# WebTorrent Documentation

WebTorrent is a streaming torrent client for **Node.js** and the **web**. WebTorrent
provides the same API in both environments.

To use WebTorrent in the browser, [WebRTC] support is required (Chrome, Firefox, Opera, Safari).

[webrtc]: https://en.wikipedia.org/wiki/WebRTC

## Install

```bash
npm install webtorrent
```

## Quick Example

```js
var client = new WebTorrent()

var torrentId = 'magnet:?xt=urn:btih:08ada5a7a6183aae1e09d831df6748d566095a10&dn=Sintel&tr=udp%3A%2F%2Fexplodie.org%3A6969&tr=udp%3A%2F%2Ftracker.coppersurfer.tk%3A6969&tr=udp%3A%2F%2Ftracker.empire-js.us%3A1337&tr=udp%3A%2F%2Ftracker.leechers-paradise.org%3A6969&tr=udp%3A%2F%2Ftracker.opentrackr.org%3A1337&tr=wss%3A%2F%2Ftracker.btorrent.xyz&tr=wss%3A%2F%2Ftracker.fastcast.nz&tr=wss%3A%2F%2Ftracker.openwebtorrent.com&ws=https%3A%2F%2Fwebtorrent.io%2Ftorrents%2F&xs=https%3A%2F%2Fwebtorrent.io%2Ftorrents%2Fsintel.torrent'

client.add(torrentId, function (torrent) {
  // Torrents can contain many files. Let's use the .mp4 file
  var file = torrent.files.find(function (file) {
    return file.name.endsWith('.mp4')
  })

  // Display the file by adding it to the DOM. Supports video, audio, image, etc. files
  file.appendTo('body')
})
```

# WebTorrent API

## `WebTorrent.WEBRTC_SUPPORT`

Is WebRTC natively supported in the environment?

```js
if (WebTorrent.WEBRTC_SUPPORT) {
  // WebRTC is supported
} else {
  // Use a fallback
}
```

## `client = new WebTorrent([opts])`

Create a new `WebTorrent` instance.

If `opts` is specified, then the default options (shown below) will be overridden.

```js
{
  maxConns: Number,        // Max number of connections per torrent (default=55)
  nodeId: String|Buffer,   // DHT protocol node ID (default=randomly generated)
  peerId: String|Buffer,   // Wire protocol peer ID (default=randomly generated)
  tracker: Boolean|Object, // Enable trackers (default=true), or options object for Tracker
  dht: Boolean|Object,     // Enable DHT (default=true), or options object for DHT
  webSeeds: Boolean        // Enable BEP19 web seeds (default=true)
}
```

For possible values of `opts.dht` see the
[`bittorrent-dht` documentation](https://github.com/webtorrent/bittorrent-dht#dht--new-dhtopts).

For possible values of `opts.tracker` see the
[`bittorrent-tracker` documentation](https://github.com/webtorrent/bittorrent-tracker#client).

## `client.add(torrentId, [opts], [function ontorrent (torrent) {}])`

Start downloading a new torrent.

`torrentId` can be one of:

- magnet uri (string)
- torrent file (buffer)
- info hash (hex string or buffer)
- parsed torrent (from [parse-torrent](https://github.com/webtorrent/parse-torrent))
- http/https url to a torrent file (string)
- filesystem path to a torrent file (string) *(Node.js only)*

If `opts` is specified, then the default options (shown below) will be overridden.

```js
{
  announce: [String],        // Torrent trackers to use (added to list in .torrent or magnet uri)
  getAnnounceOpts: Function, // Custom callback to allow sending extra parameters to the tracker
  maxWebConns: Number,       // Max number of simultaneous connections per web seed [default=4]
  path: String,              // Folder to download files to (default=`/tmp/webtorrent/`)
  store: Function            // Custom chunk store (must follow [abstract-chunk-store](https://www.npmjs.com/package/abstract-chunk-store) API)
}
```

If `ontorrent` is specified, then it will be called when **this** torrent is ready to be
used (i.e. metadata is available). Note: this is distinct from the 'torrent' event which
will fire for **all** torrents.

