ByteBufferCallbackAccumulator.writeTo should do buffer flipping

Signed-off-by: Lachlan Roberts <lachlan@webtide.com>

jetty-io/src/main/java/org/eclipse/jetty/io/ByteBufferCallbackAccumulator.java

@@ -66,21 +66,23 @@ public class ByteBufferCallbackAccumulator
 
         byte[] bytes = new byte[length];
         ByteBuffer buffer = BufferUtil.toBuffer(bytes);
-        BufferUtil.clearToFill(buffer);
+        BufferUtil.clear(buffer);
         writeTo(buffer);
         return bytes;
     }
 
     public void writeTo(ByteBuffer buffer)
     {
-        if (buffer.remaining() < _length)
+        if (BufferUtil.space(buffer) < _length)
             throw new IllegalArgumentException("not enough buffer space remaining");
 
+        int pos = BufferUtil.flipToFill(buffer);
         for (Entry entry : _entries)
         {
             buffer.put(entry.buffer);
             entry.callback.succeeded();
         }
+        BufferUtil.flipToFlush(buffer, pos);
         _entries.clear();
         _length = 0;
     }

jetty-websocket/websocket-core-common/src/main/java/org/eclipse/jetty/websocket/core/internal/messages/ByteBufferMessageSink.java

@@ -85,9 +85,7 @@ public class ByteBufferMessageSink extends AbstractMessageSink
             {
                 ByteBufferPool bufferPool = session.getByteBufferPool();
                 ByteBuffer buffer = bufferPool.acquire(out.getLength(), false);
-                BufferUtil.clearToFill(buffer);
                 out.writeTo(buffer);
-                BufferUtil.flipToFlush(buffer, 0);
 
                 try
                 {