Buffer reuse and race condition in `client.IncomingContent.stream()`

[ohait]

We've been debugging some issues using Blacksheep v1 where a reverse proxy was randomly returning a truncated response, and we narrowed it down to: https://github.com/Neoteroi/BlackSheep/blob/main/blacksheep/client/connection.py#L69-L70

I believe this code need to be changed to something like:

            buf = bytes(self._body)
            self._body.clear()
            yield bytes(buf)

I don't have an easy way to reproduce, but I observed this: task 1) data is coming in via extend_body() which notify self._chunk task 2) awakes and read the body task 2) it yields passing the body task 2) whatever codes was waiting for yield awaits task 1) detect more data and calls extend_body() again (with the notify) task 2) yields "returns" and do a _body.clear() resetting the buffer and what was added to the buffer before task 2) it loops back and don't wait on the event, since the previous notify task 2) the body is cleared, so it breaks out assuming there is no more data (while in fact, there was more)

I also expect there could be other cases where the buffer changes while yield

HTH