If you want access to the torrent object immediately in order to listen to events as the
metadata is fetched from the network, then use the return value of `client.add`. If you
just want the file data, then use `ontorrent` or the 'torrent' event.

If you provide `opts.store`, it will be called as
`opts.store(chunkLength, storeOpts)` with:

* `storeOpts.length` - size of all the files in the torrent
* `storeOpts.files` - an array of torrent file objects
* `storeOpts.torrent` - the torrent instance being stored

## `client.seed(input, [opts], [function onseed (torrent) {}])`

Start seeding a new torrent.

`input` can be any of the following:

- filesystem path to file or folder
 (string) *(Node.js only)*
- W3C [File](https://developer.mozilla.org/en-US/docs/Web/API/File) object (from an `<input>` or drag and drop) *(browser only)*
- W3C [FileList](https://developer.mozilla.org/en-US/docs/Web/API/FileList) object (basically an array of `File` objects) *(browser only)*
- Node [Buffer](https://nodejs.org/api/buffer.html) object
- Node [Readable stream](https://nodejs.org/api/stream.html#stream_class_stream_readable) object

Or, an **array of `string`, `File`, `Buffer`, or `stream.Readable` objects**.

If `opts` is specified, it should contain the following types of options:

- options for [create-torrent](https://github.com/webtorrent/create-torrent#createtorrentinput-opts-function-callback-err-torrent-) (to allow configuration of the .torrent file that is created)
- options for `client.add` (see above)

If `onseed` is specified, it will be called when the client has begun seeding the file.

**Note:** Every torrent is required to have a name. If one is not explicitly provided
through `opts.name`, one will be determined automatically using the following logic:

- If all files share a common path prefix, that will be used. For example, if all file
  paths start with `/imgs/` the torrent name will be `imgs`.
- Otherwise, the first file that has a name will determine the torrent name. For example,
  if the first file is `/foo/bar/baz.txt`, the torrent name will be `baz.txt`.
- If no files have names (say that all files are Buffer or Stream objects), then a name
  like "Unnamed Torrent <id>" will be generated.

**Note:** Every file is required to have a name. For filesystem paths or W3C File objects,
the name is included in the object. For Buffer or Readable stream types, a `name` property
can be set on the object, like this:

```js
var buf = new Buffer('Some file content')
buf.name = 'Some file name'
client.seed(buf, cb)
```

## `client.on('torrent', function (torrent) {})`

Emitted when a torrent is ready to be used (i.e. metadata is available and store is
ready). See the torrent section for more info on what methods a `torrent` has.

## `client.on('error', function (err) {})`

Emitted when the client encounters a fatal error. The client is automatically
destroyed and all torrents are removed and cleaned up when this occurs.

Always listen for the 'error' event.

## `client.remove(torrentId, [function callback (err) {}])`

Remove a torrent from the client. Destroy all connections to peers and delete all saved
file data. If `callback` is specified, it will be called when file data is removed.

*Note: This method does not currently delete torrent data (in e.g. `/tmp/webtorrent/...`, see the `path` option to `client.add`). Until this is fixed, please implement it yourself (consider using the `rimraf` npm package).

## `client.destroy([function callback (err) {}])`

Destroy the client, including all torrents and connections to peers. If `callback` is specified, it will be called when the client has gracefully closed.

## `client.torrents[...]`

An array of all torrents in the client.

## `client.get(torrentId)`

Returns the torrent with the given `torrentId`. Convenience method. Easier than searching
through the `client.torrents` array. Returns `null` if no matching torrent found.

## `client.downloadSpeed`

Total download speed for all torrents, in bytes/sec.

## `client.uploadSpeed`

Total upload speed for all torrents, in bytes/sec.

## `client.progress`

Total download progress for all **active** torrents, from 0 to 1.

## `client.ratio`

Aggregate "seed ratio" for all torrents (uploaded / downloaded), from 0 to 1.


# Torrent API

## `torrent.infoHash`

Info hash of the torrent (string).

## `torrent.magnetURI`

Magnet URI of the torrent (string).

## `torrent.torrentFile`

`.torrent` file of the torrent (Buffer).

## `torrent.torrentFileBlobURL` *(browser only)*

`.torrent` file of the torrent (Blob URL).

