Get InfoHash before downloading torrent

[HughIsaacs2]

Unless I'm mistaken there doesn't appear to be any way to get the InfoHash of a .Torrent file or Magnet link before downloading the torrent.

I think this would be useful for building WebTorrent applications that sport offline storage.

Example: I'm building something that downloads the files and stores them offline in an array using LocalForage and sets the InfoHash as the key of that storage so when a user opens a link to that same torrent it'll just search to see if it's stored offline already and use the offline stored copies instead.

[feross]

You can listen to the 'infoHash' event:

var torrent = client.add(torrentId)
torrent.on('infoHash', function (infoHash) {
  // ...
})

Another way to customize the storage location based on the infoHash is to use the store option to client.add, but you need to follow the abstract-chunk-store interface:

function Store (chunkLength, opts) {
  console.log(opts.torrent.infoHash)
}
client.add(torrentId, {
  store: Store
})

Or, probably the simplest way is to use parse-torrent to get the info hash before passing it to WebTorrent in the first place:

var parseTorrent = require('parse-torrent')

var parsed = parseTorrent(torrentId)
console.log(parsed.infoHash)

client.add(torrentId, ...)

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