Provide a way to implement an ChannelInbound/OutboundMessageHandler conveniently without extending an adapter class

- Add ChannelHandlerUtil and move the core logic of ChannelInbound/OutboundMessageHandler to ChannelHandlerUtil
- Add ChannelHandlerUtil.SingleInbound/OutboundMessageHandler and make ChannelInbound/OutboundMessageHandlerAdapter implement them.  This is a backward incompatible change because it forces all handler methods to be public (was protected previously)
- Fixes: #1119

codec-http/src/main/java/io/netty/handler/codec/http/HttpRequestEncoder.java

@@ -28,7 +28,7 @@ public class HttpRequestEncoder extends HttpObjectEncoder<HttpRequest> {
     private static final char SLASH = '/';
 
     @Override
-    protected boolean acceptOutboundMessage(Object msg) throws Exception {
+    public boolean acceptOutboundMessage(Object msg) throws Exception {
         return super.acceptOutboundMessage(msg) && !(msg instanceof HttpResponse);
     }
 

codec-http/src/main/java/io/netty/handler/codec/http/HttpResponseEncoder.java

@@ -27,7 +27,7 @@ import static io.netty.handler.codec.http.HttpConstants.*;
 public class HttpResponseEncoder extends HttpObjectEncoder<HttpResponse> {
 
     @Override
-    protected boolean acceptOutboundMessage(Object msg) throws Exception {
+    public boolean acceptOutboundMessage(Object msg) throws Exception {
         return super.acceptOutboundMessage(msg) && !(msg instanceof HttpRequest);
     }
 

codec/src/main/java/io/netty/handler/codec/MessageToByteEncoder.java

@@ -41,7 +41,7 @@ import io.netty.channel.ChannelOutboundMessageHandlerAdapter;
 public abstract class MessageToByteEncoder<I> extends ChannelOutboundMessageHandlerAdapter<I> {
 
     @Override
-    protected void flush(ChannelHandlerContext ctx, I msg) throws Exception {
+    public void flush(ChannelHandlerContext ctx, I msg) throws Exception {
         try {
             encode(ctx, msg, ctx.nextOutboundByteBuffer());
         } catch (CodecException e) {

codec/src/main/java/io/netty/handler/codec/MessageToMessageDecoder.java

@@ -45,7 +45,7 @@ import io.netty.channel.ChannelInboundMessageHandlerAdapter;
 public abstract class MessageToMessageDecoder<I> extends ChannelInboundMessageHandlerAdapter<I> {
 
     @Override
-    protected final void messageReceived(ChannelHandlerContext ctx, I msg) throws Exception {
+    public final void messageReceived(ChannelHandlerContext ctx, I msg) throws Exception {
         ctx.nextInboundMessageBuffer().unfoldAndAdd(decode(ctx, msg));
     }
 

codec/src/main/java/io/netty/handler/codec/MessageToMessageEncoder.java

@@ -43,7 +43,7 @@ import io.netty.channel.ChannelOutboundMessageHandlerAdapter;
 public abstract class MessageToMessageEncoder<I> extends ChannelOutboundMessageHandlerAdapter<I> {
 
     @Override
-    protected final void flush(ChannelHandlerContext ctx, I msg) throws Exception {
+    public final void flush(ChannelHandlerContext ctx, I msg) throws Exception {
         try {
             ctx.nextOutboundMessageBuffer().unfoldAndAdd(encode(ctx, msg));
         } catch (CodecException e) {

codec/src/main/java/io/netty/handler/codec/bytes/ByteArrayEncoder.java

@@ -60,7 +60,7 @@ public class ByteArrayEncoder extends ChannelOutboundMessageHandlerAdapter<byte[
     }
 
     @Override
-    protected void flush(ChannelHandlerContext ctx, byte[] msg) throws Exception {
+    public void flush(ChannelHandlerContext ctx, byte[] msg) throws Exception {
         if (msg.length == 0) {
             return;
         }

codec/src/main/java/io/netty/handler/codec/string/StringEncoder.java

@@ -76,7 +76,7 @@ public class StringEncoder extends ChannelOutboundMessageHandlerAdapter<CharSequ
     }
 
