def call_app(self, req, app=None):
        if app is None:
            app = self.app

        self.authorized = []

        def authorize(req):
            self.authorized.append(req)

        if 'swift.authorize' not in req.environ:
            req.environ['swift.authorize'] = authorize

        req.headers.setdefault("User-Agent", "Melted Cheddar")

        status = [None]
        headers = [None]

        def start_response(s, h, ei=None):
            status[0] = s
            headers[0] = h

        body_iter = app(req.environ, start_response)
        with utils.closing_if_possible(body_iter):
            body = b''.join(body_iter)

        return status[0], headers[0], body

    def _get_container_listing(self, req, version, account, container,
                               prefix, marker=''):
        '''
        :param version: whatever
        :param account: native
        :param container: native
        :param prefix: native
        :param marker: native
        '''
        con_req = make_subrequest(
            req.environ,
            path=wsgi_quote('/'.join([
                '', str_to_wsgi(version),
                str_to_wsgi(account), str_to_wsgi(container)])),
            method='GET',
            headers={'x-auth-token': req.headers.get('x-auth-token')},
            agent=('%(orig)s ' + 'DLO MultipartGET'), swift_source='DLO')
        con_req.query_string = 'prefix=%s' % quote(prefix)
        if marker:
            con_req.query_string += '&marker=%s' % quote(marker)

        con_resp = con_req.get_response(self.dlo.app)
        if not is_success(con_resp.status_int):
            if req.method == 'HEAD':
                con_resp.body = b''
            return con_resp, None
        with closing_if_possible(con_resp.app_iter):
            return None, json.loads(b''.join(con_resp.app_iter))

    def _fetch_sub_slo_segments(self, req, version, acc, con, obj):
        """
        Fetch the submanifest, parse it, and return it.
        Raise exception on failures.
        """
        sub_req = req.copy_get()
        sub_req.range = None
        sub_req.environ['PATH_INFO'] = '/'.join(['', version, acc, con, obj])
        sub_req.environ['swift.source'] = 'SLO'
        sub_req.user_agent = "%s SLO MultipartGET" % sub_req.user_agent
        sub_resp = sub_req.get_response(self.slo.app)

        if not is_success(sub_resp.status_int):
            raise ListingIterError(
                'ERROR: while fetching %s, GET of submanifest %s '
                'failed with status %d' % (req.path, sub_req.path,
                                           sub_resp.status_int))

        try:
            with closing_if_possible(sub_resp.app_iter):
                return json.loads(''.join(sub_resp.app_iter))
        except ValueError as err:
            raise ListingIterError(
                'ERROR: while fetching %s, JSON-decoding of submanifest %s '
                'failed with %s' % (req.path, sub_req.path, err))

    def _fetch_sub_slo_segments(self, req, version, acc, con, obj):
        """
        Fetch the submanifest, parse it, and return it.
        Raise exception on failures.
        """
        sub_req = make_subrequest(
            req.environ,
            path="/".join(["", version, acc, con, obj]),
            method="GET",
            headers={"x-auth-token": req.headers.get("x-auth-token")},
            agent=("%(orig)s " + "SLO MultipartGET"),
            swift_source="SLO",
        )
        sub_resp = sub_req.get_response(self.slo.app)

        if not is_success(sub_resp.status_int):
            close_if_possible(sub_resp.app_iter)
            raise ListingIterError(
                "ERROR: while fetching %s, GET of submanifest %s "
                "failed with status %d" % (req.path, sub_req.path, sub_resp.status_int)
            )

        try:
            with closing_if_possible(sub_resp.app_iter):
                return json.loads("".join(sub_resp.app_iter))
        except ValueError as err:
            raise ListingIterError(
                "ERROR: while fetching %s, JSON-decoding of submanifest %s "
                "failed with %s" % (req.path, sub_req.path, err)
            )

    def get_or_head_response(self, req, resp_headers, resp_iter):
        with closing_if_possible(resp_iter):
            resp_body = "".join(resp_iter)
        try:
            segments = json.loads(resp_body)
        except ValueError:
            segments = []

        etag = md5()
        content_length = 0
        for seg_dict in segments:
            if seg_dict.get("range"):
                etag.update("%s:%s;" % (seg_dict["hash"], seg_dict["range"]))
            else:
                etag.update(seg_dict["hash"])

