✨ Add support for Trio via AnyIO (#3372)

Co-authored-by: Sebastián Ramírez <[email protected]>

README.md

@@ -442,7 +442,6 @@ Used by Pydantic:
 Used by Starlette:
 
 * <a href="https://requests.readthedocs.io" target="_blank"><code>requests</code></a> - Required if you want to use the `TestClient`.
-* <a href="https://github.com/Tinche/aiofiles" target="_blank"><code>aiofiles</code></a> - Required if you want to use `FileResponse` or `StaticFiles`.
 * <a href="https://jinja.palletsprojects.com" target="_blank"><code>jinja2</code></a> - Required if you want to use the default template configuration.
 * <a href="https://andrew-d.github.io/python-multipart/" target="_blank"><code>python-multipart</code></a> - Required if you want to support form <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>, with `request.form()`.
 * <a href="https://pythonhosted.org/itsdangerous/" target="_blank"><code>itsdangerous</code></a> - Required for `SessionMiddleware` support.

docs/en/docs/advanced/async-tests.md

@@ -6,21 +6,9 @@ Being able to use asynchronous functions in your tests could be useful, for exam
 
 Let's look at how we can make that work.
 
-## pytest-asyncio
+## pytest.mark.anyio
 
-If we want to call asynchronous functions in our tests, our test functions have to be asynchronous. Pytest provides a neat library for this, called `pytest-asyncio`, that allows us to specify that some test functions are to be called asynchronously.
-
-You can install it via:
-
-<div class="termy">
-
-```console
-$ pip install pytest-asyncio
-
----> 100%
-```
-
-</div>
+If we want to call asynchronous functions in our tests, our test functions have to be asynchronous. Anyio provides a neat plugin for this, that allows us to specify that some test functions are to be called asynchronously.
 
 ## HTTPX
 
@@ -66,7 +54,7 @@ $ pytest
 
 ## In Detail
 
-The marker `@pytest.mark.asyncio` tells pytest that this test function should be called asynchronously:
+The marker `@pytest.mark.anyio` tells pytest that this test function should be called asynchronously:
 
 ```Python hl_lines="7"
 {!../../../docs_src/async_tests/test_main.py!}
@@ -97,4 +85,4 @@ that we used to make our requests with the `TestClient`.
 As the testing function is now asynchronous, you can now also call (and `await`) other `async` functions apart from sending requests to your FastAPI application in your tests, exactly as you would call them anywhere else in your code.
 
 !!! tip
-    If you encounter a `RuntimeError: Task attached to a different loop` when integrating asynchronous function calls in your tests (e.g. when using <a href="https://stackoverflow.com/questions/41584243/runtimeerror-task-attached-to-a-different-loop" class="external-link" target="_blank">MongoDB's MotorClient</a>) check out <a href="https://github.com/pytest-dev/pytest-asyncio/issues/38#issuecomment-264418154" class="external-link" target="_blank">this issue</a> in the pytest-asyncio repository.
+    If you encounter a `RuntimeError: Task attached to a different loop` when integrating asynchronous function calls in your tests (e.g. when using <a href="https://stackoverflow.com/questions/41584243/runtimeerror-task-attached-to-a-different-loop" class="external-link" target="_blank">MongoDB's MotorClient</a>) Remember to instantiate objects that need an event loop only within async functions, e.g. an `'@app.on_event("startup")` callback.

docs/en/docs/advanced/extending-openapi.md

@@ -152,21 +152,6 @@ After that, your file structure could look like:
     └── swagger-ui.css
 ```
 
-### Install `aiofiles`
-
-Now you need to install `aiofiles`:
-
-
-<div class="termy">
-
-```console
-$ pip install aiofiles
-
----> 100%
-```
-
-</div>
-
 ### Serve the static files
 
 * Import `StaticFiles`.

docs/en/docs/advanced/templates.md

@@ -20,18 +20,6 @@ $ pip install jinja2
 
 </div>
 
-If you need to also serve static files (as in this example), install `aiofiles`:
-
-<div class="termy">
-
-```console
-$ pip install aiofiles
-
----> 100%
-```
-
-</div>
-
 ## Using `Jinja2Templates`
 
 * Import `Jinja2Templates`.

docs/en/docs/index.md

@@ -443,7 +443,6 @@ Used by Pydantic:
 Used by Starlette:
 
 * <a href="https://requests.readthedocs.io" target="_blank"><code>requests</code></a> - Required if you want to use the `TestClient`.
-* <a href="https://github.com/Tinche/aiofiles" target="_blank"><code>aiofiles</code></a> - Required if you want to use `FileResponse` or `StaticFiles`.
 * <a href="https://jinja.palletsprojects.com" target="_blank"><code>jinja2</code></a> - Required if you want to use the default template configuration.
 * <a href="https://andrew-d.github.io/python-multipart/" target="_blank"><code>python-multipart</code></a> - Required if you want to support form <abbr title="converting the string that comes from an HTTP request into Python data">"parsing"</abbr>, with `request.form()`.
 * <a href="https://pythonhosted.org/itsdangerous/" target="_blank"><code>itsdangerous</code></a> - Required for `SessionMiddleware` support.

docs/en/docs/tutorial/dependencies/dependencies-with-yield.md

@@ -7,15 +7,6 @@ To do this, use `yield` instead of `return`, and write the extra steps after.
 !!! tip
     Make sure to use `yield` one single time.
 
