Decoding tcp packets using python
- by mikip
Hello
I am trying to decode data received over a tcp connection. The packets are small, no more than 100 bytes. However when there is a lot of them I receive some of the the packets joined together. Is there a way to prevent this. I am using python
I have tried to separate the packets, my source is below. The packets start with STX byte and end with ETX bytes, the byte following the STX is the packet length, (packet lengths less than 5 are invalid) the checksum is the last bytes before the ETX
def decode(data):
while True:
start = data.find(STX)
if start == -1: #no stx in message
pkt = ''
data = ''
break
#stx found , next byte is the length
pktlen = ord(data[1])
#check message ends in ETX (pktken -1) or checksum invalid
if pktlen < 5 or data[pktlen-1] != ETX or checksum_valid(data[start:pktlen]) == False:
print "Invalid Pkt"
data = data[start+1:]
continue
else:
pkt = data[start:pktlen]
data = data[pktlen:]
break
return data , pkt
I use it like this
#process reports
try:
data = sock.recv(256)
except: continue
else:
while data:
data, pkt = decode(data)
if pkt:
process(pkt)
Also if there are multiple packets in the data stream, is it best to return the packets as a collection of lists or just return the first packet
I am not that familiar with python, only C, is this method OK. Any advice would be most appreciated. Thanks in advance
Thanks
