet)
#Convert a string of 6 characters of ethernet address into a dash separated hex string
def eth_addr(a):
b = "%.2x:%.2x:%.2x:%.2x:%.2x:%.2x" % (ord(a[0]), ord(a[1]), ord(a[2]), ord(a[3]), ord(a[4]), ord(a[5]))
# Parsing captured packets
def parse_packet(packet):
eth_length = 14
# Get the protocol used from the captured packet
eth_header = packet[:eth_length]
eth = unpack('!6s6sH', eth_header)
eth_protocol = socket.ntohs(eth[2])
print 'Destination MAC : ' + eth_addr(packet[0:6])+'Source MAC: ' + eth_addr(packet[0:12]) + 'Protocol: ' +str(eth_protocol)
# Parse the IP packet
#
if eth_protocol == 8:
#Parse IP header
#take first 20 characters for the ip header
ip_header = packet[eth_length:20+eth_length]
#Now unpack them
iph = unpack('!BBHHHBBH4s4s', ip_header)
version_ihl = iph[0]
version = version_ihl >> 4
ihl = version_ihl & oxf # need to know what is the oxf
iph_length = ihl * 4
ttl = iph[5]
print "ttl value is = ", str(ttl)
protocol = ip[6]
print "protocol = ", str(protocol)
s_addr = socket.inet_ntoa(iph[8]);
print "source address = ", str(s_addr)
d_address = socket.inet_ntoa(iph[9])
print "Destination address = ", str(d_address)
#Parsing TCP header
if protocol == 6:
#if protocol = 6, it would be TCP
t = iph_length + eth_length
tcp_heder = packet
#Unpack the packet
tcph = unpack('!HHLLBBHHH', tcp_heder)
source_port = tcph[0]
print "Source port =", source_port
dst_port = tcph[1]
print "Dst port =", dst_port
ack_no = tcph[3]
print "ack_No = ", ack_no
doff_deserverved = tcph[4]
print "doff_deserved = ", doff_deserverved
tcp_length = doff_deserverved >> 4
h_size = eth_length + iph_length + tcp_length * 4
data_size = len(packet) - h_size
#get the data from the packet
data = packet[data_size:]
print "Data is = ", data
elif protocol == 1:
u = iph_length + eth_length
icmp_length = 4
icmp_header= packet[u:u+4]
#Now unpack them
icmp = unpack('!BBH' , icmp_header)
icmp_type = icmp[0]
print "Type is = ", icmp
code = icmp[1]
print "Code is = ", code
checkSum = icmp[3]
print "Check sum is ", checkSum
h_size = eth_length + iph_length + icmp_length
data_sze = len(packet)- h_size
print "Data size = ", data_size
#Get Data from the packet
data2 = packet[h_size:]
print "Data is = ", data2
#Parsing UDP packet
elif protocol == 17:
u = iph_length + eth_length
udph_leungth = 8
udp_header = packet[u:u+8]
#Now unpack them
udp_packet = unpack('!HHHH', udp_header)
s_port = udp_packet[0]
print "Source Port = ", s_port
d_port = udp_packet[1]
print "Udp Packet = ", d_port
lenth_of_packet = udp_packet[2]
print "Length of packet = ", lenth_of_packet
check_sum = udp_packet[3]
print "check sum is ", check_sum
h_size_of_packet = eth_length + iph_length + udph_leungth
actaul_size = len(packet) - h_size_of_packet
#Retrieving data packet from the size
data = packet[h_size_of_packet]
print "Actual Data = ", data
#IF there any other some protocol
else:
print "Protol other than TCP/UDP/ICMP"
main(sys.argv)
答案 0 :(得分：0)
事实证明这是无法解决的。即使是官方的富士通实用程序也无法处理这种情况。即使处理完COM端口变得无法使用，也需要重新启动计算机。您只能从此错误中优雅地失败。