Whether this is a bug or missing feature is open to interpretation ... however if we do want to provide this functionality I don't think we should change the existing default behavior for `IdleStateHandler` for backwards compatibility reasons.

`ChannelOutboundBuffer` may be able to provide the tools we need...here are some random thoughts:
- The ChannelOutboundBuffer provides a counter of "pending bytes" but it is currently only updated at the "message" (aka `ByteBuf`, `FileRegion`, etc...) granularity). Even if this was updated at a finer granularity it will not work to answer the "has something changed" between successive calls (ABA situation may occur).
- An alternative approach of "save a reference to the head of the queue, and current size then check these changed after the timeout" may also be problematic because we pool objects (again ABA). However if we couple this second approach with the completion of the future we may be able to overcome this ABA type problem. The completion of the future would mean we are now looking at a "different" object (even if it happens to be the same object because of pooling).

It would be good to explore if we can pull this off with existing tools rather than add explicit support for it in the core (unless we think this will drive other useful features). @rkapsi @Scottmitch why can't this be fixed by using a `ChannelProgressivePromise` ? @normanmaurer it'd work at the expense of garbage. `IdleStateHandler` (or some other class) would have to create and swap out the promise in the `write(...)` method and a listener that will notify the original promise that was passed into `write(...)`. A technique I'd be fine using in my project where I know the nature of the ChannelPipeline. Adding something like that to Netty could be risky. Ideally I'd like to avoid the garbage though.

I think for pure idless detection there is a difference in measuring "change" and "progress". And then there's also overall progress and progress in the context of a `write(...)`. The `ChannelProgressivePromise` covers the latter but it comes at an expense. I'd be happy with an overall progress indicator (a `long` value that says: "This Channel has transferred this many bytes in its lifetime"). Lastly something that indicates change would be fine too (for this purpose) but I don't think it'd be a good API addition.



 @rkapsi - does the approach I mentioned in https://github.com/netty/netty/issues/6150#issuecomment-268414509 work for you? @Scottmitch - I think No. 1 wouldn't work for the reason you described. No. 2 should work. We'd get the `ChannelOutboundBuffer` via `Channel#unsafe()`? > We'd get the ChannelOutboundBuffer via Channel#unsafe()?

Yip. Yah the second bullet is the approach I was referring to ... the first bullet was just to clarify that only using the existing "pending bytes" counter won't be sufficient. @Scottmitch want me to look into this? I think it can be added to `IdleStateHandler` with a configuration option (i.e. default will retain the current behavior). @rkapsi - Sounds good to me. Thanks!
maybe not when this method is currently called but it is possible the `ChannelOutboundBuffer` may be `null` (e.g. channel is closed) .. consider protecting against this or adding a comment as to why it isn't necessary. protect against `buf == null`. nit: put on previous line? consider just setting the variable unconditionally. conditionals can be expensive and this variable is not volatile. can we make this method always return NS granularity and do the conversion in the unit tests? use `channel.finishAndReleaseAll();` instead for `EmbeddedChannel`. use `channel.finishAndReleaseAll();` instead for `EmbeddedChannel`. use `channel.finishAndReleaseAll();` instead for `EmbeddedChannel`. we should take care to release any object returned by `channel.consume()` hah mathematical unit test proof done I guess Can be done but is there a downside with the current impl? `TimeUnit#convert(...)` will be a ~noop if source and destination units are the same (which is the case inside the IdleStateHandler class). My preference is to keep the production code minimal, and not have to think/worry about implementation details and/or what optimizations may or may not be made if possible. In this case it looks like the extra complexity can be isolated in the unit tests and thus simplify the production code, right? Certainly and fair enough. I'm personally of the opinion that time without units is among some of the most useless pieces of information one can have in computer programs and I never write code without stating it explicitly (encoding the unit in the field/method name being my least favorite but still better than noting stated at all). Agreed that time (or values in general) without units can be error prone. However not accepting `TimeUnit` as an argument doesn't mean you cannot indicate the units in other ways (as you indicated). For example in the function name (e.g. `timeNanos()`, `nanoTime()`) and javadocs. This function is also "internal" to this class and it not intended to be part of the public API of this class so the risk of confusion due to units is lower in this case. This is effectively equivalent to `System.nanoTime()`. Done.
Detecting actual Channels idleness vs. slowness
I don't know if you'd consider it a missing feature or a bug but there appears to be no effective way of measuring write idleness. The natural choice is to use Netty's own `IdleStateHandler` but it may not work as expected for `write()`. For the sake of simplicity I'm providing a HTTP example but we encountered it with H2.

Basically... The user's (our) intention is to close an idle connection. The `IdleStateHandler` uses the write's `ChannelFuture` to determine if a client is idle but it doesn't take into consideration that the client might be just slow and we've just thrown a large `ByteBuf` at it. I think we ran into this with H2 due to things like `CoalescingBufferQueue` which try to aggregate multiple writes into a single one.

