diff --git a/assets/scripts/app/models/artifact.coffee b/assets/scripts/app/models/artifact.coffee
index 26b87921..fb2202fd 100644
--- a/assets/scripts/app/models/artifact.coffee
+++ b/assets/scripts/app/models/artifact.coffee
@@ -1,4 +1,5 @@
 require 'travis/model'
+require 'travis/chunk_buffer'
 
 @Travis.Artifact = Em.Object.extend
   version: 1 # used to refresh log on requeue
@@ -8,82 +9,88 @@ require 'travis/model'
   init: ->
     @_super.apply this, arguments
 
-    @addObserver 'job.id', @fetchBody
-    @fetchBody()
+    @addObserver 'job.id', @fetch
+    @fetch()
 
-    @set 'queue', Ember.A([])
-    @set 'parts', Ember.ArrayProxy.create(content: [])
-
-    @addObserver 'body', @fetchWorker
-    @fetchWorker()
+    @set 'parts', Travis.ChunkBuffer.create(content: [])
 
   id: (->
     @get('job.id')
   ).property('job.id')
 
+  willDestroy: ->
+    @get('parts').destroy()
+
   clear: ->
     @set('body', '')
     @incrementProperty('version')
+    @get('parts').destroy()
+    @set 'parts', Travis.ChunkBuffer.create(content: [])
 
-  fetchBody: ->
+  fetch: ->
     if jobId = @get('job.id')
-      @removeObserver 'job.id', @fetchBody
+      @removeObserver 'job.id', @fetch
 
-      self = this
-      Travis.ajax.ajax "/jobs/#{jobId}/log.txt?cors_hax=true", 'GET',
-        dataType: 'text'
-        contentType: 'text/plain'
-        success: (data, textStatus, xhr) ->
-          if xhr.status == 204
-            logUrl = xhr.getResponseHeader('X-Log-Location')
+      handlers =
+        json: (json) => @loadParts(json['log']['parts'])
+        text: (text) => @loadText(text)
 
-            # For some reason not all browsers can fetch this header
-            unless logUrl
-              logUrl = self.s3Url("/jobs/#{jobId}/log.txt")
+      Travis.Artifact.Request.create(id: id, handlers: handlers).run() if id = @get('job.id')
 
-            $.ajax
-              url: logUrl
-              type: 'GET'
-              success: (data) ->
-                self.fetchedBody(data)
-          else
-            self.fetchedBody(data)
+  append: (part) ->
+    @fetchWorker Ember.get(part, 'content')
+    @get('parts').pushObject(part)
 
-  s3Url: (path) ->
-    endpoint = Travis.config.api_endpoint
-    staging = if endpoint.match(/-staging/) then '-staging' else ''
-    host = Travis.config.api_endpoint.replace(/^https?:\/\//, '').split('.').slice(-2).join('.')
-    "https://s3.amazonaws.com/archive#{staging}.#{host}#{path}"
+  loadParts: (parts) ->
+    console.log 'artifact model: load parts'
+    @append(part) for part in parts
+    @set('isLoaded', true)
 
+  loadText: (text) ->
+    console.log 'artifact model: load text'
+    number = -1
+    @append(number: 1, content: text)
+    @set('isLoaded', true)
 
-  fetchedBody: (body) ->
-    @set 'body', body
-    @set 'isLoaded', true
-
-  append: (body) ->
-    if @get('isInitialized')
-      @get('parts').pushObject body
-      @set('body', @get('body') + body)
-    else
-      @get('queue').pushObject(body)
-
-  recordDidLoad: (->
-    if @get('isLoaded')
-      if (body = @get 'body') && @get('parts.length') == 0
-        @get('parts').pushObject body
-
-      @set 'isInitialized', true
-
-      queue = @get('queue')
-      if queue.get('length') > 0
-        @append queue.toArray().join('')
-  ).observes('isLoaded')
-
-  fetchWorker: ->
-    if !@get('workerName') && (body = @get('body'))
-      line = body.split("\n")[0]
+  fetchWorker: (string) ->
+    if !@get('workerName')
+      line = string.split("\n")[0]
       if line && (match = line.match /Using worker: (.*)/)
         if worker = match[1]
           worker = worker.trim().split(':')[0]
           @set('workerName', worker)
-          @removeObserver 'body', @fetchWorker
+
+Travis.Artifact.Request = Em.Object.extend
+  HEADERS:
+    accept: 'application/vnd.travis-ci.2+json; chunked=true; version=2, text/plain; version=2'
+
+  run: ->
+    Travis.ajax.ajax "/jobs/#{@id}/log?cors_hax=true", 'GET',
+      dataType: 'text'
+      headers: @HEADERS
+      success: (body, status, xhr) => @handle(body, status, xhr)
+
+  handle: (body, status, xhr) ->
+    if xhr.status == 204
+      $.ajax(url: @redirectTo(xhr), type: 'GET', success: @handlers.text)
+    else if @isJson(xhr, body)
+      @handlers.json(JSON.parse(body))
+    else
+      @handlers.text(body)
+
+  redirectTo: (xhr) ->
+    # Firefox can't see the Location header on the xhr response due to the wrong
+    # status code 204. Should be some redirect code but that doesn't work with CORS.
+    xhr.getResponseHeader('Location') || @s3Url()
+
+  s3Url: ->
+    endpoint = Travis.config.api_endpoint
+    staging = if endpoint.match(/-staging/) then '-staging' else ''
+    host = endpoint.replace(/^https?:\/\//, '').split('.').slice(-2).join('.')
+    "https://s3.amazonaws.com/archive#{staging}.#{host}#{path}/jobs/#{@id}/log.txt"
+
+  isJson: (xhr, body) ->
+    # Firefox can't see the Content-Type header on the xhr response due to the wrong
+    # status code 204. Should be some redirect code but that doesn't work with CORS.
+    type = xhr.getResponseHeader('Content-Type') || ''
+    type.indexOf('json') > -1 || body.slice(0, 8) == '{"log":{'
diff --git a/assets/scripts/app/store.coffee b/assets/scripts/app/store.coffee
index 2ad698cb..bf853986 100644
--- a/assets/scripts/app/store.coffee
+++ b/assets/scripts/app/store.coffee
@@ -97,7 +97,7 @@ Travis.Store = DS.Store.extend
 
