streaming not working with newer versions of starlette

[falkben]

First, thank you for creating this! This package is the only testing utility I've found that can consume and test an asgi streaming response (fastapi/starlette).

Inside this package, with newer versions of starlette, I do see some failures with some of the streaming tests.

Starting in 0.13.3

• test_upload_stream_from_download_stream

Then in 0.13.4, the same test starts to hang, instead of outright fail.

In 0.13.5, this test starts to hang as well.

• test_request_stream

In the latest version of starlette, 0.21.0, test_request_stream hangs, while test_upload_stream_from_download_stream fails with the following error:

$ pytest async_asgi_testclient/tests/test_testing.py::test_upload_stream_from_download_stream

============================= test session starts ==============================
platform darwin -- Python 3.10.6, pytest-7.1.3, pluggy-1.0.0
rootdir: /Users/bfalk/repos/async-asgi-testclient
plugins: anyio-3.6.1, asyncio-0.19.0, cov-4.0.0
asyncio: mode=strict
collected 1 item

async_asgi_testclient/tests/test_testing.py F                            [100%]

=================================== FAILURES ===================================
___________________ test_upload_stream_from_download_stream ____________________

starlette_app = <starlette.applications.Starlette object at 0x104bf5750>

    @pytest.mark.asyncio
    async def test_upload_stream_from_download_stream(starlette_app):
        from starlette.responses import StreamingResponse
    
        async def down_stream(request):
            def gen():
                for _ in range(3):
                    yield b"X" * 1024
    
            return StreamingResponse(gen())
    
        async def up_stream(request):
            async def gen():
                async for chunk in request.stream():
                    yield chunk
    
            return StreamingResponse(gen())
    
        starlette_app.add_route("/download_stream", down_stream, methods=["GET"])
        starlette_app.add_route("/upload_stream", up_stream, methods=["POST"])
    
        async with TestClient(starlette_app) as client:
            resp = await client.get("/download_stream", stream=True)
            assert resp.status_code == 200
            resp2 = await client.post(
                "/upload_stream", data=resp.iter_content(1024), stream=True
            )
            chunks = [c async for c in resp2.iter_content(1024)]
>           assert len(b"".join(chunks)) == 3 * 1024
E           AssertionError: assert 1024 == (3 * 1024)
E            +  where 1024 = len(b'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX...XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX')
E            +    where b'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX...XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX' = <built-in method join of bytes object at 0x1030d4030>([b'XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX...XXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXXX', b'', b''])
E            +      where <built-in method join of bytes object at 0x1030d4030> = b''.join

async_asgi_testclient/tests/test_testing.py:516: AssertionError
=========================== short test summary info ============================
FAILED async_asgi_testclient/tests/test_testing.py::test_upload_stream_from_download_stream
============================== 1 failed in 0.10s ===============================

[masipcat]

Hi @falkben

Thank you for your detailed report.

It seems that starlette doesn't like reading the request body after starting the response. I changed the test to consume the request body and then start the response and this seems to work fine (#57).

I also created this example app without asgi-testclient to be sure it's not a bug in the test client, and it seems that the problem is in starlette:

# example.py
from starlette.applications import Starlette
from starlette.responses import StreamingResponse

app = Starlette()


async def buffered(request):
    chunks = [chunk async for chunk in request.stream()]

    async def gen(chunks):
        for chunk in chunks:
            yield chunk

    return StreamingResponse(gen(chunks))


async def unbuffered(request):
    return StreamingResponse(request.stream())

app.add_route("/buffered", buffered, methods=["POST"])
app.add_route("/unbuffered", unbuffered, methods=["POST"])

"""
1. Create a test file
dd if=/dev/urandom of=./file count=1024 bs=1024

2. Run server
uvicorn example:app

3. Check buffered stream works
curl -v -X POST localhost:8000/buffered --data-binary @file --output -

4. Test unbuffered stream doesn't work (empty response)
curl -v -X POST localhost:8000/unbuffered --data-binary @file --output -
"""

I was going to open a discussion in Starlette but I found this one reporting a similar problem