What’s new in Tornado 4.5

Apr 16, 2017

The tornado.websocket module now imposes a limit on the size of incoming messages, which defaults to 10MiB.

tornado.routing provides a more flexible routing system than the one built in to Application.

Reduced the number of circular references, reducing memory usage and improving performance.

The tornado.auth module has been updated for compatibility with a change to Facebook’s access_token endpoint. This includes both the changes initially released in Tornado 4.4.3 and an additional change to support the `session_expires field in the new format. The session_expires field is currently a string; it should be accessed as int(user['session_expires']) because it will change from a string to an int in Tornado 5.0.

Autoreload is now compatible with the asyncio event loop.
Autoreload no longer attempts to close the IOLoop and all registered file descriptors before restarting; it relies on the CLOEXEC flag being set instead.

Suppressed some “‘NoneType’ object not callback” messages that could be logged at shutdown.

yield None is now equivalent to yield gen.moment. moment is deprecated. This improves compatibility with asyncio.
Fixed an issue in which a generator object could be garbage collected prematurely (most often when weak references are used.
New function is_coroutine_function identifies functions wrapped by coroutine or engine.

SimpleAsyncHTTPClient now follows 308 redirects.
CurlAsyncHTTPClient will no longer accept protocols other than http and https. To override this, set pycurl.PROTOCOLS and pycurl.REDIR_PROTOCOLS in a prepare_curl_callback.
CurlAsyncHTTPClient now supports digest authentication for proxies (in addition to basic auth) via the new proxy_auth_mode argument.
The minimum supported version of libcurl is now 7.22.0.

HTTPServer now accepts the keyword argument trusted_downstream which controls the parsing of X-Forwarded-For headers. This header may be a list or set of IP addresses of trusted proxies which will be skipped in the X-Forwarded-For list.
The no_keep_alive argument works again.

Fixed 100% CPU usage after a callback returns an empty list or dict.
IOLoop.add_callback now uses a lockless implementation which makes it safe for use from __del__ methods. This improves performance of calls to add_callback from the IOLoop thread, and slightly decreases it for calls from other threads.

memoryview objects are now permitted as arguments to write.
The internal memory buffers used by IOStream now use bytearray instead of a list of bytes, improving performance.
Futures returned by write are no longer orphaned if a second call to write occurs before the previous one is finished.

Colored log output is now supported on Windows if the colorama library is installed and the application calls colorama.init() at startup.
The signature of the LogFormatter constructor has been changed to make it compatible with logging.config.dictConfig.

Worked around an issue that caused “LookupError: unknown encoding: latin1” errors on Solaris.

RedirectHandler now supports substituting parts of the matched URL into the redirect location using str.format syntax.
New methods RequestHandler.render_linked_js, RequestHandler.render_embed_js, RequestHandler.render_linked_css, and RequestHandler.render_embed_css can be overridden to customize the output of UIModule.

WebSocketHandler.on_message implementations may now be coroutines. New messages will not be processed until the previous on_message coroutine has finished.
The websocket_ping_interval and websocket_ping_timeout application settings can now be used to enable a periodic ping of the websocket connection, allowing dropped connections to be detected and closed.
The new websocket_max_message_size setting defaults to 10MiB. The connection will be closed if messages larger than this are received.
Headers set by RequestHandler.prepare or RequestHandler.set_default_headers are now sent as a part of the websocket handshake.
Return values from WebSocketHandler.get_compression_options may now include the keys compression_level and mem_level to set gzip parameters. The default compression level is now 6 instead of 9.

A new file upload demo is available in the file_upload directory.
A new TCPClient and TCPServer demo is available in the tcpecho directory.
Minor updates have been made to several existing demos, including updates to more recent versions of jquery.

The following people contributed commits to this release: