From: "Luis G." <l17339@...>
Date: 2010-12-17T02:15:19+09:00
Subject: Re: How to do UDP calls

Hey man, thanks for your reply.

I read the documentation but this is hard for me... But actually I don't 
have enough skills to do this without help...

So, as far as I understood in the structures section of the UDP tracker 
protocol documentation, the first thing I need to do is:

   1. Choose a (random) transaction ID.
   2. Fill the connect input structure.
   3. Send the packet.

connect input
64-bit integer  connection_id  0x41727101980
32-bit integer  action          0
32-bit integer  transaction_id  16

You told me that Array#pack will help me. This means that I need to put 
the the content of the connect input in an array and pack it so I can 
send it, right?
Actually I thought we need to have something like:
connection_id =>0x41727101980
action => 0
...

Anyway, see this example:

data = Array.new
data << 0x41727101980 #connection_id
data << 0 #action
data << 16 #transaction_id

host = 'tracker.openbittorrent.com'
port = 80

s = data.pack('q') #q?!

sock = UDPSocket.open
sock.connect(host, port)
sock.send(s, 0)
response = sock.recvfrom(1024)

After this I should:
   1. Receive the packet (response).
   2. Check whether the packet is at least 16 bytes.
   3. Check whether the transaction ID is equal to the one you chose.
   4. Check whether the action is connect.
   5. Store the connection ID for future use.

You can see something wrong with this code?

BTW, I tried

echo "GET /announce" | nc -u tracker.openbittorrent.com 80
sudo tcpdump -i eth0 -nn -s0 udp port 80

and I got results:
18:09:14.719638 IP 192.168.182.123.57232 > 95.215.62.26.80: UDP, length 
14

Thanks a lot,

Luis

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