-!!! info
-    For this to work, you need to use **Python 3.7** or above, or in **Python 3.6**, install the "backports":
-
-    ```
-    pip install async-exit-stack async-generator
-    ```
-
-    This installs <a href="https://github.com/sorcio/async_exit_stack" class="external-link" target="_blank">async-exit-stack</a> and <a href="https://github.com/python-trio/async_generator" class="external-link" target="_blank">async-generator</a>.
-
 !!! note "Technical Details"
     Any function that is valid to use with:
 

docs/en/docs/tutorial/sql-databases.md

@@ -441,17 +441,6 @@ You can find an example of Alembic in a FastAPI project in the templates from [P
 
 ### Create a dependency
 
-!!! info
-    For this to work, you need to use **Python 3.7** or above, or in **Python 3.6**, install the "backports":
-
-    ```console
-    $ pip install async-exit-stack async-generator
-    ```
-
-    This installs <a href="https://github.com/sorcio/async_exit_stack" class="external-link" target="_blank">async-exit-stack</a> and <a href="https://github.com/python-trio/async_generator" class="external-link" target="_blank">async-generator</a>.
-
-    You can also use the alternative method with a "middleware" explained at the end.
-
 Now use the `SessionLocal` class we created in the `sql_app/databases.py` file to create a dependency.
 
 We need to have an independent database session/connection (`SessionLocal`) per request, use the same session through all the request and then close it after the request is finished.

docs/en/docs/tutorial/static-files.md

@@ -2,20 +2,6 @@
 
 You can serve static files automatically from a directory using `StaticFiles`.
 
-## Install `aiofiles`
-
-First you need to install `aiofiles`:
-
-<div class="termy">
-
-```console
-$ pip install aiofiles
-
----> 100%
-```
-
-</div>
-
 ## Use `StaticFiles`
 
 * Import `StaticFiles`.

docs_src/async_tests/test_main.py

@@ -4,7 +4,7 @@ from httpx import AsyncClient
 from .main import app
 
 
-@pytest.mark.asyncio
+@pytest.mark.anyio
 async def test_root():
     async with AsyncClient(app=app, base_url="http://test") as ac:
         response = await ac.get("/")

fastapi/concurrency.py

@@ -1,4 +1,5 @@
-from typing import Any, Callable
+import sys
+from typing import AsyncGenerator, ContextManager, TypeVar
 
 from starlette.concurrency import iterate_in_threadpool as iterate_in_threadpool  # noqa
 from starlette.concurrency import run_in_threadpool as run_in_threadpool  # noqa
@@ -6,41 +7,21 @@ from starlette.concurrency import (  # noqa
     run_until_first_complete as run_until_first_complete,
 )
 
-asynccontextmanager_error_message = """
-FastAPI's contextmanager_in_threadpool require Python 3.7 or above,
-or the backport for Python 3.6, installed with:
-    pip install async-generator
-"""
+if sys.version_info >= (3, 7):
+    from contextlib import AsyncExitStack as AsyncExitStack
+    from contextlib import asynccontextmanager as asynccontextmanager
+else:
+    from contextlib2 import AsyncExitStack as AsyncExitStack  # noqa
+    from contextlib2 import asynccontextmanager as asynccontextmanager  # noqa
 
 
-def _fake_asynccontextmanager(func: Callable[..., Any]) -> Callable[..., Any]:
-    def raiser(*args: Any, **kwargs: Any) -> Any:
-        raise RuntimeError(asynccontextmanager_error_message)
+_T = TypeVar("_T")
 
