correctly detect UDP tracker scrape support

Before this fix, udp tracker urls needed to contain “/announce” or else
we would assume the tracker doesn’t support scrape. (This is correct
behavior for http trackers, but not udp)

Author: feross

client.js

@@ -197,14 +197,7 @@ Tracker.prototype._announce = function (opts) {
 Tracker.prototype.scrape = function () {
   var self = this
 
-  if (!self._scrapeUrl) {
-    var announce = 'announce'
-    var i = self._announceUrl.lastIndexOf('/') + 1
-
-    if (i >= 1 && self._announceUrl.slice(i, i + announce.length) === announce) {
-      self._scrapeUrl = self._announceUrl.slice(0, i) + 'scrape' + self._announceUrl.slice(i + announce.length)
-    }
-  }
+  self._scrapeUrl = self._scrapeUrl || getScrapeUrl(self._announceUrl)
 
   if (!self._scrapeUrl) {
     debug('scrape not supported by ' + self._announceUrl)
@@ -213,7 +206,7 @@ Tracker.prototype.scrape = function () {
   }
 
   debug('sent `scrape` to ' + self._announceUrl)
-  self._requestImpl(self._scrapeUrl)
+  self._requestImpl(self._scrapeUrl, { _scrape: true })
 }
 
 Tracker.prototype.setInterval = function (intervalMs) {
@@ -229,7 +222,7 @@ Tracker.prototype.setInterval = function (intervalMs) {
 Tracker.prototype._requestHttp = function (requestUrl, opts) {
   var self = this
 
-  if (isScrapeUrl(requestUrl)) {
+  if (opts._scrape) {
     opts = extend({
       info_hash: self.client._infoHash.toString('binary')
     }, opts)
@@ -307,7 +300,7 @@ Tracker.prototype._requestUdp = function (requestUrl, opts) {
           return error('invalid udp handshake')
         }
 
-        if (isScrapeUrl(requestUrl)) {
+        if (opts._scrape) {
           scrape(msg.slice(8, 16))
         } else {
           announce(msg.slice(8, 16), opts)
@@ -511,3 +504,16 @@ function toUInt64 (n) {
 function isScrapeUrl (u) {
   return u.substr(u.lastIndexOf('/') + 1, 'scrape'.length) === 'scrape'
 }
+
+var UDP_TRACKER = /^udp:\/\//
+var HTTP_SCRAPE_SUPPORT = /\/(announce)[^\/]*$/
+
+function getScrapeUrl (announceUrl) {
+  if (announceUrl.match(UDP_TRACKER)) return announceUrl
+  var match
+  if (match = announceUrl.match(HTTP_SCRAPE_SUPPORT)) {
+    var i = match.index
+    return announceUrl.slice(0, i) + '/scrape' + announceUrl.slice(i + 9)
+  }
+  return null
+}

test/client-large-torrent.js

@@ -27,7 +27,7 @@ test('large torrent: client.start()', function (t) {
     server.listen(port)
 
     // remove all tracker servers except a single UDP one, for now
-    parsedTorrent.announce = [ 'udp://127.0.0.1:' + port + '/announce' ]
+    parsedTorrent.announce = [ 'udp://127.0.0.1:' + port ]
 
     var client = new Client(peerId, 6881, parsedTorrent)
 
@@ -36,7 +36,7 @@ test('large torrent: client.start()', function (t) {
     })
 
     client.once('update', function (data) {
-      t.equal(data.announce, 'udp://127.0.0.1:' + port + '/announce')
+      t.equal(data.announce, 'udp://127.0.0.1:' + port)
       t.equal(typeof data.complete, 'number')
       t.equal(typeof data.incomplete, 'number')
     })

test/client.js

@@ -28,7 +28,10 @@ function createServer (t, serverType, cb) {
   portfinder.getPort(function (err, port) {
     if (err) return t.error(err)
 
-    announceUrl = serverType + '://127.0.0.1:' + port + '/announce'
+    announceUrl = serverType === 'http'
+      ? 'http://127.0.0.1:' + port + '/announce'
+      : 'udp://127.0.0.1:' + port
+
     parsedTorrent.announce = [ announceUrl ]
 
     server.listen(port)