## `torrent.files[...]`

Array of all files in the torrent. See documentation for `File` below to learn what
methods/properties files have.

## `torrent.timeRemaining`

Time remaining for download to complete (in milliseconds).

## `torrent.received`

Total bytes received from peers (*including* invalid data).

## `torrent.downloaded`

Total *verified* bytes received from peers.

## `torrent.uploaded`

Total bytes uploaded to peers.

## `torrent.downloadSpeed`

Torrent download speed, in bytes/sec.

## `torrent.uploadSpeed`

Torrent upload speed, in bytes/sec.

## `torrent.progress`

Torrent download progress, from 0 to 1.

## `torrent.ratio`

Torrent "seed ratio" (uploaded / downloaded), from 0 to 1.

## `torrent.numPeers`

Number of peers in the torrent swarm.

## `torrent.path`

Torrent download location.

## `torrent.destroy([callback])`

Alias for `client.remove(torrent)`. If `callback` is provided, it will be called when
the torrent is fully destroyed, i.e. all open sockets are closed, and the storage is
closed.

## `torrent.addPeer(peer)`

Add a peer to the torrent swarm. This is advanced functionality. Normally, you should not
need to call `torrent.addPeer()` manually. WebTorrent will automatically find peers using
the tracker servers or DHT. This is just for manually adding a peer to the client.

This method should not be called until the `infoHash` event has been emitted.

Returns `true` if peer was added, `false` if peer was blocked by the loaded blocklist.

The `peer` argument must be an address string in the format `12.34.56.78:4444` (for
normal TCP/uTP peers), or a [`simple-peer`](https://github.com/feross/simple-peer)
instance (for WebRTC peers).

## `torrent.addWebSeed(url)`

Add a web seed to the torrent swarm. For more information on BitTorrent web seeds, see
[BEP19](http://www.bittorrent.org/beps/bep_0019.html).

In the browser, web seed servers must have proper CORS (Cross-origin resource sharing)
headers so that data can be fetched across domain.

The `url` argument is the web seed URL.

## `torrent.removePeer(peer)`

Remove a peer from the torrent swarm. This is advanced functionality. Normally, you should
not need to call `torrent.removePeer()` manually. WebTorrent will automatically remove
peers from the torrent swarm when they're slow or don't have pieces that are needed.

The `peer` argument should be an address (i.e. "ip:port" string), a peer id (hex string),
or `simple-peer` instance.

## `torrent.select(start, end, [priority], [notify])`

Selects a range of pieces to prioritize starting with `start` and ending with `end` (both
inclusive) at the given `priority`. `notify` is an optional callback to be called when the
selection is updated with new data.

## `torrent.deselect(start, end, priority)`

Deprioritizes a range of previously selected pieces.

## `torrent.critical(start, end)`

Marks a range of pieces as critical priority to be downloaded ASAP. From `start` to `end`
(both inclusive).

## `torrent.createServer([opts])`

Create an http server to serve the contents of this torrent, dynamically fetching the
needed torrent pieces to satisfy http requests. Range requests are supported.

Returns an `http.Server` instance (got from calling `http.createServer`). If
`opts` is specified, it can have the following properties:

```js
{
  origin: String // Allow requests from specific origin. `false` for same-origin. [default: '*']
}
```

Visiting the root of the server `/` will show a list of links to individual files. Access
individual files at `/<index>` where `<index>` is the index in the `torrent.files` array
(e.g. `/0`, `/1`, etc.)

Here is a usage example:

```js
var client = new WebTorrent()
var magnetURI = 'magnet: ...'

client.add(magnetURI, function (torrent) {
  // create HTTP server for this torrent
  var server = torrent.createServer()
  server.listen(port) // start the server listening to a port

  // visit http://localhost:<port>/ to see a list of files

  // access individual files at http://localhost:<port>/<index> where index is the index
  // in the torrent.files array

  // later, cleanup...
  server.close()
  client.destroy()
})
```

## `torrent.pause()`

Temporarily stop connecting to new peers. Note that this does not pause new incoming
connections, nor does it pause the streams of existing connections or their wires.

## `torrent.resume()`

Resume connecting to new peers.

## `torrent.on('infoHash', function () {})`

Emitted when the info hash of the torrent has been determined.

