* Added LengthFieldBasedFrameDecoder.extractFrame()

* ObjectDecoder overrides extractFrame() to avoid memory copy

src/main/java/org/jboss/netty/handler/codec/frame/LengthFieldBasedFrameDecoder.java

@@ -16,8 +16,10 @@
 package org.jboss.netty.handler.codec.frame;
 
 import org.jboss.netty.buffer.ChannelBuffer;
+import org.jboss.netty.buffer.ChannelBufferFactory;
 import org.jboss.netty.channel.Channel;
 import org.jboss.netty.channel.ChannelHandlerContext;
+import org.jboss.netty.handler.codec.serialization.ObjectDecoder;
 
 /**
  * A decoder that splits the received {@link ChannelBuffer}s dynamically by the
@@ -364,6 +366,33 @@ public class LengthFieldBasedFrameDecoder extends FrameDecoder {
                     "than initialBytesToStrip: " + initialBytesToStrip);
         }
         buffer.skipBytes(initialBytesToStrip);
-        return buffer.readBytes(frameLengthInt - initialBytesToStrip);
+
+        // extract frame
+        int readerIndex = buffer.readerIndex();
+        int actualFrameLength = frameLengthInt - initialBytesToStrip;
+        ChannelBuffer frame = extractFrame(buffer, readerIndex, actualFrameLength);
+        buffer.readerIndex(readerIndex + actualFrameLength);
+        return frame;
+    }
+
+    /**
+     * Extract the sub-region of the specified buffer. This method is called by
+     * {@link #decode(ChannelHandlerContext, Channel, ChannelBuffer)} for each
+     * frame.  The default implementation returns a copy of the sub-region.
+     * For example, you could override this method to use an alternative
+     * {@link ChannelBufferFactory}.
+     * <p>
+     * If you are sure that the frame and its content are not accessed after
+     * the current {@link #decode(ChannelHandlerContext, Channel, ChannelBuffer)}
+     * call returns, you can even avoid memory copy by returning the sliced
+     * sub-region (i.e. <tt>return buffer.slice(index, length)</tt>).
+     * It's often useful when you convert the extracted frame into an object.
+     * Refer to the source code of {@link ObjectDecoder} to see how this method
+     * is overridden to avoid memory copy.
+     */
+    protected ChannelBuffer extractFrame(ChannelBuffer buffer, int index, int length) {
+        ChannelBuffer frame = buffer.factory().getBuffer(length);
+        frame.writeBytes(buffer, index, length);
+        return frame;
     }
 }

src/main/java/org/jboss/netty/handler/codec/serialization/ObjectDecoder.java

@@ -94,4 +94,9 @@ public class ObjectDecoder extends LengthFieldBasedFrameDecoder {
         return new CompactObjectInputStream(
                 new ChannelBufferInputStream(frame), classLoader).readObject();
     }
+
+    @Override
+    protected ChannelBuffer extractFrame(ChannelBuffer buffer, int index, int length) {
+        return buffer.slice(index, length);
+    }
 }