def _valid_bag(self, environ, space, container_name):
        """
        Return True if the requested entity is part of the current
        space's recipe or an ADMIN BAG. Otherwise return False
        indicating that privileges will be dropped.
        """
        store = environ['tiddlyweb.store']
        recipe_name = determine_space_recipe(environ, space.name)
        space_recipe = store.get(Recipe(recipe_name))
        template = recipe_template(environ)
        recipe_bags = [bag for bag, _ in space_recipe.get_recipe(template)]
        recipe_bags.extend(space.extra_bags())
        if environ['REQUEST_METHOD'] == 'GET':
            if container_name in recipe_bags:
                return True
            if container_name in ADMIN_BAGS:
                return True
        else:
            base_bags = space.list_bags()
            # add bags in the recipe which may have been added
            # by the recipe mgt. That is: bags which are not
            # included and not core.
            acceptable_bags = [bag for bag in recipe_bags if not (
                Space.bag_is_public(bag) or Space.bag_is_private(bag)
                or Space.bag_is_associate(bag))]
            acceptable_bags.extend(base_bags)
            acceptable_bags.extend(ADMIN_BAGS)
            if container_name in acceptable_bags:
                return True

        return False

def list_spaces(environ, start_response):
    """
    List all the spaces on the service, as a JSON list.

    If a "mine" parameter is present, just get the current
    user's spaces.
    """
    store = environ['tiddlyweb.store']
    mine = environ['tiddlyweb.query'].get('mine', [None])[0]
    current_user = environ['tiddlyweb.usersign']['name']
    if mine:
        spaces = []
        try:
            recipe_names = store.storage.cached_storage.user_spaces(
                    current_user)
        except AttributeError:
            recipe_names = store.storage.user_spaces(current_user)
        for recipe in recipe_names:
            spaces.append(Space.name_from_recipe(recipe))
    else:
        spaces = [Space.name_from_recipe(recipe.name) for
                recipe in store.list_recipes() if
                Space.recipe_is_public(recipe.name)]
    start_response('200 OK', [
        ('Cache-Control', 'no-cache'),
        ('Content-Type', 'application/json; charset=UTF-8')])
    return simplejson.dumps([{'name': space, 'uri': space_uri(environ, space)}
        for space in sorted(spaces)])

def update_space_settings(environ, name):
    """
    Read a tiddler named by SPACE_SERVER_SETTINGS in the current
    space's public bag. Parse each line as a key:value pair which
    is then injected tiddlyweb.query. The goal here is to allow
    a space member to force incoming requests to use specific
    settings, such as alpha or externalized.
    """
    store = environ['tiddlyweb.store']
    space = Space(name)
    bag_name = space.public_bag()
    tiddler = Tiddler(SPACE_SERVER_SETTINGS, bag_name)
    data_text = ''
    try:
        tiddler = store.get(tiddler)
        data_text = tiddler.text
    except StoreError:
        pass

    for line in data_text.split('\n'):
        try:
            key, value = line.split(':', 1)
            key = key.rstrip().lstrip()
            value = value.rstrip().lstrip()
            try:
                environ['tiddlyweb.query'][key].append(value)
            except KeyError:
                environ['tiddlyweb.query'][key] = [value]
        except ValueError:
            pass

def web_tiddler_url(environ, tiddler, container='bags', full=True):
    """
    Override default tiddler_url to be space+host aware.

    If the bag or recipe of the tiddler is of a space, switch to
    that space's host for the duration of uri creation.

    Do this all the time, so that we get the right URIs even
    when working around ControlView.

    If the bag does not fit in a space, then make is URI be at
    the server_host domain. If/when auxbags are made to work this
    will need to be reviewed.
    """
    if '_canonical_uri' in tiddler.fields:
        return tiddler.fields['_canonical_uri']

    saved_host = environ.get('HTTP_HOST', '')
    try:
        if container == 'recipes':
            space_name = Space.name_from_recipe(tiddler.recipe)
        else:
            space_name = Space.name_from_bag(tiddler.bag)
        space_name = space_name + '.'
    except ValueError, exc:
        space_name = ''

    def _handle_dropping_privs(self, environ, req_uri):
        """
        Determin if this request is to be considered "in space" or
        not. If it is not and the current user is not GUEST we need
        to pretend that the current user is GUEST, effectively
        "dropping" privileges.
        """
        if environ['tiddlyweb.usersign']['name'] == 'GUEST':
            return

        http_host, _ = determine_host(environ)
        space_name = determine_space(environ, http_host)

        if space_name is None:
            return

        space = Space(space_name)

        container_name = req_uri.split('/')[2]

        if (req_uri.startswith('/bags/')
                and self._valid_bag(environ, space, container_name)):
            return