     @Override
-    protected void flush(ChannelHandlerContext ctx, CharSequence msg) throws Exception {
+    public void flush(ChannelHandlerContext ctx, CharSequence msg) throws Exception {
         ByteBuf encoded = Unpooled.copiedBuffer(msg, charset);
 
         switch (nextBufferType) {

example/src/main/java/io/netty/example/http/snoop/HttpSnoopServerHandler.java

@@ -190,7 +190,7 @@ public class HttpSnoopServerHandler extends ChannelInboundMessageHandlerAdapter<
     }
 
     @Override
-    protected void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
+    public void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
         ctx.flush();
     }
 

example/src/main/java/io/netty/example/http/websocketx/autobahn/AutobahnServerHandler.java

@@ -110,7 +110,7 @@ public class AutobahnServerHandler extends ChannelInboundMessageHandlerAdapter<O
     }
 
     @Override
-    protected void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
+    public void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
         if (handshaker != null) {
             ctx.flush().addListener(ChannelFutureListener.CLOSE_ON_FAILURE);
         }

example/src/main/java/io/netty/example/rxtx/RxtxClientHandler.java

@@ -26,7 +26,7 @@ public class RxtxClientHandler extends ChannelInboundMessageHandlerAdapter<Strin
     }
 
     @Override
-    protected void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception {
+    public void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception {
         if ("OK".equals(msg)) {
             System.out.println("Serial port responded to AT");
         } else {

example/src/main/java/io/netty/example/udt/echo/message/MsgEchoClientHandler.java

@@ -68,7 +68,7 @@ public class MsgEchoClientHandler extends
     }
 
     @Override
-    protected void messageReceived(final ChannelHandlerContext ctx,
+    public void messageReceived(final ChannelHandlerContext ctx,
             final UdtMessage message) throws Exception {
         final ByteBuf byteBuf = message.data();
         meter.mark(byteBuf.readableBytes());

example/src/main/java/io/netty/example/udt/echo/message/MsgEchoServerHandler.java

@@ -47,7 +47,7 @@ public class MsgEchoServerHandler extends
     }
 
     @Override
-    protected void messageReceived(final ChannelHandlerContext ctx,
+    public void messageReceived(final ChannelHandlerContext ctx,
             final UdtMessage message) throws Exception {
         final MessageBuf<Object> out = ctx.nextOutboundMessageBuffer();
         out.add(message);

example/src/main/java/io/netty/example/udt/echo/rendevous/MsgEchoPeerHandler.java

@@ -68,7 +68,7 @@ public class MsgEchoPeerHandler extends
     }
 
     @Override
-    protected void messageReceived(final ChannelHandlerContext ctx,
+    public void messageReceived(final ChannelHandlerContext ctx,
             final UdtMessage message) throws Exception {
         final ByteBuf byteBuf = message.data();
         meter.mark(byteBuf.readableBytes());

testsuite/src/test/java/io/netty/testsuite/transport/socket/SocketStartTlsTest.java

@@ -160,7 +160,7 @@ public class SocketStartTlsTest extends AbstractSocketTest {
         }
 
         @Override
-        protected void messageReceived(final ChannelHandlerContext ctx, String msg) throws Exception {
+        public void messageReceived(final ChannelHandlerContext ctx, String msg) throws Exception {
             if ("StartTlsResponse".equals(msg)) {
                 ctx.pipeline().addAfter("logger", "ssl", sslHandler);
                 handshakeFuture = sslHandler.handshake();
@@ -202,7 +202,7 @@ public class SocketStartTlsTest extends AbstractSocketTest {
         }
 
         @Override
-        protected void messageReceived(final ChannelHandlerContext ctx, String msg) throws Exception {
+        public void messageReceived(final ChannelHandlerContext ctx, String msg) throws Exception {
             if ("StartTlsRequest".equals(msg)) {
                 ctx.pipeline().addAfter("logger", "ssl", sslHandler);
                 ctx.write("StartTlsResponse\n");

transport-sctp/src/main/java/io/netty/handler/codec/sctp/SctpInboundByteStreamHandler.java

@@ -40,7 +40,7 @@ public class SctpInboundByteStreamHandler extends ChannelInboundMessageHandlerAd
     }
 