The repro is very simple. You just need to throttle your client a little bit. I'm using Chrome's [built-in](http://imgur.com/a/WfcZQ) throtting feature for it. On the server side (the code below) we want to close the connection if the client appears to be idle for 30 seconds.

The problem is that `IdleStateHandler` will make a pure binary decision on the completeness of the `ChannelFuture` vs. taking actual progression into consideration and it appears there is no API for it.

I haven't looked at all `Channel` implementations but `NioSocketChannel` and `EpollSocketChannel` (via `AbstractEpollStreamChannel`) do have knowledge about the number of bytes written in each cycle. An easy fix could be that channel's sum up these values in a `volatile long` field and expose it to the user. Or it could be a simple `++` for each write cycle where more than 1 byte was written to the underlying socket. The user could then use it to assess whether or not any or some progress was made between two calls.
 

```java
public class IdleChannelTest {

  private static final int PORT = 8080;
  
  public static void main(String[] args) throws Exception {
    
    ChannelHandler handler = new ChannelInitializer<Channel>() {
      @Override
      protected void initChannel(Channel ch) throws Exception {
        ChannelPipeline pipeline = ch.pipeline();
        
        pipeline.addLast(new HttpServerCodec());
        pipeline.addLast(new IdleStateHandler(0L, 0L, 30L, TimeUnit.SECONDS));
        pipeline.addLast(new HttpRequestAndIdleHandler());
      }
    };
    
    EventLoopGroup group = new NioEventLoopGroup();
    
    try {
      ServerBootstrap bootstrap = new ServerBootstrap()
          .channel(NioServerSocketChannel.class)
          .group(group)
          .childHandler(handler);
      
      Channel channel = bootstrap.bind(PORT)
          .syncUninterruptibly()
          .channel();
      
      try {
        System.out.println(new Date() + ": http://localhost:" + PORT + "/");
        Thread.sleep(Long.MAX_VALUE);
      } finally {
        channel.close();
      }
    } finally {
      group.shutdownGracefully();
    }
  }
  
  private static class HttpRequestAndIdleHandler extends ChannelInboundHandlerAdapter {

    @Override
    public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
      try {
        if (!(msg instanceof HttpRequest)) {
          return;
        }
        
        HttpRequest request = (HttpRequest)msg;
        
        ByteBuf content = Unpooled.wrappedBuffer(new byte[64*1024*1024]); // 64MB
        FullHttpResponse response = new DefaultFullHttpResponse(
            HttpVersion.HTTP_1_1, HttpResponseStatus.OK, content);
        
        HttpHeaders headers = response.headers();
        headers.set(HttpHeaderNames.CONTENT_LENGTH, content.readableBytes());
        headers.set(HttpHeaderNames.CONTENT_TYPE, "application/octet-stream");
        
        System.out.println(new Date() + ": Received request, writing response: " + ctx.channel() + ", " + request.uri());
        
        ChannelFuture future = ctx.writeAndFlush(response);
        future.addListener(new ChannelFutureListener() {
          @Override
          public void operationComplete(ChannelFuture future) throws Exception {
            System.out.println(new Date() + ": Write complete: " + ctx.channel());
          }
        });
      } finally {
        ReferenceCountUtil.release(msg);
      }
    }

    @Override
    public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
      if (evt instanceof IdleStateEvent) {
        IdleStateEvent event = (IdleStateEvent)evt;
        System.out.println(new Date() + ": Channel is idle, closing it: " + ctx.channel() + ", " + event.state());
        
        ctx.close();
      }
      
      ctx.fireUserEventTriggered(evt);
    }
  }
}
```
handler/src/main/java/io/netty/handler/timeout/IdleStateHandler.java
handler/src/main/java/io/netty/handler/timeout/IdleStateHandler.java
handler/src/test/java/io/netty/handler/timeout/IdleStateHandlerTest.java
diff --git a/handler/src/main/java/io/netty/handler/timeout/IdleStateHandler.java b/handler/src/main/java/io/netty/handler/timeout/IdleStateHandler.java
index 3d2acd11650..6d6229c0e64 100644
--- a/handler/src/main/java/io/netty/handler/timeout/IdleStateHandler.java
+++ b/handler/src/main/java/io/netty/handler/timeout/IdleStateHandler.java
@@ -17,11 +17,13 @@
 
 import io.netty.bootstrap.ServerBootstrap;
 import io.netty.channel.Channel;
+import io.netty.channel.Channel.Unsafe;
 import io.netty.channel.ChannelDuplexHandler;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelInitializer;
+import io.netty.channel.ChannelOutboundBuffer;
 import io.netty.channel.ChannelPromise;
 import io.netty.util.concurrent.EventExecutor;
 
