Revert devserver update to fix factory install.

autoupdate.py

Index: autoupdate.py
diff --git a/autoupdate.py b/autoupdate.py
index c546018d9f70beeed87feae2041c8485eb74d936..07449664b559a424b8f5695e88607f0ecc5f494b 100644
--- a/autoupdate.py
+++ b/autoupdate.py
@@ -1,4 +1,4 @@
-# Copyright (c) 2009-2010 The Chromium OS Authors. All rights reserved.
+# Copyright (c) 2009 The Chromium OS Authors. All rights reserved.
 # Use of this source code is governed by a BSD-style license that can be
 # found in the LICENSE file.
 
@@ -7,88 +7,119 @@ from xml.dom import minidom
 
 import os
 import shutil
+import sys
 import time
 import web
 
-
 class Autoupdate(BuildObject):
-  """Class that contains functionality that handles Chrome OS update pings.
-
-  Members:
-    serve_only: Serve images from a pre-built image.zip file.  static_dir
-      must be set to the location of the image.zip.
-    factory_config: Path to the factory config file if handling factory
-      requests.
-    use_test_image: Use chromiumos_test_image.bin rather than the standard.
-    static_url_base: base URL, other than devserver, for update images.
-    client_prefix: The prefix for the update engine client.
-    forced_image: Path to an image to use for all updates.
-  """
+  # Basic functionality of handling ChromeOS autoupdate pings
+  # and building/serving update images.
+  # TODO(rtc): Clean this code up and write some tests.
 
   def __init__(self, serve_only=None, test_image=False, urlbase=None,
-               factory_config_path=None, client_prefix=None, forced_image=None,
+               factory_config_path=None, validate_factory_config=None,
+               client_prefix=None,
                *args, **kwargs):
     super(Autoupdate, self).__init__(*args, **kwargs)
     self.serve_only = serve_only
     self.factory_config = factory_config_path
-    self.use_test_image = test_image
+    self.test_image = test_image
     self.static_urlbase = urlbase
     self.client_prefix = client_prefix
-    self.forced_image = forced_image
+    if serve_only:
+      # If  we're  serving  out  of  an archived  build  dir  (e.g.  a
+      # buildbot), prepare this webserver's magic 'static/' dir with a
+      # link to the build archive.
+      web.debug('Autoupdate in "serve update images only" mode.')
+      if os.path.exists('static/archive'):
+        if self.static_dir != os.readlink('static/archive'):
+          web.debug('removing stale symlink to %s' % self.static_dir)
+          os.unlink('static/archive')
+          os.symlink(self.static_dir, 'static/archive')
+      else:
+         os.symlink(self.static_dir, 'static/archive')
+    if factory_config_path is not None:
+      self.ImportFactoryConfigFile(factory_config_path, validate_factory_config)
 
-  def _GetSecondsSinceMidnight(self):
-    """Returns the seconds since midnight as a decimal value."""
+  def GetSecondsSinceMidnight(self):
     now = time.localtime()
     return now[3] * 3600 + now[4] * 60 + now[5]
 
-  def _GetDefaultBoardID(self):
-    """Returns the default board id stored in .default_board."""
+  def GetUpdatePayload(self, hash, size, url):
+    payload = """<?xml version="1.0" encoding="UTF-8"?>
+      <gupdate xmlns="http://www.google.com/update2/response" protocol="2.0">
+        <daystart elapsed_seconds="%s"/>
+        <app appid="{%s}" status="ok">
+          <ping status="ok"/>
+          <updatecheck
+            codebase="%s"
+            hash="%s"
+            needsadmin="false"
+            size="%s"
+            status="ok"/>
+        </app>
+      </gupdate>
+    """
+    return payload % (self.GetSecondsSinceMidnight(),
+                      self.app_id, url, hash, size)
+
+  def GetNoUpdatePayload(self):
+    payload = """<?xml version="1.0" encoding="UTF-8"?>
+      <gupdate xmlns="http://www.google.com/update2/response" protocol="2.0">
+        <daystart elapsed_seconds="%s"/>
+        <app appid="{%s}" status="ok">
+          <ping status="ok"/>
+          <updatecheck status="noupdate"/>
+        </app>
+      </gupdate>
+    """
+    return payload % (self.GetSecondsSinceMidnight(), self.app_id)
+
+  def GetDefaultBoardID(self):
     board_file = '%s/.default_board' % (self.scripts_dir)
     try:
       return open(board_file).read()
     except IOError:
       return 'x86-generic'
 
