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Comment by aptwebapps | Hacker News Reader

DC++ used to have the most obscure stuff. I remember finding one site(?server?hub?) that had every single F1 race broadcast (practice, qualifying, and race) for many years. Basically someone had been recording every race on VHS tape and eventually digitized them all and uploaded them. This is just one example of the kind of specializing you could find. I wonder how much of it is still there.

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One of the reasons why I like IPFS is that it gives you an immutable links to files like these. If you find the file once, you can get the link and access it again later (assuming people are still seeding) and be sure you're accessing the exact same file you think you are.

I mean, magnet links are the same thing—with the exception that they aren't widely used between users, to my knowledge, i.e. people aren't too familiar with them and go to search sites instead. (Not to say that the same won't happen in IPFS if it ever gets popular.)

They're not the same thing which is why they're not as useful.

Magnet links apply to an entire collection of files, as snapshotted by the creator. There is no way to pick a single file and refer to it, immutably. It's all or nothing. Additionally, metadata besides the file contents will change the hash. This includes filenames, directory structure and piece length (chosen at snapshot time, by the creator).

All of these limitations are enough in practice to make magnets useless for widespread per-file distribution.

Do magnet links work across torrents? Do two different torrents of the same file have the same magnet URI?

The infohash (which identifies the torrent, and thus the magnet link) is a hash of the following structure:

http://bittorrent.org/beps/bep_0003.html#info-dictionary

There are some things, beyond the content of the file, that will change the hash:

- Path of the file (nature_documentary.avi vs root/nature_documentary.avi)

- Name of the file (nature_documentary.avi vs nature_doc.avi)

- The pieces length

Ah, if it's the entire dictionary and not filtered by the clients to just those fields, then presumably additional data may be shoved in—specifically the trackers to contact.

No, look at the content of the dictionary: trackers are not part of the "info" dict, so you can add all the trackers you want, it won't change the identity of the torrent. Identity is defined by the infohash.

Trackers are added in the magnet link by adding parameters to the URI: see http://bittorrent.org/beps/bep_0009.html

Not sure if any metadata other than the file name affects the hash—e.g. modification times. Chunk sizes likely do. Otherwise, I'd expect the hash to address actual content, though frankly I haven't checked.

Edit: in fact, my hasty, belated and superficial skimming suggests that IPFS is an implementation of just a DHT (presumably with some metadata and chunking built in)—i.e. it keeps data itself in about the same way that Bittorrent stores torrent descriptions in the Mainline DHT.

magnets are just hashes of the contents

For me it was WinMX. I remember around 2001 I found all GameDev magazines there. Something that was just not available in any other p2p network.

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