def check_for_updates(up_to_date_callback=None):
    """Checks the AUTOUPDATE_URL for the recent version.

    The ``up_to_date_callback`` is a function that should take no
    arguments and return nothing.
    """
    import miro.plat
    if miro.plat.AUTOUPDATE == False:
        logging.info("this platform has autoupdate disabled.  skipping.")
        return

    global check_in_progress
    if not check_in_progress:
        check_in_progress = True
        logging.info("Checking for updates...")
        if app.config.get(prefs.APP_FINAL_RELEASE) == u"0":
            # if this is not a final release, look at the beta
            # channel
            url = app.config.get(prefs.AUTOUPDATE_BETA_URL)
            logging.info("Using the beta channel")
        else:
            # if this is a final release, look at the final
            # channel
            url = app.config.get(prefs.AUTOUPDATE_URL)
            logging.info("Using the final channel")
        logging.info("check_for_updates: checking %s", url)
        update_handler = lambda data: _handle_app_cast(
            data, up_to_date_callback)
        error_handler = _handle_error
        grab_url(url, update_handler, error_handler)

def _scrape_youtube_url(url, callback):
    check_u(url)

    components = urlparse.urlsplit(url)
    params = cgi.parse_qs(components[3])

    video_id = None
    if components[2] == u'/watch' and 'v' in params:
        try:
            video_id = params['v'][0]
        except IndexError:
            pass
    elif components[2].startswith('/v/'):
        m = re.compile(r'/v/([\w-]+)').match(components[2])
        if m is not None:
            video_id = m.group(1)

    if video_id is None:
        logging.warning('_scrape_youtube_url: unable to scrape YouTube Video URL')
        callback(None)
        return

    try:
        url = u"http://www.youtube.com/get_video_info?video_id=%s&el=embedded&ps=default&eurl=" % video_id
        httpclient.grab_url(
            url,
            lambda x: _youtube_callback_step2(x, video_id, callback),
            lambda x: _youtube_errback(x, callback))

    except StandardError:
        logging.exception("youtube_callback: unable to scrape YouTube Video URL")
        callback(None)

    def callback(headers):
        """We need to figure out if the URL is a external video link,
        or a link to a feed.
        """
        if check_url_exists(url):
            return

        content_type = headers.get("content-type")
        if content_type:
            if filetypes.is_feed_content_type(content_type):
                add_feeds([url])
                return

            if flashscraper.is_maybe_flashscrapable(url):
                entry = _build_entry(url, "video/x-flv", additional=metadata)
                download_video(entry)
                return

            if filetypes.is_maybe_feed_content_type(content_type):
                logging.info("%s content type is %s.  " "going to peek to see if it's a feed....", url, content_type)
                httpclient.grab_url(url, callback_peek, errback)
                return

        entry = _build_entry(url, content_type)

        if filetypes.is_video_enclosure(entry["enclosures"][0]):
            download_video(entry)
        else:
            handle_unknown_callback(url)

def add_subscription_url(prefix, expected_content_type, url):
    real_url = url[len(prefix):]
    def callback(info):
        if info.get('content-type') == expected_content_type:
            subscription_list = autodiscover.parse_content(info['body'])
            if subscription_list is None:
                text = _(
                    "This %(appname)s podcast file has an invalid format: "
                    "%(url)s.  Please notify the publisher of this file.",
                    {"appname": app.config.get(prefs.SHORT_APP_NAME),
                     "url": real_url}
                    )
                _complain_about_subscription_url(text)
            else:
                subscription.Subscriber().add_subscriptions(
                    subscription_list)
        else:
            text = _(
                "This %(appname)s podcast file has the wrong content type: "
                "%(url)s. Please notify the publisher of this file.",
                {"appname": app.config.get(prefs.SHORT_APP_NAME),
                 "url": real_url}
                )
            _complain_about_subscription_url(text)