-  def _GetLatestImageDir(self, board_id):
-    """Returns the latest image dir based on shell script."""
+  def GetLatestImagePath(self, board_id):
     cmd = '%s/get_latest_image.sh --board %s' % (self.scripts_dir, board_id)
     return os.popen(cmd).read().strip()
 
-  def _GetVersionFromDir(self, image_dir):
-    """Returns the version of the image based on the name of the directory."""
-    latest_version = os.path.basename(image_dir)
+  def GetLatestVersion(self, latest_image_path):
+    latest_version = latest_image_path.split('/')[-1]
+
+    # Removes the portage build prefix.
+    latest_version = latest_version.lstrip('g-')
     return latest_version.split('-')[0]
 
-  def _CanUpdate(self, client_version, latest_version):
-    """Returns true if the latest_version is greater than the client_version."""
+  def CanUpdate(self, client_version, latest_version):
+    """
+      Returns true iff the latest_version is greater than the client_version.
+    """
     client_tokens = client_version.replace('_', '').split('.')
     latest_tokens = latest_version.replace('_', '').split('.')
-    web.debug('client version %s latest version %s'
-              % (client_version, latest_version))
+    web.debug('client version %s latest version %s' \
+        % (client_version, latest_version))
     for i in range(4):
       if int(latest_tokens[i]) == int(client_tokens[i]):
         continue
       return int(latest_tokens[i]) > int(client_tokens[i])
     return False
 
-  def _UnpackStatefulPartition(self, image_path, stateful_file):
-    """Given an image, unpacks its stateful partition to stateful_file."""
-    image_dir = os.path.dirname(image_path)
-    image_file = os.path.basename(image_path)
-
+  def UnpackStatefulPartition(self, image_path, image_file, stateful_file):
+    """Given an image, unpacks the stateful partition to stateful_file."""
     get_offset = '$(cgpt show -b -i 1 %s)' % image_file
     get_size = '$(cgpt show -s -i 1 %s)' % image_file
     unpack_command = (
         'cd %s && '
-        'dd if=%s of=%s bs=512 skip=%s count=%s' % (image_dir, image_file,
-                                                    stateful_file, get_offset,
-                                                    get_size))
+        'dd if=%s of=%s bs=512 skip=%s count=%s' % (image_path, image_file,
+            stateful_file, get_offset, get_size))
     web.debug(unpack_command)
     return os.system(unpack_command) == 0
 
-  def _UnpackZip(self, image_dir):
-    """Unpacks an image.zip into a given directory."""
-    image = os.path.join(image_dir, self._GetImageName())
+  def UnpackZip(self, image_path, image_file):
+    image = os.path.join(image_path, image_file)
     if os.path.exists(image):
       return True
     else:
@@ -96,231 +127,81 @@ class Autoupdate(BuildObject):
       # simultaneously by multiple request handlers. This means that
       # we're assuming each image.zip file lives in a versioned
       # directory (a la Buildbot).
-      return os.system('cd %s && unzip -n image.zip' % image_dir) == 0
+      return os.system('cd %s && unzip -n image.zip %s unpack_partitions.sh' %
+                       (image_path, image_file)) == 0
 
-  def _GetImageName(self):
-    """Returns the name of the image that should be used."""
-    if self.use_test_image:
-      image_name = 'chromiumos_test_image.bin'
+  def GetImageBinPath(self, image_path):
+    if self.test_image:
+      image_file = 'chromiumos_test_image.bin'
     else:
-      image_name = 'chromiumos_image.bin'
-    return image_name
-
-  def _IsImageNewerThanCached(self, image_path, cached_file_path):
-    """Returns true if the image is newer than the cached image."""
-    if os.path.exists(cached_file_path) and os.path.exists(image_path):
-      web.debug('Usable cached image found.')
-      return os.path.getmtime(image_path) > os.path.getmtime(cached_file_path)
-    elif not os.path.exists(cached_file_path) and not os.path.exists(image_path):
-      raise Exception('Image does not exist and cached image missing')
-    else:
-      # Only one is missing, figure out which one.
-      if os.path.exists(image_path):
-        web.debug('No cached image found - image generation required.')
-        return True
-      else:
-        web.debug('Only cached image found to serve.')
-        return False
+      image_file = 'chromiumos_image.bin'
+    return image_file
 