     @Override
-    protected final boolean acceptInboundMessage(Object msg) throws Exception {
+    public final boolean acceptInboundMessage(Object msg) throws Exception {
         if (super.acceptInboundMessage(msg)) {
             return acceptInboundMessage((SctpMessage) msg);
         }
@@ -52,7 +52,7 @@ public class SctpInboundByteStreamHandler extends ChannelInboundMessageHandlerAd
     }
 
     @Override
-    protected void messageReceived(ChannelHandlerContext ctx, SctpMessage msg) throws Exception {
+    public void messageReceived(ChannelHandlerContext ctx, SctpMessage msg) throws Exception {
         if (!msg.isComplete()) {
             throw new CodecException(String.format("Received SctpMessage is not complete, please add %s in the " +
                     "pipeline before this handler", SctpMessageCompletionHandler.class.getSimpleName()));

transport-sctp/src/main/java/io/netty/handler/codec/sctp/SctpMessageCompletionHandler.java

@@ -36,13 +36,13 @@ public class SctpMessageCompletionHandler extends ChannelInboundMessageHandlerAd
     private boolean assembled;
 
     @Override
-    protected boolean beginMessageReceived(ChannelHandlerContext ctx) throws Exception {
+    public boolean beginMessageReceived(ChannelHandlerContext ctx) throws Exception {
         assembled = false;
         return super.beginMessageReceived(ctx);
     }
 
     @Override
-    protected void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
+    public void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
         if (assembled) {
             assembled = false;
             ctx.fireInboundBufferUpdated();
@@ -51,7 +51,7 @@ public class SctpMessageCompletionHandler extends ChannelInboundMessageHandlerAd
     }
 
     @Override
-    protected void messageReceived(ChannelHandlerContext ctx, SctpMessage msg) throws Exception {
+    public void messageReceived(ChannelHandlerContext ctx, SctpMessage msg) throws Exception {
 
         final ByteBuf byteBuf = msg.data();
         final int protocolIdentifier = msg.protocolIdentifier();

transport-udt/src/test/java/io/netty/test/udt/util/EchoMessageHandler.java

@@ -75,7 +75,7 @@ public class EchoMessageHandler extends
     }
 
     @Override
-    protected void messageReceived(final ChannelHandlerContext ctx, final UdtMessage message) throws Exception {
+    public void messageReceived(final ChannelHandlerContext ctx, final UdtMessage message) throws Exception {
 
         final ByteBuf byteBuf = message.data();
 

