Implements BEP53 to allow file selection using &so in magnetURI.

lib/torrent.js

@@ -30,6 +30,7 @@ var speedometer = require('speedometer')
 var uniq = require('uniq')
 var utMetadata = require('ut_metadata')
 var utPex = require('ut_pex') // browser exclude
+var parseRange = require('parse-numeric-range')
 
 var File = require('./file')
 var Peer = require('./peer')
@@ -482,11 +483,6 @@ Torrent.prototype._onMetadata = function (metadata) {
     })
   }
 
-  // start off selecting the entire torrent with low priority
-  if (self.pieces.length !== 0) {
-    self.select(0, self.pieces.length - 1, false)
-  }
-
   self._rarityMap = new RarityMap(self)
 
   self.store = new ImmediateChunkStore(
@@ -509,6 +505,22 @@ Torrent.prototype._onMetadata = function (metadata) {
     return new File(self, file)
   })
 
+  // Only select specified files (BEP53)
+  if (self.so) {
+    var specificFiles = parseRange.parse(self.so)
+    // https://github.com/webtorrent/webtorrent/issues/164
+    self.deselect(0, self.pieces.length - 1, false)
+
+    self.files.forEach(function (v, i) {
+      specificFiles.indexOf(i) === -1 ? self.files[i].deselect() : self.files[i].select(true)
+    })
+  } else {
+    // start off selecting the entire torrent with low priority
+    if (self.pieces.length !== 0) {
+      self.select(0, self.pieces.length - 1, false)
+    }
+  }
+
   self._hashes = self.pieces
 
   self.pieces = self.pieces.map(function (hash, i) {

package.json

@@ -42,6 +42,7 @@
     "mime": "^2.2.0",
     "multistream": "^2.0.5",
     "package-json-versionify": "^1.0.2",
+    "parse-numeric-range": "^0.0.2",
     "parse-torrent": "^6.0.0",
     "pump": "^3.0.0",
     "random-iterate": "^1.0.1",