-  def _GetSize(self, update_path):
-    """Returns the size of the file given."""
-    return os.path.getsize(update_path)
-
-  def _GetHash(self, update_path):
-    """Returns the sha1 of the file given."""
-    cmd = ('cat %s | openssl sha1 -binary | openssl base64 | tr \'\\n\' \' \';'
-           % update_path)
-    return os.popen(cmd).read().rstrip()
-
-  def GetUpdatePayload(self, hash, size, url):
-    """Returns a payload to the client corresponding to a new update.
-
-    Args:
-      hash: hash of update blob
-      size: size of update blob
-      url: where to find update blob
-    Returns:
-      Xml string to be passed back to client.
-    """
-    payload = """<?xml version="1.0" encoding="UTF-8"?>
-      <gupdate xmlns="http://www.google.com/update2/response" protocol="2.0">
-        <daystart elapsed_seconds="%s"/>
-        <app appid="{%s}" status="ok">
-          <ping status="ok"/>
-          <updatecheck
-            codebase="%s"
-            hash="%s"
-            needsadmin="false"
-            size="%s"
-            status="ok"/>
-        </app>
-      </gupdate>
-    """
-    return payload % (self._GetSecondsSinceMidnight(),
-                      self.app_id, url, hash, size)
+  def BuildUpdateImage(self, image_path):
+    stateful_file = '%s/stateful.image' % image_path
+    image_file = self.GetImageBinPath(image_path)
+    bin_path = os.path.join(image_path, image_file)
 
-  def GetNoUpdatePayload(self):
-    """Returns a payload to the client corresponding to no update."""
-    payload = """ < ?xml version = "1.0" encoding = "UTF-8"? >
-      < gupdate xmlns = "http://www.google.com/update2/response" protocol = "2.0" >
-        < daystart elapsed_seconds = "%s" />
-        < app appid = "{%s}" status = "ok" >
-          < ping status = "ok" />
-          < updatecheck status = "noupdate" />
-        </ app >
-      </ gupdate >
-    """
-    return payload % (self._GetSecondsSinceMidnight(), self.app_id)
-
-  def GenerateUpdateFile(self, image_path):
-    """Generates an update gz given a full path to an image.
-
-    Args:
-      image_path: Full path to image.
-    Returns:
-      Path to created update_payload or None on error.
-    """
-    image_dir = os.path.dirname(image_path)
-    update_path = os.path.join(image_dir, 'update.gz')
-    web.debug('Generating update image %s' % update_path)
-
-    mkupdate_command = (
-        '%s/cros_generate_update_payload --image=%s --output=%s '
-        '--patch_kernel' % (self.scripts_dir, image_path, update_path))
-    if os.system(mkupdate_command) != 0:
-      web.debug('Failed to create base update file')
-      return None
-
-    return update_path
-
-  def GenerateStatefulFile(self, image_path):
-    """Generates a stateful update gz given a full path to an image.
-
-    Args:
-      image_path: Full path to image.
-    Returns:
-      Path to created stateful update_payload or None on error.
-    """
-    stateful_partition_path = '%s/stateful.image' % os.path.dirname(image_path)
-
-    # Unpack to get stateful partition.
-    if self._UnpackStatefulPartition(image_path, stateful_partition_path):
-      mkstatefulupdate_command = 'gzip -f %s' % stateful_partition_path
-      if os.system(mkstatefulupdate_command) == 0:
-        web.debug('Successfully generated %s.gz' % stateful_partition_path)
-        return '%s.gz' % stateful_partition_path
-
-    web.debug('Failed to create stateful update file')
-    return None
-
-  def MoveImagesToStaticDir(self, update_path, stateful_update_path,
-                            static_image_dir):
-    """Moves gz files from their directories to serving directories.
-
-    Args:
-      update_path: full path to main update gz.
-      stateful_update_path: full path to stateful partition gz.
-      static_image_dir: where to put files.
-    Returns:
-      Returns True if the files were moved over successfully.
-    """
-    try:
-      shutil.copy(update_path, static_image_dir)
-      shutil.copy(stateful_update_path, static_image_dir)
-      os.remove(update_path)
-      os.remove(stateful_update_path)
-    except Exception:
-      web.debug('Failed to move %s and %s to %s' % (update_path,
-                                                    stateful_update_path,
-                                                    static_image_dir))
-      return False
-
-    return True
-
-  def GenerateUpdateImage(self, image_path, move_to_static_dir=False,
-                          static_image_dir=None):
-    """Force generates an update payload based on the given image_path.
-
-    Args:
-      image_path: full path to the image.
-      move_to_static_dir: Moves the files from their dir to the static dir.
-      static_image_dir: the directory to move images to after generating.
-    Returns:
-      True if the update payload was created successfully.
-    """
-    web.debug('Generating update for image %s' % image_path)
-    update_path = self.GenerateUpdateFile(image_path)
-    stateful_update_path = self.GenerateStatefulFile(image_path)
-    if not update_path or not stateful_update_path:
-      web.debug('Failed to generate update')
-      return False
-
-    if move_to_static_dir:
-      return self.MoveImagesToStaticDir(update_path, stateful_update_path,
-                                        static_image_dir)
+    # Get appropriate update.gz to compare timestamps.
+    if self.serve_only:
+      cached_update_file = os.path.join(image_path, 'update.gz')
     else:
-      return True
+      cached_update_file = os.path.join(self.static_dir, 'update.gz')
 
