body ergonomics v3 (#2468)

actix-http/src/body/either.rs

@@ -0,0 +1,83 @@
+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! {
+    #[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` using left variant and boxed right variant.
+    pub fn new(body: L) -> Self {
+        Self::Left { body }
+    }
+}
+
+impl<L, R> EitherBody<L, R> {
+    /// Creates new `EitherBody` using left variant.
+    pub fn left(body: L) -> Self {
+        Self::Left { body }
+    }
+
+    /// Creates new `EitherBody` using right variant.
+    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;
+
+    fn size(&self) -> BodySize {
+        match self {
+            EitherBody::Left { body } => body.size(),
+            EitherBody::Right { body } => body.size(),
+        }
+    }
+
+    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)),
+        }
+    }
+}
+
+#[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(());
+    }
+}