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BitTorrent

Bram Cohen invented BitTorrent protocol in 2001 and wrote the first client in Python. It is a peer-to-peer file sharing protocol where those who share a file are called seeders and those who download are called peers. All seeders and peers related to a particular torrent comprise the swarm. The tracker server or tracker serves as a repository for information about peers associated with the same file. Files are downloaded in hashed pieces from multiple seeders to distribute the burden of seeding a file. ^

A Torrent Descriptor file is a hashmap file

Torrent Descriptor property Description
Announce URL of the tracker
Info dictionary whose keys depend on whether one or more files are being shared, including:
Files: list of dictionaries, only exists when multiple files are being shared, each dictionary has two keys and corresponds to a file
Length: size of the file in bytes
Path: list of strings corresponding to subdirectory names, the last of which is the actual filename
length size of the file in bytes (when one file is being shared
name suggested file or directory name
Pieces length number of bytes per piece; must be a power of 2 and at least 16KiB
Pieces list of SHA-1 160-bit hashes calculated on various parts of data 
{
  "Announce": "url of tracker",
  "Info": {
  "Files": [{ 
    "Length": 16, 
    "path": "/folder/to/path" }, 
    { "length": 193, 
    "path": "/another/folder" }] 
  },
  "length": 192, 
  "name":" Ubuntu.iso", 
  "Pieces length": 262144, 
  "Pieces": [AAF4C61DDCC5E8A2DABEDE0F3B482CD9AEA9434D, CFEA2496442C091FDDD1BA215D62A69EC34E94D0]
}

BitTorrent clients

  • Deluge ^ ^
  • command-line functionality
  • open-source with expandable functionalities
  • chosen as the best torrent client by Lifehacker
  • qBittorrent open-source, ad-free alternative to uTorrent
  • Tixati closed-source
  • Transmission installed by default on Ubuntu (ca. 2017)
  • Tribler
  • Vuze has ads and is closed-source
  • Frostwire: multiplatform, including Android
  • WebTorrent Desktop