-  def GenerateLatestUpdateImage(self, board_id, client_version,
-                                static_image_dir=None):
-    """Generates an update using the latest image that has been built.
-
-    This will only generate an update if the newest update is newer than that
-    on the client or client_version is 'ForcedUpdate'.
-
-    Args:
-      board_id: Name of the board.
-      client_version: Current version of the client or 'ForcedUpdate'
-      static_image_dir: the directory to move images to after generating.
-    Returns:
-      True if the update payload was created successfully.
-    """
-    latest_image_dir = self._GetLatestImageDir(board_id)
-    latest_version = self._GetVersionFromDir(latest_image_dir)
-    latest_image_path = os.path.join(latest_image_dir, self._GetImageName())
-
-    web.debug('Preparing to generate update from latest built image %s.' %
-              latest_image_path)
-
-     # Check to see whether or not we should update.
-    if client_version != 'ForcedUpdate' and not self._CanUpdate(
-        client_version, latest_version):
-      web.debug('no update')
-      return False
-
-    cached_file_path = os.path.join(static_image_dir, 'update.gz')
-    if (os.path.exists(cached_file_path) and
-        not self._IsImageNewerThanCached(latest_image_path, cached_file_path)):
-      return True
+    # If the new chromiumos image is newer, re-create everything.
+    if (os.path.exists(cached_update_file) and
+        os.path.getmtime(cached_update_file) >= os.path.getmtime(bin_path)):
+      web.debug('Using cached update image at %s instead of %s' %
+                (cached_update_file, bin_path))
+    else:
+      # Unpack zip file if we are serving from a directory.
+      if self.serve_only and not self.UnpackZip(image_path, image_file):
+        web.debug('unzip image.zip failed.')
+        return False
 
-    return self.GenerateUpdateImage(latest_image_path, move_to_static_dir=True,
-                                    static_image_dir=static_image_dir)
+      update_file = os.path.join(image_path, 'update.gz')
+      web.debug('Generating update image %s' % update_file)
+      mkupdate_command = (
+          '%s/cros_generate_update_payload --image=%s --output=%s '
+          '--patch_kernel' % (self.scripts_dir, bin_path, update_file))
+      if os.system(mkupdate_command) != 0:
+        web.debug('Failed to create update image')
+        return False
 
-  def GenerateImageFromZip(self, static_image_dir):
-    """Generates an update from an image zip file.
+      # Unpack to get stateful partition.
+      if not self.UnpackStatefulPartition(image_path, image_file,
+                                          stateful_file):
+        web.debug('Failed to unpack stateful partition.')
+        return False
 
-    This method assumes you have an image.zip in directory you are serving
-    from.  If this file is newer than a previously cached file, it will unzip
-    this file, create a payload and serve it.
+      mkstatefulupdate_command = 'gzip -f %s' % stateful_file
+      if os.system(mkstatefulupdate_command) != 0:
+        web.debug('Failed to create stateful update gz')
+        return False
 
-    Args:
-      static_image_dir: Directory where the zip file exists.
-    Returns:
-      True if the update payload was created successfully.
-    """
-    web.debug('Preparing to generate update from zip in %s.' % static_image_dir)
-    image_path = os.path.join(static_image_dir, self._GetImageName())
-    cached_file_path = os.path.join(static_image_dir, 'update.gz')
-    zip_file_path = os.path.join(static_image_dir, 'image.zip')
-    if not self._IsImageNewerThanCached(zip_file_path, cached_file_path):
-      return True
+      # Add gz suffix
+      stateful_file = '%s.gz' % stateful_file
+
+      # Cleanup of image files.
+      if not self.serve_only:
+        try:
+          web.debug('Found a new image to serve, copying it to static')
+          shutil.copy(update_file, self.static_dir)
+          shutil.copy(stateful_file, self.static_dir)
+          os.remove(update_file)
+          os.remove(stateful_file)
+        except Exception, e:
+          web.debug('%s' % e)
+          return False
+    return True
 
