feat: add Limited body (#61)

* feat: add `Limited` body

* fix: correct size_hint, remove const generic

* chore: use boxed error, pin project

Co-authored-by: Programatik <programatik29@gmail.com>

Co-authored-by: Programatik <programatik29@gmail.com>

src/lib.rs

@@ -15,6 +15,7 @@
 
 mod empty;
 mod full;
+mod limited;
 mod next;
 mod size_hint;
 
@@ -22,6 +23,7 @@ pub mod combinators;
 
 pub use self::empty::Empty;
 pub use self::full::Full;
+pub use self::limited::{LengthLimitError, Limited};
 pub use self::next::{Data, Trailers};
 pub use self::size_hint::SizeHint;
 

src/limited.rs

@@ -0,0 +1,299 @@
+use crate::{Body, SizeHint};
+use bytes::Buf;
+use http::HeaderMap;
+use pin_project_lite::pin_project;
+use std::error::Error;
+use std::fmt;
+use std::pin::Pin;
+use std::task::{Context, Poll};
+
+pin_project! {
+    /// A length limited body.
+    ///
+    /// This body will return an error if more than the configured number
+    /// of bytes are returned on polling the wrapped body.
+    #[derive(Clone, Copy, Debug)]
+    pub struct Limited<B> {
+        remaining: usize,
+        #[pin]
+        inner: B,
+    }
+}
+
+impl<B> Limited<B> {
+    /// Create a new `Limited`.
+    pub fn new(inner: B, limit: usize) -> Self {
+        Self {
+            remaining: limit,
+            inner,
+        }
+    }
+}
+
+impl<B> Body for Limited<B>
+where
+    B: Body,
+    B::Error: Into<Box<dyn Error + Send + Sync>>,
+{
+    type Data = B::Data;
+    type Error = Box<dyn Error + Send + Sync>;
+
+    fn poll_data(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
+        let this = self.project();
+        let res = match this.inner.poll_data(cx) {
+            Poll::Pending => return Poll::Pending,
+            Poll::Ready(None) => None,
+            Poll::Ready(Some(Ok(data))) => {
+                if data.remaining() > *this.remaining {
+                    *this.remaining = 0;
+                    Some(Err(LengthLimitError.into()))
+                } else {
+                    *this.remaining -= data.remaining();
+                    Some(Ok(data))
+                }
+            }
+            Poll::Ready(Some(Err(err))) => Some(Err(err.into())),
+        };
+
+        Poll::Ready(res)
+    }
+
+    fn poll_trailers(
+        self: Pin<&mut Self>,
+        cx: &mut Context<'_>,
+    ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
+        let this = self.project();
+        let res = match this.inner.poll_trailers(cx) {
+            Poll::Pending => return Poll::Pending,
+            Poll::Ready(Ok(data)) => Ok(data),
+            Poll::Ready(Err(err)) => Err(err.into()),
+        };
+
+        Poll::Ready(res)
+    }
+
+    fn is_end_stream(&self) -> bool {
+        self.inner.is_end_stream()
+    }
+
+    fn size_hint(&self) -> SizeHint {
+        use std::convert::TryFrom;
+        match u64::try_from(self.remaining) {
+            Ok(n) => {
+                let mut hint = self.inner.size_hint();
+                if hint.lower() >= n {
+                    hint.set_exact(n)
+                } else if let Some(max) = hint.upper() {
+                    hint.set_upper(n.min(max))
+                } else {
+                    hint.set_upper(n)
+                }
+                hint
+            }
+            Err(_) => self.inner.size_hint(),
+        }
+    }
+}
+
+/// An error returned when body length exceeds the configured limit.
+#[derive(Debug)]
+#[non_exhaustive]
+pub struct LengthLimitError;
+
+impl fmt::Display for LengthLimitError {
+    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
+        f.write_str("length limit exceeded")
+    }
+}
+
+impl Error for LengthLimitError {}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use crate::Full;
+    use bytes::Bytes;
+    use std::convert::Infallible;
+
+    #[tokio::test]
+    async fn read_for_body_under_limit_returns_data() {
+        const DATA: &[u8] = b"testing";
+        let inner = Full::new(Bytes::from(DATA));
+        let body = &mut Limited::new(inner, 8);
+
+        let mut hint = SizeHint::new();
+        hint.set_upper(7);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        let data = body.data().await.unwrap().unwrap();
+        assert_eq!(data, DATA);
+        hint.set_upper(0);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        assert!(matches!(body.data().await, None));
+    }
+
+    #[tokio::test]
+    async fn read_for_body_over_limit_returns_error() {
+        const DATA: &[u8] = b"testing a string that is too long";
+        let inner = Full::new(Bytes::from(DATA));
+        let body = &mut Limited::new(inner, 8);
+
+        let mut hint = SizeHint::new();
+        hint.set_upper(8);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        let error = body.data().await.unwrap().unwrap_err();
