TestClient.request does not honor stream=True

[ergoithz]

Checklist

• The bug is reproducible against the latest release and/or master.
• There are no similar issues or pull requests to fix it yet.

Describe the bug

The requests.request interface exposes an stream=True option which results on the call not waiting for the entire body to arrive.
stream=True is not handled properly by starlette.testclient._ASGIAdapter.send, as it is unconditionally waiting for the entire request to finish:

https://github.com/encode/starlette/blob/e4307065ea6dbe708fba9643d14fe7adfff06d46/starlette/testclient.py#L240

To reproduce

1. Perform an event wait asyncio.Event wait() after your ASGI application responds with your headers (http.response.start) and first chunk (http.response.body), this can be easily done inside the generator passed to starlette.StreamingResponse.
2. Set the event viaasyncio.Event set() only after doing the request with stream=True.
3. Deadlock.

Expected behavior

With stream=True, TestClient.request should return right after first http.response.body (asgiref defines server must sent http.response.start headers only after the first http.response.body event is generated).

Streaming-related response methods (like iter_content) should be implemented via awaiting further http.response.body until more_body is missing or False.

Actual behavior

Deadlock.

Additional context

I suspect #533 could be related to this.

[Kludex]

@falkben How did you overcome this issue?

[falkben]

Yes, I believe we ran into this issue as well.

We found that async_asgi_testclient worked when we needed to consume a stream from a response. Though at the moment, I'm having trouble getting it to work with async generators.

See: #1102 (comment)

[adriangb]

I think this is relevant now: encode/httpx#1491

[reidmeyer]

Any update on this? I'm trying to test my sse endpoint by using the testclient to call the sse endpoint and then pass it to https://pypi.org/project/sseclient-py/ so I can parse the event data. But indeed, the testclient hangs.

[falkben]

Version >= 0.19.0 of Starlette seems to not work with async-asgi-testclient stream. Version 0.18 and below I could test the streaming response.

[reidmeyer]

Version >= 0.19.0 of Starlette seems to not work with async-asgi-testclient stream. Version 0.18 and below I could test the streaming response.

By "test the streaming response", you mean viewing the response with iter_content, correct? I got that to work with starlette 0.20.4. This post helped me do that. Thank you.

The task I'm currently working on is taking the streaming response, and processing it into a SSE object (event, data, id, retry). https://pypi.org/project/sseclient-py/ attempts to do this, but the response returned by async_asgi_testclient.TestClient.get doesn't seem to work. I believe the starlette testclient might have worked, but it hangs (stream=true doesn't seem to work), I believe because of the issue described here.

Any thoughts on this?

[falkben]

By "test the streaming response", you mean viewing the response with iter_content, correct? I got that to work with starlette 0.20.4. This post helped me do that. Thank you.

You're correct, it does work with newer versions of starlette. I had a problem in one of my middleware's that was trying to consume the client (from scope).

Also, my example above wasn't quite starlette code. here's a better example:

from async_asgi_testclient import TestClient
from starlette.applications import Starlette
from starlette.responses import StreamingResponse
from typing import Generator
from typing import Literal

import pytest

app = Starlette(debug=True)


@app.route("/stream_y")
async def get_stream_y(request) -> StreamingResponse:
    """Stream "y" forever"""

    # stream at most 1000 characters
    max_lines = 1000

    def gen_y() -> Generator[Literal["y"], None, None]:
        i = 0
        while i < max_lines:
            yield "y"
            i += 1

    return StreamingResponse(gen_y())


@pytest.mark.asyncio
async def test_stream_y():
    max_lines = 100
    i = 0

    async with TestClient(app) as client:
        resp = await client.get("/stream_y", stream=True)
        assert resp.status_code == 200
        async for line in resp.iter_content(2):
            if i > max_lines:
                break

            line = line.decode("utf-8").strip()
            assert line == "y"
            i += 1

As for the error in converting the SSE object into a response, that seems more like a async-asgi-testclient issue, or maybe an sseclient-py issue, but what is the error you are getting?

[Kludex]

You can use the follow reference to test SSE: https://github.com/florimondmanca/httpx-sse/blob/master/tests/test_asgi.py.

[Kludex]

The description mentions requests, and although we don't use it anymore, the issue is still valid.

We need the following to be implemented on httpx before acting here: encode/httpx#2186 (if action is really needed after that is implemented there).