New API: Add file.getURL()

Fixes #217

README.md

@@ -311,6 +311,14 @@ Seed ratio for all torrents in the client.
 
 ### torrent api
 
+#### `torrent.infoHash`
+
+Get the info hash of the torrent.
+
+#### `torrent.magnetURI`
+
+Get the magnet URI of the torrent.
+
 #### `torrent.files[...]`
 
 An array of all files in the torrent. See the file section for more info on what methods
@@ -415,6 +423,25 @@ You can pass `opts` to stream only a slice of a file.
 
 Both `start` and `end` are inclusive.
 
+#### `file.getBlobURL(function callback (err, url) {})`
+
+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 when it is ready. `callback` must be specified and may be called with a an `Error`
+or the blob url (`String`) when the file data is available and ready to be used.
+
+```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
+  body.appendChild(a)
+})
+```
+
 ### Modules
 
 Most of the active development is happening inside of small npm modules which are used by WebTorrent.

lib/storage.js

@@ -240,7 +240,6 @@ File.prototype.deselect = function () {
  */
 File.prototype.createReadStream = function (opts) {
   var self = this
-  debug('createReadStream')
   opts = extend({
     pieceLength: self.pieceLength
   }, opts)
@@ -254,6 +253,24 @@ File.prototype.createReadStream = function (opts) {
   return stream
 }
 
+/**
+ * TODO: detect errors and call callback with error
+ * @param {function} cb
+ */
+File.prototype.getBlobURL = function (cb) {
+  var self = this
+  var chunks = []
+  self.createReadStream()
+    .on('data', function (chunk) {
+      chunks.push(chunk)
+    })
+    .on('end', function () {
+      var buf = Buffer.concat(chunks)
+      var url = URL.createObjectURL(new Blob([ buf ]))
+      cb(null, url)
+    })
+}
+
 File.prototype._checkDone = function () {
   var self = this
   self.done = self.pieces.every(function (piece) {