            if config_true_value(seg_dict.get("sub_slo")):
                override_bytes_from_content_type(seg_dict, logger=self.slo.logger)
            content_length += self._segment_length(seg_dict)

        response_headers = [(h, v) for h, v in resp_headers if h.lower() not in ("etag", "content-length")]
        response_headers.append(("Content-Length", str(content_length)))
        response_headers.append(("Etag", '"%s"' % etag.hexdigest()))

        if req.method == "HEAD":
            return self._manifest_head_response(req, response_headers)
        else:
            return self._manifest_get_response(req, content_length, response_headers, segments)

    def call_dlo(self, req, app=None, expect_exception=False):
        if app is None:
            app = self.dlo

        req.headers.setdefault("User-Agent", "Soap Opera")

        status = [None]
        headers = [None]

        def start_response(s, h, ei=None):
            status[0] = s
            headers[0] = h

        body_iter = app(req.environ, start_response)
        body = ''
        caught_exc = None
        try:
            # appease the close-checker
            with closing_if_possible(body_iter):
                for chunk in body_iter:
                    body += chunk
        except Exception as exc:
            if expect_exception:
                caught_exc = exc
            else:
                raise

        if expect_exception:
            return status[0], headers[0], body, caught_exc
        else:
            return status[0], headers[0], body

    def PUT(self, req):
        """HTTP PUT request handler."""
        container_info = self.container_info(
            self.account_name, self.container_name, req)

        req.acl = container_info['write_acl']
        req.environ['swift_sync_key'] = container_info['sync_key']

        # is request authorized
        if 'swift.authorize' in req.environ:
            aresp = req.environ['swift.authorize'](req)
            if aresp:
                return aresp

        old_slo_manifest = None
        # If versioning is disabled, we must check if the object exists.
        # If it's a SLO, we will have to delete the parts if the current
        # operation is a success.
        if (self.app.delete_slo_parts and
                not container_info['sysmeta'].get('versions-location', None)):
            try:
                dest_info = get_object_info(req.environ, self.app)
                if 'slo-size' in dest_info['sysmeta']:
                    manifest_env = req.environ.copy()
                    manifest_env['QUERY_STRING'] = 'multipart-manifest=get'
                    manifest_req = make_subrequest(manifest_env, 'GET')
                    manifest_resp = manifest_req.get_response(self.app)
                    old_slo_manifest = json.loads(manifest_resp.body)
            except Exception as exc:
                self.app.logger.warn(('Failed to check existence of %s. If '
                                      'overwriting a SLO, old parts may '
                                      'remain. Error was: %s') %
                                     (req.path, exc))

        self._update_content_type(req)

        self._update_x_timestamp(req)

        # check constraints on object name and request headers
        error_response = check_object_creation(req, self.object_name) or \
            check_content_type(req)
        if error_response:
            return error_response

        if req.headers.get('Oio-Copy-From'):
            return self._link_object(req)

        data_source = req.environ['wsgi.input']
        if req.content_length:
            data_source = ExpectedSizeReader(data_source, req.content_length)

        headers = self._prepare_headers(req)
        with closing_if_possible(data_source):
            resp = self._store_object(req, data_source, headers)
        if old_slo_manifest and resp.is_success:
            self.app.logger.debug(
                'Previous object %s was a SLO, deleting parts',
                req.path)
            self._delete_slo_parts(req, old_slo_manifest)
        return resp

    def _fetch_sub_slo_segments(self, req, version, acc, con, obj):
        """
        Fetch the submanifest, parse it, and return it.
        Raise exception on failures.
        """
        sub_req = make_subrequest(
            req.environ, path='/'.join(['', version, acc, con, obj]),
            method='GET',
            headers={'x-auth-token': req.headers.get('x-auth-token')},
            agent=('%(orig)s ' + 'SLO MultipartGET'), swift_source='SLO')
        sub_resp = sub_req.get_response(self.slo.app)

        if not is_success(sub_resp.status_int):
            close_if_possible(sub_resp.app_iter)
            raise ListingIterError(
                'ERROR: while fetching %s, GET of submanifest %s '
                'failed with status %d' % (req.path, sub_req.path,
                                           sub_resp.status_int))

        try:
            with closing_if_possible(sub_resp.app_iter):
                return json.loads(''.join(sub_resp.app_iter))
        except ValueError as err:
            raise ListingIterError(
                'ERROR: while fetching %s, JSON-decoding of submanifest %s '
                'failed with %s' % (req.path, sub_req.path, err))

    def multipart_response_iter(self, resp, boundary, body_key, crypto_meta):
        """
        Decrypts a multipart mime doc response body.