        if (req_uri.startswith('/recipes/')
                and container_name in space.list_recipes()):
            return

        self._drop_privs(environ)
        return

def determine_space_recipe(environ, space_name):
    """
    Given a space name, check if the current user is a member of that
    named space. If so, use the private recipe.
    """
    store = environ['tiddlyweb.store']
    usersign = environ['tiddlyweb.usersign']
    try:
        space = Space(space_name)
        recipe = Recipe(space.public_recipe())
        recipe = store.get(recipe)
    except (ValueError, StoreError), exc:
        raise HTTP404('Space for %s does not exist: %s' % (space_name, exc))

def _validate_subscription(environ, name, recipe):
    """
    Determine if this space can be subscribed to.

    We know that the space exists, what we want to determine here is if
    it has been blacklisted or already been subscribed.
    """
    space = Space(name)
    if name in environ['tiddlyweb.config'].get('blacklisted_spaces', []):
        raise HTTP409('Subscription not allowed to space: %s' % name)
    elif [space.public_bag(), ''] in recipe:
        raise HTTP409('Space already subscribed: %s' % name)
    return space

def make_space(space_name, store, member):
    """
    The details of creating the bags and recipes that make up a space.
    """
    space = Space(space_name)

    for bag_name in space.list_bags():
        bag = Bag(bag_name)
        bag.policy = _make_policy(member)
        if Space.bag_is_public(bag_name):
            bag.policy.read = []
        store.put(bag)

    info_tiddler = Tiddler('SiteInfo', space.public_bag())
    info_tiddler.text = 'Space %s' % space_name
    store.put(info_tiddler)

    public_recipe = Recipe(space.public_recipe())
    public_recipe.set_recipe(space.public_recipe_list())
    private_recipe = Recipe(space.private_recipe())
    private_recipe.set_recipe(space.private_recipe_list())
    private_recipe.policy = _make_policy(member)
    public_recipe.policy = _make_policy(member)
    public_recipe.policy.read = []
    store.put(public_recipe)
    store.put(private_recipe)

def update_space_settings(environ, name):
    """
    Read a tiddler named by SPACE_SERVER_SETTINGS in the current
    space's public bag. Parse each line as a key:value pair which
    is then injected tiddlyweb.query. The goal here is to allow
    a space member to force incoming requests to use specific
    settings, such as alpha or externalized.
    """
    store = environ['tiddlyweb.store']
    space = Space(name)
    bag_name = space.public_bag()
    tiddler = Tiddler(SPACE_SERVER_SETTINGS, bag_name)
    data_text = ''
    try:
        tiddler = store.get(tiddler)
        data_text = tiddler.text
    except StoreError:
        return _figure_default_index(environ, bag_name, space), False

    query_strings = []
    index = ''
    lazy = False
    for line in data_text.split('\n'):
        try:
            key, value = line.split(':', 1)
            key = key.rstrip().lstrip()
            value = value.rstrip().lstrip()
            if key == 'index':
                index = value
            elif key == 'lazy':
                if value.lower() == 'true':
                    lazy = True
            else:
                query_strings.append('%s=%s' % (key, value))
        except ValueError:
            pass

    index = _figure_default_index(environ, bag_name, space, index)

    query_string = ';'.join(query_strings)

    filters, leftovers = parse_for_filters(query_string, environ)
    environ['tiddlyweb.filters'].extend(filters)
    query_data = parse_qs(leftovers, keep_blank_values=True)
    environ['tiddlyweb.query'].update(dict(
        [(key, [value for value in values])
            for key, values in query_data.items()]))

    return index, lazy

def confirm_space(environ, start_response):
    """
    Confirm a spaces exists. If it does, raise 204. If
    not, raise 404.
    """
    store = environ['tiddlyweb.store']
    space_name = environ['wsgiorg.routing_args'][1]['space_name']
    try:
        space = Space(space_name)
        store.get(Recipe(space.public_recipe()))
        store.get(Recipe(space.private_recipe()))
    except NoRecipeError:
        raise HTTP404('%s does not exist' % space_name)
    start_response('204 No Content', [])
    return ['']

def confirm_space(environ, start_response):
    """
    Confirm a spaces exists. If it does, raise 204. If
    not, raise 404.
    """
    store = environ['tiddlyweb.store']
    space_name = get_route_value(environ, 'space_name')
    try:
        space = Space(space_name)
        store.get(Recipe(space.public_recipe()))
        store.get(Recipe(space.private_recipe()))
    except (NoRecipeError, ValueError):
        raise HTTP404('%s does not exist' % space_name)
    start_response('204 No Content', [])
    return ['']