transport/src/main/java/io/netty/channel/ChannelHandlerUtil.java

@@ -0,0 +1,227 @@
+/*
+ * Copyright 2013 The Netty Project
+ *
+ * The Netty Project licenses this file to you under the Apache License,
+ * version 2.0 (the "License"); you may not use this file except in compliance
+ * with the License. You may obtain a copy of the License at:
+ *
+ *   http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
+ * WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
+ * License for the specific language governing permissions and limitations
+ * under the License.
+ */
+
+package io.netty.channel;
+
+import io.netty.buffer.BufUtil;
+import io.netty.buffer.MessageBuf;
+import io.netty.util.Signal;
+import io.netty.util.internal.logging.InternalLogger;
+import io.netty.util.internal.logging.InternalLoggerFactory;
+
+public final class ChannelHandlerUtil {
+
+    public static final Signal ABORT = new Signal(ChannelHandlerUtil.class.getName() + ".ABORT");
+
+    private static final InternalLogger logger = InternalLoggerFactory.getInstance(ChannelHandlerUtil.class);
+
+    public static <T> void handleInboundBufferUpdated(
+            ChannelHandlerContext ctx, SingleInboundMessageHandler<T> handler) throws Exception {
+        MessageBuf<Object> in = ctx.inboundMessageBuffer();
+        if (in.isEmpty() || !handler.beginMessageReceived(ctx)) {
+            return;
+        }
+
+        MessageBuf<Object> out = ctx.nextInboundMessageBuffer();
+        int oldOutSize = out.size();
+        try {
+            for (;;) {
+                Object msg = in.poll();
+                if (msg == null) {
+                    break;
+                }
+
+                if (!handler.acceptInboundMessage(msg)) {
+                    out.add(msg);
+                    continue;
+                }
+
+                @SuppressWarnings("unchecked")
+                T imsg = (T) msg;
+                try {
+                    handler.messageReceived(ctx, imsg);
+                } finally {
+                    BufUtil.release(imsg);
+                }
+            }
+        } catch (Signal abort) {
+            abort.expect(ABORT);
+        } finally {
+            if (oldOutSize != out.size()) {
+                ctx.fireInboundBufferUpdated();
+            }
+
+            handler.endMessageReceived(ctx);
+        }
+    }
+
+    public static <T> void handleFlush(
+            ChannelHandlerContext ctx, ChannelPromise promise,
+            SingleOutboundMessageHandler<T> handler) throws Exception {
+
+        handleFlush(ctx, promise, true, handler);
+    }
+
+    public static <T> void handleFlush(
+            ChannelHandlerContext ctx, ChannelPromise promise, boolean closeOnFailedFlush,
+            SingleOutboundMessageHandler<T> handler) throws Exception {
+
+        MessageBuf<Object> in = ctx.outboundMessageBuffer();
+        MessageBuf<Object> out = null;
+
+        final int inSize = in.size();
+        if (inSize == 0) {
+            ctx.flush(promise);
+            return;
+        }
+
+        int processed = 0;
+        try {
+            handler.beginFlush(ctx);
+            for (;;) {
+                Object msg = in.poll();
+                if (msg == null) {
+                    break;
+                }
+
+                if (!handler.acceptOutboundMessage(msg)) {
+                    if (out == null) {
+                        out = ctx.nextOutboundMessageBuffer();
+                    }
+                    out.add(msg);
+                    processed ++;
+                    continue;
+                }
+
+                @SuppressWarnings("unchecked")
+                T imsg = (T) msg;
+                try {
+                    handler.flush(ctx, imsg);
+                    processed ++;
+                } finally {
+                    BufUtil.release(imsg);
+                }
+            }
+        } catch (Throwable t) {
+            PartialFlushException pfe;
+            String msg = processed + " out of " + inSize + " message(s) flushed";
+            if (t instanceof Signal) {
+                Signal abort = (Signal) t;
+                abort.expect(ABORT);
+                pfe = new PartialFlushException("aborted: " + msg);
+            } else {
+                pfe = new PartialFlushException(msg, t);
+            }
+            fail(ctx, promise, closeOnFailedFlush, pfe);
+        }
+
+        try {
+            handler.endFlush(ctx);
+        } catch (Throwable t) {
+            if (promise.isDone()) {
+                logger.warn("endFlush() raised a masked exception due to failed flush().", t);
+            } else {
+                fail(ctx, promise, closeOnFailedFlush, t);
+            }
+        }
+
+        if (!promise.isDone()) {
+            ctx.flush(promise);
+        }
+    }
+
+    private static void fail(
+            ChannelHandlerContext ctx, ChannelPromise promise, boolean closeOnFailedFlush, Throwable cause) {
+        promise.setFailure(cause);
+        if (closeOnFailedFlush) {
+            ctx.close();
+        }
+    }
+
+    private ChannelHandlerUtil() { }
+
+    public interface SingleInboundMessageHandler<T> {
+        /**
+         * Returns {@code true} if and only if the specified message can be handled by this handler.
+         *
+         * @param msg the message
+         */
+        boolean acceptInboundMessage(Object msg) throws Exception;
+
+        /**
+         * Will get notified once {@link #inboundBufferUpdated(ChannelHandlerContext)} was called.
+         *
+         * If this method returns {@code false} no further processing of the {@link MessageBuf}
+         * will be done until the next call of {@link #inboundBufferUpdated(ChannelHandlerContext)}.
+         *
+         * This will return {@code true} by default, and may get overriden by sub-classes for
+         * special handling.
+         *
+         * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
+         */
+        boolean beginMessageReceived(ChannelHandlerContext ctx) throws Exception;
+
+        /**
+         * Is called once a message was received.
+         *
+         * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
+         * @param msg           the message to handle
+         */
+        void messageReceived(ChannelHandlerContext ctx, T msg) throws Exception;
+
+        /**
+         * Is called when {@link #messageReceived(ChannelHandlerContext, Object)} returns.
+         *
+         * Super-classes may-override this for special handling.
+         *
+         * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
+         */
+        void endMessageReceived(ChannelHandlerContext ctx) throws Exception;
+    }
+
+    public interface SingleOutboundMessageHandler<T> {
+        /**
+         * Returns {@code true} if and only if the specified message can be handled by this handler.
+         *
+         * @param msg the message
+         */
+        boolean acceptOutboundMessage(Object msg) throws Exception;
+
+        /**
+         * Will get notified once {@link #flush(ChannelHandlerContext, ChannelPromise)} was called.
+         *
+         * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
+         */
+        void beginFlush(ChannelHandlerContext ctx) throws Exception;
+
+        /**
+         * Is called once a message is being flushed.
+         *
+         * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
+         * @param msg           the message to handle
+         */
+        void flush(ChannelHandlerContext ctx, T msg) throws Exception;
+
+        /**
+         * Is called when {@link #flush(ChannelHandlerContext, ChannelPromise)} returns.
+         *
+         * Super-classes may-override this for special handling.
+         *
+         * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
+         */
+        void endFlush(ChannelHandlerContext ctx) throws Exception;
+    }
+}