@@ -101,11 +103,12 @@ public class IdleStateHandler extends ChannelDuplexHandler {
     private final ChannelFutureListener writeListener = new ChannelFutureListener() {
         @Override
         public void operationComplete(ChannelFuture future) throws Exception {
-            lastWriteTime = System.nanoTime();
+            lastWriteTime = ticksInNanos();
             firstWriterIdleEvent = firstAllIdleEvent = true;
         }
     };
 
+    private final boolean observeOutput;
     private final long readerIdleTimeNanos;
     private final long writerIdleTimeNanos;
     private final long allIdleTimeNanos;
@@ -124,6 +127,10 @@ public void operationComplete(ChannelFuture future) throws Exception {
     private byte state; // 0 - none, 1 - initialized, 2 - destroyed
     private boolean reading;
 
+    private long lastChangeCheckTimeStamp;
+    private int lastMessageHashCode;
+    private long lastPendingWriteBytes;
+
     /**
      * Creates a new instance firing {@link IdleStateEvent}s.
      *
@@ -149,9 +156,21 @@ public IdleStateHandler(
              TimeUnit.SECONDS);
     }
 
+    /**
+     * @see #IdleStateHandler(boolean, long, long, long, TimeUnit)
+     */
+    public IdleStateHandler(
+            long readerIdleTime, long writerIdleTime, long allIdleTime,
+            TimeUnit unit) {
+        this(false, readerIdleTime, writerIdleTime, allIdleTime, unit);
+    }
+
     /**
      * Creates a new instance firing {@link IdleStateEvent}s.
      *
+     * @param observeOutput
+     *        whether or not the consumption of {@code bytes} should be taken into
+     *        consideration when assessing write idleness. The default is {@code false}.
      * @param readerIdleTime
      *        an {@link IdleStateEvent} whose state is {@link IdleState#READER_IDLE}
      *        will be triggered when no read was performed for the specified
@@ -168,13 +187,15 @@ public IdleStateHandler(
      *        the {@link TimeUnit} of {@code readerIdleTime},
      *        {@code writeIdleTime}, and {@code allIdleTime}
      */
-    public IdleStateHandler(
+    public IdleStateHandler(boolean observeOutput,
             long readerIdleTime, long writerIdleTime, long allIdleTime,
             TimeUnit unit) {
         if (unit == null) {
             throw new NullPointerException("unit");
         }
 
+        this.observeOutput = observeOutput;
+
         if (readerIdleTime <= 0) {
             readerIdleTimeNanos = 0;
         } else {
@@ -269,7 +290,7 @@ public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception
     @Override
     public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
         if ((readerIdleTimeNanos > 0 || allIdleTimeNanos > 0) && reading) {
-            lastReadTime = System.nanoTime();
+            lastReadTime = ticksInNanos();
             reading = false;
         }
         ctx.fireChannelReadComplete();
@@ -297,27 +318,37 @@ private void initialize(ChannelHandlerContext ctx) {
         }
 
         state = 1;
+        initOutputChanged(ctx);
 
-        EventExecutor loop = ctx.executor();
-
-        lastReadTime = lastWriteTime = System.nanoTime();
+        lastReadTime = lastWriteTime = ticksInNanos();
         if (readerIdleTimeNanos > 0) {
-            readerIdleTimeout = loop.schedule(
-                    new ReaderIdleTimeoutTask(ctx),
+            readerIdleTimeout = schedule(ctx, new ReaderIdleTimeoutTask(ctx),
                     readerIdleTimeNanos, TimeUnit.NANOSECONDS);
         }
         if (writerIdleTimeNanos > 0) {
-            writerIdleTimeout = loop.schedule(
-                    new WriterIdleTimeoutTask(ctx),
+            writerIdleTimeout = schedule(ctx, new WriterIdleTimeoutTask(ctx),
                     writerIdleTimeNanos, TimeUnit.NANOSECONDS);
         }
         if (allIdleTimeNanos > 0) {
-            allIdleTimeout = loop.schedule(
-                    new AllIdleTimeoutTask(ctx),
+            allIdleTimeout = schedule(ctx, new AllIdleTimeoutTask(ctx),
                     allIdleTimeNanos, TimeUnit.NANOSECONDS);
         }
     }
 
+    /**
+     * This method is visible for testing!
+     */
+    long ticksInNanos() {
+        return System.nanoTime();
+    }
+
+    /**
+     * This method is visible for testing!
+     */
+    ScheduledFuture<?> schedule(ChannelHandlerContext ctx, Runnable task, long delay, TimeUnit unit) {
+        return ctx.executor().schedule(task, delay, unit);
+    }
+
     private void destroy() {
         state = 2;
 
