End-to-end Publishing Using Bittorrent

Bittorrent Bittorrent is a widely used peer-to- peer network used to distribute files, especially large ones It has a number of legal uses which separate it from other P2P

Practical Applications Distributing large files Podcasting Vlogging Disk images Legal distribution of movies (see bittorrent.com)‏

Traditional vs. Bittorrent One server provides many clients Many clients provide many clients

Terminology Swarm – clients downloading or uploading a given file through Bittorrent Tracker – centralized server that clients connect to to ask for lists of other clients connected to the swarm Seed – A client that has a complete copy of the file Peer (Leecher) – A client that does not have a complete copy of the file

Problem Torrents that are less popular may eventually “die” when there are no longer any complete copies of the file in the swarm

Everseed Permanent seed running on the same server as the tracker Guarantees that there will always be a complete copy of the file

Related Research The creator of Bittorrent wrote a paper on the process of downloading a file using Bittorrent at Maintainers of various Bittorrent clients wrote which is like the official specification except far more in depth Osprey ( seems to have thought of something similar, but haven't made much progresshttp://osprey.ibiblio.org/

Explanation The.torrent metadata file tells client tracker URL & other data Client connects to tracker Tracker gives client a list of other clients Client downloads file from other clients (not a centralized server)‏ Periodic update with tracker

Goals Complete internet publishing solution using Bittorrent Metadata file generator (.torrent)‏ Tracker “Everseed” Web interface

.torrent File Official docs on bittorrent.org Metadata on the file to be downloaded (tracker URL, filename, size, checksum hashes)‏ Stored as “bencoded” strings, integers, lists, dictionaries

Bencoding Integer: 6 => “i6e” String: “hello” => “5:hello” List: [“hello”,”world”] => “l5:hello5:worlde” Dictionary: {“hello”:”world”} => “d5:hello5:worlde”

Bencoding implementation Python has good string manipulation Structure of a.torrent file is a dictionary containing string keys and integer, string, list, and dictionary values Recursion to encode/decode

Tracker Makes use of the bencoding algorithm Handles two types of requests: “announce” and “scrape” Stores data on peers and torrents in a SQLite database No performance issues

Network performance Peer List Size

Database performance

Announce request “Announces” client's presence to tracker Used to get lists of IP addresses and BT ports of other clients in the swarm

Announce request “Compact” peer list response Recognition of seeding status

Scrape request “Scrapes” data from the tracker Used to get info on the different torrents that the tracker is tracking # peers, # seeds, total downloaded, total uploaded, # completed etc...

Scrape request Client sends an HTTP GET request to tracker's scrape URL Tracker urldecodes request, selects the data the client is interested in Tracker responds with a bencoded text/plain document

Summary Python Benefits of P2P technology “Everseed” concept.torrent files and bencoding Tracker