ByteBuf.readBytes(...) should use the allocator of the buffer to create the new buffer. Related to [#5093]

Motivation:

ByteBuf.readBytes(...) uses Unpooled.buffer(...) internally which will use a heap ByteBuf and also not able to make use of the allocator which may be pooled. We should better make use of the allocator.

Modifications:

Use the allocator for thenew buffer.

Result:

Take allocator into account when copy bytes.

buffer/src/main/java/io/netty/buffer/AbstractByteBuf.java

@@ -786,8 +786,7 @@ public abstract class AbstractByteBuf extends ByteBuf {
             return Unpooled.EMPTY_BUFFER;
         }
 
-        // Use an unpooled heap buffer because there's no way to mandate a user to free the returned buffer.
-        ByteBuf buf = Unpooled.buffer(length, maxCapacity);
+        ByteBuf buf = alloc().buffer(length, maxCapacity);
         buf.writeBytes(this, readerIndex, length);
         readerIndex += length;
         return buf;

buffer/src/test/java/io/netty/buffer/AbstractByteBufTest.java

@@ -1496,6 +1496,7 @@ public abstract class AbstractByteBufTest {
             // Make sure if it is a copied buffer.
             actualValue.setByte(0, (byte) (actualValue.getByte(0) + 1));
             assertFalse(buffer.getByte(i) == actualValue.getByte(0));
+            actualValue.release();
         }
     }
 
@@ -2980,6 +2981,21 @@ public abstract class AbstractByteBufTest {
         }
     }
 
+    @Test
+    public void testReadBytes() {
+        ByteBuf buffer = newBuffer(8);
+        byte[] bytes = new byte[8];
+        buffer.writeBytes(bytes);
+
+        ByteBuf buffer2 = buffer.readBytes(4);
+        assertSame(buffer.alloc(), buffer2.alloc());
+        assertEquals(4, buffer.readerIndex());
+        assertTrue(buffer.release());
+        assertEquals(0, buffer.refCnt());
+        assertTrue(buffer2.release());
+        assertEquals(0, buffer2.refCnt());
+    }
+
     private void testRefCnt0(final boolean parameter) throws Exception {
         for (int i = 0; i < 10; i++) {
             final CountDownLatch latch = new CountDownLatch(1);

buffer/src/test/java/io/netty/buffer/SlicedByteBufTest.java

@@ -117,7 +117,13 @@ public class SlicedByteBufTest extends AbstractByteBufTest {
     @Test
     @Override
     public void testLittleEndianWithExpand() {
-       // ignore for SlicedByteBuf
+        // ignore for SlicedByteBuf
+    }
+
+    @Test
+    @Override
+    public void testReadBytes() {
+        // ignore for SlicedByteBuf
     }
 
     @Test