Am 10.07.2011 22:59 schrieb Littlefield, Tyler:
Hello all:
I'm working on a server that will need to parse packets sent from a
client, and construct it's own packets.
Are these packets sent as separate UDP packets or embedded in a TCP
stream? In the first case, you already have packets and only have to
parse them. In a stream, you first have to split them up.
In the following, I will talk about UDP datagrams. For TCP, further work
is needed.
The setup is something like this: the first two bytes is the type of the
packet.
Then you have
type = struct.unpack(">H", packet),
payload1 = packet[2:]
So, lets say we have a packet set to connect. There are two types of
connect packet: a auth packet and a connect packet.
The connect packet then has two bytes with the type, another byte that
notes that it is a connect packet, and 4 bytes that contains the version
of the client.
if type == CONNECT:
subtype = struct.unpack("B", payload1)
payload2 = payload1[1:]
if subtype == CONNECT:
upx = payload2.split("\0")
assert len(upx) == 3 and upx[-1] == ''
username, password = upx[:2]
else:
assert len(payload2) == 4
version = struct.unpack(">L", payload2)
The auth packet has the two bytes that tells what packet it is, one byte
denoting that it is an auth packet, then the username, a NULL character,
and a password and a NULL character.
With all of this said, I'm kind of curious how I would 1) parse out
something like this (I am using twisted, so it'll just be passed to my
Receive function),
I. e., you already have your packets distinct? That's fine.
> and how I get the length of the packet with multiple NULL values.
With len(), how else?
> I'm also looking to build a packet and send it back out, is
there something that will allow me to designate two bytes, set
individual bits, then put it altogether in a packet to be sent out?
The same: with struct.pack().
Thomas
--
http://mail.python.org/mailman/listinfo/python-list
