Torrent debugging tools

Question

Is there some sort of tools to debug bittorrent? e.g. I wish to query tracker to get peer list. I wish to check if I able to connect to certain peer.

I have odd behavior in my home network. I wish to understand how it works and I can't find any tools to simulate torrent.

PS I already made a simple python app to check if I can receive UDP packets

import socket
port = 50000
s = socket.socket(socket.AF_INET, socket.SOCK_DGRAM)
s.bind(("", port))
print "waiting on port:", port
while 1:
    data, addr = s.recvfrom(1024)
    print data

and I can send ncat $IP $PORT -u -v

But now when I know I can send packet to certain port and it is opened. I wish to check if I can talk with torrent app on that port.

One torrent client works and other don't I want to know what is wrong.

Answer 1

There is no "The Bittorrent Debugger", but you can use various tools to diagnose problems.

You can use nmap locally or web services providing a frontend to remote nmap instances to probe the reachability of ports.

You can use wireshark with the bittorrent dissector to debug the protocol itself, some understanding of the bittorrent protocol is required for that.

Some clients (e.g. vuze) provide very verbose logging, down to individual bittorrent messages which can help with diagnosing problems.

You can run a second client on a different port or on a virtual machine and have them talk to each other over the local network to exclude potential router/firewall issues.

Answer 2

What I have done to debug protocol issues in my own code is that I have various VMs/containers set up with 1 running a tracker (opentracker) and others running various clients and my host running my own client which I test regularly. Then I selectively start and stop the clients and make them talk to my client and the tracker and then I can easily analyze all the bittorrent traffic that's passing through between all the pieces with wireshark. You can easily extend the same setup to include multiple machines in a real network rather than VMs/containers and virtual networks.

To "make" the clients talk to each other, just create a torrent with one of the clients (most clients can make torrents from files you have) and add your own tracker to the torrent. Then add the torrent file to your other clients and they start talking to each other and distributing the data immediately.

At the end, you'll have something like this:

                    +-----------+
Debug client <----> |           | <----> opentracker <--------> another client
     ^              | Wireshark |                                     ^
     |              |           |                                     |
     +------------> |           | <-----------------------------------+
                    +-----------+

And you can precisely analyse the traffic you're getting through the bittorrent protocol. Wireshark even has dissectors for bittorrent TCP protocol, so you don't even have to decipher the cryptic bytes yourself.

Note that you'll have to know about the protocol itself:

• Protocol and .torrent file spec
• Tracker spec