Bittorrent and DHT library and scripts

[Gorjan Petrovski <mogi57 () gmail com>]

Hello,

I've written a bittorrent library which allows the user to discover
peers and nodes using a torrent file or a magnet link as well as
decode . This is my first library so any comments are welcome.
You may find it in the nmap-exp/gorjan/ repository under the name
bittorrent.lua

The workflow for using this library would be to initialize a new
Torrent object, load information about it with a magnet link or a
torrent file, then request the discovery of peers using trackers, and
then discover peers using the DHT protocol for a certain time period.
The following code illustrates how this would be achieved.

<code>
  local filename = "/home/user/name.torrent"
  local torrent = bittorrent.Torrent:new()
  torrent:load_from_file(filename)
  torrent:trackers_peers() -- to load peers from the trackers
  torrent:dht_peers() -- to further load peers using the DHT protocol
from existing peers
</code>
 After these operations the peers and nodes can be found in the
torrent.peers and torrent.nodes tables respectively.

I've also implemented a script which discovers the nodes and peers for
a given magnet link or a torrent file. I decided to separate the
library and the script because the code is more clean and I also have
another idea for discovery of nodes which I intend to implement soon.
The script may be checked out from
nmap-exp/gorjan/bittorrent-discovery.nse

The script discovers bittorrent peers and nodes using the Bittorrent
and DHT protocol when
supplied with a valid torrent file or a magnet link. The peers implement the
Bittorrent protocol and share the torrent, whereas the nodes implement the DHT
protocol and are used to track the peers. The sets of peers and nodes are not
the same, but they usually intersect.

If the newtargets script-arg is supplied it adds the discovered
peers as targets.

usage string:
 nmap --script bittorrent-discovery --script-args
bittorrent-discovery.torrent=<filename>,
 bittorrent-discovery.magnet=<magnet_link>[,bittorrent-discovery.dht_timeout=<seconds>]
 [,bittorrent-discovery.nodes-only][,bittorrent-discovery.peers-only][,newtargets]

The script accepts 5 types of script-arguments:
<torrent>, a string containing the filename of the torrent file
<magnet>, a string containing the magnet link of the torrent
<timeout>, desired (not actual) timeout for the DHT discovery (default = 30 s)
<nodes-only>, boolean selecting whether to show only nodes
<peers-only>, boolean selecting whether to show only peers

Notice that if both nodes-only and peers-only arguments are supplied
no output is produced

Sample output:
 | bittorrent-peers:
 |   Peers:
 |     97.88.178.168
 |     89.100.184.36
 |     86.185.55.212
 |     Total of 3 peers discovered
 |   Nodes:
 |     68.103.0.189
 |     67.164.32.71
 |     24.121.13.69
 |     207.112.100.224
 |     Total of 4 nodes discovered
 |_  Use the newtargets script-arg to add the results as targets

-- 
Gorjan
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