## `torrent.on('metadata', function () {})`

Emitted when the metadata of the torrent has been determined. This includes the full
contents of the .torrent file, including list of files, torrent length, piece hashes,
piece length, etc.

## `torrent.on('ready', function () {})`

Emitted when the torrent is ready to be used (i.e. metadata is available and store is
ready).

## `torrent.on('warning', function (err) {})`

Emitted when there is a warning. This is purely informational and it is not necessary to
listen to this event, but it may aid in debugging.

## `torrent.on('error', function (err) {})`

Emitted when the torrent encounters a fatal error. The torrent is automatically destroyed
and removed from the client when this occurs.

**Note:** Torrent errors are emitted at `torrent.on('error')`. If there are no
'error' event handlers on the torrent instance, then the error will be emitted at
`client.on('error')`. This prevents throwing an uncaught exception (unhandled
'error' event), but it makes it impossible to distinguish client errors versus
torrent errors. Torrent errors are not fatal, and the client is still usable
afterwards. Therefore, always listen for errors in both places
(`client.on('error')` and `torrent.on('error')`).

## `torrent.on('done', function () {})`

Emitted when all the torrent files have been downloaded.

Here is a usage example:

```js
torrent.on('done', function(){
  console.log('torrent finished downloading');
  torrent.files.forEach(function(file){
     // do something with file
  })
})
```

## `torrent.on('download', function (bytes) {})`

Emitted whenever data is downloaded. Useful for reporting the current torrent status, for
instance:

```js
torrent.on('download', function (bytes) {
  console.log('just downloaded: ' + bytes)
  console.log('total downloaded: ' + torrent.downloaded);
  console.log('download speed: ' + torrent.downloadSpeed)
  console.log('progress: ' + torrent.progress)
})
```

## `torrent.on('upload', function (bytes) {})`

Emitted whenever data is uploaded. Useful for reporting the current torrent status.

## `torrent.on('wire', function (wire) {})`

Emitted whenever a new peer is connected for this torrent. `wire` is an instance of
[`bittorrent-protocol`](https://github.com/webtorrent/bittorrent-protocol), which is a
node.js-style duplex stream to the remote peer. This event can be used to specify
[custom BitTorrent protocol extensions](https://github.com/webtorrent/bittorrent-protocol#extension-api).

Here is a usage example:

```js
var MyExtension = require('./my-extension')

torrent1.on('wire', function (wire, addr) {
  console.log('connected to peer with address ' + addr)
  wire.use(MyExtension)
})
```

See the `bittorrent-protocol`
[extension api docs](https://github.com/webtorrent/bittorrent-protocol#extension-api) for more
information on how to define a protocol extension.

## `torrent.on('noPeers', function (announceType) {})`

Emitted whenever a DHT or tracker announce occurs, but no peers have been found.  `announceType` is either `'tracker'` or `'dht'` depending on which announce occurred to trigger this event.  Note that if you're attempting to discover peers from both a tracker and a DHT, you'll see this event separately for each.

# File API

## `file.name`

File name, as specified by the torrent. *Example: 'some-filename.txt'*

## `file.path`

File path, as specified by the torrent. *Example: 'some-folder/some-filename.txt'*

## `file.length`

File length (in bytes), as specified by the torrent. *Example: 12345*

## `file.downloaded`

Total *verified* bytes received from peers, for this file.

## `file.progress`

File download progress, from 0 to 1.

## `file.select()`

Selects the file to be downloaded, but at a lower priority than files with streams.
Useful if you know you need the file at a later stage.

## `file.deselect()`

Deselects the file, which means it won't be downloaded unless someone creates a stream
for it.

*Note: This method is currently not working as expected, see [dcposch answer on #164](https://github.com/webtorrent/webtorrent/issues/164) for a nice work around solution.

## `stream = file.createReadStream([opts])`

Create a [readable stream](https://nodejs.org/api/stream.html#stream_class_stream_readable)
to the file. Pieces needed by the stream will be prioritized highly and fetched from the
swarm first.

You can pass `opts` to stream only a slice of a file.

```js
{
  start: startByte,
  end: endByte
}
```

Both `start` and `end` are inclusive.

