buf: implement FromBufStream for Bytes (#1009)

tokio-buf/src/util/from.rs

@@ -1,6 +1,6 @@
 use SizeHint;
 
-use bytes::{Buf, BufMut};
+use bytes::{Buf, BufMut, Bytes};
 
 use std::usize;
 
@@ -47,12 +47,18 @@ pub struct CollectVecError {
     _p: (),
 }
 
+/// Error returned from collecting into a `Bytes`
+#[derive(Debug)]
+pub struct CollectBytesError {
+    _p: (),
+}
+
 impl<T: Buf> FromBufStream<T> for Vec<u8> {
     type Builder = Vec<u8>;
     type Error = CollectVecError;
 
-    fn builder(_hint: &SizeHint) -> Vec<u8> {
-        Vec::new()
+    fn builder(hint: &SizeHint) -> Vec<u8> {
+        Vec::with_capacity(hint.lower() as usize)
     }
 
     fn extend(builder: &mut Self, buf: &mut T, hint: &SizeHint) -> Result<(), Self::Error> {
@@ -110,3 +116,21 @@ impl<T: Buf> FromBufStream<T> for Vec<u8> {
         Ok(builder)
     }
 }
+
+impl<T: Buf> FromBufStream<T> for Bytes {
+    type Builder = Vec<u8>;
+    type Error = CollectBytesError;
+
+    fn builder(hint: &SizeHint) -> Vec<u8> {
+        <Vec<u8> as FromBufStream<T>>::builder(hint)
+    }
+
+    fn extend(builder: &mut Vec<u8>, buf: &mut T, hint: &SizeHint) -> Result<(), Self::Error> {
+        <Vec<u8> as FromBufStream<T>>::extend(builder, buf, hint)
+            .map_err(|_| CollectBytesError { _p: () })
+    }
+
+    fn build(builder: Vec<u8>) -> Result<Self, Self::Error> {
+        Ok(builder.into())
+    }
+}

tokio-buf/src/util/mod.rs

@@ -14,7 +14,7 @@ pub mod error {
     //! Error types
 
     pub use super::collect::CollectError;
-    pub use super::from::CollectVecError;
+    pub use super::from::{CollectBytesError, CollectVecError};
     pub use super::limit::LimitError;
 }