Proposal: "http.response.sendfile" extension.

Add the sendfile extension to allow ASGI programs to return response through sendfile.

In scope:

"scope": {
    ...
    "extensions": {
        "http.response.sendfile": {},
    },
}

Response:

await send({"type": "http.response.start", ...})
await send({"type": "http.response.sendfile", "file": file-obj})

Some related links:

https://docs.python.org/3.7/library/asyncio-eventloop.html#asyncio.loop.sendfile https://github.com/encode/uvicorn/issues/35

[abersheeran]

@synodriver Maybe the PR https://github.com/encode/uvicorn/pull/1210 can help you.

[abersheeran]

loop.sendfile just wraps os.sendfile.

The standard uses integer (file descriptor) to make it easier for servers written in C, Rust, and so on to handle this.