-    if not self._UnpackZip(static_image_dir):
-      web.debug('unzip image.zip failed.')
-      return False
+  def GetSize(self, update_path):
+    return os.path.getsize(update_path)
 
-    return self.GenerateUpdateImage(image_path, move_to_static_dir=False,
-                                    static_image_dir=None)
+  def GetHash(self, update_path):
+    cmd = "cat %s | openssl sha1 -binary | openssl base64 | tr \'\\n\' \' \';" \
+        % update_path
+    return os.popen(cmd).read().rstrip()
 
   def ImportFactoryConfigFile(self, filename, validate_checksums=False):
     """Imports a factory-floor server configuration file. The file should
@@ -373,26 +254,24 @@ class Autoupdate(BuildObject):
         suffix = '_image'
         if key.endswith(suffix):
           kind = key[:-len(suffix)]
-          stanza[kind + '_size'] = os.path.getsize(os.path.join(
-              self.static_dir, stanza[kind + '_image']))
+          stanza[kind + '_size'] = \
+            os.path.getsize(self.static_dir + '/' + stanza[kind + '_image'])
           if validate_checksums:
-            factory_checksum = self._GetHash(self.static_dir + ' / ' +
-                                             stanza[kind + '_image'])
+            factory_checksum = self.GetHash(self.static_dir + '/' +
+                                            stanza[kind + '_image'])
             if factory_checksum != stanza[kind + '_checksum']:
-              print ('Error: checksum mismatch for %s. Expected "%s" but file '
-                     'has checksum "%s".' % (stanza[kind + '_image'],
-                                             stanza[kind + '_checksum'],
-                                             factory_checksum))
+              print 'Error: checksum mismatch for %s. Expected "%s" but file ' \
+                  'has checksum "%s".' % (stanza[kind + '_image'],
+                                          stanza[kind + '_checksum'],
+                                          factory_checksum)
               success = False
-
     if validate_checksums:
       if success is False:
         raise Exception('Checksum mismatch in conf file.')
-
       print 'Config file looks good.'
 
   def GetFactoryImage(self, board_id, channel):
-    kind = channel.rsplit(' - ', 1)[0]
+    kind = channel.rsplit('-', 1)[0]
     for stanza in self.factory_config:
       if board_id not in stanza['qual_ids']:
         continue
@@ -403,84 +282,75 @@ class Autoupdate(BuildObject):
               stanza[kind + '_size'])
     return (None, None, None)
 
-  def HandleFactoryRequest(self, hostname, board_id, channel):
-    (filename, checksum, size) = self.GetFactoryImage(board_id, channel)
-    if filename is None:
-      web.debug('unable to find image for board %s' % board_id)
-      return self.GetNoUpdatePayload()
-    url = 'http://%s/static/%s' % (hostname, filename)
-    web.debug('returning update payload ' + url)
-    return self.GetUpdatePayload(checksum, size, url)
-
   def HandleUpdatePing(self, data, label=None):
-    """Handles an update ping from an update client.
-
-    Args:
-      data: xml blob from client.
-      label: optional label for the update.
-    Returns:
-      Update payload message for client.
-    """
-    web.debug('handling update ping: %s' % data)
+    web.debug('handle update ping: %s' % data)
     update_dom = minidom.parseString(data)
     root = update_dom.firstChild
-
-    # Check the client prefix to make sure you can support this type of update.
-    if (root.hasAttribute('updaterversion') and
-        not root.getAttribute('updaterversion').startswith(self.client_prefix)):
-      web.debug('Got update from unsupported updater:' +
-                root.getAttribute('updaterversion'))
+    if root.hasAttribute('updaterversion') and \
+        not root.getAttribute('updaterversion').startswith(
+        self.client_prefix):
+      web.debug('Got update from unsupported updater:' + \
+          root.getAttribute('updaterversion'))
       return self.GetNoUpdatePayload()
-
-    # We only generate update payloads for updatecheck requests.
-    update_check = root.getElementsByTagName('o:updatecheck')
-    if not update_check:
-      web.debug('Non-update check received.  Returning blank payload.')
-      # TODO(sosa): Generate correct non-updatecheck payload to better test
-      # update clients.
-      return self.GetNoUpdatePayload()
-
-    # Since this is an updatecheck, get information about the requester.
-    hostname = web.ctx.host
     query = root.getElementsByTagName('o:app')[0]
     client_version = query.getAttribute('version')
     channel = query.getAttribute('track')
-    board_id = (query.hasAttribute('board') and query.getAttribute('board')
-                or self._GetDefaultBoardID())
+    board_id = query.hasAttribute('board') and query.getAttribute('board') \
+        or self.GetDefaultBoardID()
+    latest_image_path = self.GetLatestImagePath(board_id)
+    latest_version = self.GetLatestVersion(latest_image_path)
+    hostname = web.ctx.host
 