@@ -355,15 +386,77 @@ protected IdleStateEvent newIdleStateEvent(IdleState state, boolean first) {
             case WRITER_IDLE:
                 return first ? IdleStateEvent.FIRST_WRITER_IDLE_STATE_EVENT : IdleStateEvent.WRITER_IDLE_STATE_EVENT;
             default:
-                throw new Error();
+                throw new IllegalArgumentException("Unhandled: state=" + state + ", first=" + first);
         }
     }
 
-    private final class ReaderIdleTimeoutTask implements Runnable {
+    /**
+     * @see #hasOutputChanged(ChannelHandlerContext, boolean)
+     */
+    private void initOutputChanged(ChannelHandlerContext ctx) {
+        if (observeOutput) {
+            Channel channel = ctx.channel();
+            Unsafe unsafe = channel.unsafe();
+            ChannelOutboundBuffer buf = unsafe.outboundBuffer();
+
+            if (buf != null) {
+                lastMessageHashCode = System.identityHashCode(buf.current());
+                lastPendingWriteBytes = buf.totalPendingWriteBytes();
+            }
+        }
+    }
+
+    /**
+     * Returns {@code true} if and only if the {@link IdleStateHandler} was constructed
+     * with {@link #observeOutput} enabled and there has been an observed change in the
+     * {@link ChannelOutboundBuffer} between two consecutive calls of this method.
+     *
+     * https://github.com/netty/netty/issues/6150
+     */
+    private boolean hasOutputChanged(ChannelHandlerContext ctx, boolean first) {
+        if (observeOutput) {
+
+            // We can take this shortcut if the ChannelPromises that got passed into write()
+            // appear to complete. It indicates "change" on message level and we simply assume
+            // that there's change happening on byte level. If the user doesn't observe channel
+            // writability events then they'll eventually OOME and there's clearly a different
+            // problem and idleness is least of their concerns.
+            if (lastChangeCheckTimeStamp != lastWriteTime) {
+                lastChangeCheckTimeStamp = lastWriteTime;
+
+                // But this applies only if it's the non-first call.
+                if (!first) {
+                    return true;
+                }
+            }
+
+            Channel channel = ctx.channel();
+            Unsafe unsafe = channel.unsafe();
+            ChannelOutboundBuffer buf = unsafe.outboundBuffer();
+
+            if (buf != null) {
+                int messageHashCode = System.identityHashCode(buf.current());
+                long pendingWriteBytes = buf.totalPendingWriteBytes();
+
+                if (messageHashCode != lastMessageHashCode || pendingWriteBytes != lastPendingWriteBytes) {
+                    lastMessageHashCode = messageHashCode;
+                    lastPendingWriteBytes = pendingWriteBytes;
+
+                    if (!first) {
+                        return true;
+                    }
+                }
+            }
+        }
+
+        return false;
+    }
+
+    private abstract static class AbstractIdleTask implements Runnable {
 
         private final ChannelHandlerContext ctx;
 
-        ReaderIdleTimeoutTask(ChannelHandlerContext ctx) {
+        AbstractIdleTask(ChannelHandlerContext ctx) {
             this.ctx = ctx;
         }
 
@@ -373,98 +466,107 @@ public void run() {
                 return;
             }
 
+            run(ctx);
+        }
+
+        protected abstract void run(ChannelHandlerContext ctx);
+    }
+
+    private final class ReaderIdleTimeoutTask extends AbstractIdleTask {
+
+        ReaderIdleTimeoutTask(ChannelHandlerContext ctx) {
+            super(ctx);
+        }
+
+        @Override
+        protected void run(ChannelHandlerContext ctx) {
             long nextDelay = readerIdleTimeNanos;
             if (!reading) {
-                nextDelay -= System.nanoTime() - lastReadTime;
+                nextDelay -= ticksInNanos() - lastReadTime;
             }
 
             if (nextDelay <= 0) {
                 // Reader is idle - set a new timeout and notify the callback.
-                readerIdleTimeout =
-                    ctx.executor().schedule(this, readerIdleTimeNanos, TimeUnit.NANOSECONDS);
-                try {
-                    IdleStateEvent event = newIdleStateEvent(IdleState.READER_IDLE, firstReaderIdleEvent);
-                    if (firstReaderIdleEvent) {
-                        firstReaderIdleEvent = false;
-                    }
+                readerIdleTimeout = schedule(ctx, this, readerIdleTimeNanos, TimeUnit.NANOSECONDS);
 
+                boolean first = firstReaderIdleEvent;
+                firstReaderIdleEvent = false;
+
+                try {
+                    IdleStateEvent event = newIdleStateEvent(IdleState.READER_IDLE, first);
                     channelIdle(ctx, event);
                 } catch (Throwable t) {
                     ctx.fireExceptionCaught(t);
                 }
             } else {
                 // Read occurred before the timeout - set a new timeout with shorter delay.
-                readerIdleTimeout = ctx.executor().schedule(this, nextDelay, TimeUnit.NANOSECONDS);
+                readerIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
             }
         }
     }
 
