Another one where the script was more or less perfect as it was, minus the usual socket read/writes and print statements. One really odd thing is I guess there was a print error in the book.
The IP header structure was defined as
_fields_ = [
("ihl", c_ubyte, 4),
("version", c_ubyte, 4),
("tos", c_ubyte),
("len", c_ushort),
("id", c_ushort),
("offset", c_ushort),
("ttl", c_ubyte),
("protocol_num", c_ubyte),
("sum", c_ushort),
("src", c_ulong),
("dst", c_ulong)
]Which I needed to change to
_fields_ = [
("ihl", c_ubyte, 4),
("version", c_ubyte, 4),
("tos", c_ubyte),
("len", c_ushort),
("id", c_ushort),
("offset", c_ushort),
("ttl", c_ubyte),
("protocol_num", c_ubyte),
("sum", c_ushort),
# Changed from c_ulong to c_uint
("src", c_uint),
("dst", c_uint)
]Little strange, still trying to track down why that was, since sizeof
returns the same in python 2 and 3. Thought maybe it’s a 32-bit/64-bit
inconsistency, but again that doesn’t really make sense, since a
32 bit long is still going to be 8 bytes vs the int which will be 4.
Will have to check into it to understand it, though I’m leaning toward
it being a print error.
Enhancements
I’d like to modify this script to be a little bit smarter on when it’s time to terminate. Maybe just a timeout parameter or something to start with to kill off the thread listening on the socket. Just to tidy it up a bit more.
I’m also trying my best to keep to the quick and dirty mindset of the book, rather than going all out like in a couple of my previous posts. Feel as if I’ll procrastinate less and churn out these blogs more regularly and keep a schedule a little easier.