-    return raiser
 
-
-try:
-    from contextlib import asynccontextmanager as asynccontextmanager  # type: ignore
-except ImportError:
-    try:
-        from async_generator import (  # type: ignore  # isort: skip
-            asynccontextmanager as asynccontextmanager,
-        )
-    except ImportError:  # pragma: no cover
-        asynccontextmanager = _fake_asynccontextmanager
-
-try:
-    from contextlib import AsyncExitStack as AsyncExitStack  # type: ignore
-except ImportError:
-    try:
-        from async_exit_stack import AsyncExitStack as AsyncExitStack  # type: ignore
-    except ImportError:  # pragma: no cover
-        AsyncExitStack = None  # type: ignore
-
-
-@asynccontextmanager  # type: ignore
-async def contextmanager_in_threadpool(cm: Any) -> Any:
+@asynccontextmanager
+async def contextmanager_in_threadpool(
+    cm: ContextManager[_T],
+) -> AsyncGenerator[_T, None]:
     try:
         yield await run_in_threadpool(cm.__enter__)
     except Exception as e:

fastapi/dependencies/utils.py

@@ -1,4 +1,3 @@
-import asyncio
 import dataclasses
 import inspect
 from contextlib import contextmanager
@@ -6,6 +5,7 @@ from copy import deepcopy
 from typing import (
     Any,
     Callable,
+    Coroutine,
     Dict,
     List,
     Mapping,
@@ -17,10 +17,10 @@ from typing import (
     cast,
 )
 
+import anyio
 from fastapi import params
 from fastapi.concurrency import (
     AsyncExitStack,
-    _fake_asynccontextmanager,
     asynccontextmanager,
     contextmanager_in_threadpool,
 )
@@ -266,18 +266,6 @@ def get_typed_annotation(param: inspect.Parameter, globalns: Dict[str, Any]) ->
     return annotation
 
 
-async_contextmanager_dependencies_error = """
-FastAPI dependencies with yield require Python 3.7 or above,
-or the backports for Python 3.6, installed with:
-    pip install async-exit-stack async-generator
-"""
-
-
-def check_dependency_contextmanagers() -> None:
-    if AsyncExitStack is None or asynccontextmanager == _fake_asynccontextmanager:
-        raise RuntimeError(async_contextmanager_dependencies_error)  # pragma: no cover
-
-
 def get_dependant(
     *,
     path: str,
@@ -289,8 +277,6 @@ def get_dependant(
     path_param_names = get_path_param_names(path)
     endpoint_signature = get_typed_signature(call)
     signature_params = endpoint_signature.parameters
-    if is_gen_callable(call) or is_async_gen_callable(call):
-        check_dependency_contextmanagers()
     dependant = Dependant(call=call, name=name, path=path, use_cache=use_cache)
     for param_name, param in signature_params.items():
         if isinstance(param.default, params.Depends):
@@ -452,14 +438,6 @@ async def solve_generator(
     if is_gen_callable(call):
         cm = contextmanager_in_threadpool(contextmanager(call)(**sub_values))
     elif is_async_gen_callable(call):
-        if not inspect.isasyncgenfunction(call):
-            # asynccontextmanager from the async_generator backfill pre python3.7
-            # does not support callables that are not functions or methods.
-            # See https://github.com/python-trio/async_generator/issues/32
-            #
-            # Expand the callable class into its __call__ method before decorating it.
-            # This approach will work on newer python versions as well.
-            call = getattr(call, "__call__", None)
         cm = asynccontextmanager(call)(**sub_values)
     return await stack.enter_async_context(cm)
 
@@ -539,10 +517,7 @@ async def solve_dependencies(
             solved = dependency_cache[sub_dependant.cache_key]
         elif is_gen_callable(call) or is_async_gen_callable(call):
             stack = request.scope.get("fastapi_astack")
-            if stack is None:
-                raise RuntimeError(
-                    async_contextmanager_dependencies_error
-                )  # pragma: no cover
+            assert isinstance(stack, AsyncExitStack)
             solved = await solve_generator(
                 call=call, stack=stack, sub_values=sub_values
             )
@@ -697,9 +672,18 @@ async def request_body_to_args(
                 and lenient_issubclass(field.type_, bytes)
                 and isinstance(value, sequence_types)
             ):
-                awaitables = [sub_value.read() for sub_value in value]
-                contents = await asyncio.gather(*awaitables)
-                value = sequence_shape_to_type[field.shape](contents)
+                results: List[Union[bytes, str]] = []
+
+                async def process_fn(
+                    fn: Callable[[], Coroutine[Any, Any, Any]]
+                ) -> None:
+                    result = await fn()
+                    results.append(result)
+
+                async with anyio.create_task_group() as tg:
+                    for sub_value in value:
+                        tg.start_soon(process_fn, sub_value.read)
+                value = sequence_shape_to_type[field.shape](results)
 
             v_, errors_ = field.validate(value, values, loc=loc)
 