-    private final class WriterIdleTimeoutTask implements Runnable {
-
-        private final ChannelHandlerContext ctx;
+    private final class WriterIdleTimeoutTask extends AbstractIdleTask {
 
         WriterIdleTimeoutTask(ChannelHandlerContext ctx) {
-            this.ctx = ctx;
+            super(ctx);
         }
 
         @Override
-        public void run() {
-            if (!ctx.channel().isOpen()) {
-                return;
-            }
+        protected void run(ChannelHandlerContext ctx) {
 
             long lastWriteTime = IdleStateHandler.this.lastWriteTime;
-            long nextDelay = writerIdleTimeNanos - (System.nanoTime() - lastWriteTime);
+            long nextDelay = writerIdleTimeNanos - (ticksInNanos() - lastWriteTime);
             if (nextDelay <= 0) {
                 // Writer is idle - set a new timeout and notify the callback.
-                writerIdleTimeout = ctx.executor().schedule(
-                        this, writerIdleTimeNanos, TimeUnit.NANOSECONDS);
+                writerIdleTimeout = schedule(ctx, this, writerIdleTimeNanos, TimeUnit.NANOSECONDS);
+
+                boolean first = firstWriterIdleEvent;
+                firstWriterIdleEvent = false;
+
                 try {
-                    IdleStateEvent event = newIdleStateEvent(IdleState.WRITER_IDLE, firstWriterIdleEvent);
-                    if (firstWriterIdleEvent) {
-                        firstWriterIdleEvent = false;
+                    if (hasOutputChanged(ctx, first)) {
+                        return;
                     }
 
+                    IdleStateEvent event = newIdleStateEvent(IdleState.WRITER_IDLE, first);
                     channelIdle(ctx, event);
                 } catch (Throwable t) {
                     ctx.fireExceptionCaught(t);
                 }
             } else {
                 // Write occurred before the timeout - set a new timeout with shorter delay.
-                writerIdleTimeout = ctx.executor().schedule(this, nextDelay, TimeUnit.NANOSECONDS);
+                writerIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
             }
         }
     }
 
-    private final class AllIdleTimeoutTask implements Runnable {
-
-        private final ChannelHandlerContext ctx;
+    private final class AllIdleTimeoutTask extends AbstractIdleTask {
 
         AllIdleTimeoutTask(ChannelHandlerContext ctx) {
-            this.ctx = ctx;
+            super(ctx);
         }
 
         @Override
-        public void run() {
-            if (!ctx.channel().isOpen()) {
-                return;
-            }
+        protected void run(ChannelHandlerContext ctx) {
 
             long nextDelay = allIdleTimeNanos;
             if (!reading) {
-                nextDelay -= System.nanoTime() - Math.max(lastReadTime, lastWriteTime);
+                nextDelay -= ticksInNanos() - Math.max(lastReadTime, lastWriteTime);
             }
             if (nextDelay <= 0) {
                 // Both reader and writer are idle - set a new timeout and
                 // notify the callback.
-                allIdleTimeout = ctx.executor().schedule(
-                        this, allIdleTimeNanos, TimeUnit.NANOSECONDS);
+                allIdleTimeout = schedule(ctx, this, allIdleTimeNanos, TimeUnit.NANOSECONDS);
+
+                boolean first = firstAllIdleEvent;
+                firstAllIdleEvent = false;
+
                 try {
-                    IdleStateEvent event = newIdleStateEvent(IdleState.ALL_IDLE, firstAllIdleEvent);
-                    if (firstAllIdleEvent) {
-                        firstAllIdleEvent = false;
+                    if (hasOutputChanged(ctx, first)) {
+                        return;
                     }
 
+                    IdleStateEvent event = newIdleStateEvent(IdleState.ALL_IDLE, first);
                     channelIdle(ctx, event);
                 } catch (Throwable t) {
                     ctx.fireExceptionCaught(t);
@@ -472,7 +574,7 @@ public void run() {
             } else {
                 // Either read or write occurred before the timeout - set a new
                 // timeout with shorter delay.
-                allIdleTimeout = ctx.executor().schedule(this, nextDelay, TimeUnit.NANOSECONDS);
+                allIdleTimeout = schedule(ctx, this, nextDelay, TimeUnit.NANOSECONDS);
             }
         }
     }