transport/src/main/java/io/netty/channel/ChannelInboundMessageHandlerAdapter.java

@@ -15,9 +15,9 @@
  */
 package io.netty.channel;
 
-import io.netty.buffer.BufUtil;
 import io.netty.buffer.MessageBuf;
 import io.netty.buffer.Unpooled;
+import io.netty.channel.ChannelHandlerUtil.SingleInboundMessageHandler;
 import io.netty.util.Signal;
 import io.netty.util.internal.TypeParameterMatcher;
 
@@ -44,12 +44,13 @@ import io.netty.util.internal.TypeParameterMatcher;
  * @param <I>   The type of the messages to handle
  */
 public abstract class ChannelInboundMessageHandlerAdapter<I>
-        extends ChannelStateHandlerAdapter implements ChannelInboundMessageHandler<I> {
+        extends ChannelStateHandlerAdapter
+        implements ChannelInboundMessageHandler<I>, SingleInboundMessageHandler<I> {
 
     /**
      * Thrown by {@link #messageReceived(ChannelHandlerContext, Object)} to abort message processing.
      */
-    protected static final Signal ABORT = new Signal(ChannelInboundMessageHandlerAdapter.class.getName() + ".ABORT");
+    protected static final Signal ABORT = ChannelHandlerUtil.ABORT;
 
     private final TypeParameterMatcher msgMatcher;
 
@@ -69,86 +70,21 @@ public abstract class ChannelInboundMessageHandlerAdapter<I>
 
     @Override
     public final void inboundBufferUpdated(ChannelHandlerContext ctx) throws Exception {
-        MessageBuf<Object> in = ctx.inboundMessageBuffer();
-        if (in.isEmpty() || !beginMessageReceived(ctx)) {
-            return;
-        }
-
-        MessageBuf<Object> out = ctx.nextInboundMessageBuffer();
-        int oldOutSize = out.size();
-        try {
-            for (;;) {
-                Object msg = in.poll();
-                if (msg == null) {
-                    break;
-                }
-
-                if (!acceptInboundMessage(msg)) {
-                    out.add(msg);
-                    continue;
-                }
-
-                @SuppressWarnings("unchecked")
-                I imsg = (I) msg;
-                try {
-                    messageReceived(ctx, imsg);
-                } finally {
-                    BufUtil.release(imsg);
-                }
-            }
-        } catch (Signal abort) {
-            abort.expect(ABORT);
-        } finally {
-            if (oldOutSize != out.size()) {
-                ctx.fireInboundBufferUpdated();
-            }
-
-            endMessageReceived(ctx);
-        }
+        ChannelHandlerUtil.handleInboundBufferUpdated(ctx, this);
     }
 
