More thorough object cleanup

- Only pass `torrent.infoHash` to the Chunk Store constructor, instead
of the `Torrent`
  instance itself, to prevent accidental memory leaks of the `Torrent`
object by the
  store. (Open an issue if you were using other properties. They can be
re-added.)

- Non-fatal errors with a single torrent will be emitted at
`torrent.on('error')`. You
  should listen to this event. Previously, all torrent errors were also
emitted on
  `client.on('error')` and handling `torrent.on('error')` was optional.
This design is
  better since now it is possible to distinguish between fatal client
errors
  (`client.on('error')`) when the whole client becomes unusable versus
recoverable errors
  where only a single torrent fails (`torrent.on('error')`) but the
client can continue to
  be used. However, if there is no `torrent.on('error')` event, then
the error will be
  forwarded to `client.on('error')`. This prevents crashing the client
when the user
  only has a listener on the client, but it makes it impossible for
them to determine
  a client error versus a torrent error.

- Errors creating a torrent with `client.seed` are now emitted on the
returned `torrent`
  object instead of the client (unless there is no event listeners on
  `torrent.on('error')` as previously discussed). The torrent object is
now also destroyed
  automatically for the user, as was probably expected.

- If `client.get` is passed a `Torrent` instance, it now only returns
it if it is present
  in the client.

3 files changed, 31 insertions, 10 deletions

diff --git a/lib/file.js b/lib/file.js
index bfa032e..c73fc38 100644
--- a/lib/file.js
+++ b/lib/file.js
@@ -1,5 +1,3 @@
-// TODO: cleanup reference to torrent (i.e. Torrent object)
-
 module.exports = File
 
 var eos = require('end-of-stream')
@@ -89,3 +87,7 @@ File.prototype.renderTo = function (elem, cb) {
   if (typeof window === 'undefined') throw new Error('browser-only method')
   render.render(this, elem, cb)
 }
+
+File.prototype._destroy = function () {
+  this._torrent = null
+}
diff --git a/lib/rarity-map.js b/lib/rarity-map.js
index c362077..430f62f 100644
--- a/lib/rarity-map.js
+++ b/lib/rarity-map.js
@@ -3,8 +3,6 @@ module.exports = RarityMap
 /**
  * Mapping of torrent pieces to their respective availability in the torrent swarm. Used
  * by the torrent manager for implementing the rarest piece first selection strategy.
- *
- * @param {Torrent} torrent
  */
 function RarityMap (torrent) {
   var self = this
diff --git a/lib/torrent.js b/lib/torrent.js
index fc5f495..296f579 100644
--- a/lib/torrent.js
+++ b/lib/torrent.js
@@ -92,10 +92,10 @@ function Torrent (torrentId, client, opts) {
 
   this.metadata = null
   this.store = null
-  this.files = null
+  this.files = []
+  this.pieces = []
 
   this._amInterested = false
-  this.pieces = []
   this._selections = []
   this._critical = []
 
@@ -253,6 +253,7 @@ Torrent.prototype._onParsedTorrent = function (parsedTorrent) {
   if (self._rechokeIntervalId.unref) self._rechokeIntervalId.unref()
 
   self.emit('infoHash', self.infoHash)
+  if (self.destroyed) return // user might destroy torrent in `infoHash` event handler
 
   if (self.client.listening) {
     self._onListening()
@@ -371,7 +372,9 @@ Torrent.prototype._onMetadata = function (metadata) {
 
   self.store = new ImmediateChunkStore(
     new self._store(self.pieceLength, {
-      torrent: self,
+      torrent: {
+        infoHash: self.infoHash
+      },
       files: self.files.map(function (file) {
         return {
           path: path.join(self.path, file.path),
@@ -464,6 +467,7 @@ Torrent.prototype._verifyPieces = function () {
   var self = this
   parallelLimit(self.pieces.map(function (_, index) {
     return function (cb) {
+      if (self.destroyed) return cb(new Error('torrent is destroyed'))
       self.store.get(index, function (err, buf) {
         if (err) return cb(null) // ignore error
         sha1(buf, function (hash) {
@@ -523,7 +527,7 @@ Torrent.prototype._destroy = function (err, cb) {
   self.destroyed = true
   self._debug('destroy')
 
-  self.client.remove(self)
+  self.client._remove(self)
 
   clearInterval(self._rechokeIntervalId)
 
@@ -535,6 +539,10 @@ Torrent.prototype._destroy = function (err, cb) {
     self.removePeer(id)
   }
 
+  self.files.forEach(function (file) {
+    if (file instanceof File) file._destroy()
+  })
+
   var tasks = self._servers.map(function (server) {
     return function (cb) {
       server.destroy(cb)
@@ -546,6 +554,7 @@ Torrent.prototype._destroy = function (err, cb) {
       self.discovery.destroy(cb)
     })
   }
+
   if (self.store) {
     tasks.push(function (cb) {
       self.store.close(cb)
@@ -555,14 +564,26 @@ Torrent.prototype._destroy = function (err, cb) {
   parallel(tasks, cb)
 
   if (err) {
-    // When there is no `torrent.on('error')` listener, emit `client.on('error')` instead.
-    // The more-specific, torrent error handler is preferred.
+    // Torrent errors are emitted at `torrent.on('error')`. If there are no 'error' event
+    // handlers on the torrent instance, the error will be emitted at
+    // `client.on('error')`. This prevents crashing the user's program, but it makes it
+    // impossible to determine a client error versus a torrent error (where the client
+    // is still usable afterwards). Users are recommended for errors in both places
+    // to distinguish between the error types.
     if (self.listenerCount('error') === 0) {
       self.client.emit('error', err)
     } else {
       self.emit('error', err)
     }
   }
+
+  self.client = null
+  self.files = []
+  self.discovery = null
+  self.store = null
+  self._rarityMap = null
+  self._peers = null
+  self._servers = null
 }
 
 Torrent.prototype.addPeer = function (peer) {