StreamResponse, MultipartWriter with multipart/x-mixed-replace not working

[james4388]

Long story short

StreamResponse MultipartWriter with multipart/x-mixed-replace not working
(MJpeg Streaming Protocol)

Expected behaviour

Streamable jpeg series

Actual behaviour

Image not loading

Steps to reproduce

This is server code I use

import asyncio
import cv2
from aiohttp import web, MultipartWriter


async def mjpeg_handler(request):
    my_boundary = "boundarydonotcross"
    response = web.StreamResponse(status=200, reason='OK', headers={
        'Content-Type': 'multipart/x-mixed-replace; '
                        'boundary=--%s' % my_boundary,
    })
    await response.prepare(request)
    wc = cv2.VideoCapture(0)
    encode_param = (int(cv2.IMWRITE_JPEG_QUALITY), 90)

    while True:
        _, frame = wc.read()
        if frame is None:
            continue
        with MultipartWriter('image/jpeg', boundary=my_boundary) as mpwriter:
            result, encimg = cv2.imencode('.jpg', frame, encode_param)
            data = encimg.tostring()
            mpwriter.append(data, {
                'Content-Type': 'image/jpeg'
            })
            await mpwriter.write(response)
        await response.drain()
    wc.shutdown()
    return response


async def index(request):
    return web.Response(text='<img src="/image"/>', content_type='text/html')


async def start_server(loop, address, port):
    app = web.Application(loop=loop)
    app.router.add_route('GET', "/", index)
    app.router.add_route('GET', "/image", mjpeg_handler)
    return await loop.create_server(app.make_handler(), address, port)


if __name__ == '__main__':
    loop = asyncio.get_event_loop()
    loop.run_until_complete(start_server(loop, '0.0.0.0', 8888))
    print("Server ready!")

    try:
        loop.run_forever()
    except KeyboardInterrupt:
        print("Shutting Down!")
        loop.close()

When I inspect return stream with curl I see that boundary is being send twice, one for open, one for closing

--boundary
<data>
--boundary--

which is correct with w3c spec but that break the mjpeg

I try to comment await writer.write(b'--' + self._boundary + b'--\r\n') in multipart.py line 821 and it works fine.

This is my manual workaround and it works

async def mjpeg_handler(request):
    boundary = "boundarydonotcross"
    response = web.StreamResponse(status=200, reason='OK', headers={
        'Content-Type': 'multipart/x-mixed-replace; '
                        'boundary=--%s' % boundary,
    })
    await response.prepare(request)
    wc = cv2.VideoCapture(0)
    encode_param = (int(cv2.IMWRITE_JPEG_QUALITY), 90)

    while True:
        _, frame = wc.read()
        if frame is None:
            continue
        
        result, encimg = cv2.imencode('.jpg', frame, encode_param)
        data = encimg.tostring()
        await response.write(
            '--{}\r\n'.format(boundary).encode('utf-8'))
        await response.write(b'Content-Type: image/jpeg\r\n')
        await response.write('Content-Length: {}\r\n'.format(
                len(data)).encode('utf-8'))
        await response.write(b"\r\n")
        # Write data
        await response.write(data)
        await response.write(b"\r\n")
        await response.drain()
    wc.shutdown()
    return response

Your environment

aiohttp server 3.3.2
raspberry pi
cv2 (OpenCV3)

[asvetlov]

Sorry, I don't follow.
Do you propose to break RFC but add mjpeg support?

[james4388]

No but add an option to omit mime closing boundary may be?

[asvetlov]

It's possible but the mode should be documented with this case mentioned.
Would you make a pull request? Looks like an easy task.

[james4388]

Hi @asvetlov I've created #3106. Please tell me what needs to be improve. Thanks

[asvetlov]

Fixed by #3106

[lock]

This thread has been automatically locked since there has not been any recent activity after it was closed. Please open a [new issue] for related bugs.
If you feel like there's important points made in this discussion, please include those exceprts into that [new issue].
[new issue]: https://github.com/aio-libs/aiohttp/issues/new