diff --git a/lib/swarm.js b/lib/swarm.js
new file mode 100644
index 0000000..2413139
--- /dev/null
+++ b/lib/swarm.js
@@ -0,0 +1,133 @@
+var debug = require('debug')('bittorrent-tracker')
+var string2compact = require('string2compact')
+
+module.exports = Swarm
+
+// Regard this as the default implementation of an interface that you
+// need to support when overriding Server.getSwarm()
+function Swarm (infoHash, server) {
+  this.peers = {}
+  this.complete = 0
+  this.incomplete = 0
+  this.emit = server.emit.bind(server)
+}
+
+Swarm.prototype.announce = function (params, cb) {
+  var self = this
+  var peer = self.peers[params.addr]
+
+  var start = function () {
+    if (peer) {
+      debug('unexpected `started` event from peer that is already in swarm')
+      return update() // treat as an update
+    }
+    if (params.left === 0) self.complete += 1
+    else self.incomplete += 1
+    peer = self.peers[params.addr] = {
+      ip: params.ip,
+      port: params.port,
+      peerId: params.peer_id
+    }
+    self.emit('start', params.addr)
+  }
+
+  var stop = function () {
+    if (!peer) {
+      debug('unexpected `stopped` event from peer that is not in swarm')
+      return // do nothing
+    }
+    if (peer.complete) self.complete -= 1
+    else self.incomplete -= 1
+    self.peers[params.addr] = null
+    self.emit('stop', params.addr)
+  }
+
+  var complete = function () {
+    if (!peer) {
+      debug('unexpected `completed` event from peer that is not in swarm')
+      return start() // treat as a start
+    }
+    if (peer.complete) {
+      debug('unexpected `completed` event from peer that is already marked as completed')
+      return // do nothing
+    }
+    self.complete += 1
+    self.incomplete -= 1
+    peer.complete = true
+    self.emit('complete', params.addr)
+  }
+
+  var update = function () {
+    if (!peer) {
+      debug('unexpected `update` event from peer that is not in swarm')
+      return start() // treat as a start
+    }
+    self.emit('update', params.addr)
+  }
+
+  switch (params.event) {
+  case 'started':
+    start()
+    break
+  case 'stopped':
+    stop()
+    break
+  case 'completed':
+    complete()
+    break
+  case '': case undefined: case 'empty': case 'update': // update
+    update()
+    break
+  default:
+    return cb(new Error('invalid event')) // early return
+  }
+
+  if (params.left === 0 && peer) peer.complete = true
+
+  // send peers
+  var peers = params.compact === 1
+        ? self._getPeersCompact(params.numwant)
+        : self._getPeers(params.numwant)
+
+  cb(null, {
+    complete: this.complete,
+    incomplete: this.incomplete,
+    peers: peers
+  })
+}
+
+Swarm.prototype._getPeers = function (numwant) {
+  var peers = []
+  for (var peerId in this.peers) {
+    if (peers.length >= numwant) break
+    var peer = this.peers[peerId]
+    if (!peer) continue // ignore null values
+    peers.push({
+      'peer id': peer.peerId,
+      ip: peer.ip,
+      port: peer.port
+    })
+  }
+  return peers
+}
+
+Swarm.prototype._getPeersCompact = function (numwant) {
+  var peers = []
+
+  for (var peerId in this.peers) {
+    if (peers.length >= numwant) break
+    var peer = this.peers[peerId]
+    if (!peer) continue // ignore null values
+    peers.push(peer.ip + ':' + peer.port)
+  }
+
+  return string2compact(peers)
+}
+
+
+Swarm.prototype.scrape = function (infoHash, params, cb) {
+  cb(null, {
+    complete: this.complete,
+    incomplete: this.incomplete
+  })
+}
diff --git a/package.json b/package.json
index a83fc5c..e002d8a 100644
--- a/package.json
+++ b/package.json
@@ -26,6 +26,7 @@
     "ip": "^0.3.0",
     "once": "^1.3.0",
     "portfinder": "^0.2.1",
+    "run-series": "^1.0.2",
     "string2compact": "^1.1.1"
   },
   "devDependencies": {
diff --git a/server.js b/server.js
index d84de01..241e12c 100644
--- a/server.js
+++ b/server.js
@@ -1,7 +1,6 @@
 module.exports = Server
 
 var bencode = require('bencode')
-var common = require('./lib/common')
 var debug = require('debug')('bittorrent-tracker')
 var dgram = require('dgram')
 var EventEmitter = require('events').EventEmitter
@@ -9,8 +8,10 @@ var http = require('http')
 var inherits = require('inherits')
 var ipLib = require('ip')
 var portfinder = require('portfinder')
-var string2compact = require('string2compact')
+var series = require('run-series')
 
+var common = require('./lib/common')
+var Swarm = require('./lib/swarm')
 var parseHttpRequest = require('./lib/parse_http')
 var parseUdpRequest = require('./lib/parse_udp')
 
