typing for httpx.ASGITransport does not allow starlette applications

[RommelLayco]

The typing for the app field in httpx.ASGITransport was changed #2468.

Previously the type of the app field was a Callable now it is

httpx/httpx/_transports/asgi.py

Lines 22 to 24 in 053bc57

	_ASGIApp = typing.Callable[
	[typing.Dict[str, typing.Any], _Receive, _Send], typing.Coroutine[None, None, None]
	]

This causes apps that uses starlette to fail the type check when using mypy.

Steps to reproduce

1. Create this script

from starlette.applications import Starlette
from starlette.responses import HTMLResponse
from starlette.routing import Route

import httpx


async def hello(request):
    return HTMLResponse("Hello World!")


app = Starlette(routes=[Route("/", hello)])

transport = httpx.ASGITransport(app=app, client=("1.2.3.4", 123))

NB taken from https://www.python-httpx.org/async/#calling-into-python-web-apps

2. Run mypy against the above script

mypy example.py

Expected

mypy to pass no errors

Actual

example.py:14: error: Argument "app" to "ASGITransport" has incompatible type "Starlette"; expected "Callable[[dict[str, Any], Callable[[], Awaitable[dict[str, Any]]], Callable[[dict[str, Any]], Coroutine[None, None, None]]], Coroutine[None, None, None]]"  [arg-type]
example.py:14: note: "Starlette.__call__" has type "Callable[[Arg(MutableMapping[str, Any], 'scope'), Arg(Callable[[], Awaitable[MutableMapping[str, Any]]], 'receive'), Arg(Callable[[MutableMapping[str, Any]], Awaitable[None]], 'send')], Coroutine[Any, Any, None]]"

[YDX-2147483647]

I can reproduce this with starlette 0.31.1 and httpx 0.25.0.

The key is that httpx._transports.asgi._Send needs Dict[str, Any], but starlette.types.Message gives MutableMapping[str, Any].
MutableMapping also includes collections.defaultdict, collections.OrderedDict and collections.Counter, etc. according to Python Doc.

Possible Fix

Loose _Message from Dict to MutableMapping, and annotate relevant interfaces as _Message (as starlette does).

master...YDX-2147483647:httpx:message-typing or YDX-2147483647@be45c13

Note

Mypy is happy about that, but I have NOT checked other things. Therefore no PR for now.

[antonwnk]

looks like it's solved now

https://github.com/encode/httpx/issues/3111