def _do_unsubscriptions(space_name, unsubscriptions, public_recipe_list,
        private_recipe_list, store):
    """
    Remove unsubscriptions from the space represented by
    public_recipe_list and private_recipe_list.
    """
    for space in unsubscriptions:
        if space == space_name:
            raise HTTP409('Attempt to unsubscribe self')
        try:
            unsubscribed_space = Space(space)
            bag = unsubscribed_space.public_bag()
            public_recipe_list.remove([bag, ""])
            private_recipe_list.remove([bag, ""])
        except ValueError, exc:
            raise HTTP409('Invalid content for unsubscription: %s' % exc)

def get_space_tiddlers(environ, start_response):
    """
    Get the tiddlers that make up the current space in
    whatever the reqeusted representation is. Choose recipe
    based on membership status.
    """
    _setup_friendly_environ(environ)
    _extra_query_update(environ)

    ext = environ.get('tiddlyweb.extension')
    types = environ['tiddlyweb.config']['extension_types']

    # If not a wiki, limit the tiddlers
    if 'text/x-tiddlywiki' not in environ['tiddlyweb.type']:
        # If filters not set, sort by -modified.
        if not environ['tiddlyweb.filters']:
            environ['tiddlyweb.filters'] = parse_for_filters(
                    'sort=-modified', environ)[0]

        # Filter out core bags.
        core_bag_filters = []
        for bag in Space.core_bags():
            core_bag_filters.append('select=bag:!%s' % bag)
        core_bag_filters = parse_for_filters(';'.join(core_bag_filters),
                environ)[0]
        environ['tiddlyweb.filters'].extend(core_bag_filters)

    if ext and ext not in types:
        environ['wsgiorg.routing_args'][1]['recipe_name'] += '.%s' % ext
    return get_tiddlers(environ, start_response)

def _make_space(environ, space_name):
    """
    The details of creating the bags and recipes that make up a space.
    """
    store = environ['tiddlyweb.store']
    member = environ['tiddlyweb.usersign']['name']

    # XXX stub out the clumsy way for now
    # can make this much more declarative

    space = Space(space_name)

    for bag_name in space.list_bags():
        bag = Bag(bag_name)
        bag.policy = _make_policy(member)
        if Space.bag_is_public(bag_name):
            bag.policy.read = []
        store.put(bag)

    public_recipe = Recipe(space.public_recipe())
    public_recipe.set_recipe(space.public_recipe_list())
    private_recipe = Recipe(space.private_recipe())
    private_recipe.set_recipe(space.private_recipe_list())
    private_recipe.policy = _make_policy(member)
    public_recipe.policy = _make_policy(member)
    public_recipe.policy.read = []
    store.put(public_recipe)
    store.put(private_recipe)

def web_tiddler_url(environ, tiddler, container='bags', full=True,
        friendly=False):
    """
    Override default tiddler_url to be space+host aware.

    If the bag or recipe of the tiddler is of a space, switch to
    that space's host for the duration of uri creation.

    Do this all the time, so that we get the right URIs even
    when working around ControlView.

    If the bag does not fit in a space, then make is URI be at
    the server_host domain. If/when auxbags are made to work this
    will need to be reviewed.
    """
    saved_host = environ.get('HTTP_HOST', '')
    try:
        if container == 'recipes':
            space_name = Space.name_from_recipe(tiddler.recipe)
        else:
            space_name = Space.name_from_bag(tiddler.bag)
        space_name = space_name + '.'
    except ValueError:
        space_name = ''

    host = environ['tiddlyweb.config']['server_host']['host']
    port = environ['tiddlyweb.config']['server_host']['port']
    if port is '443' or port is '80':
        port = ''
    else:
        port = ':%s' % port
    environ['HTTP_HOST'] = '%s%s%s' % (space_name.encode('utf-8'),
        host, port)

    if friendly and space_name:
        url = '%s/%s' % (tiddlyweb.web.util.server_base_url(environ),
                tiddlyweb.web.util.encode_name(tiddler.title))
    else:
        url = original_tiddler_url(environ, tiddler, container, full)
    if saved_host:
        environ['HTTP_HOST'] = saved_host
    elif 'HTTP_HOST' in environ:
        del environ['HTTP_HOST']
    return url

def update_space_settings(environ, name):
    """
    Read a tiddler named by SPACE_SERVER_SETTINGS in the current
    space's public bag. Parse each line as a key:value pair which
    is then injected tiddlyweb.query. The goal here is to allow
    a space member to force incoming requests to use specific
    settings, such as alpha or externalized.
    """
    store = environ['tiddlyweb.store']
    # double assign to avoid later updates to the defaults
    environ['tiddlyweb.space_settings'] = {}
    environ['tiddlyweb.space_settings'].update(DEFAULT_SERVER_SETTINGS)
    try:
        space = Space(name)
    except ValueError:
        return
    bag_name = space.public_bag()
    tiddler = Tiddler(SPACE_SERVER_SETTINGS, bag_name)
    data_text = ''
    try:
        tiddler = store.get(tiddler)
        data_text = tiddler.text
    except StoreError:
        data_text = ''

    query_strings = []
    for line in data_text.split('\n'):
        try:
            key, value = line.split(':', 1)
            key = key.strip()
            value = value.strip()
            if key in SERVER_SETTINGS_KEYS:
                environ['tiddlyweb.space_settings'][key] = value
            else:
                query_strings.append('%s=%s' % (key, value))
        except ValueError:
            pass