    def errback(error):
        text = _(
            "Could not download the %(appname)s podcast file: %(url)s",
            {"appname": app.config.get(prefs.SHORT_APP_NAME),
             "url": real_url}
            )
        _complain_about_subscription_url(text)

    httpclient.grab_url(real_url, callback, errback)

    def request_icon(self):
        if self.removed:
            app.icon_cache_updater.update_finished()
            return

        self.dbItem.confirm_db_thread()
        if self.updating:
            self.needsUpdate = True
            app.icon_cache_updater.update_finished()
            return

        if hasattr(self.dbItem, "get_thumbnail_url"):
            url = self.dbItem.get_thumbnail_url()
        else:
            url = self.url

        # Only verify each icon once per run unless the url changes
        if (url == self.url and self.filename
                and fileutil.access(self.filename, os.R_OK)):
            app.icon_cache_updater.update_finished()
            return

        self.updating = True

        # No need to extract the icon again if we already have it.
        if url is None or url.startswith(u"/") or url.startswith(u"file://"):
            self.error_callback(url)
            return

        # Last try, get the icon from HTTP.
        httpclient.grab_url(url, lambda info: self.update_icon_cache(url, info),
                lambda error: self.error_callback(url, error))

 def query_7digital(self, release_id):
     if release_id not in self.seven_digital_cache:
         self.release_id = release_id
         seven_digital_url = self._make_7digital_url(release_id)
         httpclient.grab_url(seven_digital_url,
                             self.seven_digital_callback,
                             self.seven_digital_errback)
     else:
         self.handle_7digital_cache_hit(release_id)

 def query_echonest_with_code(self, code, version, metadata):
     post_vars = {
         'api_key': ECHO_NEST_API_KEY,
         'bucket': ['tracks', 'id:7digital'],
         'query': self._make_echonest_query(code, version, metadata),
     }
     url = 'http://echonest.pculture.org/api/v4/song/identify?'
     httpclient.grab_url(url,
                         self.echonest_callback, self.echonest_errback,
                         post_vars=post_vars)

def _scrape_vimeo_moogaloop_url(url, callback):
    try:
        id_ = MEGALOOP_RE.match(url).group(2)
        url = u"http://www.vimeo.com/moogaloop/load/clip:%s" % id_
        httpclient.grab_url(
            url, lambda x: _scrape_vimeo_callback(x, callback), lambda x: _scrape_vimeo_errback(x, callback)
        )
    except StandardError:
        logging.warning("Unable to scrape vimeo.com moogaloop URL: %s", url)
        callback(None)

 def query_echonest_with_echonest_id(self, echonest_id):
     url_data = [
         ('api_key', ECHO_NEST_API_KEY),
         ('bucket', 'tracks'),
         ('bucket', 'id:7digital'),
         ('id', echonest_id),
     ]
     url = ('http://echonest.pculture.org/api/v4/song/profile?' +
             urllib.urlencode(url_data))
     httpclient.grab_url(url,
                         self.echonest_callback, self.echonest_errback)

def _scrape_veohtv_video_url(url, callback):
    try:
        components = urlparse.urlsplit(url)
        params = cgi.parse_qs(components[3])
        t = params['type'][0]
        permalink_id = params['permalinkId'][0]
        url = u'http://www.veoh.com/movieList.html?type=%s&permalinkId=%s&numResults=45' % (t, permalink_id)
        httpclient.grab_url(url, lambda x: _scrape_veohtv_callback(x, callback),
                           lambda x: _scrape_veohtv_errback(x, callback))
    except StandardError:
        logging.warning("unable to scrape Veoh URL: %s", url)
        callback(None)

def _scrape_vimeo_video_url_try_2(url, callback, vimeo_id):
    """Try scraping vimeo URLs by scraping the javascript code.

