Python 3.10b3 is now supported (#10224)
Type hinting was added to twisted.internet.defer, making this is the first release of Twisted where you might reasonably be able to use mypy without your own custom stub files (#10017)

Bugfixes

The changes to DelayedCall.__repr__ and LoopingCall.__repr__ from 21.7.0.rc1 were reverted as the wrong assumption that __qualname__ is available on all the supported Python versions. (#10235)
The automated release process was updated to generate and release wheel files to PyPy (#10236)
twisted.internet.defer.inlineCallbacks has an improved type annotation, to avoid typing errors when it is used on a function which returns a non-None result. (#10231)
trial.runner.filenameToModule now sets the correct module.__name__ and sys.modules key (#10230)
twisted.internet.process can now pause and resume producing in python 3 (#9933)
When installing Twisted it now requires a minimum Python 3.6.7 version to match the version used with automated testing. This is the minimum Python version that we know that Twisted works with. (#10098)
twisted.internet.asyncioreactor.AsyncioSelectorReactor will no longer raise a TypeError like "SelectorEventLoop required, instead got: <uvloop.Loop ...>" (broken since 21.2.0). (#10106)
twisted.web.template.flatten and flattenString will no longer raise RecursionError if a large number of synchronous Deferreds are included in a document. (#10125)
Fix type hint for http.Request.uri (from str to bytes). (#10139)
twisted.web.http_headers.getRawHeaders and twisted.web.http_headers.getAllRawHeaders are now typed to return immutable sequences of header values instead of lists. twisted.web.http_headers.getRawHeaders is now typed to return a non-optional value if a non-None default value is given. (#10142)
Fixed type hint for addr argument to twisted.internet.interfaces.buildProtocol. (#10147)
twisted.trial._dist.worker.LocalWorker.connectionMade now always writes the log file using UTF-8 encoding. In previous versions it was using the system default encoding. This was causing encoding errors as the distributed trial workers are sending Unicode data and the system default encoding might not always be Unicode compatible. For example, it can be CP1252 on Windows. (#10157)
twisted.words.protocols.irc.ctcpExtract was updated to work with PYPY 3.7.4. (#10189)
twisted.conch.ssh.transport.SSHServerTransport and twisted.conch.ssh.transport.SSHClientTransport no longer use the hardcoded SHA1 digest for non-group key exchanges. (#10203)
haproxy transport wrapper now returns hosts of type str for getPeer() and getHost(), as specified by IPv4Address and IPv6Address documentation. Previously it was returning bytes for the host. (#10211)

Improved Documentation

Remove dead link in twisted.internet._dumbwin32proc module docstring (#9520)
Sync API docs templates with pydoctor 21.2.2 release. (#10105)
Twisted IRC channels are now hosted by Libera.Chat. (#10213)

Deprecations and Removals

Python 3.5 is no longer supported. (#9958)

Misc

#9816, #9915, #10068, #10085, #10094, #10102, #10107, #10108, #10109, #10110, #10112, #10119, #10120, #10121, #10122, #10123, #10140, #10143, #10145, #10150, #10151, #10155, #10159, #10168, #10169, #10171, #10172, #10173, #10174, #10179, #10194, #10201, #10212, #10215, #10217, #11017

Conch

Misc ~~~~

#10097

Web

Features ~~~~~~~~

twisted.web.template.renderElement() now accepts any IRequest implementer instead of only twisted.web.server.Request. Add type hints to twisted.web.template. (#10184)

Bugfixes ~~~~~~~~

The server-side HTTP/1.1 chunking implementation no longer performs quadratic work when input arrives in small chunks, preventing CPU exhaustion. (#3795)
twisted.web.http's chunked encoding support now rejects chunk sizes that are invalid because they look like negative hexadecimal integers. (#10130)
The type hint of twisted.web.server.Request.postpath is now correctly listed as Optional[List[bytes]]. This was incorrect in Twisted v21.2.0. (#10136)
The server-side HTTP/1.1 chunking implementation now rejects invalid chunk boundaries, preventing unbounded buffering. (#10137)
The server-side HTTP/1.1 chunking implementation now limits the length of the chunk size line (which includes chunk extensions) to twisted.web.http.maxChunkSizeLineLength — 1 KiB — so that it may not consume an unbounded amount of memory. (#10144)
Calling twisted.web.server.Site now registers its expiration timeout using the reactor associated with its twisted.web.server.Site. Site now a reactor attribute via its superclass, twisted.web.http.HTTPFactory. (#10177)

Misc ~~~~

#9659, #10100, #10154, #10186

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