BitTorrent Client

BitTorrent overview

BitTorrent is a peer-peer file sharing protocol in which data is transferred between a bundle of peers on the internet. Instead of files being distributed from a centralized server, data is downloaded/uploaded from multiple peers simultaneously, which reduces latency.

• The .torrent file moderates the integrity of file 'pieces', and the amount of pieces.
• BitTorrent Specification

.torrent files

BitTorrent clients are endpoints that implement the BitTorrent protocol, namely uTorrent, Tixati & Deluge. Each client has to read the file specifications (filename, file size, URL & its source from the .torrent file (meta data).

• Metadata values are encoded as bencode dictionaries, a binary format useful for distributing unstructured data.
• Bencode supports four data types:
  • byte strings
  • integers
  • lists
  • dictionaries
• Bencoded data can easily be converted to JSON or object literals in Python.

Features

[x] Downloading pieces

[ ] Uploading pieces

[ ] Tests

Walkthrough

Bencoding:

• Encodes python objects to a sequence of loosley structured bytes.
• Decodes bencoded data to the corresponding python object.

TorrentClient:

• Connects to the tracker and retrieves available peers to initiate a connection.
• Creates a queue of active peers
• Moderates the order & amount of pieces to be requested from remote peers.

Communication

• Handles the downloading/uploaded of a torrent's pieces.
• Retrieves an available peer from the queue, attempts to open a connection, and perfoms a BitTorrent 'handshake' to the peer.
• Once the handshake is initiated, the endpoint cant request any more data from remote peers until a response is returned from the peer.
• If the connection drops, the endpoint moves on to the next available peer in the queue.