    This method seems less reliable than the regular method, but it works for
    private videos.  See #19305
    """
    video_url = u'http://vimeo.com/%s' % vimeo_id

    httpclient.grab_url(
            video_url,
            lambda x: _scrape_vimeo_download_try_2_callback(x, callback,
                                                            vimeo_id),
            lambda x: _scrape_vimeo_download_errback(x, callback, url))

def _scrape_vimeo_video_url(url, callback):
    try:
        id_ = VIMEO_RE.match(url).group(2)
        url = u"http://www.vimeo.com/moogaloop/load/clip:%s" % id_
        httpclient.grab_url(
            url,
            lambda x: _scrape_vimeo_callback(x, callback),
            lambda x: _scrape_vimeo_errback(x, callback))
    except (SystemExit, KeyboardInterrupt):
        raise
    except:
        logging.warning("Unable to scrape vimeo.com video URL: %s", url)
        callback(None)

def _scrape_vmix_video_url(url, callback):
    try:
        components = urlparse.urlsplit(url)
        params = cgi.parse_qs(components[3])
        type_ = params['type'][0]
        id_ = params['id'][0]
        l = params['l'][0]
        url = (u"http://sdstage01.vmix.com/videos.php?type=%s&id=%s&l=%s" %
               (type_, id_, l))
        httpclient.grab_url(url, lambda x: _scrape_vmix_callback(x, callback),
                           lambda x: _scrape_vmix_errback(x, callback))

    except StandardError:
        logging.warning("unable to scrape VMix Video URL: %s", url)
        callback(None)

    def get_metainfo(self):
        if self.metainfo is None:
            if self.url.startswith('file://'):
                path = get_file_url_path(self.url)
                try:
                    metainfoFile = open(path, 'rb')
                except IOError:
                    self.handle_error(
                        _("Torrent file deleted"),
                        _("The torrent file for this item was deleted "
                          "outside of %(appname)s.",
                          {"appname": app.config.get(prefs.SHORT_APP_NAME)}
                          ))

                    return
                try:
                    metainfo = metainfoFile.read()
                finally:
                    metainfoFile.close()

                self.handle_metainfo(metainfo)
            else:
                self.description_client = httpclient.grab_url(self.url,
                        self.on_metainfo_download,
                        self.on_metainfo_download_error,
                        content_check_callback=self.check_description)
        else:
            self.got_metainfo()

    def __init__(self, report, description, send_database):
        signals.SignalEmitter.__init__(self)
        self.create_signal('finished')

        self.is_done = False

        backupfile = None
        if send_database:
            try:
                logging.info("Sending entire database")
                backupfile = self._backup_support_dir()
            except StandardError:
                logging.exception("Failed to backup database")

        if isinstance(report, str):
            report = report.decode(locale.getpreferredencoding())
        report = report.encode("utf-8", "ignore")
        if isinstance(description, str):
            description = description.decode(locale.getpreferredencoding())
        description = description.encode("utf-8", "ignore")
        post_vars = {"description": description,
                     "app_name": app.config.get(prefs.LONG_APP_NAME),
                     "log": report}
        if backupfile:
            post_files = {"databasebackup":
                              {"filename": "databasebackup.zip",
                               "mimetype": "application/octet-stream",
                               "handle": backupfile,
                               }}
        else:
            post_files = None
        logging.info("Sending crash report....")
        self.client = httpclient.grab_url(BOGON_URL,
                           self.callback, self.errback,
                           post_vars=post_vars, post_files=post_files)

    def add_subscriptions(self, subscriptions_list, parent_folder=None):
        """
        We loop through the list of subscriptions, creating things as
        we go (if needed).  We also keep track of what we've added.

        Each type (folder, feed, site, download) gets dispatched to
        one of our methods.  Each dispatcher returns True if it's
        added the subscription, anything else if it's been ignored for
        some reason (generally because it's already present in the
        DB).

        The only exception to this is the 'folder' type, which has the
        same return signature as this method.