     if event == 'job:log'
       if job = @find(Travis.Job, data['job']['id'])
-        job.appendLog(data['job']['_log'])
+        job.appendLog(number: data['job']['number'], content: data['job']['_log'])
     else if data[type.singularName()]
       @_loadOne(this, type, data)
     else if data[type.pluralName()]
diff --git a/assets/scripts/app/views/job.coffee b/assets/scripts/app/views/job.coffee
index 086346cc..974cb4af 100644
--- a/assets/scripts/app/views/job.coffee
+++ b/assets/scripts/app/views/job.coffee
@@ -104,7 +104,7 @@
       job = @get('job')
       job.subscribe() if job && !job.get('isFinished')
       null
-    ).property('job', 'job.state')
+    ).property('job', 'job.isFinished')
 
     logUrl: (->
       repo = @get('job.repo')
@@ -133,7 +133,7 @@
       @_super.apply this, arguments
 
       Ember.run.next this, ->
-        if @get 'log.isInitialized'
+        if @get 'log'
           @logDidChange()
 
     willDestroy: ->
@@ -148,9 +148,9 @@
     ).observes('log.version')
 
     logDidChange: (->
-      if @get('log.isInitialized') && @state == 'inDOM'
+      if @get('log') && @state == 'inDOM'
         @attachLogObservers()
-    ).observes('log', 'log.isInitialized')
+    ).observes('log')
 
     attachLogObservers: ->
       return if @get('logPartsObserversAttached') == Ember.guidFor(@get('log'))
diff --git a/assets/scripts/lib/travis/chunk_buffer.coffee b/assets/scripts/lib/travis/chunk_buffer.coffee
new file mode 100644
index 00000000..b5cdf326
--- /dev/null
+++ b/assets/scripts/lib/travis/chunk_buffer.coffee
@@ -0,0 +1,92 @@
+get = Ember.get
+
+Travis.ChunkBuffer = Em.ArrayProxy.extend
+  timeout: 5000
+  checkTimeoutFrequency: 1000
+  start: 1
+  next: 1
+
+  init: ->
+    @_super.apply this, arguments
+
+    @lastInsert = 0
+
+    @set('next', @get('start'))
+
+    @checkTimeout()
+
+    if @get('content.length')
+      @get('queue.content').pushObjects @get('content').toArray()
+
+  arrangedContent: (->
+    []
+  ).property('content')
+
+  addObject: (obj) ->
+    @get('content').pushObject(obj)
+
+  removeObject: (obj) ->
+    @get('content').removeObject(obj)
+
+  replaceContent: (idx, amt, objects) ->
+    @get('content').replace(idx, amt, objects)
+
+  queue: (->
+    Em.ArrayProxy.create(Em.SortableMixin,
+      content: []
+      sortProperties: ['number']
+      sortAscending: true
+    )
+  ).property()
+
+  contentArrayDidChange: (array, index, removedCount, addedCount) ->
+    @_super.apply this, arguments
+
+    if addedCount
+      queue = @get('queue.content')
+      addedObjects = array.slice(index, index + addedCount)
+      console.log 'Added log parts with numbers:', addedObjects.map( (element) -> get(element, 'number') )+'', 'current', @get('next')
+      queue.pushObjects addedObjects
+      @check()
+      @inserted()
+
+  check: ->
+    queue = @get('queue')
+    next  = @get('next')
+
+    arrangedContent = @get('arrangedContent')
+    toPush = []
+
+    while queue.get('firstObject.number') <= next
+      element = queue.shiftObject()
+      if get(element, 'number') == next
+        toPush.pushObject get(element, 'content')
+        next += 1
+
+    if toPush.length
+      arrangedContent.pushObjects toPush
+
+    @set('next', next)
+
+  inserted: ->
+    now = @now()
+    @lastInsert = now
+
+  checkTimeout: ->
+    now = @now()
+    if now - @lastInsert > @get('timeout')
+      @giveUpOnMissingParts()
+    @set 'runLaterId', Ember.run.later(this, @checkTimeout, @get('checkTimeoutFrequency'))
+
+  willDestroy: ->
+    Ember.run.cancel @get('runLaterId')
+    @_super.apply this, arguments
+
+  now: ->
+    (new Date()).getTime()
+
+  giveUpOnMissingParts: ->
+    if number = @get('queue.firstObject.number')
+      console.log 'Giving up on missing parts in the buffer, switching to:', number
+      @set('next', number)
+      @check()
diff --git a/assets/scripts/spec/spec_helper.coffee b/assets/scripts/spec/spec_helper.coffee
index e49fa538..5fc2dd46 100644
--- a/assets/scripts/spec/spec_helper.coffee
+++ b/assets/scripts/spec/spec_helper.coffee
@@ -26,11 +26,6 @@ minispade.require 'app'
       runs ->
         foo = 'bar'
 
