body ergonomics v3 (#2468)

actix-http/src/body/boxed.rs

@@ -0,0 +1,80 @@
+use std::{
+    error::Error as StdError,
+    fmt,
+    pin::Pin,
+    task::{Context, Poll},
+};
+
+use bytes::Bytes;
+
+use super::{BodySize, MessageBody, MessageBodyMapErr};
+use crate::Error;
+
+/// A boxed message body with boxed errors.
+pub struct BoxBody(Pin<Box<dyn MessageBody<Error = Box<dyn StdError>>>>);
+
+impl BoxBody {
+    /// Boxes a `MessageBody` and any errors it generates.
+    pub fn new<B>(body: B) -> Self
+    where
+        B: MessageBody + 'static,
+    {
+        let body = MessageBodyMapErr::new(body, Into::into);
+        Self(Box::pin(body))
+    }
+
+    /// Returns a mutable pinned reference to the inner message body type.
+    pub fn as_pin_mut(
+        &mut self,
+    ) -> Pin<&mut (dyn MessageBody<Error = Box<dyn StdError>>)> {
+        self.0.as_mut()
+    }
+}
+
+impl fmt::Debug for BoxBody {
+    fn fmt(&self, f: &mut fmt::Formatter<'_>) -> fmt::Result {
+        f.write_str("BoxBody(dyn MessageBody)")
+    }
+}
+
+impl MessageBody for BoxBody {
+    type Error = Error;
+
+    fn size(&self) -> BodySize {
+        self.0.size()
+    }
+
+    fn poll_next(
+        mut self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Bytes, Self::Error>>> {
+        self.0
+            .as_mut()
+            .poll_next(cx)
+            .map_err(|err| Error::new_body().with_cause(err))
+    }
+}
+
+#[cfg(test)]
+mod tests {
+
+    use static_assertions::{assert_impl_all, assert_not_impl_all};
+
+    use super::*;
+    use crate::body::to_bytes;
+
+    assert_impl_all!(BoxBody: MessageBody, fmt::Debug, Unpin);
+
+    assert_not_impl_all!(BoxBody: Send, Sync, Unpin);
+
+    #[actix_rt::test]
+    async fn nested_boxed_body() {
+        let body = Bytes::from_static(&[1, 2, 3]);
+        let boxed_body = BoxBody::new(BoxBody::new(body));
+
+        assert_eq!(
+            to_bytes(boxed_body).await.unwrap(),
+            Bytes::from(vec![1, 2, 3]),
+        );
+    }
+}