change implementation and add size hint

Co-authored-by: neoeinstein <marcus@griep.us>

src/limited.rs

@@ -1,6 +1,6 @@
 //! Body types.
 
-use crate::Body;
+use crate::{Body, SizeHint};
 use bytes::Buf;
 use pin_project_lite::pin_project;
 use std::{
@@ -16,8 +16,7 @@ pin_project! {
     pub struct Limited<B> {
         #[pin]
         inner: B,
-        limit: usize,
-        read: usize,
+        remaining: usize,
     }
 }
 
@@ -26,8 +25,7 @@ impl<B> Limited<B> {
     pub fn new(inner: B, limit: usize) -> Self {
         Self {
             inner,
-            limit,
-            read: 0,
+            remaining: limit,
         }
     }
 }
@@ -46,20 +44,22 @@ where
     ) -> Poll<Option<Result<Self::Data, Self::Error>>> {
         let this = self.project();
 
-        match this.inner.poll_data(cx) {
+        let res = match this.inner.poll_data(cx) {
             Poll::Ready(Some(Ok(data))) => {
-                *this.read += data.remaining();
-
-                if this.read <= this.limit {
-                    Poll::Ready(Some(Ok(data)))
+                if data.remaining() > *this.remaining {
+                    *this.remaining = 0;
+                    Some(Err("length limit exceeded".into()))
                 } else {
-                    Poll::Ready(Some(Err("body limit exceeded".into())))
+                    *this.remaining -= data.remaining();
+                    Some(Ok(data))
                 }
             }
-            Poll::Ready(Some(Err(e))) => Poll::Ready(Some(Err(e.into()))),
-            Poll::Ready(None) => Poll::Ready(None),
-            Poll::Pending => Poll::Pending,
-        }
+            Poll::Ready(Some(Err(e))) => Some(Err(e.into())),
+            Poll::Ready(None) => None,
+            Poll::Pending => return Poll::Pending,
+        };
+
+        Poll::Ready(res)
     }
 
     fn poll_trailers(
@@ -72,6 +72,24 @@ where
     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(),
+        }
+    }
 }
 
 #[cfg(test)]