Support FileResponse.prepare() to be re-entrant just as StreamResponse.prepare().

[momocow]

🐣 Is your feature request related to a problem? Please describe.

There is no way to know when a file is sent if the file is required to be removed after consumed.

As the docs of FileResponse reads,

The actual body sending happens in overridden prepare().

I tried to call await file_resp.prepare() myself in a handler function just like what we are used to do with StreamResponse, and then the file is removed after leaving the handler.

An Exception was raised after leaving the handler since prepare() was called again here without checking if the response had already been prepared.

aiohttp/aiohttp/web_protocol.py

Line 461 in 0dbf937

await prepare_meth(request)

Although I can use a StreamResponse instead of a FileResponse to tackle this problem, doing the same thing as what FileResponse._sendfile_fallback() does. I think it's the responsibility of a FileResponse to send a file (though a file to be removed soon), also to avoid code duplication.

💡 Describe the solution you'd like

Just like what StreamResponse.prepare() does, I think the same check should also be implemented in FileResponse.prepare().

aiohttp/aiohttp/web_response.py

Lines 347 to 350 in 0dbf937

	if self._eof_sent:
	return None
	if self._payload_writer is not None:
	return self._payload_writer

❓ Describe alternatives you've considered

Provide any way for developers to know a file is sent, maybe an asyncio.Event or a signal.

---

I know there are tons of issues here, but I think it's an improvement for the library to be more comprehensive.
Thank you!

[webknjaz]

You can try sending a PR.

[pohmelie]

Voting up. No way to send temporary file, which created and removed by handler (archive, for example).