diff --git a/handler/src/test/java/io/netty/handler/timeout/IdleStateHandlerTest.java b/handler/src/test/java/io/netty/handler/timeout/IdleStateHandlerTest.java
new file mode 100644
index 00000000000..f7e1c42153e
--- /dev/null
+++ b/handler/src/test/java/io/netty/handler/timeout/IdleStateHandlerTest.java
@@ -0,0 +1,395 @@
+/*
+ * Copyright 2016 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.handler.timeout;
+
+import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertNotEquals;
+import static org.junit.Assert.assertNotNull;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertSame;
+import static org.junit.Assert.assertTrue;
+
+import io.netty.buffer.Unpooled;
+import io.netty.channel.ChannelHandler;
+import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.ChannelInboundHandlerAdapter;
+import io.netty.channel.ChannelOutboundBuffer;
+import io.netty.channel.embedded.EmbeddedChannel;
+import io.netty.util.ReferenceCountUtil;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.ScheduledFuture;
+import java.util.concurrent.TimeUnit;
+
+import org.junit.Test;
+
+public class IdleStateHandlerTest {
+
+    @Test
+    public void testReaderIdle() throws Exception {
+        TestableIdleStateHandler idleStateHandler = new TestableIdleStateHandler(
+                false, 1L, 0L, 0L, TimeUnit.SECONDS);
+
+        // We start with one FIRST_READER_IDLE_STATE_EVENT, followed by an infinite number of READER_IDLE_STATE_EVENTs
+        anyIdle(idleStateHandler, IdleStateEvent.FIRST_READER_IDLE_STATE_EVENT,
+                IdleStateEvent.READER_IDLE_STATE_EVENT, IdleStateEvent.READER_IDLE_STATE_EVENT);
+    }
+
+    @Test
+    public void testWriterIdle() throws Exception {
+        TestableIdleStateHandler idleStateHandler = new TestableIdleStateHandler(
+                false, 0L, 1L, 0L, TimeUnit.SECONDS);
+
+        anyIdle(idleStateHandler, IdleStateEvent.FIRST_WRITER_IDLE_STATE_EVENT,
+                IdleStateEvent.WRITER_IDLE_STATE_EVENT, IdleStateEvent.WRITER_IDLE_STATE_EVENT);
+    }
+
+    @Test
+    public void testAllIdle() throws Exception {
+        TestableIdleStateHandler idleStateHandler = new TestableIdleStateHandler(
+                false, 0L, 0L, 1L, TimeUnit.SECONDS);
+
+        anyIdle(idleStateHandler, IdleStateEvent.FIRST_ALL_IDLE_STATE_EVENT,
+                IdleStateEvent.ALL_IDLE_STATE_EVENT, IdleStateEvent.ALL_IDLE_STATE_EVENT);
+    }
+
+    private void anyIdle(TestableIdleStateHandler idleStateHandler, Object... expected) throws Exception {
+
+        assertTrue("The number of expected events must be >= 1", expected.length >= 1);
+
+        final List<Object> events = new ArrayList<Object>();
+        ChannelInboundHandlerAdapter handler = new ChannelInboundHandlerAdapter() {
+            @Override
+            public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
+                events.add(evt);
+            }
+        };
+
+        EmbeddedChannel channel = new EmbeddedChannel(idleStateHandler, handler);
+        try {
+            // For each expected event advance the ticker and run() the task. Each
+            // step should yield in an IdleStateEvent because we haven't written
+            // or read anything from the channel.
+            for (int i = 0; i < expected.length; i++) {
+                idleStateHandler.tickRun();
+            }
+
+            assertEquals(expected.length, events.size());
+
+            // Compare the expected with the actual IdleStateEvents
+            for (int i = 0; i < expected.length; i++) {
+                Object evt = events.get(i);
+                assertSame("Element " + i + " is not matching", expected[i], evt);
+            }
+        } finally {
+            channel.finishAndReleaseAll();
+        }
+    }
+
+    @Test
+    public void testReaderNotIdle() throws Exception {
+        TestableIdleStateHandler idleStateHandler = new TestableIdleStateHandler(
+                false, 1L, 0L, 0L, TimeUnit.SECONDS);
+
+        Action action = new Action() {
+            @Override
+            public void run(EmbeddedChannel channel) throws Exception {
+                channel.writeInbound("Hello, World!");
+            }
+        };
+
+        anyNotIdle(idleStateHandler, action, IdleStateEvent.FIRST_READER_IDLE_STATE_EVENT);
+    }
+
+    @Test
+    public void testWriterNotIdle() throws Exception {
+        TestableIdleStateHandler idleStateHandler = new TestableIdleStateHandler(
+                false, 0L, 1L, 0L, TimeUnit.SECONDS);
+
+        Action action = new Action() {
+            @Override
+            public void run(EmbeddedChannel channel) throws Exception {
+                channel.writeAndFlush("Hello, World!");
+            }
+        };
+
+        anyNotIdle(idleStateHandler, action, IdleStateEvent.FIRST_WRITER_IDLE_STATE_EVENT);
+    }
+
+    @Test
+    public void testAllNotIdle() throws Exception {
