Keep capacity when unsplit on empty other buf (#502)

2 files changed, 26 insertions, 1 deletions

diff --git a/src/bytes_mut.rs b/src/bytes_mut.rs
index 2af58e3..8e42079 100644
--- a/src/bytes_mut.rs
+++ b/src/bytes_mut.rs
@@ -819,7 +819,7 @@ impl BytesMut {
     }
 
     fn try_unsplit(&mut self, other: BytesMut) -> Result<(), BytesMut> {
-        if other.is_empty() {
+        if other.capacity() == 0 {
             return Ok(());
         }
 
diff --git a/tests/test_bytes.rs b/tests/test_bytes.rs
index b9e6ce4..2d22fdd 100644
--- a/tests/test_bytes.rs
+++ b/tests/test_bytes.rs
@@ -785,6 +785,31 @@ fn bytes_mut_unsplit_empty_self() {
 }
 
 #[test]
+fn bytes_mut_unsplit_other_keeps_capacity() {
+    let mut buf = BytesMut::with_capacity(64);
+    buf.extend_from_slice(b"aabb");
+
+    // non empty other created "from" buf
+    let mut other = buf.split_off(buf.len());
+    other.extend_from_slice(b"ccddee");
+    buf.unsplit(other);
+
+    assert_eq!(buf.capacity(), 64);
+}
+
+#[test]
+fn bytes_mut_unsplit_empty_other_keeps_capacity() {
+    let mut buf = BytesMut::with_capacity(64);
+    buf.extend_from_slice(b"aabbccddee");
+
+    // empty other created "from" buf
+    let other = buf.split_off(buf.len());
+    buf.unsplit(other);
+
+    assert_eq!(buf.capacity(), 64);
+}
+
+#[test]
 fn bytes_mut_unsplit_arc_different() {
     let mut buf = BytesMut::with_capacity(64);
     buf.extend_from_slice(b"aaaabbbbeeee");