Starlette

This release includes major changes to the low-level asynchronous parts of Starlette. As a result, **Starlette now depends on [AnyIO](https://anyio.readthedocs.io/en/stable/)** and some minor API changes have occurred. Another significant change with this release is the **deprecation of built-in GraphQL support**.

Added
* Starlette now supports [Trio](https://trio.readthedocs.io/en/stable/) as an async runtime via AnyIO - [#1157](https://github.com/encode/starlette/pull/1157).
* `TestClient.websocket_connect()` now must be used as a context manager.
* Initial support for Python 3.10 - [1201](https://github.com/encode/starlette/pull/1201).
* The compression level used in `GZipMiddleware` is now adjustable - [1128](https://github.com/encode/starlette/pull/1128).

Fixed
* Several fixes to `CORSMiddleware`. See [1111](https://github.com/encode/starlette/pull/1111), [#1112](https://github.com/encode/starlette/pull/1112), [#1113](https://github.com/encode/starlette/pull/1113), [#1199](https://github.com/encode/starlette/pull/1199).
* Improved exception messages in the case of duplicated path parameter names - [1177](https://github.com/encode/starlette/pull/1177).
* `RedirectResponse` now uses `quote` instead of `quote_plus` encoding for the `Location` header to better match the behaviour in other frameworks such as Django - [1164](https://github.com/encode/starlette/pull/1164).
* Exception causes are now preserved in more cases - [1158](https://github.com/encode/starlette/pull/1158).
* Session cookies now use the ASGI root path in the case of mounted applications - [1147](https://github.com/encode/starlette/pull/1147).
* Fixed a cache invalidation bug when static files were deleted in certain circumstances - [1023](https://github.com/encode/starlette/pull/1023).
* Improved memory usage of `BaseHTTPMiddleware` when handling large responses - [1012](https://github.com/encode/starlette/issues/1012) fixed via #1157

Deprecated/removed

* Built-in GraphQL support via the `GraphQLApp` class has been deprecated and will be removed in a future release. Please see [619](https://github.com/encode/starlette/issues/619). GraphQL is not supported on Python 3.10.
* The `executor` parameter to `GraphQLApp` was removed. Use `executor_class` instead.
* The `workers` parameter to `WSGIMiddleware` was removed. This hasn't had any effect since Starlette v0.6.3.

Fixed

* Fixed `ServerErrorMiddleware` compatibility with Python 3.9.1/3.8.7 when debug mode is enabled - [1132](https://github.com/encode/starlette/pull/1132).
* Fixed unclosed socket `ResourceWarning`s when using the `TestClient` with WebSocket endpoints - 1132.
* Improved detection of `async` endpoints wrapped in `functools.partial` on Python 3.8+ - [1106](https://github.com/encode/starlette/pull/1106).

Removed

* `UJSONResponse` was removed (this change was intended to be included in 0.14.0). Please see the [documentation](https://www.starlette.io/responses/#custom-json-serialization) for how to implement responses using custom JSON serialization - [1074](https://github.com/encode/starlette/pull/1047).

Added

* Starlette now officially supports Python3.9.
* In `StreamingResponse`, allow custom async iterator such as objects from classes implementing `__aiter__`.
* Allow usage of `functools.partial` async handlers in Python versions 3.6 and 3.7.
* Add 418 I'm A Teapot status code.

Changed

* Create tasks from handler coroutines before sending them to `asyncio.wait`.
* Use `format_exception` instead of `format_tb` in `ServerErrorMiddleware`'s `debug` responses.
* Be more lenient with handler arguments when using the `requires` decorator.

* Revert `Queue(maxsize=1)` fix for `BaseHTTPMiddleware` middleware classes and streaming responses.

* The `StaticFiles` constructor now allows `pathlib.Path` in addition to strings for its `directory` argument.

* Fix high memory usage when using BaseHTTPMiddleware middleware classes and streaming responses.