Implement Default for HttpBody1ToHttpBody04

[howardjohn]

see hyperium/tonic#1307

Tonic interceptors require a Default on the body. This makes it easier to use an adapter type tonic.

FWIW the default type I am using:

#[derive(Default)]
pub enum DefaultIncoming {
    Some(Incoming),
    #[default]
    Empty
}

impl Body for DefaultIncoming {
    type Data = Bytes;
    type Error = hyper::Error;

    fn poll_frame(self: Pin<&mut Self>, cx: &mut Context<'_>) -> Poll<Option<Result<Frame<Self::Data>, Self::Error>>> {
        match self.get_mut() {
            DefaultIncoming::Some(ref mut i) => Pin::new(i).poll_frame(cx),
            DefaultIncoming::Empty => Pin::new(&mut http_body_util::Empty::<Bytes>::new()).poll_frame(cx).map_err(|_| unreachable!())
        }
    }
}

[davidpdrsn]

Can you use #[derive(Default)]?

[howardjohn]

Can you use #[derive(Default)]?

I don't think so, because we only want to implement Default if B: Default? Or I don't know how to, at least 🙂

[davidpdrsn]

I don't think so, because we only want to implement Default if B: Default?

That is how it works. How else could it create a body?

[howardjohn]

I don't think so, because we only want to implement Default if B: Default?

That is how it works. How else could it create a body?

Today you can use the adaptor without B: Default though. Derive would mean it MUST be Default, the approach here makes it Default only if the inner type is? In particular, hyper Incoming is not Default so I am not sure we should require it

[davidpdrsn]

I think you're misunderstanding how #[derive(Default)] works. These two things are exactly the same:

#[derive(Default)] // this derive...
pub struct HttpBody1ToHttpBody04<B> {
    body: B,
    trailers: Option<HeaderMap>,
}

// ...is the same as

impl<B: Default> Default for HttpBody1ToHttpBody04<B> {
    fn default() -> Self {
        Self {
            body: B::default(),
            trailers: <Option<HeaderMap>>::default(),
        }
    }
}

It does not add this

#[derive(Default)]
pub struct HttpBody1ToHttpBody04<B: Default> {
                              // ^^^^^^^^^^
    body: B,
    trailers: Option<HeaderMap>,
}

[howardjohn]

Oh that is great, thanks for the tip. I wasn't aware the derive was that smart.

[davidpdrsn]

Published in 0.1.3 🎉