-    /**
-     * Returns {@code true} if and only if the specified message can be handled by this handler.
-     *
-     * @param msg the message
-     */
-    protected boolean acceptInboundMessage(Object msg) throws Exception {
+    @Override
+    public boolean acceptInboundMessage(Object msg) throws Exception {
         return msgMatcher.match(msg);
     }
 
-    /**
-     * Will get notified once {@link #inboundBufferUpdated(ChannelHandlerContext)} was called.
-     *
-     * If this method returns {@code false} no further processing of the {@link MessageBuf}
-     * will be done until the next call of {@link #inboundBufferUpdated(ChannelHandlerContext)}.
-     *
-     * This will return {@code true} by default, and may get overriden by sub-classes for
-     * special handling.
-     *
-     * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
-     */
-    protected boolean beginMessageReceived(
-            @SuppressWarnings("UnusedParameters") ChannelHandlerContext ctx) throws Exception {
+    @Override
+    public boolean beginMessageReceived(ChannelHandlerContext ctx) throws Exception {
         return true;
     }
 
-    /**
-     * Is called once a message was received.
-     *
-     * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
-     * @param msg           the message to handle
-     */
-    protected abstract void messageReceived(ChannelHandlerContext ctx, I msg) throws Exception;
-
-    /**
-     * Is called when {@link #messageReceived(ChannelHandlerContext, Object)} returns.
-     *
-     * Super-classes may-override this for special handling.
-     *
-     * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
-     */
-    protected void endMessageReceived(
-            @SuppressWarnings("UnusedParameters") ChannelHandlerContext ctx) throws Exception {
+    @Override
+    public void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
         // NOOP
     }
 }

transport/src/main/java/io/netty/channel/ChannelOutboundMessageHandlerAdapter.java

@@ -15,12 +15,11 @@
  */
 package io.netty.channel;
 
-import io.netty.buffer.BufUtil;
 import io.netty.buffer.MessageBuf;
 import io.netty.buffer.Unpooled;
+import io.netty.channel.ChannelHandlerUtil.SingleOutboundMessageHandler;
 import io.netty.util.Signal;
 import io.netty.util.internal.TypeParameterMatcher;
-import io.netty.util.internal.logging.InternalLoggerFactory;
 
 /**
  * Abstract base class which handles messages of a specific type.
@@ -28,12 +27,13 @@ import io.netty.util.internal.logging.InternalLoggerFactory;
  * @param <I>   The type of the messages to handle
  */
 public abstract class ChannelOutboundMessageHandlerAdapter<I>
-        extends ChannelOperationHandlerAdapter implements ChannelOutboundMessageHandler<I> {
+        extends ChannelOperationHandlerAdapter
+        implements ChannelOutboundMessageHandler<I>, SingleOutboundMessageHandler<I> {
 
     /**
      * Thrown by {@link #flush(ChannelHandlerContext, Object)} to abort message processing.
      */
-    protected static final Signal ABORT = new Signal(ChannelOutboundMessageHandlerAdapter.class.getName() + ".ABORT");
+    protected static final Signal ABORT = ChannelHandlerUtil.ABORT;
 
     private final TypeParameterMatcher msgMatcher;
     private boolean closeOnFailedFlush = true;
@@ -60,110 +60,19 @@ public abstract class ChannelOutboundMessageHandlerAdapter<I>
         ctx.outboundMessageBuffer().release();
     }
 
-    /**
-     * Returns {@code true} if and only if the specified message can be handled by this handler.
-     *
-     * @param msg the message
-     */
-    protected boolean acceptOutboundMessage(Object msg) throws Exception {
+    @Override
+    public final void flush(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
+        ChannelHandlerUtil.handleFlush(ctx, promise, isCloseOnFailedFlush(), this);
+    }
+
+    @Override
+    public boolean acceptOutboundMessage(Object msg) throws Exception {
         return msgMatcher.match(msg);
     }
 
     @Override
-    public final void flush(ChannelHandlerContext ctx, ChannelPromise promise) throws Exception {
-        MessageBuf<Object> in = ctx.outboundMessageBuffer();
-        MessageBuf<Object> out = null;
+    public void beginFlush(ChannelHandlerContext ctx) throws Exception { }
 
