implement Body::size_hint

Co-authored-by: neoeinstein <[email protected]>

Author: programatik29

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::{
@@ -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.limit) {
+            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)]