CODEWITHSUNDEEP
protocolsbittorrent
Matt Elson
Matt Elson

Reputation: 4355

Tracker GET request parameters in Bittorrent

When using Bittorrent, I saw there are the parameters "numwant", "corrupt" and "key" in URL.

However, I found these paremeters don't be defined in BEP 3 (http://www.bittorrent.org/beps/bep_0003.html), so could someone tell me the meaning of the parameters, and where are the 3 parameters defined?

Also, before asking the questsion, I had searched the keyword "numwant" in the site www.bittorrent.org, and just found "numwant" appears in BEP 8, but the definition or explanation of the keyword can't be found.

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Upvotes: 2

Views: 1418

Answers (1)

Encombe
Encombe

Reputation: 2089

While BEP3 is official, it's a terse and dense document. I would instead recommend you to use the inofficial: https://wiki.theory.org/index.php/BitTorrentSpecification

It's a lot easier to read and understand. It also document some early extensions to the protocol that you can't find elsewhere.

There you will find:

  • numwant: Optional. Number of peers that the client would like to receive from the tracker. This value is permitted to be zero. If omitted, typically defaults to 50 peers.
  • key: Optional. An additional identification that is not shared with any other peers. It is intended to allow a client to prove their identity should their IP address change.

Regarding corrupt, there is afaik no written documentation how it is defined, but it's rather simple; When a piece fails the hash check, that amount of data is accounted on the corrupt counter instead of the downloaded counter.

There is also a similar redundant counter, where data that is discharged because it's redundant is acconuted. This happens, for example, in end game mode, when the same chunk is requested from more than one peer.

Also, there is some additional info in my answer here: Understanding Bittorrent Tracker Request

Upvotes: 2

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