@@ -119,11 +120,7 @@ Server.prototype.getSwarm = function (binaryInfoHash) {
   if (Buffer.isBuffer(binaryInfoHash)) binaryInfoHash = binaryInfoHash.toString('binary')
   var swarm = self.torrents[binaryInfoHash]
   if (!swarm) {
-    swarm = self.torrents[binaryInfoHash] = {
-      complete: 0,
-      incomplete: 0,
-      peers: {}
-    }
+    swarm = self.torrents[binaryInfoHash] = new Swarm(binaryInfoHash, this)
   }
   return swarm
 }
@@ -214,89 +211,13 @@ Server.prototype._onRequest = function (params, cb) {
 
 Server.prototype._onAnnounce = function (params, cb) {
   var self = this
-
   var swarm = self.getSwarm(params.info_hash)
-  var peer = swarm.peers[params.addr]
-
-  var start = function () {
-    if (peer) {
-      debug('unexpected `started` event from peer that is already in swarm')
-      return update() // treat as an update
+  swarm.announce(params, function (err, response) {
+    if (response) {
+      if (!response.action) response.action = common.ACTIONS.ANNOUNCE
+      if (!response.intervalMs) response.intervalMs = self._intervalMs
     }
-    if (params.left === 0) swarm.complete += 1
-    else swarm.incomplete += 1
-    peer = swarm.peers[params.addr] = {
-      ip: params.ip,
-      port: params.port,
-      peerId: params.peer_id
-    }
-    self.emit('start', params.addr)
-  }
-
-  var stop = function () {
-    if (!peer) {
-      debug('unexpected `stopped` event from peer that is not in swarm')
-      return // do nothing
-    }
-    if (peer.complete) swarm.complete -= 1
-    else swarm.incomplete -= 1
-    swarm.peers[params.addr] = null
-    self.emit('stop', params.addr)
-  }
-
-  var complete = function () {
-    if (!peer) {
-      debug('unexpected `completed` event from peer that is not in swarm')
-      return start() // treat as a start
-    }
-    if (peer.complete) {
-      debug('unexpected `completed` event from peer that is already marked as completed')
-      return // do nothing
-    }
-    swarm.complete += 1
-    swarm.incomplete -= 1
-    peer.complete = true
-    self.emit('complete', params.addr)
-  }
-
-  var update = function () {
-    if (!peer) {
-      debug('unexpected `update` event from peer that is not in swarm')
-      return start() // treat as a start
-    }
-    self.emit('update', params.addr)
-  }
-
-  switch (params.event) {
-  case 'started':
-    start()
-    break
-  case 'stopped':
-    stop()
-    break
-  case 'completed':
-    complete()
-    break
-  case '': case undefined: case 'empty': case 'update': // update
-    update()
-    break
-  default:
-    return cb(new Error('invalid event')) // early return
-  }
-
-  if (params.left === 0 && peer) peer.complete = true
-
-  // send peers
-  var peers = params.compact === 1
-        ? self._getPeersCompact(swarm, params.numwant)
-        : self._getPeers(swarm, params.numwant)
-
-  cb(null, {
-    action: common.ACTIONS.ANNOUNCE,
-    complete: swarm.complete,
-    incomplete: swarm.incomplete,
-    peers: peers,
-    intervalMs: self._intervalMs
+    cb(err, response)
   })
 }
 
@@ -324,46 +245,31 @@ Server.prototype._onScrape = function (params, cb) {
       min_request_interval: self._intervalMs
     }
   }
-  
-  params.info_hash.some(function (infoHash) {
+
+  series(params.info_hash.map(function (infoHash) {
     var swarm = self.getSwarm(infoHash)
-    
-    response.files[infoHash] = {
-      complete: swarm.complete,
-      incomplete: swarm.incomplete,
-      downloaded: swarm.complete // TODO: this only provides a lower-bound
+    return function (cb) {
+      swarm.scrape(infoHash, params, function (err, scrapeInfo) {
+        cb(err, scrapeInfo && {
+          infoHash: infoHash,
+          complete: scrapeInfo.complete || 0,
+          incomplete: scrapeInfo.incomplete || 0
+        })
+      })
     }
-  })
+  }), function (err, results) {
+    if (err) return cb(err)
 
-  cb(null, response)
-}
-
-Server.prototype._getPeers = function (swarm, numwant) {
-  var peers = []
-  for (var peerId in swarm.peers) {
-    if (peers.length >= numwant) break
-    var peer = swarm.peers[peerId]
-    if (!peer) continue // ignore null values
-    peers.push({
-      'peer id': peer.peerId,
-      ip: peer.ip,
-      port: peer.port
+    results.forEach(function (result) {
+      response.files[result.infoHash] = {
+        complete: result.complete,
+        incomplete: result.incomplete,
+        downloaded: result.complete // TODO: this only provides a lower-bound
+      }
     })
-  }
-  return peers
-}
 
-Server.prototype._getPeersCompact = function (swarm, numwant) {
-  var peers = []
-
-  for (var peerId in swarm.peers) {
-    if (peers.length >= numwant) break
-    var peer = swarm.peers[peerId]
-    if (!peer) continue // ignore null values
-    peers.push(peer.ip + ':' + peer.port)
-  }
-
-  return string2compact(peers)
+    cb(null, response)
+  })
 }