Allow checking out AppendBufs from Pool

test/test_append.rs

@@ -1,4 +1,5 @@
 use bytes::{ByteStr, Buf, MutBuf};
+use bytes::alloc::Pool;
 use bytes::buf::AppendBuf;
 
 #[test]
@@ -28,3 +29,33 @@ pub fn test_initial_buf_empty() {
         assert_eq!(dst, b"hello world");
     }
 }
+
+#[test]
+pub fn test_append_buf_from_pool() {
+    let pool = Pool::with_capacity(2, 256);
+
+    // Run in a loop a bunch in hope that if there is a memory issue, it will
+    // be exposed
+    for _ in 0..1000 {
+        let mut buf = pool.new_append_buf().unwrap();
+        let mut dst: Vec<u8> = vec![];
+
+        assert_eq!(buf.remaining(), 256);
+
+        buf.write_slice(b"hello world");
+        assert_eq!(buf.remaining(), 245);
+        assert_eq!(buf.bytes(), b"hello world");
+
+        let view1 = buf.slice(0, 11);
+        view1.buf().copy_to(&mut dst).unwrap();
+
+        assert_eq!(dst, b"hello world");
+        assert_eq!(view1, buf.slice(0, 11));
+
+        drop(buf);
+        let mut buf = pool.new_append_buf().unwrap();
+        buf.write_slice(b"zomg no no no no");
+
+        assert_eq!(dst, b"hello world");
+    }
+}