        Returns a tuple of dictionaries (added, ignored).  Each
        dictionary maps a subscription type (feed, site, download) to
        the number of added/ignored items in this subscription.
        """
        added = {}
        ignored = {}
        for subscription in subscriptions_list:
            subscription_type = subscription['type']
            handler = getattr(self, 'handle_%s' % subscription_type, None)
            if handler:
                trackback = subscription.get('trackback')
                if trackback:
                    httpclient.grab_url(trackback, lambda x: None,
                                       lambda x: None)
                ret = handler(subscription, parent_folder)
                if ret:
                    if subscription_type == 'folder':
                        for key, value in ret[0].items():
                            added.setdefault(key, [])
                            added[key].extend(value)
                        for key, value in ret[1].items():
                            ignored.setdefault(key, [])
                            ignored[key].extend(value)
                    else:
                        added.setdefault(subscription_type, [])
                        added[subscription_type].append(subscription)
                else:
                    ignored.setdefault(subscription_type, [])
                    ignored[subscription_type].append(subscription)
            else:
                raise ValueError('unknown subscription type: %s' %
                                 subscription_type)
        return added, ignored

 def query_echonest_with_tags(self, metadata):
     url_data = [
         ('api_key', ECHO_NEST_API_KEY),
         ('bucket', 'tracks'),
         ('bucket', 'id:7digital'),
         # In case there are multiple songs for the same artist/title, only
         # use the "hottest" song, AKA the most popular.
         ('results', '1'),
         ('sort', 'song_hotttnesss-desc'),
     ]
     for key in ('title', 'artist'):
         if key in metadata:
             url_data.append((key, metadata[key].encode('utf-8')))
     url = ('http://echonest.pculture.org/api/v4/song/search?' +
             urllib.urlencode(url_data))
     httpclient.grab_url(url, self.echonest_callback,
                         self.echonest_errback)

def _scrape_vimeo_video_url(url, callback, countdown=10):
    try:
        id_ = VIMEO_RE.match(url).group(2)
        url = 'http://vimeo.com/%s?action=download' % id_
        httpclient.grab_url(
            url,
            lambda x: _scrape_vimeo_download_callback(x, callback),
            lambda x: _scrape_vimeo_download_errback(x, callback, url),
            extra_headers={
                'Referer': 'http://vimeo.com/%s' % id_,
                'X-Requested-With': 'XMLHttpRequest',
                'User-Agent': ('Mozilla/5.0 (X11; Linux x86_64) '
                               'AppleWebKit/536.11 (KHTML, like Gecko) '
                               'Chrome/20.0.1132.8 Safari/536.11')
                })
    except StandardError:
        logging.exception("Unable to scrape vimeo.com video URL: %s", url)
        callback(None)

def check_for_updates(up_to_date_callback=None):
    """Checks the AUTOUPDATE_URL for the recent version.

    The ``up_to_date_callback`` is a function that should take no
    arguments and return nothing.
    """
    import miro.plat
    if miro.plat.AUTOUPDATE == False:
        logging.info("this platform has autoupdate disabled.  skipping.")
        return

    global check_in_progress
    if not check_in_progress:
        check_in_progress = True
        logging.info("Checking for updates...")
        url = app.config.get(prefs.AUTOUPDATE_URL)
        update_handler = lambda data: _handle_app_cast(data,
                                                       up_to_date_callback)
        error_handler = _handle_error
        grab_url(url, update_handler, error_handler)

    def start_download(self, resume=True):
        if self.retryDC:
            self.retryDC.cancel()
            self.retryDC = None
        if resume:
            resume = self._resume_sanity_check()

        logging.info("start_download: %s", self.url)

        self.client = httpclient.grab_url(
            self.url, self.on_download_finished, self.on_download_error,
            header_callback=self.on_headers, write_file=self.filename,
            resume=resume)
        self.update_client()
        eventloop.add_timeout(self.CHECK_STATS_TIMEOUT, self.update_stats,
                'update http downloader stats')