Streaming response middleware executes twice

[ahopkins]

Describe the bug
When responding with the response object from a streaming handler, the response middleware is executed twice.

Code snippet
Compare:

@app.get("/")
async def handler(request: Request):
    logger.info("handler")
    resp = await request.respond()
    logger.info("sending")
    await resp.send(b"Now I'm free, free-falling")
    logger.info("sent")
    await resp.send(b"Now I'm free, free-falling")
    logger.info("sent")
    await resp.eof()
    logger.info("done")
    return resp


@app.on_request
async def req(_):
    logger.info("request")


@app.on_response
async def res(*_):
    logger.info("response")

With:

@app.get("/")
async def handler(request: Request):
    logger.info("handler")
    resp = await request.respond()
    logger.info("sending")
    await resp.send(b"Now I'm free, free-falling")
    logger.info("sent")
    await resp.send(b"Now I'm free, free-falling")
    logger.info("sent")
    await resp.eof()
    logger.info("done")
    # return resp


@app.on_request
async def req(_):
    logger.info("request")


@app.on_response
async def res(*_):
    logger.info("response")

[2021-07-14 09:23:36 +0300] [1772072] [INFO] request
[2021-07-14 09:23:36 +0300] [1772072] [INFO] handler
[2021-07-14 09:23:36 +0300] [1772072] [INFO] response
[2021-07-14 09:23:36 +0300] [1772072] [INFO] sending
[2021-07-14 09:23:36 +0300] - (sanic.access)[INFO][127.0.0.1:48476]: GET http://localhost:9999/  200 26
[2021-07-14 09:23:36 +0300] [1772072] [INFO] sent
[2021-07-14 09:23:36 +0300] [1772072] [INFO] sent
[2021-07-14 09:23:36 +0300] [1772072] [INFO] done
[2021-07-14 09:23:36 +0300] [1772072] [INFO] response
---
[2021-07-14 09:24:04 +0300] [1772197] [INFO] request
[2021-07-14 09:24:04 +0300] [1772197] [INFO] handler
[2021-07-14 09:24:04 +0300] [1772197] [INFO] response
[2021-07-14 09:24:04 +0300] [1772197] [INFO] sending
[2021-07-14 09:24:04 +0300] - (sanic.access)[INFO][127.0.0.1:48484]: GET http://localhost:9999/  200 26
[2021-07-14 09:24:04 +0300] [1772197] [INFO] sent
[2021-07-14 09:24:04 +0300] [1772197] [INFO] sent
[2021-07-14 09:24:04 +0300] [1772197] [INFO] done

Expected behavior
Response middleware does not execute twice per streaming request.

There probably is still a use case for wanting some middleware type event at the conclusion of the handler, but this is can be covered by #1630 when #2160 is finally implemented.

Environment (please complete the following information):

• Version main

[ahopkins]

There are probably two ways to handle this:

1. prevent handle_request from calling respond() a second time
2. prevent respond from executing the middleware a second time

[ChihweiLHBird]

Should has been fixed in #2327

[ahopkins]

Yes this is resolved with the new change. I will update the documentation about streaming to also let users know that they should NOT be returning an object from the handler when streaming.