        :param resp: application response
        :param boundary: multipart boundary string
        :param body_key: decryption key for the response body
        :param crypto_meta: crypto_meta for the response body
        :return: generator for decrypted response body
        """
        with closing_if_possible(resp):
            parts_iter = multipart_byteranges_to_document_iters(
                FileLikeIter(resp), boundary)
            for first_byte, last_byte, length, headers, body in parts_iter:
                yield b"--" + boundary + b"\r\n"

                for header, value in headers:
                    yield b"%s: %s\r\n" % (wsgi_to_bytes(header),
                                           wsgi_to_bytes(value))

                yield b"\r\n"

                decrypt_ctxt = self.crypto.create_decryption_ctxt(
                    body_key, crypto_meta['iv'], first_byte)
                for chunk in iter(lambda: body.read(DECRYPT_CHUNK_SIZE), b''):
                    yield decrypt_ctxt.update(chunk)

                yield b"\r\n"

            yield b"--" + boundary + b"--"

    def get_or_head_response(self, req, resp_headers, resp_iter):
        with closing_if_possible(resp_iter):
            resp_body = ''.join(resp_iter)
        try:
            segments = json.loads(resp_body)
        except ValueError:
            segments = []

        etag = md5()
        content_length = 0
        for seg_dict in segments:
            if seg_dict.get('range'):
                etag.update('%s:%s;' % (seg_dict['hash'], seg_dict['range']))
            else:
                etag.update(seg_dict['hash'])

            if config_true_value(seg_dict.get('sub_slo')):
                override_bytes_from_content_type(
                    seg_dict, logger=self.slo.logger)
            content_length += self._segment_length(seg_dict)

        response_headers = [(h, v) for h, v in resp_headers
                            if h.lower() not in ('etag', 'content-length')]
        response_headers.append(('Content-Length', str(content_length)))
        response_headers.append(('Etag', '"%s"' % etag.hexdigest()))

        if req.method == 'HEAD':
            return self._manifest_head_response(req, response_headers)
        else:
            return self._manifest_get_response(
                req, content_length, response_headers, segments)

    def _get_manifest_read(self, resp_iter):
        with closing_if_possible(resp_iter):
            resp_body = ''.join(resp_iter)
        try:
            segments = json.loads(resp_body)
        except ValueError:
            segments = []

        return segments

 def process_json_resp(self, req, resp_iter):
     """
     Parses json body listing and decrypt encrypted entries. Updates
     Content-Length header with new body length and return a body iter.
     """
     with closing_if_possible(resp_iter):
         resp_body = b''.join(resp_iter)
     body_json = json.loads(resp_body)
     new_body = json.dumps([self.decrypt_obj_dict(req, obj_dict)
                            for obj_dict in body_json]).encode('ascii')
     self.update_content_length(len(new_body))
     return [new_body]

 def _process_json_resp(self, resp_iter, req):
     """
     Iterate through json body looking for symlinks and modify its content
     :return: modified json body
     """
     with closing_if_possible(resp_iter):
         resp_body = b''.join(resp_iter)
     body_json = json.loads(resp_body)
     swift_version, account, _junk = split_path(req.path, 2, 3, True)
     new_body = json.dumps(
         [self._extract_symlink_path_json(obj_dict, swift_version, account)
          for obj_dict in body_json]).encode('ascii')
     self.update_content_length(len(new_body))
     return [new_body]

    def response_iter(self, resp, body_key, crypto_meta, offset):
        """
        Decrypts a response body.