+        assert!(matches!(error.downcast_ref(), Some(LengthLimitError)));
+    }
+
+    struct Chunky(&'static [&'static [u8]]);
+
+    impl Body for Chunky {
+        type Data = &'static [u8];
+        type Error = Infallible;
+
+        fn poll_data(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+        ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
+            let mut this = self;
+            match this.0.split_first().map(|(&head, tail)| (Ok(head), tail)) {
+                Some((data, new_tail)) => {
+                    this.0 = new_tail;
+
+                    Poll::Ready(Some(data))
+                }
+                None => Poll::Ready(None),
+            }
+        }
+
+        fn poll_trailers(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
+            Poll::Ready(Ok(Some(HeaderMap::new())))
+        }
+    }
+
+    #[tokio::test]
+    async fn read_for_chunked_body_around_limit_returns_first_chunk_but_returns_error_on_over_limit_chunk(
+    ) {
+        const DATA: &[&[u8]] = &[b"testing ", b"a string that is too long"];
+        let inner = Chunky(DATA);
+        let body = &mut Limited::new(inner, 8);
+
+        let mut hint = SizeHint::new();
+        hint.set_upper(8);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        let data = body.data().await.unwrap().unwrap();
+        assert_eq!(data, DATA[0]);
+        hint.set_upper(0);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        let error = body.data().await.unwrap().unwrap_err();
+        assert!(matches!(error.downcast_ref(), Some(LengthLimitError)));
+    }
+
+    #[tokio::test]
+    async fn read_for_chunked_body_over_limit_on_first_chunk_returns_error() {
+        const DATA: &[&[u8]] = &[b"testing a string", b" that is too long"];
+        let inner = Chunky(DATA);
+        let body = &mut Limited::new(inner, 8);
+
+        let mut hint = SizeHint::new();
+        hint.set_upper(8);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        let error = body.data().await.unwrap().unwrap_err();
+        assert!(matches!(error.downcast_ref(), Some(LengthLimitError)));
+    }
+
+    #[tokio::test]
+    async fn read_for_chunked_body_under_limit_is_okay() {
+        const DATA: &[&[u8]] = &[b"test", b"ing!"];
+        let inner = Chunky(DATA);
+        let body = &mut Limited::new(inner, 8);
+
+        let mut hint = SizeHint::new();
+        hint.set_upper(8);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        let data = body.data().await.unwrap().unwrap();
+        assert_eq!(data, DATA[0]);
+        hint.set_upper(4);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        let data = body.data().await.unwrap().unwrap();
+        assert_eq!(data, DATA[1]);
+        hint.set_upper(0);
+        assert_eq!(body.size_hint().upper(), hint.upper());
+
+        assert!(matches!(body.data().await, None));
+    }
+
+    #[tokio::test]
+    async fn read_for_trailers_propagates_inner_trailers() {
+        const DATA: &[&[u8]] = &[b"test", b"ing!"];
+        let inner = Chunky(DATA);
+        let body = &mut Limited::new(inner, 8);
+        let trailers = body.trailers().await.unwrap();
+        assert_eq!(trailers, Some(HeaderMap::new()))
+    }
+
+    #[derive(Debug)]
+    enum ErrorBodyError {
+        Data,
+        Trailers,
+    }
+
+    impl fmt::Display for ErrorBodyError {
+        fn fmt(&self, _f: &mut fmt::Formatter) -> fmt::Result {
+            Ok(())
+        }
+    }
+
+    impl Error for ErrorBodyError {}
+
+    struct ErrorBody;
+
+    impl Body for ErrorBody {
+        type Data = &'static [u8];
+        type Error = ErrorBodyError;
+
+        fn poll_data(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+        ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
+            Poll::Ready(Some(Err(ErrorBodyError::Data)))
+        }
+
+        fn poll_trailers(
+            self: Pin<&mut Self>,
+            _cx: &mut Context<'_>,
+        ) -> Poll<Result<Option<HeaderMap>, Self::Error>> {
+            Poll::Ready(Err(ErrorBodyError::Trailers))
+        }
+    }
+
+    #[tokio::test]
+    async fn read_for_body_returning_error_propagates_error() {
+        let body = &mut Limited::new(ErrorBody, 8);
+        let error = body.data().await.unwrap().unwrap_err();
+        assert!(matches!(error.downcast_ref(), Some(ErrorBodyError::Data)));
+    }
+
+    #[tokio::test]
+    async fn trailers_for_body_returning_error_propagates_error() {
+        let body = &mut Limited::new(ErrorBody, 8);
+        let error = body.trailers().await.unwrap_err();
+        assert!(matches!(
+            error.downcast_ref(),
+            Some(ErrorBodyError::Trailers)
+        ));
+    }
+}