Beispiel #1
0
class ManualCapClient(BaseCapClient):
    def capitalize(self, request_data, callback=None):
        logging.info("capitalize")
        self.request_data = request_data
        self.stream = IOStream(socket.socket(), io_loop=self.io_loop)
        self.stream.connect(('127.0.0.1', self.port),
                            callback=self.handle_connect)
        self.future = Future()
        if callback is not None:
            self.future.add_done_callback(
                stack_context.wrap(lambda future: callback(future.result())))
        return self.future

    def handle_connect(self):
        logging.info("handle_connect")
        self.stream.write(utf8(self.request_data + "\n"))
        self.stream.read_until(b'\n', callback=self.handle_read)

    def handle_read(self, data):
        logging.info("handle_read")
        self.stream.close()
        try:
            self.future.set_result(self.process_response(data))
        except CapError as e:
            self.future.set_exception(e)
Beispiel #2
0
 def test_100_continue(self):
     # Run through a 100-continue interaction by hand:
     # When given Expect: 100-continue, we get a 100 response after the
     # headers, and then the real response after the body.
     stream = IOStream(socket.socket(), io_loop=self.io_loop)
     stream.connect(("127.0.0.1", self.get_http_port()), callback=self.stop)
     self.wait()
     stream.write(b"\r\n".join([
         b"POST /hello HTTP/1.1", b"Content-Length: 1024",
         b"Expect: 100-continue", b"Connection: close", b"\r\n"
     ]),
                  callback=self.stop)
     self.wait()
     stream.read_until(b"\r\n\r\n", self.stop)
     data = self.wait()
     self.assertTrue(data.startswith(b"HTTP/1.1 100 "), data)
     stream.write(b"a" * 1024)
     stream.read_until(b"\r\n", self.stop)
     first_line = self.wait()
     self.assertTrue(first_line.startswith(b"HTTP/1.1 200"), first_line)
     stream.read_until(b"\r\n\r\n", self.stop)
     header_data = self.wait()
     headers = HTTPHeaders.parse(native_str(header_data.decode('latin1')))
     stream.read_bytes(int(headers["Content-Length"]), self.stop)
     body = self.wait()
     self.assertEqual(body, b"Got 1024 bytes in POST")
     stream.close()
Beispiel #3
0
 def capitalize(self, request_data, callback):
     logging.info('capitalize')
     stream = IOStream(socket.socket(), io_loop=self.io_loop)
     logging.info('connecting')
     yield gen.Task(stream.connect, ('127.0.0.1', self.port))
     stream.write(utf8(request_data + '\n'))
     logging.info('reading')
     data = yield gen.Task(stream.read_until, b'\n')
     logging.info('returning')
     stream.close()
     callback(self.process_response(data))
Beispiel #4
0
 def test_timeout(self):
     stream = IOStream(socket.socket())
     try:
         yield stream.connect(('127.0.0.1', self.get_http_port()))
         # Use a raw stream because AsyncHTTPClient won't let us read a
         # response without finishing a body.
         stream.write(b'PUT /streaming?body_timeout=0.1 HTTP/1.0\r\n'
                      b'Content-Length: 42\r\n\r\n')
         with ExpectLog(gen_log, 'Timeout reading body'):
             response = yield stream.read_until_close()
         self.assertEqual(response, b'')
     finally:
         stream.close()
Beispiel #5
0
class HTTP1ConnectionTest(AsyncTestCase):
    def setUp(self):
        super(HTTP1ConnectionTest, self).setUp()
        self.asyncSetUp()

    @gen_test
    def asyncSetUp(self):
        listener, port = bind_unused_port()
        event = Event()

        def accept_callback(conn, addr):
            self.server_stream = IOStream(conn)
            self.addCleanup(self.server_stream.close)
            event.set()

        add_accept_handler(listener, accept_callback)
        self.client_stream = IOStream(socket.socket())
        self.addCleanup(self.client_stream.close)
        yield [self.client_stream.connect(('127.0.0.1', port)), event.wait()]
        self.io_loop.remove_handler(listener)
        listener.close()

