Channels cannot be used with StreamingHttpResponse

[zhangzhao1114]

When using Channels, StreamingHttpResponse is blocked.

def gen():
    while True:
        image = cv2.imread('a.jpg')
        ret, jpeg = cv2.imencode('.jpg', image)
        img_frame = jpeg.tobytes()
        yield (b'--frame\r\n'
               b'Content-Type: image/jpeg\r\n\r\n' + img_frame + b'\r\n\r\n')

def index(request):
    return StreamingHttpResponse(gen(), content_type="multipart/x-mixed-replace;boundary=frame")

But without ‘while true’, the request is passed

[KenWhitesell]

You haven’t really provided any details or context about what you’re trying to achieve, but it appears to me that what you’re trying to do here doesn’t make a whole lot of sense.

Channels and HttpResponses are two completely separate things.

A StreamingHttpResponse is used for returning data as the response to your page request.

Channels are established and used after a page has been received and rendered.

You don’t send HttpResponses through channels.

If you provide more details about what you’re trying to do, we might be able to assist you.

[zhangzhao1114]

Not channels.Use ASGI to deploy Django,StreamingHttpResponse cannot be accessed.
If I use ‘while True’,the request is always pending.

[KenWhitesell]

So you’re saying that this exact code works if you run it under a wsgi container?

[zhangzhao1114]

Wsgi is fine, but ASGi is not

[emrementese]

@zhangzhao1114

ot

same +1 “While True” always wait to infinity.

[carltongibson]

Async support for StreamingHttpResponse was only added in Django 4.2.

Assuming you’re using that, please open an issue on the Channels repo with a full reproduce. Django’s 4.2’s ASGIHandler streams the response into ASGI messages, so this should work in theory — but without a concrete example it’s not possible to say what’s going on.

[emrementese]

Hi Carl,

1. I’m working on Django 4.2 with daphne, channels, opencv-python
   2.I’ve been following this issue for a long time: Daphne does not stream · Issue #413 · django/daphne · GitHub

• This my class. its captured the my webcam and stream to frontend.

• My View

• urls.py

path("camera_feed/", video_feed, name="video_feed"),

• on tamplate (HTML)

<div>
    <img src="{% url 'video_feed' %}" alt="">
</div>

• This my solution working good. not bad. But if i try the change for loop to while loop and remove the asyncio.sleep:

async def get_frame(self):
       while True:
            if self.video.isOpened():
                success, frame = self.video.read()
                ret, jpeg = cv2.imencode('.jpg',frame)
                jpeg_bytes = jpeg.tobytes()
                yield (b'--frame\r\n'
                    b'Content-Type: image/jpeg\r\n\r\n' + jpeg_bytes + b'\r\n\r\n')
            else:
                yield b'a'

• Now get_frame not a aysnc generating frame. İts waiting the loop finish and while condition is True. Thats why request is always pending. to infinity.