2 files changed, 75 insertions, 2 deletions
diff --git a/src/bytes.rs b/src/bytes.rs
index b4745a9..0404a72 100644
--- a/src/bytes.rs
+++ b/src/bytes.rs
@@ -807,8 +807,36 @@ impl From<&'static str> for Bytes {
 
 impl From<Vec<u8>> for Bytes {
     fn from(vec: Vec<u8>) -> Bytes {
-        let slice = vec.into_boxed_slice();
-        slice.into()
+        let mut vec = vec;
+        let ptr = vec.as_mut_ptr();
+        let len = vec.len();
+        let cap = vec.capacity();
+
+        // Avoid an extra allocation if possible.
+        if len == cap {
+            return Bytes::from(vec.into_boxed_slice());
+        }
+
+        let shared = Box::new(Shared {
+            buf: ptr,
+            cap,
+            ref_cnt: AtomicUsize::new(1),
+        });
+        mem::forget(vec);
+
+        let shared = Box::into_raw(shared);
+        // The pointer should be aligned, so this assert should
+        // always succeed.
+        debug_assert!(
+            0 == (shared as usize & KIND_MASK),
+            "internal: Box<Shared> should have an aligned pointer",
+        );
+        Bytes {
+            ptr,
+            len,
+            data: AtomicPtr::new(shared as _),
+            vtable: &SHARED_VTABLE,
+        }
     }
 }
 
diff --git a/tests/test_bytes.rs b/tests/test_bytes.rs
index 4ddb24d..5ec60a5 100644
--- a/tests/test_bytes.rs
+++ b/tests/test_bytes.rs
@@ -1163,3 +1163,48 @@ fn test_bytes_into_vec_promotable_even() {
     assert_eq!(Vec::from(b2), vec[20..]);
     assert_eq!(Vec::from(b1), vec[..20]);
 }
+
+#[test]
+fn test_bytes_vec_conversion() {
+    let mut vec = Vec::with_capacity(10);
+    vec.extend(b"abcdefg");
+    let b = Bytes::from(vec);
+    let v = Vec::from(b);
+    assert_eq!(v.len(), 7);
+    assert_eq!(v.capacity(), 10);
+
+    let mut b = Bytes::from(v);
+    b.advance(1);
+    let v = Vec::from(b);
+    assert_eq!(v.len(), 6);
+    assert_eq!(v.capacity(), 10);
+    assert_eq!(v.as_slice(), b"bcdefg");
+}
+
+#[test]
+fn test_bytes_mut_conversion() {
+    let mut b1 = BytesMut::with_capacity(10);
+    b1.extend(b"abcdefg");
+    let b2 = Bytes::from(b1);
+    let v = Vec::from(b2);
+    assert_eq!(v.len(), 7);
+    assert_eq!(v.capacity(), 10);
+
+    let mut b = Bytes::from(v);
+    b.advance(1);
+    let v = Vec::from(b);
+    assert_eq!(v.len(), 6);
+    assert_eq!(v.capacity(), 10);
+    assert_eq!(v.as_slice(), b"bcdefg");
+}
+
+#[test]
+fn test_bytes_capacity_len() {
+    for cap in 0..100 {
+        for len in 0..=cap {
+            let mut v = Vec::with_capacity(cap);
+            v.resize(len, 0);
+            let _ = Bytes::from(v);
+        }
+    }
+}