-_Date = Date
-@Date = (date) ->
-  new _Date(date || '2012-07-02T00:03:00Z')
-@Date.UTC = _Date.UTC
-
 # hacks for missing features in webkit
 unless Function::bind
   Function::bind = (oThis) ->
diff --git a/assets/scripts/spec/unit/chunk_buffer_spec.coffee b/assets/scripts/spec/unit/chunk_buffer_spec.coffee
new file mode 100644
index 00000000..399dcbb3
--- /dev/null
+++ b/assets/scripts/spec/unit/chunk_buffer_spec.coffee
@@ -0,0 +1,93 @@
+createChunk = (number, content) ->
+  Em.Object.create(number: number, content: content)
+
+describe 'Travis.ChunkBuffer', ->
+  it 'waits for parts to be in order before revealing them', ->
+    buffer = Travis.ChunkBuffer.create(content: [])
+
+    buffer.pushObject createChunk(3, "baz")
+    buffer.pushObject createChunk(2, "bar")
+
+    expect(buffer.get('length')).toEqual(0)
+
+    buffer.pushObject createChunk(1, "foo")
+
+    expect(buffer.get('length')).toEqual(3)
+
+    expect(buffer.toArray()).toEqual(['foo', 'bar', 'baz'])
+
+  it 'ignores a part if it fails to be delivered within timeout', ->
+    buffer = Travis.ChunkBuffer.create(content: [], timeout: 20, checkTimeoutFrequency: 5)
+
+    buffer.pushObject createChunk(3, "baz")
+
+    expect(buffer.get('length')).toEqual(0)
+
+    buffer.pushObject createChunk(1, "foo")
+
+    expect(buffer.get('length')).toEqual(1)
+
+    waits 40
+    runs ->
+      expect(buffer.get('length')).toEqual(2)
+      expect(buffer.toArray()).toEqual(['foo', 'baz'])
+
+      buffer.destroy()
+
+  it 'works correctly when parts are passed as content', ->
+    content = [createChunk(2, 'bar')]
+
+    buffer = Travis.ChunkBuffer.create(content: content)
+
+    expect(buffer.get('length')).toEqual(0)
+
+    buffer.pushObject createChunk(1, "foo")
+
+    expect(buffer.get('length')).toEqual(2)
+    expect(buffer.toArray()).toEqual(['foo', 'bar'])
+
+  it 'works correctly when parts duplicated', ->
+    buffer = Travis.ChunkBuffer.create(content: [])
+
+    buffer.pushObject createChunk(1, "foo")
+    buffer.pushObject createChunk(2, "bar")
+    buffer.pushObject createChunk(3, "baz")
+
+    buffer.pushObject createChunk(2, "bar")
+    buffer.pushObject createChunk(3, "baz")
+    buffer.pushObject createChunk(4, "qux")
+
+    expect(buffer.get('length')).toEqual(4)
+    expect(buffer.toArray()).toEqual(['foo', 'bar', 'baz', 'qux'])
+
+  it 'fires array observers properly', ->
+    changes = []
+    buffer = Travis.ChunkBuffer.create(content: [])
+
+    observer = Em.Object.extend(
+      init: ->
+        @_super.apply this, arguments
+
+        @get('content').addArrayObserver this,
+          willChange: 'arrayWillChange',
+          didChange: 'arrayDidChange'
+
+      arrayWillChange: (->)
+      arrayDidChange: (array, index, removedCount, addedCount) ->
+        changes.pushObject([index, addedCount])
+    ).create(content: buffer)
+
+    buffer.pushObject createChunk(2, "baz")
+
+    expect(buffer.get('length')).toEqual(0)
+    expect(changes.length).toEqual(0)
+
+    buffer.pushObject createChunk(1, "foo")
+
+    expect(buffer.get('length')).toEqual(2)
+    expect(changes.length).toEqual(1)
+    expect(changes[0]).toEqual([0, 2])
+
+  it 'sets next to start if start is given at init', ->
+    buffer = Travis.ChunkBuffer.create(content: [], start: 5)
+    expect(buffer.get('next')).toEqual(5)