## `file.getBuffer(function callback (err, buffer) {})`

Get the file contents as a `Buffer`.

The file will be fetched from the network with highest priority, and `callback` will be
called once the file is ready. `callback` must be specified, and will be called with a an
`Error` (or `null`) and the file contents as a `Buffer`.

```js
file.getBuffer(function (err, buffer) {
  if (err) throw err
  console.log(buffer) // <Buffer 00 98 00 01 ...>
})
```

## `file.appendTo(rootElem, [opts], [function callback (err, elem) {}])` *(browser only)*

Show the file in a the browser by appending it to the DOM. This is a powerful function
that handles many file types like video (.mp4, .webm, .m4v, etc.), audio (.m4a, .mp3,
.wav, etc.), images (.jpg, .gif, .png, etc.), and other file formats (.pdf, .md, .txt,
etc.).

The file will be fetched from the network with highest priority and streamed into the page
(if it's video or audio). In some cases, video or audio files will not be streamable
because they're not in a format that the browser can stream so the file will be fully
downloaded before being played. For other non-streamable file types like images and PDFs,
the file will be downloaded then displayed.

`rootElem` is a container element (CSS selector or reference to DOM node) that the content
will be shown in. A new DOM node will be created for the content and appended to
`rootElem`.

If provided, `opts` can contain the following options:

- `autoplay`: Autoplay video/audio files (default: `true`)
- `controls`: Show video/audio player controls (default: `true`)
- `maxBlobLength`: Files above this size will skip the "blob" strategy and fail (default: `200 * 1000 * 1000` bytes)

If provided, `callback` will be called once the file is visible to the user.
`callback` is called with an `Error` (or `null`) and the new DOM node that is
displaying the content.

```js
file.appendTo('#containerElement', function (err, elem) {
  if (err) throw err // file failed to download or display in the DOM
  console.log('New DOM node with the content', elem)
})
```

Streaming support depends on support for `MediaSource` API in the browser. All
modern browsers have `MediaSource` support.

For video and audio, webtorrent tries multiple methods of playing the file:

- [`videostream`][videostream] -- best option, supports streaming **with seeking**,
  but only works with MP4-based files for now (uses `MediaSource` API)
- [`mediasource`][mediasource] -- supports more formats, supports streaming
  **without seeking** (uses `MediaSource` API)
- Blob URL -- supports the most formats of all (anything the `<video>` tag supports
  from an http url), **with seeking**, but **does not support streaming** (entire
  file must be downloaded first)

[videostream]: https://www.npmjs.com/package/videostream
[mediasource]: https://www.npmjs.com/package/mediasource

The Blob URL strategy will not be attempted if the file is over
`opts.maxBlobLength` (200 MB by default) since it requires the entire file to be
downloaded before playback can start which gives the appearance of the `<video>`
tag being stalled. If you increase the size, be sure to indicate loading progress
to the user in the UI somehow.

For other media formats, like images, the file is just added to the DOM.

For text-based formats, like html files, pdfs, etc., the file is added to the DOM
via a sandboxed `<iframe>` tag.

## `file.renderTo(elem, [opts], [function callback (err, elem) {}])` *(browser only)*

Like `file.appendTo` but renders directly into given element (or CSS selector). For
example, to render a video, provide a `<video>` element like
`file.renderTo('video#player')`.

## `file.getBlob(function callback (err, blob) {})` *(browser only)*

Get a W3C `Blob` object which contains the file data.

The file will be fetched from the network with highest priority, and `callback` will be
called once the file is ready. `callback` must be specified, and will be called with a an
`Error` (or `null`) and the `Blob` object.

## `file.getBlobURL(function callback (err, url) {})` *(browser only)*

Get a url which can be used in the browser to refer to the file.

The file will be fetched from the network with highest priority, and `callback` will be
called once the file is ready. `callback` must be specified, and will be called with a an
`Error` (or `null`) and the Blob URL (`String`).

This method is useful for creating a file download link, like this:

```js
file.getBlobURL(function (err, url) {
  if (err) throw err
  var a = document.createElement('a')
  a.download = file.name
  a.href = url
  a.textContent = 'Download ' + file.name
  document.body.appendChild(a)
})
```