+        // Reader...
+        TestableIdleStateHandler idleStateHandler = new TestableIdleStateHandler(
+                false, 0L, 0L, 1L, TimeUnit.SECONDS);
+
+        Action reader = new Action() {
+            @Override
+            public void run(EmbeddedChannel channel) throws Exception {
+                channel.writeInbound("Hello, World!");
+            }
+        };
+
+        anyNotIdle(idleStateHandler, reader, IdleStateEvent.FIRST_ALL_IDLE_STATE_EVENT);
+
+        // Writer...
+        idleStateHandler = new TestableIdleStateHandler(
+                false, 0L, 0L, 1L, TimeUnit.SECONDS);
+
+        Action writer = new Action() {
+            @Override
+            public void run(EmbeddedChannel channel) throws Exception {
+                channel.writeAndFlush("Hello, World!");
+            }
+        };
+
+        anyNotIdle(idleStateHandler, writer, IdleStateEvent.FIRST_ALL_IDLE_STATE_EVENT);
+    }
+
+    private void anyNotIdle(TestableIdleStateHandler idleStateHandler,
+            Action action, Object expected) throws Exception {
+
+        final List<Object> events = new ArrayList<Object>();
+        ChannelInboundHandlerAdapter handler = new ChannelInboundHandlerAdapter() {
+            @Override
+            public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
+                events.add(evt);
+            }
+        };
+
+        EmbeddedChannel channel = new EmbeddedChannel(idleStateHandler, handler);
+        try {
+            idleStateHandler.tick(1L, TimeUnit.NANOSECONDS);
+            action.run(channel);
+
+            // Advance the ticker by some fraction and run() the task.
+            // There shouldn't be an IdleStateEvent getting fired because
+            // we've just performed an action on the channel that is meant
+            // to reset the idle task.
+            long delayInNanos = idleStateHandler.delay(TimeUnit.NANOSECONDS);
+            assertNotEquals(0L, delayInNanos);
+
+            idleStateHandler.tickRun(delayInNanos / 2L, TimeUnit.NANOSECONDS);
+            assertEquals(0, events.size());
+
+            // Advance the ticker by the full amount and it should yield
+            // in an IdleStateEvent.
+            idleStateHandler.tickRun();
+            assertEquals(1, events.size());
+            assertSame(expected, events.get(0));
+        } finally {
+            channel.finishAndReleaseAll();
+        }
+    }
+
+    @Test
+    public void testObserveWriterIdle() throws Exception {
+        observeOutputIdle(true);
+    }
+
+    @Test
+    public void testObserveAllIdle() throws Exception {
+        observeOutputIdle(false);
+    }
+
+    private void observeOutputIdle(boolean writer) throws Exception {
+
+        long writerIdleTime = 0L;
+        long allIdleTime = 0L;
+        IdleStateEvent expeced = null;
+
+        if (writer) {
+            writerIdleTime = 5L;
+            expeced = IdleStateEvent.FIRST_WRITER_IDLE_STATE_EVENT;
+        } else {
+            allIdleTime = 5L;
+            expeced = IdleStateEvent.FIRST_ALL_IDLE_STATE_EVENT;
+        }
+
+        TestableIdleStateHandler idleStateHandler = new TestableIdleStateHandler(
+                true, 0L, writerIdleTime, allIdleTime, TimeUnit.SECONDS);
+
+        final List<Object> events = new ArrayList<Object>();
+        ChannelInboundHandlerAdapter handler = new ChannelInboundHandlerAdapter() {
+            @Override
+            public void userEventTriggered(ChannelHandlerContext ctx, Object evt) throws Exception {
+                events.add(evt);
+            }
+        };
+
+        ObservableChannel channel = new ObservableChannel(idleStateHandler, handler);
+        try {
+            // We're writing 3 messages that will be consumed at different rates!
+            channel.writeAndFlush(Unpooled.wrappedBuffer(new byte[] { 1 }));
+            channel.writeAndFlush(Unpooled.wrappedBuffer(new byte[] { 2 }));
+            channel.writeAndFlush(Unpooled.wrappedBuffer(new byte[] { 3 }));
+
+            // Establish a baseline. We're not consuming anything and let it idle once.
+            idleStateHandler.tickRun();
+            assertEquals(1, events.size());
+            assertSame(expeced, events.get(0));
+            events.clear();
+
+            // Our ticker should be at second 5
+            assertEquals(5L, idleStateHandler.tick(TimeUnit.SECONDS));
+
+            // Consume one message in 4 seconds, then be idle for 2 seconds,
+            // then run the task and we shouldn't get an IdleStateEvent because
+            // we haven't been idle for long enough!
+            idleStateHandler.tick(4L, TimeUnit.SECONDS);
+            assertNotNullAndRelease(channel.consume());
+
+            idleStateHandler.tickRun(2L, TimeUnit.SECONDS);
+            assertEquals(0, events.size());
+            assertEquals(11L, idleStateHandler.tick(TimeUnit.SECONDS)); // 5s + 4s + 2s