-    # Separate logic as Factory requests have static url's that override
-    # other options.
+    # If this is a factory floor server, return the image here:
     if self.factory_config:
-      return self.HandleFactoryRequest(hostname, board_id, channel)
-    else:
-      static_image_dir = self.static_dir
-      if label:
-        static_image_dir = os.path.join(static_image_dir, label)
-
-      # Not for factory, find and serve the correct image given the options.
-      if self.forced_image:
-        has_built_image = self.GenerateUpdateImage(
-            self.forced_image, move_to_static_dir=True,
-            static_image_dir=static_image_dir)
-        # Now that we've generated it, clear out so that other pings of same
-        # devserver instance do not generate new images.
-        self.forced_image = None
-      elif self.serve_only:
-        has_built_image = self.GenerateImageFromZip(static_image_dir)
-      else:
-        has_built_image = self.GenerateLatestUpdateImage(board_id,
-                                                         client_version,
-                                                         static_image_dir)
-
-      if has_built_image:
-        hash = self._GetHash(os.path.join(static_image_dir, 'update.gz'))
-        size = self._GetSize(os.path.join(static_image_dir, 'update.gz'))
-        if self.static_urlbase and label:
-          url = '%s/%s/update.gz' % (self.static_urlbase, label)
-        elif self.serve_only:
-          url = 'http://%s/static/archive/update.gz' % hostname
-        else:
-          url = 'http://%s/static/update.gz' % hostname
-        return self.GetUpdatePayload(hash, size, url)
+      (filename, checksum, size) = \
+          self.GetFactoryImage(board_id, channel)
+      if filename is None:
+        web.debug('unable to find image for board %s' % board_id)
+        return self.GetNoUpdatePayload()
+      url = 'http://%s/static/%s' % (hostname, filename)
+      web.debug('returning update payload ' + url)
+      return self.GetUpdatePayload(checksum, size, url)
+
+    if client_version != 'ForcedUpdate' \
+        and not self.CanUpdate(client_version, latest_version):
+      web.debug('no update')
+      return self.GetNoUpdatePayload()
+    if label:
+      web.debug('Client requested version %s' % label)
+      # Check that matching build exists
+      image_path = '%s/%s' % (self.static_dir, label)
+      if not os.path.exists(image_path):
+        web.debug('%s not found.' % image_path)
+        return self.GetNoUpdatePayload()
+      # Construct a response
+      ok = self.BuildUpdateImage(image_path)
+      if ok != True:
+        web.debug('Failed to build an update image')
+        return self.GetNoUpdatePayload()
+      web.debug('serving update: ')
+      hash = self.GetHash('%s/%s/update.gz' % (self.static_dir, label))
+      size = self.GetSize('%s/%s/update.gz' % (self.static_dir, label))
+      # In case we configured images to be hosted elsewhere
+      # (e.g. buildbot's httpd), use that. Otherwise, serve it
+      # ourselves using web.py's static resource handler.
+      if self.static_urlbase:
+        urlbase = self.static_urlbase
       else:
+        urlbase = 'http://%s/static/archive/' % hostname
+
+      url = '%s/%s/update.gz' % (urlbase, label)
+      return self.GetUpdatePayload(hash, size, url)
+      web.debug('DONE')
+    else:
+      web.debug('update found %s ' % latest_version)
+      ok = self.BuildUpdateImage(latest_image_path)
+      if ok != True:
+        web.debug('Failed to build an update image')
         return self.GetNoUpdatePayload()
+
+      hash = self.GetHash('%s/update.gz' % self.static_dir)
+      size = self.GetSize('%s/update.gz' % self.static_dir)
+
+      url = 'http://%s/static/update.gz' % hostname
+      return self.GetUpdatePayload(hash, size, url)