-        final int inSize = in.size();
-        if (inSize == 0) {
-            ctx.flush(promise);
-            return;
-        }
-
-        int processed = 0;
-        try {
-            beginFlush(ctx);
-            for (;;) {
-                Object msg = in.poll();
-                if (msg == null) {
-                    break;
-                }
-
-                if (!acceptOutboundMessage(msg)) {
-                    if (out == null) {
-                        out = ctx.nextOutboundMessageBuffer();
-                    }
-                    out.add(msg);
-                    processed ++;
-                    continue;
-                }
-
-                @SuppressWarnings("unchecked")
-                I imsg = (I) msg;
-                try {
-                    flush(ctx, imsg);
-                    processed ++;
-                } finally {
-                    BufUtil.release(imsg);
-                }
-            }
-        } catch (Throwable t) {
-            PartialFlushException pfe;
-            String msg = processed + " out of " + inSize + " message(s) flushed";
-            if (t instanceof Signal) {
-                Signal abort = (Signal) t;
-                abort.expect(ABORT);
-                pfe = new PartialFlushException("aborted by " + getClass().getSimpleName() + ": " + msg);
-            } else {
-                pfe = new PartialFlushException(msg, t);
-            }
-            fail(ctx, promise, pfe);
-        }
-
-        try {
-            endFlush(ctx);
-        } catch (Throwable t) {
-            if (promise.isDone()) {
-                InternalLoggerFactory.getInstance(getClass()).warn(
-                        "endFlush() raised a masked exception due to failed flush().", t);
-            } else {
-                fail(ctx, promise, t);
-            }
-        }
-
-        if (!promise.isDone()) {
-            ctx.flush(promise);
-        }
-    }
-
-    private void fail(ChannelHandlerContext ctx, ChannelPromise promise, Throwable cause) {
-        promise.setFailure(cause);
-        if (isCloseOnFailedFlush()) {
-            ctx.close();
-        }
-    }
-
-    /**
-     * Will get notified once {@link #flush(ChannelHandlerContext, ChannelPromise)} was called.
-     *
-     * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
-     */
-    protected void beginFlush(@SuppressWarnings("UnusedParameters") ChannelHandlerContext ctx) throws Exception { }
-
-    /**
-     * Is called once a message is being flushed.
-     *
-     * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
-     * @param msg           the message to handle
-     */
-    protected abstract void flush(ChannelHandlerContext ctx, I msg) throws Exception;
-
-    /**
-     * Is called when {@link #flush(ChannelHandlerContext, ChannelPromise)} returns.
-     *
-     * Super-classes may-override this for special handling.
-     *
-     * @param ctx           the {@link ChannelHandlerContext} which this {@link ChannelHandler} belongs to
-     */
-    protected void endFlush(@SuppressWarnings("UnusedParameters") ChannelHandlerContext ctx) throws Exception { }
+    @Override
+    public void endFlush(ChannelHandlerContext ctx) throws Exception { }
 }

transport/src/test/java/io/netty/channel/DefaultChannelPipelineTest.java

@@ -39,12 +39,12 @@ public class DefaultChannelPipelineTest {
         final DefaultChannelPipeline pipeline = new DefaultChannelPipeline(channel);
         pipeline.addLast(new ChannelInboundMessageHandlerAdapter<Object>() {
             @Override
-            protected void messageReceived(ChannelHandlerContext ctx, Object msg) throws Exception {
+            public void messageReceived(ChannelHandlerContext ctx, Object msg) throws Exception {
                 forwarded.set(ctx.nextInboundMessageBuffer().add(msg));
             }
 
             @Override
-            protected void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
+            public void endMessageReceived(ChannelHandlerContext ctx) throws Exception {
                 ctx.fireInboundBufferUpdated();
             }
         });
@@ -178,13 +178,13 @@ public class DefaultChannelPipelineTest {
         boolean called;
 
         @Override
-        protected boolean acceptInboundMessage(Object msg) throws Exception {
+        public boolean acceptInboundMessage(Object msg) throws Exception {
             called = true;
             return super.acceptInboundMessage(msg);
         }
 
         @Override
-        protected void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception {
+        public void messageReceived(ChannelHandlerContext ctx, String msg) throws Exception {
             fail();
         }
     }