impl From<Box<[u8]>> for Bytes (#504)

src/bytes.rs

@@ -797,14 +797,20 @@ impl From<&'static str> for Bytes {
 
 impl From<Vec<u8>> for Bytes {
     fn from(vec: Vec<u8>) -> Bytes {
-        // into_boxed_slice doesn't return a heap allocation for empty vectors,
+        let slice = vec.into_boxed_slice();
+        slice.into()
+    }
+}
+
+impl From<Box<[u8]>> for Bytes {
+    fn from(slice: Box<[u8]>) -> Bytes {
+        // Box<[u8]> doesn't contain a heap allocation for empty slices,
         // so the pointer isn't aligned enough for the KIND_VEC stashing to
         // work.
-        if vec.is_empty() {
+        if slice.is_empty() {
             return Bytes::new();
         }
 
-        let slice = vec.into_boxed_slice();
         let len = slice.len();
         let ptr = Box::into_raw(slice) as *mut u8;
 

tests/test_bytes.rs

@@ -994,3 +994,11 @@ fn bytes_put_bytes() {
     bytes.put_bytes(19, 2);
     assert_eq!([17, 19, 19], bytes.as_ref());
 }
+
+#[test]
+fn box_slice_empty() {
+    // See https://github.com/tokio-rs/bytes/issues/340
+    let empty: Box<[u8]> = Default::default();
+    let b = Bytes::from(empty);
+    assert!(b.is_empty());
+}