Add zero-copy make_mut (#695)

tests/test_bytes_odd_alloc.rs

@@ -95,3 +95,53 @@ fn test_bytes_into_vec() {
     assert_eq!(Vec::from(b2), vec[20..]);
     assert_eq!(Vec::from(b1), vec[..20]);
 }
+
+#[test]
+fn test_bytes_make_mut_vec() {
+    let vec = vec![33u8; 1024];
+
+    // Test case where kind == KIND_VEC
+    let b1 = Bytes::from(vec.clone());
+    let b1m = b1.make_mut();
+    assert_eq!(b1m, vec);
+}
+
+#[test]
+fn test_bytes_make_mut_arc_1() {
+    let vec = vec![33u8; 1024];
+
+    // Test case where kind == KIND_ARC, ref_cnt == 1
+    let b1 = Bytes::from(vec.clone());
+    drop(b1.clone());
+    let b1m = b1.make_mut();
+    assert_eq!(b1m, vec);
+}
+
+#[test]
+fn test_bytes_make_mut_arc_2() {
+    let vec = vec![33u8; 1024];
+
+    // Test case where kind == KIND_ARC, ref_cnt == 2
+    let b1 = Bytes::from(vec.clone());
+    let b2 = b1.clone();
+    let b1m = b1.make_mut();
+    assert_eq!(b1m, vec);
+
+    // Test case where vtable = SHARED_VTABLE, kind == KIND_ARC, ref_cnt == 1
+    let b2m = b2.make_mut();
+    assert_eq!(b2m, vec);
+}
+
+#[test]
+fn test_bytes_make_mut_arc_offset() {
+    let vec = vec![33u8; 1024];
+
+    // Test case where offset != 0
+    let mut b1 = Bytes::from(vec.clone());
+    let b2 = b1.split_off(20);
+    let b1m = b1.make_mut();
+    let b2m = b2.make_mut();
+
+    assert_eq!(b2m, vec[20..]);
+    assert_eq!(b1m, vec[..20]);
+}