What’s new in Tornado 4.1

Feb 7, 2015

If a Future contains an exception but that exception is never examined or re-raised (e.g. by yielding the Future), a stack trace will be logged when the Future is garbage-collected.
New class tornado.gen.WaitIterator provides a way to iterate over Futures in the order they resolve.
The tornado.websocket module now supports compression via the “permessage-deflate” extension. Override WebSocketHandler.get_compression_options to enable on the server side, and use the compression_options keyword argument to websocket_connect on the client side.
When the appropriate packages are installed, it is possible to yield asyncio.Future or Twisted Defered objects in Tornado coroutines.

HTTPServer now calls start_request with the correct arguments. This change is backwards-incompatible, affecting any application which implemented HTTPServerConnectionDelegate by following the example of Application instead of the documented method signatures.

If a Future contains an exception but that exception is never examined or re-raised (e.g. by yielding the Future), a stack trace will be logged when the Future is garbage-collected.
Future now catches and logs exceptions in its callbacks.

tornado.curl_httpclient now supports request bodies for PATCH and custom methods.
tornado.curl_httpclient now supports resubmitting bodies after following redirects for methods other than POST.
curl_httpclient now runs the streaming and header callbacks on the IOLoop.
tornado.curl_httpclient now uses its own logger for debug output so it can be filtered more easily.

New class tornado.gen.WaitIterator provides a way to iterate over Futures in the order they resolve.
When the singledispatch library is available (standard on Python 3.4, available via pip install singledispatch on older versions), the convert_yielded function can be used to make other kinds of objects yieldable in coroutines.
New function tornado.gen.sleep is a coroutine-friendly analogue to time.sleep.
gen.engine now correctly captures the stack context for its callbacks.

tornado.httpclient.HTTPRequest accepts a new argument raise_error=False to suppress the default behavior of raising an error for non-200 response codes.

HTTPServer now calls start_request with the correct arguments. This change is backwards-incompatible, afffecting any application which implemented HTTPServerConnectionDelegate by following the example of Application instead of the documented method signatures.
HTTPServer now tolerates extra newlines which are sometimes inserted between requests on keep-alive connections.
HTTPServer can now use keep-alive connections after a request with a chunked body.
HTTPServer now always reports HTTP/1.1 instead of echoing the request version.

New function tornado.httputil.split_host_and_port for parsing the netloc portion of URLs.
The context argument to HTTPServerRequest is now optional, and if a context is supplied the remote_ip attribute is also optional.
HTTPServerRequest.body is now always a byte string (previously the default empty body would be a unicode string on python 3).
Header parsing now works correctly when newline-like unicode characters are present.
Header parsing again supports both CRLF and bare LF line separators.
Malformed multipart/form-data bodies will always be logged quietly instead of raising an unhandled exception; previously the behavior was inconsistent depending on the exact error.

The kqueue and select IOLoop implementations now report writeability correctly, fixing flow control in IOStream.
When a new IOLoop is created, it automatically becomes “current” for the thread if there is not already a current instance.
New method PeriodicCallback.is_running can be used to see whether the PeriodicCallback has been started.

IOStream.start_tls now uses the server_hostname parameter for certificate validation.
SSLIOStream will no longer consume 100% CPU after certain error conditions.
SSLIOStream no longer logs EBADF errors during the handshake as they can result from nmap scans in certain modes.

It is now possible to yield asyncio.Future objects in coroutines when the singledispatch library is available and tornado.platform.asyncio has been imported.
New methods tornado.platform.asyncio.to_tornado_future and to_asyncio_future convert between the two libraries’ Future classes.

It is now possible to yield Deferred objects in coroutines when the singledispatch library is available and tornado.platform.twisted has been imported.

AsyncTestCase has better support for multiple exceptions. Previously it would silently swallow all but the last; now it raises the first and logs all the rest.
AsyncTestCase now cleans up Subprocess state on tearDown when necessary.

The asynchronous decorator now understands concurrent.futures.Future in addition to tornado.concurrent.Future.
StaticFileHandler no longer logs a stack trace if the connection is closed while sending the file.
RequestHandler.send_error now supports a reason keyword argument, similar to tornado.web.HTTPError.
RequestHandler.locale now has a property setter.
Application.add_handlers hostname matching now works correctly with IPv6 literals.
Redirects for the Application default_host setting now match the request protocol instead of redirecting HTTPS to HTTP.
Malformed _xsrf cookies are now ignored instead of causing uncaught exceptions.
Application.start_request now has the same signature as HTTPServerConnectionDelegate.start_request.

The tornado.websocket module now supports compression via the “permessage-deflate” extension. Override WebSocketHandler.get_compression_options to enable on the server side, and use the compression_options keyword argument to websocket_connect on the client side.
WebSocketHandler no longer logs stack traces when the connection is closed.
WebSocketHandler.open now accepts *args, **kw for consistency with RequestHandler.get and related methods.
The Sec-WebSocket-Version header now includes all supported versions.
websocket_connect now has a on_message_callback keyword argument for callback-style use without read_message().