What's new in Tornado 6.1.0
===========================

Oct 30, 2020
------------

Deprecation notice
~~~~~~~~~~~~~~~~~~

- This is the last release of Tornado to support Python 3.5. Future versions
  will require Python 3.6 or newer.

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

- Windows support has been improved. Tornado is now compatible with the proactor
  event loop (which became the default in Python 3.8) by automatically falling
  back to running a selector in a second thread. This means that it is no longer
  necessary to explicitly configure a selector event loop, although doing so may
  improve performance. This does not change the fact that Tornado is significantly
  less scalable on Windows than on other platforms. 
- Binary wheels are now provided for Windows, MacOS, and Linux (amd64 and arm64).

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

- `.coroutine` now has better support for the Python 3.7+ ``contextvars`` module. 
  In particular, the ``ContextVar.reset`` method is now supported.

`tornado.http1connection`
~~~~~~~~~~~~~~~~~~~~~~~~~

- ``HEAD`` requests to handlers that used chunked encoding no longer produce malformed output. 
- Certain kinds of malformed ``gzip`` data no longer cause an infinite loop.

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

- Setting ``decompress_response=False`` now works correctly with
  ``curl_httpclient``. 
- Mixing requests with and without proxies works correctly in ``curl_httpclient``
  (assuming the version of pycurl is recent enough).
- A default ``User-Agent`` of ``Tornado/$VERSION`` is now used if the
  ``user_agent`` parameter is not specified. 
- After a 303 redirect, ``tornado.simple_httpclient`` always uses ``GET``.
  Previously this would use ``GET`` if the original request was a ``POST`` and
  would otherwise reuse the original request method. For ``curl_httpclient``, the
  behavior depends on the version of ``libcurl`` (with the most recent versions
  using ``GET`` after 303 regardless of the original method).
- Setting ``request_timeout`` and/or ``connect_timeout`` to zero is now supported
  to disable the timeout.

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

- Header parsing is now faster.
- `.parse_body_arguments` now accepts incompletely-escaped non-ASCII inputs.

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

- `ssl.CertificateError` during the SSL handshake is now handled correctly.
- Reads that are resolved while the stream is closing are now handled correctly.

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

- When colored logging is enabled, ``logging.CRITICAL`` messages are now
  recognized and colored magenta.

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

- ``EADDRNOTAVAIL`` is now ignored when binding to ``localhost`` with IPv6. This
  error is common in docker.

`tornado.platform.asyncio`
~~~~~~~~~~~~~~~~~~~~~~~~~~

- `.AnyThreadEventLoopPolicy` now also configures a selector event loop for
  these threads (the proactor event loop only works on the main thread)

``tornado.platform.auto``
~~~~~~~~~~~~~~~~~~~~~~~~~

- The ``set_close_exec`` function has been removed.

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

- `.ExpectLog` now has a ``level`` argument to ensure that the given log level
  is enabled.

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

- ``RedirectHandler.get`` now accepts keyword arguments.
- When sending 304 responses, more headers (including ``Allow``) are now preserved.
- ``reverse_url`` correctly handles escaped characters in the regex route. 
- Default ``Etag`` headers are now generated with SHA-512 instead of MD5.

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

- The ``ping_interval`` timer is now stopped when the connection is closed.
- `.websocket_connect` now raises an error when it encounters a redirect instead of hanging.