    @gen_test
    def test_http10_no_content_length(self):
        # Regression test for a bug in which can_keep_alive would crash
        # for an HTTP/1.0 (not 1.1) response with no content-length.
        conn = HTTP1Connection(self.client_stream, True)
        self.server_stream.write(b"HTTP/1.0 200 Not Modified\r\n\r\nhello")
        self.server_stream.close()

        event = Event()
        test = self
        body = []

        class Delegate(HTTPMessageDelegate):
            def headers_received(self, start_line, headers):
                test.code = start_line.code

            def data_received(self, data):
                body.append(data)

            def finish(self):
                event.set()

        yield conn.read_response(Delegate())
        yield event.wait()
        self.assertEqual(self.code, 200)
        self.assertEqual(b''.join(body), b'hello')
Beispiel #6
0
class UnixSocketTest(AsyncTestCase):
    """HTTPServers can listen on Unix sockets too.

    Why would you want to do this?  Nginx can proxy to backends listening
    on unix sockets, for one thing (and managing a namespace for unix
    sockets can be easier than managing a bunch of TCP port numbers).

    Unfortunately, there's no way to specify a unix socket in a url for
    an HTTP client, so we have to test this by hand.
    """
    def setUp(self):
        super(UnixSocketTest, self).setUp()
        self.tmpdir = tempfile.mkdtemp()
        self.sockfile = os.path.join(self.tmpdir, "test.sock")
        sock = netutil.bind_unix_socket(self.sockfile)
        app = Application([("/hello", HelloWorldRequestHandler)])
        self.server = HTTPServer(app, io_loop=self.io_loop)
        self.server.add_socket(sock)
        self.stream = IOStream(socket.socket(socket.AF_UNIX),
                               io_loop=self.io_loop)
        self.stream.connect(self.sockfile, self.stop)
        self.wait()

    def tearDown(self):
        self.stream.close()
        self.server.stop()
        shutil.rmtree(self.tmpdir)
        super(UnixSocketTest, self).tearDown()

    def test_unix_socket(self):
        self.stream.write(b"GET /hello HTTP/1.0\r\n\r\n")
        self.stream.read_until(b"\r\n", self.stop)
        response = self.wait()
        self.assertEqual(response, b"HTTP/1.1 200 OK\r\n")
        self.stream.read_until(b"\r\n\r\n", self.stop)
        headers = HTTPHeaders.parse(self.wait().decode('latin1'))
        self.stream.read_bytes(int(headers["Content-Length"]), self.stop)
        body = self.wait()
        self.assertEqual(body, b"Hello world")

    def test_unix_socket_bad_request(self):
        # Unix sockets don't have remote addresses so they just return an
        # empty string.
        with ExpectLog(gen_log, "Malformed HTTP message from"):
            self.stream.write(b"garbage\r\n\r\n")
            self.stream.read_until_close(self.stop)
            response = self.wait()
        self.assertEqual(response, b"")
Beispiel #7
0
class DecoratorCapClient(BaseCapClient):
    @return_future
    def capitalize(self, request_data, callback):
        logging.info("capitalize")
        self.request_data = request_data
        self.stream = IOStream(socket.socket(), io_loop=self.io_loop)
        self.stream.connect(('127.0.0.1', self.port),
                            callback=self.handle_connect)
        self.callback = callback

    def handle_connect(self):
        logging.info("handle_connect")
        self.stream.write(utf8(self.request_data + "\n"))
        self.stream.read_until(b'\n', callback=self.handle_read)

    def handle_read(self, data):
        logging.info("handle_read")
        self.stream.close()
        self.callback(self.process_response(data))
Beispiel #8
0
 def test_body_size_override_reset(self):
     # The max_body_size override is reset between requests.
     stream = IOStream(socket.socket())
     try:
         yield stream.connect(('127.0.0.1', self.get_http_port()))
         # Use a raw stream so we can make sure it's all on one connection.
         stream.write(b'PUT /streaming?expected_size=10240 HTTP/1.1\r\n'
                      b'Content-Length: 10240\r\n\r\n')
         stream.write(b'a' * 10240)
         headers, response = yield gen.Task(read_stream_body, stream)
         self.assertEqual(response, b'10240')
         # Without the ?expected_size parameter, we get the old default value
         stream.write(b'PUT /streaming HTTP/1.1\r\n'
                      b'Content-Length: 10240\r\n\r\n')
         with ExpectLog(gen_log, '.*Content-Length too long'):
             data = yield stream.read_until_close()
         self.assertEqual(data, b'')
     finally:
         stream.close()
Beispiel #9
0
class IPCClient(object):
    """
    A Tornado IPC client very similar to Tornado's TCPClient class
    but using either UNIX domain sockets or TCP sockets

    This was written because Tornado does not have its own IPC
    server/client implementation.