+
+            // Consume one message in 3 seconds, then be idle for 4 seconds,
+            // then run the task and we shouldn't get an IdleStateEvent because
+            // we haven't been idle for long enough!
+            idleStateHandler.tick(3L, TimeUnit.SECONDS);
+            assertNotNullAndRelease(channel.consume());
+
+            idleStateHandler.tickRun(4L, TimeUnit.SECONDS);
+            assertEquals(0, events.size());
+            assertEquals(18L, idleStateHandler.tick(TimeUnit.SECONDS)); // 11s + 3s + 4s
+
+            // Don't consume a message and be idle for 5 seconds.
+            // We should get an IdleStateEvent!
+            idleStateHandler.tickRun(5L, TimeUnit.SECONDS);
+            assertEquals(1, events.size());
+            assertEquals(23L, idleStateHandler.tick(TimeUnit.SECONDS)); // 18s + 5s
+            events.clear();
+
+            // Consume one message in 2 seconds, then be idle for 1 seconds,
+            // then run the task and we shouldn't get an IdleStateEvent because
+            // we haven't been idle for long enough!
+            idleStateHandler.tick(2L, TimeUnit.SECONDS);
+            assertNotNullAndRelease(channel.consume());
+
+            idleStateHandler.tickRun(1L, TimeUnit.SECONDS);
+            assertEquals(0, events.size());
+            assertEquals(26L, idleStateHandler.tick(TimeUnit.SECONDS)); // 23s + 2s + 1s
+
+            // There are no messages left! Advance the ticker by 3 seconds,
+            // attempt a consume() but it will be null, then advance the
+            // ticker by an another 2 seconds and we should get an IdleStateEvent
+            // because we've been idle for 5 seconds.
+            idleStateHandler.tick(3L, TimeUnit.SECONDS);
+            assertNull(channel.consume());
+
+            idleStateHandler.tickRun(2L, TimeUnit.SECONDS);
+            assertEquals(1, events.size());
+            assertEquals(31L, idleStateHandler.tick(TimeUnit.SECONDS)); // 26s + 3s + 2s
+
+            // q.e.d.
+        } finally {
+            channel.finishAndReleaseAll();
+        }
+    }
+
+    private static void assertNotNullAndRelease(Object msg) {
+        assertNotNull(msg);
+        ReferenceCountUtil.release(msg);
+    }
+
+    private interface Action {
+        void run(EmbeddedChannel channel) throws Exception;
+    }
+
+    private static class TestableIdleStateHandler extends IdleStateHandler {
+
+        private Runnable task;
+
+        private long delayInNanos;
+
+        private long ticksInNanos;
+
+        public TestableIdleStateHandler(boolean observeOutput,
+                long readerIdleTime, long writerIdleTime, long allIdleTime,
+                TimeUnit unit) {
+            super(observeOutput, readerIdleTime, writerIdleTime, allIdleTime, unit);
+        }
+
+        public long delay(TimeUnit unit) {
+            return unit.convert(delayInNanos, TimeUnit.NANOSECONDS);
+        }
+
+        public void run() {
+            task.run();
+        }
+
+        public void tickRun() {
+            tickRun(delayInNanos, TimeUnit.NANOSECONDS);
+        }
+
+        public void tickRun(long delay, TimeUnit unit) {
+            tick(delay, unit);
+            run();
+        }
+
+        /**
+         * Advances the current ticker by the given amount.
+         */
+        public void tick(long delay, TimeUnit unit) {
+            ticksInNanos += unit.toNanos(delay);
+        }
+
+        /**
+         * Returns {@link #ticksInNanos()} in the given {@link TimeUnit}.
+         */
+        public long tick(TimeUnit unit) {
+            return unit.convert(ticksInNanos(), TimeUnit.NANOSECONDS);
+        }
+
+        @Override
+        long ticksInNanos() {
+            return ticksInNanos;
+        }
+
+        @Override
+        ScheduledFuture<?> schedule(ChannelHandlerContext ctx, Runnable task, long delay, TimeUnit unit) {
+            this.task = task;
+            this.delayInNanos = unit.toNanos(delay);
+            return null;
+        }
+    }
+
+    private static class ObservableChannel extends EmbeddedChannel {
+
+        public ObservableChannel(ChannelHandler... handlers) {
+            super(handlers);
+        }
+
+        @Override
+        protected void doWrite(ChannelOutboundBuffer in) throws Exception {
+            // Overridden to change EmbeddedChannel's default behavior. We went to keep
+            // the messages in the ChannelOutboundBuffer.
+        }
+
+        public Object consume() {
+            ChannelOutboundBuffer buf = unsafe().outboundBuffer();
+            if (buf != null) {
+                Object msg = buf.current();
+                if (msg != null) {
+                    ReferenceCountUtil.retain(msg);
+                    buf.remove();
+                    return msg;
+                }
+            }
+            return null;
+        }
+    }
+}