pyproject.toml

@@ -33,8 +33,10 @@ classifiers = [
     "Topic :: Internet :: WWW/HTTP",
 ]
 requires = [
-    "starlette ==0.14.2",
-    "pydantic >=1.6.2,!=1.7,!=1.7.1,!=1.7.2,!=1.7.3,!=1.8,!=1.8.1,<2.0.0"
+    "starlette ==0.15.0",
+    "pydantic >=1.6.2,!=1.7,!=1.7.1,!=1.7.2,!=1.7.3,!=1.8,!=1.8.1,<2.0.0",
+    # TODO: remove contextlib2 as a direct dependency after upgrading Starlette
+    "contextlib2 >= 21.6.0; python_version < '3.7'",
 ]
 description-file = "README.md"
 requires-python = ">=3.6.1"
@@ -46,7 +48,6 @@ Documentation = "https://fastapi.tiangolo.com/"
 test = [
     "pytest >=6.2.4,<7.0.0",
     "pytest-cov >=2.12.0,<4.0.0",
-    "pytest-asyncio >=0.14.0,<0.16.0",
     "mypy ==0.910",
     "flake8 >=3.8.3,<4.0.0",
     "black ==21.9b0",
@@ -60,11 +61,9 @@ test = [
     "orjson >=3.2.1,<4.0.0",
     "ujson >=4.0.1,<5.0.0",
     "python-multipart >=0.0.5,<0.0.6",
-    "aiofiles >=0.5.0,<0.8.0",
     # TODO: try to upgrade after upgrading Starlette
     "flask >=1.1.2,<2.0.0",
-    "async_exit_stack >=1.0.1,<2.0.0; python_version < '3.7'",
-    "async_generator >=1.10,<2.0.0; python_version < '3.7'",
+    "anyio[trio] >=3.2.1,<4.0.0",
 
     # types
     "types-ujson ==0.1.1",
@@ -90,7 +89,6 @@ dev = [
 ]
 all = [
     "requests >=2.24.0,<3.0.0",
-    "aiofiles >=0.5.0,<0.8.0",
     # TODO: try to upgrade after upgrading Starlette
     "jinja2 >=2.11.2,<3.0.0",
     "python-multipart >=0.0.5,<0.0.6",
@@ -103,8 +101,6 @@ all = [
     "orjson >=3.2.1,<4.0.0",
     "email_validator >=1.1.1,<2.0.0",
     "uvicorn[standard] >=0.12.0,<0.16.0",
-    "async_exit_stack >=1.0.1,<2.0.0; python_version < '3.7'",
-    "async_generator >=1.10,<2.0.0; python_version < '3.7'",
 ]
 
 [tool.isort]
@@ -148,6 +144,8 @@ junit_family = "xunit2"
 filterwarnings = [
     "error",
     'ignore:"@coroutine" decorator is deprecated since Python 3\.8, use "async def" instead:DeprecationWarning',
+    # TODO: needed by AnyIO in Python 3.9, try to remove after an AnyIO upgrade
+    'ignore:The loop argument is deprecated since Python 3\.8, and scheduled for removal in Python 3\.10:DeprecationWarning',
     # TODO: if these ignores are needed, enable them, otherwise remove them
     # 'ignore:The explicit passing of coroutine objects to asyncio\.wait\(\) is deprecated since Python 3\.8:DeprecationWarning',
     # 'ignore:Exception ignored in. <socket\.socket fd=-1:pytest.PytestUnraisableExceptionWarning',

tests/test_fakeasync.py

@@ -1,12 +0,0 @@
-import pytest
-from fastapi.concurrency import _fake_asynccontextmanager
-
-
-@_fake_asynccontextmanager
-def never_run():
-    pass  # pragma: no cover
-
-
-def test_fake_async():
-    with pytest.raises(RuntimeError):
-        never_run()

tests/test_tutorial/test_async_tests/test_main.py

@@ -3,6 +3,6 @@ import pytest
 from docs_src.async_tests.test_main import test_root
 
 
-@pytest.mark.asyncio
+@pytest.mark.anyio
 async def test_async_testing():
     await test_root()

tests/test_tutorial/test_websockets/test_tutorial002.py

@@ -72,9 +72,15 @@ def test_websocket_with_header_and_query():
 
 def test_websocket_no_credentials():
     with pytest.raises(WebSocketDisconnect):
-        client.websocket_connect("/items/foo/ws")
+        with client.websocket_connect("/items/foo/ws"):
+            pytest.fail(
+                "did not raise WebSocketDisconnect on __enter__"
+            )  # pragma: no cover
 
 
 def test_websocket_invalid_data():
     with pytest.raises(WebSocketDisconnect):
-        client.websocket_connect("/items/foo/ws?q=bar&token=some-token")
+        with client.websocket_connect("/items/foo/ws?q=bar&token=some-token"):
+            pytest.fail(
+                "did not raise WebSocketDisconnect on __enter__"
+            )  # pragma: no cover