    :param IOLoop io_loop: A Tornado ioloop to handle scheduling
    :param str/int socket_path: A path on the filesystem where a socket
                                belonging to a running IPCServer can be
                                found.
                                It may also be of type 'int', in which
                                case it is used as the port for a tcp
                                localhost connection.
    """

    def __init__(self, socket_path, io_loop=None):
        """
        Create a new IPC client

        IPC clients cannot bind to ports, but must connect to
        existing IPC servers. Clients can then send messages
        to the server.

        """
        self.io_loop = io_loop or salt.ext.tornado.ioloop.IOLoop.current()
        self.socket_path = socket_path
        self._closing = False
        self.stream = None
        # msgpack deprecated `encoding` starting with version 0.5.2
        if salt.utils.msgpack.version >= (0, 5, 2):
            # Under Py2 we still want raw to be set to True
            msgpack_kwargs = {"raw": six.PY2}
        else:
            if six.PY2:
                msgpack_kwargs = {"encoding": None}
            else:
                msgpack_kwargs = {"encoding": "utf-8"}
        self.unpacker = salt.utils.msgpack.Unpacker(**msgpack_kwargs)

    def connected(self):
        return self.stream is not None and not self.stream.closed()

    def connect(self, callback=None, timeout=None):
        """
        Connect to the IPC socket
        """
        # pylint: disable=access-member-before-definition
        if hasattr(self, "_connecting_future") and not self._connecting_future.done():
            future = self._connecting_future
        # pylint: enable=access-member-before-definition
        else:
            if hasattr(self, "_connecting_future"):
                # read previous future result to prevent the "unhandled future exception" error
                self._connecting_future.exception()  # pylint: disable=E0203
            future = salt.ext.tornado.concurrent.Future()
            self._connecting_future = future
            self._connect(timeout=timeout)

        if callback is not None:

            def handle_future(future):
                response = future.result()
                self.io_loop.add_callback(callback, response)

            future.add_done_callback(handle_future)

        return future

    @salt.ext.tornado.gen.coroutine
    def _connect(self, timeout=None):
        """
        Connect to a running IPCServer
        """
        if isinstance(self.socket_path, int):
            sock_type = socket.AF_INET
            sock_addr = ("127.0.0.1", self.socket_path)
        else:
            sock_type = socket.AF_UNIX
            sock_addr = self.socket_path

        self.stream = None
        if timeout is not None:
            timeout_at = time.time() + timeout

        while True:
            if self._closing:
                break

            if self.stream is None:
                with salt.utils.asynchronous.current_ioloop(self.io_loop):
                    self.stream = IOStream(socket.socket(sock_type, socket.SOCK_STREAM))
            try:
                log.trace("IPCClient: Connecting to socket: %s", self.socket_path)
                yield self.stream.connect(sock_addr)
                self._connecting_future.set_result(True)
                break
            except Exception as e:  # pylint: disable=broad-except
                if self.stream.closed():
                    self.stream = None

                if timeout is None or time.time() > timeout_at:
                    if self.stream is not None:
                        self.stream.close()
                        self.stream = None
                    self._connecting_future.set_exception(e)
                    break

                yield salt.ext.tornado.gen.sleep(1)

    # pylint: disable=W1701
    def __del__(self):
        try:
            self.close()
        except TypeError:
            # This is raised when Python's GC has collected objects which
            # would be needed when calling self.close()
            pass

    # pylint: enable=W1701

    def close(self):
        """
        Routines to handle any cleanup before the instance shuts down.
        Sockets and filehandles should be closed explicitly, to prevent
        leaks.
        """
        if self._closing:
            return

        self._closing = True

        log.debug("Closing %s instance", self.__class__.__name__)

        if self.stream is not None and not self.stream.closed():
            try:
                self.stream.close()
            except socket.error as exc:
                if exc.errno != errno.EBADF:
                    # If its not a bad file descriptor error, raise
                    six.reraise(*sys.exc_info())
Beispiel #10
0
class KeepAliveTest(AsyncHTTPTestCase):
    """Tests various scenarios for HTTP 1.1 keep-alive support.

