Wrapping hyper::body::Incoming using a custom body with custom data

[OldMansKid]

Hi everyone,
When implementing hyper::body::Body for use in the context of proxy, I find it very difficult to wrap hyper::body::Incoming if the custom body type doesn't use Bytes. For example:

pub enum BodyWrapper { Incoming(hyper::body::Incoming), LocalCache(DataChannel) }
impl hyper::body::Body for BodyWrapper {
    type Data = DataAdapter;
    fn poll_frame(self: Pin<&mut Self>, cx: &mut Context<'_>,)
     -> Poll<Option<Result<Frame<DataAdapter>, Self::Error>>> {
        match self.get_mut() {
            BodyWrapper::Incoming(incoming) => {
                match incoming.frame().poll_unpin(cx)
                ...
            }
            ...
        }
    }
}
pub enum DataAdapter {Owned(Bytes), Shared(ReusableBuf)}
impl Buf for DataAdapter {...}

Because polling Frame<Incoming> would get a Frame<Bytes>, which doesn't implement Buf, nor can it be converted to Bytes either if the data type is trailer. So the only way I can think of to make this compatible when Frame<Bytes> is trailers, is to convert the HeaderMap<HeaderValue> items one by one into bytes. Although trailers aren't common, there probably won't be much overhead, but is this the only possible way?

[dswij]

Are you expecting only to handle data frames? Perhaps you can get the data and then map it: https://docs.rs/hyper/latest/hyper/body/struct.Frame.html#method.into_data

[OldMansKid]

I just used into_data() and into_trailers(). To be honest, I've been a little confused by the hyper::body::Body trait, as the poll_frame() seems to only return body data, while hyper::body::Incoming can return both body frames and trailer frames. So I just converted HeaderMap into u8 slice in my Buf implementation, then send trailer along with body anyway.

[dswij]

poll_frame returns both data and trailer frames. https://docs.rs/hyper/latest/src/hyper/body/incoming.rs.html#270

But I get that the issue is that you're trying to wrap both data and trailers but the type needs to be converted first.

I wonder if it makes sense to provide some function for HeaderMap to convert to Bytes/implement Buf for convenience.

[OldMansKid]

Yeah, exactly that. I have to do pretty much the opposite of the parsing done by Frame, like inserting b"0\r\n", just to make the types compatible.

[sfackler]

Why are you trying to convert the trailers to bytes? Just make a trailers frame: https://docs.rs/http-body/latest/http_body/struct.Frame.html#method.trailers, or use map_data like Sean said.

[OldMansKid]

Sorry, I'm not that experienced in Rust and didn't get Sean's idea earlier. And similarly, I thought Frame::traiers(t) would return a Frame<HeaderMap> thus incompatible with Frame<DataAdapter>, but now I saw it is a generic function and its type isn't determined by the HeaderMap passed in. All good now, I'm going to just use map_data(). Thanks for pointing that out.