How to write a simple Bittorrent application?

Question

How to write a simple bittorrent application. Something like a "hello world" using a bittorrent library, I mean a simplest of the application to understand the working of bittorrent. I would prefer a python or a C/C++ implementation, but it can be any language. Platform is not an issues either, but i would prefer Linux.

Recommendations for the library to follow, I have downloaded the source code for one (i think official bittorrent) from - http://sourceforge.net/projects/bittorrent/develop. But, I see a lot of other libraries at http://en.wikipedia.org/wiki/Comparison_of_BitTorrent_clients#Libraries. I would appreciate recommendations on this.

How to test an application if all you have is one laptop.

Answer 1

You should try libtorrent (rasterbar). http://libtorrent.org

If you want to write your client in python, on linux, install it with:

sudo apt-get install python-libtorrent

A very simple example of python code to use it to download a torrent:

import libtorrent as lt
import time
import sys

ses = lt.session()
ses.listen_on(6881, 6891)

info = lt.torrent_info(sys.argv[1])
h = ses.add_torrent({'ti': info, 'save_path': './'})
print 'starting', h.name()

while (not h.is_seed()):
   s = h.status()

   state_str = ['queued', 'checking', 'downloading metadata', \
      'downloading', 'finished', 'seeding', 'allocating', 'checking fastresume']
   print '\r%.2f%% complete (down: %.1f kb/s up: %.1f kB/s peers: %d) %s' % \
      (s.progress * 100, s.download_rate / 1000, s.upload_rate / 1000, \
      s.num_peers, state_str[s.state]),
   sys.stdout.flush()

   time.sleep(1)

print h.name(), 'complete'