falcon: bug: sse-stream not properly consumed

I recently implemented an async route, where I “awaited” some result, but had to send a “keep-alive”-message in case the result takes longer than a certain time (1m in my case).

The exact same code works when setting the generator as value for response.stream, but will get stuck if instead setting it as response.sse (will work for small data, though).

This is my code:

# works:
async def wait_for_result_and_yield_keepalives():
    nonlocal awaitable
    while True:
        done, pending = await asyncio.wait((awaitable,), timeout=30)
        if not done:
            logger.info('sending keep-alive')
            awaitable = pending.pop()
            yield b' '
            continue
        break
    result = done.pop().result()
    logger.info(f'scan done {result=}')
    yield json.dumps(result).encode('utf-8')

resp.stream = wait_for_result_and_yield_keepalives()

# does not work (will get stuck):
async def wait_for_result_and_yield_keepalives():
    nonlocal awaitable
    while True:
        done, pending = await asyncio.wait((awaitable,), timeout=30)
        if not done:
            logger.info('sending keep-alive')
            awaitable = pending.pop()
            yield falcon.asgi.SSEvent(event='keep-alive')
            continue
        break
    result = done.pop().result()
    logger.info(f'scan done {result=}')
    yield falcon.asgi.SSEvent(event='result', json=result)

resp.sse = wait_for_result_and_yield_keepalives()

To be fair, I am so far not very familiar w/ “async”, so maybe my code is conceptionally flawed (feedback welcome…). However, I still would expect that behaviour between using response.stream and response.sse ought to be consistent.

Maybe there are more elegant ways of sending those “keep-alives”? I have to send those, because in my (kubernetes) environment, stale HTTP connections are closed (I think by Load-Balancer) after about 1m of inactivity (just in case you wonder why I want to do such a thing in the first place).