    # XXX: Disable the default new user app switcher temporarily
    # TODO: Turn this back on when the app switcher is more complete
    #_figure_default_index(environ, bag_name, space)

    environ['tiddlyweb.space_settings'][
            'extra_query'] = ';'.join(query_strings)

def list_space_members(environ, start_response):
    """
    List the members of the named space. You must be a member
    to list the members.
    """
    store = environ['tiddlyweb.store']
    space_name = environ['wsgiorg.routing_args'][1]['space_name']
    current_user = environ['tiddlyweb.usersign']
    try:
        space = Space(space_name)
        private_space_bag = store.get(Bag(space.private_bag()))
        private_space_bag.policy.allows(current_user, 'manage')
        members = [member for member in private_space_bag.policy.manage if
                not member.startswith('R:')]
    except (ValueError, NoBagError):
        raise HTTP404('No space for %s' % space_name)
    start_response('200 OK', [
        ('Cache-Control', 'no-cache'),
        ('Content-Type', 'application/json; charset=UTF-8')])
    return simplejson.dumps(members)

def test_bag_is():
    assert Space.bag_is_public('cat_public')
    assert not Space.bag_is_public('cat_private')
    assert not Space.bag_is_public('_public')
    assert Space.bag_is_private('cat_private')
    assert not Space.bag_is_private('cat_public')
    assert not Space.bag_is_private('_private')

def web_tiddler_url(environ, tiddler, container='bags', full=True):
    """
    Override default tiddler_url to be space+host aware.

    If the bag or recipe of the tiddler is of a space, switch to
    that space's host for the duration of uri creation.

    Do this all the time, so that we get the right URIs even
    when working around ControlView.
    """
    if '_canonical_uri' in tiddler.fields:
        return tiddler.fields['_canonical_uri']

    saved_host = environ.get('HTTP_HOST', '')
    try:
        if container == 'recipes':
            space_name = Space.name_from_recipe(tiddler.recipe)
        else:
            space_name = Space.name_from_bag(tiddler.bag)

        host = environ['tiddlyweb.config']['server_host']['host']
        port = environ['tiddlyweb.config']['server_host']['port']
        if port is '443' or port is '80':
            port = ''
        else:
            port = ':%s' % port
        environ['HTTP_HOST'] = '%s.%s%s' % (space_name.encode('utf-8'),
            host, port)
    except ValueError:
        pass
    url = original_tiddler_url(environ, tiddler, container, full)
    if saved_host:
        environ['HTTP_HOST'] = saved_host
    elif 'HTTP_HOST' in environ:
        del environ['HTTP_HOST']
    return url

def make_space(space_name, store, member):
    """
    The details of creating the bags and recipes that make up a space.
    """
    space = Space(space_name)

    for bag_name in space.list_bags():
        bag = Bag(bag_name)
        bag.policy = _make_policy(member)
        if Space.bag_is_public(bag_name):
            bag.policy.read = []
        store.put(bag)

    info_tiddler = Tiddler('SiteInfo', space.public_bag())
    info_tiddler.text = 'Space %s' % space_name
    info_tiddler.modifier = store.environ.get('tiddlyweb.usersign',
            {}).get('name', 'GUEST')
    store.put(info_tiddler)

    # Duplicate GettingStarted into public bag.
    getting_started_tiddler = Tiddler(GETTING_STARTED_TIDDLER['title'],
            GETTING_STARTED_TIDDLER['bag'])
    try:
        getting_started_tiddler = store.get(getting_started_tiddler)
        getting_started_tiddler.bag = space.public_bag()
        store.put(getting_started_tiddler)
    except StoreError:
        pass

    public_recipe = Recipe(space.public_recipe())
    public_recipe.set_recipe(space.public_recipe_list())
    private_recipe = Recipe(space.private_recipe())
    private_recipe.set_recipe(space.private_recipe_list())
    private_recipe.policy = _make_policy(member)
    public_recipe.policy = _make_policy(member)
    public_recipe.policy.read = []
    store.put(public_recipe)
    store.put(private_recipe)