I'm trying to process the IP packet length field, as recorded by pcap
(Ethereal) and recovered using pcapy. When I slice out those bytes, I
get a value that shows in '\x00' format, rather than '0x00'. Neither
int() nor eval() are working. How do I handle this?
Earl Eiland 3 2120
Earl Eiland wrote: I'm trying to process the IP packet length field, as recorded by pcap (Ethereal) and recovered using pcapy. When I slice out those bytes, I get a value that shows in '\x00' format, rather than '0x00'. Neither int() nor eval() are working. How do I handle this?
Earl Eiland
You could either reconstruct the value yourself from the ord() values of
the individual bytes, or look at the struct module which can help you
with this kind of decoding task.
regards
Steve
--
Meet the Python developers and your c.l.py favorites March 23-25
Come to PyCon DC 2005 http://www.pycon.org/
Steve Holden http://www.holdenweb.com/
Earl,
Try this: ord('\x00')
0
or:
import struct struct.unpack(' b', '\x00')
(0,)
If you're needing to pull values out of multiple bytes (shorts, longs,
floats, etc.), have a look at the struct module. Here's an example:
struct.unpack(' f', '\x00\x00(B')
(42.0,)
Hope this helps,
Alan
Earl Eiland wrote: I'm trying to process the IP packet length field, as recorded by pcap (Ethereal) and recovered using pcapy. When I slice out those bytes, I get a value that shows in '\x00' format, rather than '0x00'. Neither int() nor eval() are working. How do I handle this?
Earl Eiland
On Sat, 05 Feb 2005 06:51:32 -0700, Earl Eiland <ee*@nmt.edu> wrote: I'm trying to process the IP packet length field, as recorded by pcap (Ethereal) and recovered using pcapy. When I slice out those bytes, I get a value that shows in '\x00' format, rather than '0x00'. Neither int() nor eval() are working. How do I handle this?
From my unpublished protocol analyzing hack:
class Ip:
"IPv4 header"
def __init__(self, frame):
(vi, tos, tlen,
id, ffoff,
ttl, proto, checksum,
source,
dest) = struct.unpack(' ! BBH HH BBH LL', frame[:20])
self.len = 4 * (vi & 0xf)
if proto==6:
self.proto=Tcp
elif proto==17:
self.proto=Udp
elif proto==1:
self.proto=Icmp
self.source = Address(source)
self.dest = Address(dest)
That doesn't take IP options into account (or are they part of Ip.len? I
forget.), but it has the nifty feature that IP.proto tells the caller what
factory function (if any) she should feed the rest of the frame into.
/Jorgen
--
// Jorgen Grahn <jgrahn@ Ph'nglui mglw'nafh Cthulhu
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