Proposal: "http.response.sendfile" extension.

[abersheeran]

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
encode/uvicorn#35

[andrewgodwin]

Yes, I can see this being sensible, since having it as an extension means that things not on (a new enough) asyncio can just not provide it.

[abersheeran]

Can I submit a PR to add this section to the ASGI document?

[andrewgodwin]

Totally - I think it's best to iterate on a draft here, so we can make sure the specification is nailed down properly.

[abersheeran]

Okay.

[davidism]

It seems like this isn't (directly) related to X-SendFile in httpd/lighttpd and X-Accel-Redirect in Nginx. Those set headers pointing to a path (SendFile) or internal URI (Accel) that tell the HTTP server to do the sendfile call.

The extension should make it clear that these aren't the same. Or maybe it would be possible to accommodate them along with allowing the ASGI server to use loop.sendfile.

[andrewgodwin]

Yeah, we need to make this very clear in terms of what it does and allows. Maybe a rename to make it clearer - something like http.response.direct-file-stream.

[abersheeran]

All right. If the name isn't clear enough, we can consider using zero-copy. That's what this extension is all about. What do you think?

[andrewgodwin]

I'd be OK with zero-copy, that seems reasonable, though maybe zero-copy-send to be a bit more precise?

[abersheeran]

I agree. @andrewgodwin

[synodriver]

Hi, I'm trying to implement this extension in hypercorn, but hava some question about it. The document said file is an integer, while loop.sendfile accepts only file object. I'm using os.fdopen in this case, however, that just make more trouble. Here is my code that did not work. Can you give me some advice?

[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.

[abersheeran]

@synodriver Maybe the PR encode/uvicorn#1210 can help you.