    These tests don't use AsyncHTTPClient because we want to control
    connection reuse and closing.
    """
    def get_app(self):
        class HelloHandler(RequestHandler):
            def get(self):
                self.finish('Hello world')

            def post(self):
                self.finish('Hello world')

        class LargeHandler(RequestHandler):
            def get(self):
                # 512KB should be bigger than the socket buffers so it will
                # be written out in chunks.
                self.write(''.join(chr(i % 256) * 1024 for i in range(512)))

        class FinishOnCloseHandler(RequestHandler):
            @asynchronous
            def get(self):
                self.flush()

            def on_connection_close(self):
                # This is not very realistic, but finishing the request
                # from the close callback has the right timing to mimic
                # some errors seen in the wild.
                self.finish('closed')

        return Application([('/', HelloHandler), ('/large', LargeHandler),
                            ('/finish_on_close', FinishOnCloseHandler)])

    def setUp(self):
        super(KeepAliveTest, self).setUp()
        self.http_version = b'HTTP/1.1'

    def tearDown(self):
        # We just closed the client side of the socket; let the IOLoop run
        # once to make sure the server side got the message.
        self.io_loop.add_timeout(datetime.timedelta(seconds=0.001), self.stop)
        self.wait()

        if hasattr(self, 'stream'):
            self.stream.close()
        super(KeepAliveTest, self).tearDown()

    # The next few methods are a crude manual http client
    def connect(self):
        self.stream = IOStream(socket.socket(), io_loop=self.io_loop)
        self.stream.connect(('127.0.0.1', self.get_http_port()), self.stop)
        self.wait()

    def read_headers(self):
        self.stream.read_until(b'\r\n', self.stop)
        first_line = self.wait()
        self.assertTrue(first_line.startswith(b'HTTP/1.1 200'), first_line)
        self.stream.read_until(b'\r\n\r\n', self.stop)
        header_bytes = self.wait()
        headers = HTTPHeaders.parse(header_bytes.decode('latin1'))
        return headers

    def read_response(self):
        self.headers = self.read_headers()
        self.stream.read_bytes(int(self.headers['Content-Length']), self.stop)
        body = self.wait()
        self.assertEqual(b'Hello world', body)

    def close(self):
        self.stream.close()
        del self.stream

    def test_two_requests(self):
        self.connect()
        self.stream.write(b'GET / HTTP/1.1\r\n\r\n')
        self.read_response()
        self.stream.write(b'GET / HTTP/1.1\r\n\r\n')
        self.read_response()
        self.close()

    def test_request_close(self):
        self.connect()
        self.stream.write(b'GET / HTTP/1.1\r\nConnection: close\r\n\r\n')
        self.read_response()
        self.stream.read_until_close(callback=self.stop)
        data = self.wait()
        self.assertTrue(not data)
        self.close()

    # keepalive is supported for http 1.0 too, but it's opt-in
    def test_http10(self):
        self.http_version = b'HTTP/1.0'
        self.connect()
        self.stream.write(b'GET / HTTP/1.0\r\n\r\n')
        self.read_response()
        self.stream.read_until_close(callback=self.stop)
        data = self.wait()
        self.assertTrue(not data)
        self.assertTrue('Connection' not in self.headers)
        self.close()

    def test_http10_keepalive(self):
        self.http_version = b'HTTP/1.0'
        self.connect()
        self.stream.write(b'GET / HTTP/1.0\r\nConnection: keep-alive\r\n\r\n')
        self.read_response()
        self.assertEqual(self.headers['Connection'], 'Keep-Alive')
        self.stream.write(b'GET / HTTP/1.0\r\nConnection: keep-alive\r\n\r\n')
        self.read_response()
        self.assertEqual(self.headers['Connection'], 'Keep-Alive')
        self.close()

    def test_http10_keepalive_extra_crlf(self):
        self.http_version = b'HTTP/1.0'
        self.connect()
        self.stream.write(
            b'GET / HTTP/1.0\r\nConnection: keep-alive\r\n\r\n\r\n')
        self.read_response()
        self.assertEqual(self.headers['Connection'], 'Keep-Alive')
        self.stream.write(b'GET / HTTP/1.0\r\nConnection: keep-alive\r\n\r\n')
        self.read_response()
        self.assertEqual(self.headers['Connection'], 'Keep-Alive')
        self.close()

