What's new in Tornado 6.4.1
===========================

Jun 6, 2024
-----------

Security Improvements
~~~~~~~~~~~~~~~~~~~~~

- Parsing of the ``Transfer-Encoding`` header is now stricter. Unexpected transfer-encoding values
  were previously ignored and treated as the HTTP/1.0 default of read-until-close. This can lead to
  framing issues with certain proxies. We now treat any unexpected value as an error.
- Handling of whitespace in headers now matches the RFC more closely. Only space and tab characters
  are treated as whitespace and stripped from the beginning and end of header values. Other unicode
  whitespace characters are now left alone. This could also lead to framing issues with certain
  proxies. 
- ``tornado.curl_httpclient`` now prohibits carriage return and linefeed headers in HTTP headers
  (matching the behavior of ``simple_httpclient``). These characters could be used for header
  injection or request smuggling if untrusted data were used in headers.

General Changes
~~~~~~~~~~~~~~~

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

- `.SSLIOStream` now understands changes to error codes from OpenSSL 3.2. The main result of this
  change is to reduce the noise in the logs for certain errors.

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

- ``simple_httpclient`` now prohibits carriage return characters in HTTP headers. It had previously
  prohibited only linefeed characters.

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

- `.AsyncTestCase` subclasses can now be instantiated without being associated with a test
  method. This improves compatibility with test discovery in Pytest 8.2.