PyBitTorrent

A Python package for download torrent files.

How to use:

from PyBitTorrent import TorrentClient

client = TorrentClient('~/Downloads/Big Buck Bunny (1920x1080 h.264).torrent')
client.start()

That's it. The TorrentClient accepts the following parameters:

TorrentClient(
    torrent: str,
    max_peers: int,
    use_progress_bar: bool,
    peers_file: str,
    output_dir: str,
)

• torrent: path to a .torent file
• max_peers: max peers should connect. after reaching this value, stop connecting to other peers. Big value will lead to more connected peers and therefore faster download speed, but this will make the handshake process slower. The default should be good for most uses (12)
• use_progress_bar: should show the progress bar or the logger printing. The first option intended for better look in a terminal, but you should use the other one if you want detailed information about your download process. the default is False
• peers_file: path to a text file contain list of peers should connect to. for example:

  83.255.134.75:1
  68.235.36.213:1
  5.170.40.245:6881
  62.108.207.11:6881
  5.104.120.250:63356
  

  Default value is None
• output_dir: path to the directory the output files should be saved. default is None

Simple usage:

You can always use in the Client.py attached in the exampled folder

python examples/Client.py --help

usage: 
    Script for downloading torrent files
     [-h] --torrent TORRENT [--peers PEERS] [--output-directory OUTPUT_DIRECTORY] [--use-progress-bar] [--max-peers MAX_PEERS]

optional arguments:
  -h, --help            show this help message and exit
  --torrent TORRENT     Path of the Torrent file
  --peers PEERS         Path to file contain peers (in the format ip:port for each line)
  --output-directory OUTPUT_DIRECTORY
                        Path to the output directory
  --use-progress-bar    should show progress bar
  --max-peers MAX_PEERS
                        Max connected peers

Example of downloading torrent to "Downloads":

python examples/Client.py --torrent "~/Downloads/Big Buck Bunny (1920x1080 h.264).torrent"--output-directory ~/Downloads
2022-12-24 11:44:48.577 INFO TorrentFile - __init__: Start reading from BitTorrent file
{
    'announce': 'udp://tracker.leechers-paradise.org:6969/announce',
    'announce-list': [
        ['udp://tracker.leechers-paradise.org:6969/announce'],
        ['udp://tracker.internetwarriors.net:1337/announce'],
        ['udp://tracker.opentrackr.org:1337/announce'],
        ...
    ],
    'comment': 'dynamic metainfo from client',
    'created by': 'go.torrent',
    'creation date': 1670818208,
    'info': {'length': 725106140, 'name': 'big_buck_bunny_1080p_h264.mov', 'piece length': 262144, 'pieces': ''}}
}
2022-12-24 11:45:14.507 INFO UDPTracker - get_peers: success in scraping udp://tracker.moeking.me:6969/announce got 88 peers
2022-12-24 11:45:14.923 INFO UDPTracker - get_peers: success in scraping udp://exodus.desync.com:6969/announce got 200 peers
2022-12-24 11:45:25.687 DEBUG PeersManager - send_handshakes: Poll number 1/13
2022-12-24 11:45:25.687 ERROR Bittorrent - handle_messages: No peers found, sleep for 2 seconds
2022-12-24 11:45:25.885 INFO PeersManager - _send_handshake: Trying handshake with peer 92.176.121.23
2022-12-24 11:45:25.984 DEBUG PeersManager - _send_handshake: Adding peer 92.176.121.23, 10982 which is 1/12
2022-12-24 11:45:26.020 INFO PeersManager - _send_handshake: Trying handshake with peer 107.190.125.222
2022-12-24 11:45:26.187 DEBUG Peer - receive_message: Client in ip 107.190.125.222 with id 00000000000000000000 disconnected
2022-12-24 11:45:36.439 DEBUG PeersManager - _send_handshake: Adding peer 189.179.233.150, 35087 which is 2/12
...

List of BitTorrent messages and their support

Type	supported	id
Handshake	yes	-
Keep Alive	yes	0
Choke	yes	1
Unchoke	yes	2
Interested	no	3
Not interested	no	4
BitField	yes	5
Request	yes	6
Piece	yes	7
Cancel	no	8
Port	no	9

The architecture of the program

• At first, we retrieve all available peers, using the trackers from the torrent file, or from the peers file provided.
• Then, we try to connect each one of them, until the value of max_peers achieved. The handshakes happen in a poll of threads. each thread contain MAX_HANDSHAKE_THREADS of peers to handshake with. the number_of_polls calculated according to the length of the given peers divided by the MAX_HANDSHAKE_THREADS, so we can cover all the peers. note that this process happens in parallel to the other 2 threads. continue to read for more details.
• Right after launching the handshakes thread polls, we start listening for incomming messages using the handle_messages function, that calling the receive_messages in the PeersManager in his turn. This function will search for readable socket, and then parse the data to one of the PyBitTorrent.Message classes. This contains one of the two main threads of the program, that continue until completion of the download.
• Meanwhile we can start requesting for pieces. we do that by calling the function piece_requester in different threads. this function search after connected peer (unchocked connected peer) that have the piece index we currently in. The current strategy for piece picking is what we can call Asynchronous Chronological. Means that we start requesting for piece index 0, 1, 2, until the end of the file, but don't stop the program if one of them is not full yet. Better strategy can be implemented, like Rarest-Piece-First, But i noticed that most of the torrent download process is in front of seeders, so i thought it will be useless right now. But of curs in communicating with actual peers (like in a new torrent file that just explode over the internet), smarter strategies can help.
• After all pieces have been received, if the torrent file contain folders we create them and rewrite them in the correct order. until then, all files are written to temp file.

Charted flow of the program:

---

Important notes:

• We are a dirty Leecher: The current implementation is a leecher. That's mean you can only download file, and not upload anything. You can conclude that other peers might see that in a bad eye and therefore give you a lower rate and bandwidth, and as a result you won't unchoked by them, resulting lower speed rate comparing to popular torrent clients. Keep in mind that the infrastructure for acting as peer/seeder has been laid, so implement it should be easy.
• statistic bug: In the current architecture of the program, it is multi threaded. it seems that it cause some undefined bug in interacting with the select function in the receive_messages of the PeersManager. it means stuck messages, that get released after the stuck peer will send any message. You sometimes experience it when you see that all the peers are choked for few seconds/minutes, when in fact they are not.
• over memory usage in big torrent: if the given torrent file contain multiply folders, the actual content is written to a temp file using the tempfile library. afterwards, we read chunks in the size of each inner file, and write them to the correct path. this read calls can cause over memory use in big torrents. we can avoid that by not copy the bytes using this function, but using other only disk-operation function, like the dd command. I haven't found this one yet.