    def test_pipelined_requests(self):
        self.connect()
        self.stream.write(b'GET / HTTP/1.1\r\n\r\nGET / HTTP/1.1\r\n\r\n')
        self.read_response()
        self.read_response()
        self.close()

    def test_pipelined_cancel(self):
        self.connect()
        self.stream.write(b'GET / HTTP/1.1\r\n\r\nGET / HTTP/1.1\r\n\r\n')
        # only read once
        self.read_response()
        self.close()

    def test_cancel_during_download(self):
        self.connect()
        self.stream.write(b'GET /large HTTP/1.1\r\n\r\n')
        self.read_headers()
        self.stream.read_bytes(1024, self.stop)
        self.wait()
        self.close()

    def test_finish_while_closed(self):
        self.connect()
        self.stream.write(b'GET /finish_on_close HTTP/1.1\r\n\r\n')
        self.read_headers()
        self.close()

    def test_keepalive_chunked(self):
        self.http_version = b'HTTP/1.0'
        self.connect()
        self.stream.write(b'POST / HTTP/1.0\r\n'
                          b'Connection: keep-alive\r\n'
                          b'Transfer-Encoding: chunked\r\n'
                          b'\r\n'
                          b'0\r\n'
                          b'\r\n')
        self.read_response()
        self.assertEqual(self.headers['Connection'], 'Keep-Alive')
        self.stream.write(b'GET / HTTP/1.0\r\nConnection: keep-alive\r\n\r\n')
        self.read_response()
        self.assertEqual(self.headers['Connection'], 'Keep-Alive')
        self.close()
Beispiel #11
0
class HTTPServerRawTest(AsyncHTTPTestCase):
    def get_app(self):
        return Application([
            ('/echo', EchoHandler),
        ])

    def setUp(self):
        super(HTTPServerRawTest, self).setUp()
        self.stream = IOStream(socket.socket())
        self.stream.connect(('127.0.0.1', self.get_http_port()), self.stop)
        self.wait()

    def tearDown(self):
        self.stream.close()
        super(HTTPServerRawTest, self).tearDown()

    def test_empty_request(self):
        self.stream.close()
        self.io_loop.add_timeout(datetime.timedelta(seconds=0.001), self.stop)
        self.wait()

    def test_malformed_first_line(self):
        with ExpectLog(gen_log, '.*Malformed HTTP request line'):
            self.stream.write(b'asdf\r\n\r\n')
            # TODO: need an async version of ExpectLog so we don't need
            # hard-coded timeouts here.
            self.io_loop.add_timeout(datetime.timedelta(seconds=0.05),
                                     self.stop)
            self.wait()

    def test_malformed_headers(self):
        with ExpectLog(gen_log, '.*Malformed HTTP headers'):
            self.stream.write(b'GET / HTTP/1.0\r\nasdf\r\n\r\n')
            self.io_loop.add_timeout(datetime.timedelta(seconds=0.05),
                                     self.stop)
            self.wait()

    def test_chunked_request_body(self):
        # Chunked requests are not widely supported and we don't have a way
        # to generate them in AsyncHTTPClient, but HTTPServer will read them.
        self.stream.write(b"""\
POST /echo HTTP/1.1
Transfer-Encoding: chunked
Content-Type: application/x-www-form-urlencoded

4
foo=
3
bar
0

""".replace(b"\n", b"\r\n"))
        read_stream_body(self.stream, self.stop)
        headers, response = self.wait()
        self.assertEqual(json_decode(response), {u'foo': [u'bar']})

    def test_chunked_request_uppercase(self):
        # As per RFC 2616 section 3.6, "Transfer-Encoding" header's value is
        # case-insensitive.
        self.stream.write(b"""\
POST /echo HTTP/1.1
Transfer-Encoding: Chunked
Content-Type: application/x-www-form-urlencoded