        :param resp: application response
        :param body_key: decryption key for the response body
        :param crypto_meta: crypto_meta for the response body
        :param offset: offset into object content at which response body starts
        :return: generator for decrypted response body
        """
        decrypt_ctxt = self.crypto.create_decryption_ctxt(
            body_key, crypto_meta['iv'], offset)
        with closing_if_possible(resp):
            for chunk in resp:
                yield decrypt_ctxt.update(chunk)

    def _get_container_listing(self, req, version, account, container,
                               prefix, marker=''):
        con_req = make_subrequest(
            req.environ, path='/'.join(['', version, account, container]),
            method='GET',
            headers={'x-auth-token': req.headers.get('x-auth-token')},
            agent=('%(orig)s ' + 'DLO MultipartGET'), swift_source='DLO')
        con_req.query_string = 'format=json&prefix=%s' % quote(prefix)
        if marker:
            con_req.query_string += '&marker=%s' % quote(marker)

        con_resp = con_req.get_response(self.dlo.app)
        if not is_success(con_resp.status_int):
            return con_resp, None
        with closing_if_possible(con_resp.app_iter):
            return None, json.loads(''.join(con_resp.app_iter))

    def _list_objects(self, env, account, ct_parts, header_cb,
                      prefix='', limit=DEFAULT_LIMIT,
                      marker=None, force_master=False):
        """
        returns items
        """
        sub_path = quote(self.DELIMITER.join(
            ('', 'v1', account, self.ENCODED_DELIMITER.join(ct_parts))))

        LOG.debug("%s: listing objects from '%s' "
                  "(limit=%d, prefix=%s, marker=%s)",
                  self.SWIFT_SOURCE, sub_path, limit, prefix, marker)
        sub_req = make_subrequest(env.copy(), method='GET', path=sub_path,
                                  body='',
                                  swift_source=self.SWIFT_SOURCE)
        params = sub_req.params
        params.pop('delimiter', None)  # allow list-multipart-uploads
        params['limit'] = str(limit)  # FIXME: why is it str?
        params['prefix'] = prefix
        params['format'] = 'json'
        if marker:
            params['marker'] = marker
        else:
            params.pop('marker', None)
        if force_master:
            sub_req.environ.setdefault('oio.query', {})
            sub_req.environ['oio.query']['force_master'] = True

        sub_req.params = params
        resp = sub_req.get_response(self.app)
        obj_prefix = ''
        if len(ct_parts) > 1:
            obj_prefix = self.DELIMITER.join(ct_parts[1:] + ['', ])

        if not resp.is_success or resp.content_length == 0:
            LOG.warn("%s: Failed to list %s",
                     self.SWIFT_SOURCE, sub_path)
            return
        with closing_if_possible(resp.app_iter):
            items = json.loads(resp.body)
        if header_cb:
            header_cb(resp.headers)

        for obj in items:
            if 'name' in obj:
                obj['name'] = obj_prefix.decode('utf-8') + obj['name']
                yield obj

 def process_xml_resp(self, key, resp_iter):
     """
     Parses xml body listing and decrypt encrypted entries. Updates
     Content-Length header with new body length and return a body iter.
     """
     with closing_if_possible(resp_iter):
         resp_body = ''.join(resp_iter)
     tree = ElementTree.fromstring(resp_body)
     for elem in tree.iter('hash'):
         ciphertext = elem.text.encode('utf8')
         plain = self.decrypt_value_with_meta(ciphertext, key)
         elem.text = plain.decode('utf8')
     new_body = ElementTree.tostring(tree, encoding='UTF-8').replace(
         "<?xml version='1.0' encoding='UTF-8'?>",
         '<?xml version="1.0" encoding="UTF-8"?>', 1)
     self.update_content_length(len(new_body))
     return [new_body]

    def call_dlo(self, req, app=None):
        if app is None:
            app = self.dlo

        req.headers.setdefault("User-Agent", "Soap Opera")

        status = [None]
        headers = [None]

        def start_response(s, h, ei=None):
            status[0] = s
            headers[0] = h

        body_iter = app(req.environ, start_response)
        body = b''
        # appease the close-checker
        with closing_if_possible(body_iter):
            for chunk in body_iter:
                body += chunk
        return status[0], headers[0], body

    def make_request(
            self, method, path, headers, acceptable_statuses, body_file=None,
            params=None):
        """Makes a request to Swift with retries.

        :param method: HTTP method of request.
        :param path: Path of request.
        :param headers: Headers to be sent with request.
        :param acceptable_statuses: List of acceptable statuses for request.
        :param body_file: Body file to be passed along with request,
                          defaults to None.
        :param params: A dict of params to be set in request query string,
                       defaults to None.

