What's new in Tornado 6.0
=========================

Mar 1, 2019
-----------

Backwards-incompatible changes
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- Python 2.7 and 3.4 are no longer supported; the minimum supported
  Python version is 3.5.2.
- APIs deprecated in Tornado 5.1 have been removed. This includes the
  ``tornado.stack_context`` module and most ``callback`` arguments
  throughout the package. All removed APIs emitted
  `DeprecationWarning` when used in Tornado 5.1, so running your
  application with the ``-Wd`` Python command-line flag or the
  environment variable ``PYTHONWARNINGS=d`` should tell you whether
  your application is ready to move to Tornado 6.0.
- ``.WebSocketHandler.get`` is now a coroutine and must be called
  accordingly in any subclasses that override this method (but note
  that overriding ``get`` is not recommended; either ``prepare`` or
  ``open`` should be used instead).

General changes
~~~~~~~~~~~~~~~

- Tornado now includes type annotations compatible with ``mypy``.
  These annotations will be used when type-checking your application
  with ``mypy``, and may be usable in editors and other tools.
- Tornado now uses native coroutines internally, improving performance.

`tornado.auth`
~~~~~~~~~~~~~~

- All ``callback`` arguments in this package have been removed. Use
  the coroutine interfaces instead.
- The ``OAuthMixin._oauth_get_user`` method has been removed.
  Override `~.OAuthMixin._oauth_get_user_future` instead.

`tornado.concurrent`
~~~~~~~~~~~~~~~~~~~~

- The ``callback`` argument to `.run_on_executor` has been removed.
- ``return_future`` has been removed.

`tornado.gen`
~~~~~~~~~~~~~

- Some older portions of this module have been removed. This includes
  ``engine``, ``YieldPoint``, ``Callback``, ``Wait``, ``WaitAll``,
  ``MultiYieldPoint``, and ``Task``.
- Functions decorated with ``@gen.coroutine`` no longer accept
  ``callback`` arguments.

`tornado.httpclient`
~~~~~~~~~~~~~~~~~~~~

- The behavior of ``raise_error=False`` has changed. Now only
  suppresses the errors raised due to completed responses with non-200
  status codes (previously it suppressed all errors).
- The ``callback`` argument to `.AsyncHTTPClient.fetch` has been removed.

`tornado.httputil`
~~~~~~~~~~~~~~~~~~

- ``HTTPServerRequest.write`` has been removed. Use the methods of
  ``request.connection`` instead.
- Unrecognized ``Content-Encoding`` values now log warnings only for
  content types that we would otherwise attempt to parse.

`tornado.ioloop`
~~~~~~~~~~~~~~~~

- ``IOLoop.set_blocking_signal_threshold``,
  ``IOLoop.set_blocking_log_threshold``, ``IOLoop.log_stack``,
  and ``IOLoop.handle_callback_exception`` have been removed.
- Improved performance of `.IOLoop.add_callback`.

`tornado.iostream`
~~~~~~~~~~~~~~~~~~

- All ``callback`` arguments in this module have been removed except
  for `.BaseIOStream.set_close_callback`.
- ``streaming_callback`` arguments to `.BaseIOStream.read_bytes` and
  `.BaseIOStream.read_until_close` have been removed.
- Eliminated unnecessary logging of "Errno 0".

`tornado.log`
~~~~~~~~~~~~~

- Log files opened by this module are now explicitly set to UTF-8 encoding.

`tornado.netutil`
~~~~~~~~~~~~~~~~~

- The results of ``getaddrinfo`` are now sorted by address family to
  avoid partial failures and deadlocks.

`tornado.platform.twisted`
~~~~~~~~~~~~~~~~~~~~~~~~~~

- ``TornadoReactor`` and ``TwistedIOLoop`` have been removed.

``tornado.simple_httpclient``
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

- The default HTTP client now supports the ``network_interface``
  request argument to specify the source IP for the connection.
- If a server returns a 3xx response code without a ``Location``
  header, the response is raised or returned directly instead of
  trying and failing to follow the redirect.
- When following redirects, methods other than ``POST`` will no longer
  be transformed into ``GET`` requests. 301 (permanent) redirects are
  now treated the same way as 302 (temporary) and 303 (see other)
  redirects in this respect.
- Following redirects now works with ``body_producer``.

``tornado.stack_context``
~~~~~~~~~~~~~~~~~~~~~~~~~

- The ``tornado.stack_context`` module has been removed.

`tornado.tcpserver`
~~~~~~~~~~~~~~~~~~~

- `.TCPServer.start` now supports a ``max_restarts`` argument (same as
  `.fork_processes`).

`tornado.testing`
~~~~~~~~~~~~~~~~~

- `.AsyncHTTPTestCase` now drops all references to the `.Application`
  during ``tearDown``, allowing its memory to be reclaimed sooner.
- `.AsyncTestCase` now cancels all pending coroutines in ``tearDown``,
  in an effort to reduce warnings from the python runtime about
  coroutines that were not awaited. Note that this may cause
  ``asyncio.CancelledError`` to be logged in other places. Coroutines
  that expect to be running at test shutdown may need to catch this
  exception.

`tornado.web`
~~~~~~~~~~~~~

- The ``asynchronous`` decorator has been removed.
- The ``callback`` argument to `.RequestHandler.flush` has been removed.
- `.StaticFileHandler` now supports large negative values for the
  ``Range`` header and returns an appropriate error for ``end >
  start``.
- It is now possible to set ``expires_days`` in ``xsrf_cookie_kwargs``.

`tornado.websocket`
~~~~~~~~~~~~~~~~~~~

- Pings and other messages sent while the connection is closing are
  now silently dropped instead of logging exceptions.
- Errors raised by ``open()`` are now caught correctly when this method
  is a coroutine.

`tornado.wsgi`
~~~~~~~~~~~~~~

- ``WSGIApplication`` and ``WSGIAdapter`` have been removed.