4
foo=
3
bar
0

""".replace(b"\n", b"\r\n"))
        read_stream_body(self.stream, self.stop)
        headers, response = self.wait()
        self.assertEqual(json_decode(response), {u'foo': [u'bar']})

    def test_invalid_content_length(self):
        with ExpectLog(gen_log, '.*Only integer Content-Length is allowed'):
            self.stream.write(b"""\
POST /echo HTTP/1.1
Content-Length: foo

bar

""".replace(b"\n", b"\r\n"))
            self.stream.read_until_close(self.stop)
            self.wait()
Beispiel #12
0
class TestIOStreamStartTLS(AsyncTestCase):
    def setUp(self):
        try:
            super(TestIOStreamStartTLS, self).setUp()
            self.listener, self.port = bind_unused_port()
            self.server_stream = None
            self.server_accepted = Future()
            netutil.add_accept_handler(self.listener, self.accept)
            self.client_stream = IOStream(socket.socket())
            self.io_loop.add_future(self.client_stream.connect(
                ('127.0.0.1', self.port)), self.stop)
            self.wait()
            self.io_loop.add_future(self.server_accepted, self.stop)
            self.wait()
        except Exception as e:
            print(e)
            raise

    def tearDown(self):
        if self.server_stream is not None:
            self.server_stream.close()
        if self.client_stream is not None:
            self.client_stream.close()
        self.listener.close()
        super(TestIOStreamStartTLS, self).tearDown()

    def accept(self, connection, address):
        if self.server_stream is not None:
            self.fail("should only get one connection")
        self.server_stream = IOStream(connection)
        self.server_accepted.set_result(None)

    @gen.coroutine
    def client_send_line(self, line):
        self.client_stream.write(line)
        recv_line = yield self.server_stream.read_until(b"\r\n")
        self.assertEqual(line, recv_line)

    @gen.coroutine
    def server_send_line(self, line):
        self.server_stream.write(line)
        recv_line = yield self.client_stream.read_until(b"\r\n")
        self.assertEqual(line, recv_line)

    def client_start_tls(self, ssl_options=None, server_hostname=None):
        client_stream = self.client_stream
        self.client_stream = None
        return client_stream.start_tls(False, ssl_options, server_hostname)

    def server_start_tls(self, ssl_options=None):
        server_stream = self.server_stream
        self.server_stream = None
        return server_stream.start_tls(True, ssl_options)

    @gen_test
    def test_start_tls_smtp(self):
        # This flow is simplified from RFC 3207 section 5.
        # We don't really need all of this, but it helps to make sure
        # that after realistic back-and-forth traffic the buffers end up
        # in a sane state.
        yield self.server_send_line(b"220 mail.example.com ready\r\n")
        yield self.client_send_line(b"EHLO mail.example.com\r\n")
        yield self.server_send_line(b"250-mail.example.com welcome\r\n")
        yield self.server_send_line(b"250 STARTTLS\r\n")
        yield self.client_send_line(b"STARTTLS\r\n")
        yield self.server_send_line(b"220 Go ahead\r\n")
        client_future = self.client_start_tls(dict(cert_reqs=ssl.CERT_NONE))
        server_future = self.server_start_tls(_server_ssl_options())
        self.client_stream = yield client_future
        self.server_stream = yield server_future
        self.assertTrue(isinstance(self.client_stream, SSLIOStream))
        self.assertTrue(isinstance(self.server_stream, SSLIOStream))
        yield self.client_send_line(b"EHLO mail.example.com\r\n")
        yield self.server_send_line(b"250 mail.example.com welcome\r\n")

    @gen_test
    def test_handshake_fail(self):
        server_future = self.server_start_tls(_server_ssl_options())
        # Certificates are verified with the default configuration.
        client_future = self.client_start_tls(server_hostname="localhost")
        with ExpectLog(gen_log, "SSL Error"):
            with self.assertRaises(ssl.SSLError):
                yield client_future
        with self.assertRaises((ssl.SSLError, socket.error)):
            yield server_future

    @unittest.skipIf(not hasattr(ssl, 'create_default_context'),
                     'ssl.create_default_context not present')
    @gen_test
    def test_check_hostname(self):
        # Test that server_hostname parameter to start_tls is being used.
        # The check_hostname functionality is only available in python 2.7 and
        # up and in python 3.4 and up.
        server_future = self.server_start_tls(_server_ssl_options())
        client_future = self.client_start_tls(
            ssl.create_default_context(),
            server_hostname='127.0.0.1')
        with ExpectLog(gen_log, "SSL Error"):
            with self.assertRaises(ssl.SSLError):
                # The client fails to connect with an SSL error.
                yield client_future
        with self.assertRaises(Exception):
            # The server fails to connect, but the exact error is unspecified.
            yield server_future