        :returns: Response object on success.

        :raises UnexpectedResponse: Exception raised when make_request() fails
                                    to get a response with an acceptable status
        :raises Exception: Exception is raised when code fails in an
                           unexpected way.
        """

        headers = dict(headers)
        headers['user-agent'] = self.user_agent
        for attempt in range(self.request_tries):
            resp = exc_type = exc_value = exc_traceback = None
            req = Request.blank(
                path, environ={'REQUEST_METHOD': method}, headers=headers)
            if body_file is not None:
                if hasattr(body_file, 'seek'):
                    body_file.seek(0)
                req.body_file = body_file
            if params:
                req.params = params
            try:
                resp = req.get_response(self.app)
            except (Exception, Timeout):
                exc_type, exc_value, exc_traceback = exc_info()
            else:
                if resp.status_int in acceptable_statuses or \
                        resp.status_int // 100 in acceptable_statuses:
                    return resp
                elif not is_server_error(resp.status_int):
                    # No sense retrying when we expect the same result
                    break
            # sleep only between tries, not after each one
            if attempt < self.request_tries - 1:
                if resp:
                    # always close any resp.app_iter before we discard it
                    with closing_if_possible(resp.app_iter):
                        # for non 2XX requests it's safe and useful to drain
                        # the response body so we log the correct status code
                        if resp.status_int // 100 != 2:
                            for iter_body in resp.app_iter:
                                pass
                sleep(2 ** (attempt + 1))
        if resp:
            msg = 'Unexpected response: %s' % resp.status
            if resp.status_int // 100 != 2 and resp.body:
                # provide additional context (and drain the response body) for
                # non 2XX responses
                msg += ' (%s)' % resp.body
            raise UnexpectedResponse(msg, resp)
        if exc_type:
            # To make pep8 tool happy, in place of raise t, v, tb:
            six.reraise(exc_type, exc_value, exc_traceback)

    def __call__(self, env, start_response):
        # a lot of this is cribbed from listing_formats / swob.Request
        if env['REQUEST_METHOD'] != 'GET':
            # Nothing to translate
            return self.app(env, start_response)

        try:
            v, a, c = split_path(env.get('SCRIPT_NAME', '') +
                                 env['PATH_INFO'], 3, 3)
            if not valid_api_version(v):
                raise ValueError
        except ValueError:
            # not a container request; pass through
            return self.app(env, start_response)

        ctx = WSGIContext(self.app)
        resp_iter = ctx._app_call(env)

        content_type = content_length = cl_index = None
        for index, (header, value) in enumerate(ctx._response_headers):
            header = header.lower()
            if header == 'content-type':
                content_type = value.split(';', 1)[0].strip()
                if content_length:
                    break
            elif header == 'content-length':
                cl_index = index
                try:
                    content_length = int(value)
                except ValueError:
                    pass  # ignore -- we'll bail later
                if content_type:
                    break

        if content_type != 'application/json' or content_length is None or \
                content_length > MAX_CONTAINER_LISTING_CONTENT_LENGTH:
            start_response(ctx._response_status, ctx._response_headers,
                           ctx._response_exc_info)
            return resp_iter

        # We've done our sanity checks, slurp the response into memory
        with closing_if_possible(resp_iter):
            body = b''.join(resp_iter)

        try:
            listing = json.loads(body)
            for item in listing:
                if 'subdir' in item:
                    continue
                value, params = parse_header(item['hash'])
                if 's3_etag' in params:
                    item['s3_etag'] = '"%s"' % params.pop('s3_etag')
                    item['hash'] = value + ''.join(
                        '; %s=%s' % kv for kv in params.items())
        except (TypeError, KeyError, ValueError):
            # If anything goes wrong above, drop back to original response
            start_response(ctx._response_status, ctx._response_headers,
                           ctx._response_exc_info)
            return [body]

        body = json.dumps(listing).encode('ascii')
        ctx._response_headers[cl_index] = (
            ctx._response_headers[cl_index][0],
            str(len(body)),
        )
        start_response(ctx._response_status, ctx._response_headers,
                       ctx._response_exc_info)
        return [body]