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use std::{
pin::Pin,
task::{Context, Poll},
};
use bytes::Bytes;
use pin_project_lite::pin_project;
use super::{BodySize, BoxBody, MessageBody};
use crate::Error;
pin_project! {
/// An "either" type specialized for body types.
///
/// It is common, in middleware especially, to conditionally return an inner service's unknown/
/// generic body `B` type or return early with a new response. This type's "right" variant
/// defaults to `BoxBody` since error responses are the common case.
///
/// For example, middleware will often have `type Response = ServiceResponse<EitherBody<B>>`.
/// This means that the inner service's response body type maps to the `Left` variant and the
/// middleware's own error responses use the default `Right` variant of `BoxBody`. Of course,
/// there's no reason it couldn't use `EitherBody<B, String>` instead if its alternative
/// responses have a known type.
#[project = EitherBodyProj]
#[derive(Debug, Clone)]
pub enum EitherBody<L, R = BoxBody> {
/// A body of type `L`.
Left { #[pin] body: L },
/// A body of type `R`.
Right { #[pin] body: R },
}
}
impl<L> EitherBody<L, BoxBody> {
/// Creates new `EitherBody` left variant with a boxed right variant.
///
/// If the expected `R` type will be inferred and is not `BoxBody` then use the
/// [`left`](Self::left) constructor instead.
#[inline]
pub fn new(body: L) -> Self {
Self::Left { body }
}
}
impl<L, R> EitherBody<L, R> {
/// Creates new `EitherBody` using left variant.
#[inline]
pub fn left(body: L) -> Self {
Self::Left { body }
}
/// Creates new `EitherBody` using right variant.
#[inline]
pub fn right(body: R) -> Self {
Self::Right { body }
}
}
impl<L, R> MessageBody for EitherBody<L, R>
where
L: MessageBody + 'static,
R: MessageBody + 'static,
{
type Error = Error;
#[inline]
fn size(&self) -> BodySize {
match self {
EitherBody::Left { body } => body.size(),
EitherBody::Right { body } => body.size(),
}
}
#[inline]
fn poll_next(
self: Pin<&mut Self>,
cx: &mut Context<'_>,
) -> Poll<Option<Result<Bytes, Self::Error>>> {
match self.project() {
EitherBodyProj::Left { body } => body
.poll_next(cx)
.map_err(|err| Error::new_body().with_cause(err)),
EitherBodyProj::Right { body } => body
.poll_next(cx)
.map_err(|err| Error::new_body().with_cause(err)),
}
}
#[inline]
fn try_into_bytes(self) -> Result<Bytes, Self> {
match self {
EitherBody::Left { body } => body
.try_into_bytes()
.map_err(|body| EitherBody::Left { body }),
EitherBody::Right { body } => body
.try_into_bytes()
.map_err(|body| EitherBody::Right { body }),
}
}
#[inline]
fn boxed(self) -> BoxBody {
match self {
EitherBody::Left { body } => body.boxed(),
EitherBody::Right { body } => body.boxed(),
}
}
}
#[cfg(test)]
mod tests {
use super::*;
#[test]
fn type_parameter_inference() {
let _body: EitherBody<(), _> = EitherBody::new(());
let _body: EitherBody<_, ()> = EitherBody::left(());
let _body: EitherBody<(), _> = EitherBody::right(());
}
}