ChannelInitializer: change propagation of channelRegistered event

Motivation:

If a handler is added to the pipeline within ChannelInitializer::initChannel via
addFirst(...) then it will not receive the channelRegistered event.  The same
handler added via addLast(...) will receive the event.  This different behavior
is unlikely to be expected by users and can cause confusion.

Modifications:

Let ChannelInitializer::channelRegistered propagate the event by passing it to
the pipeline instead of firing it on the ChannelHandlerContext.

Result:

The channelRegistered event is propagated to handlers regardless of the method
used to add it to the pipeline (addFirst/addLast).

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

@@ -67,7 +67,7 @@ public abstract class ChannelInitializer<C extends Channel> extends ChannelInbou
     public final void channelRegistered(ChannelHandlerContext ctx) throws Exception {
         initChannel((C) ctx.channel());
         ctx.pipeline().remove(this);
-        ctx.fireChannelRegistered();
+        ctx.pipeline().fireChannelRegistered();
     }
 
     /**

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

@@ -0,0 +1,107 @@
+/*
+ * 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.channel;
+
+import io.netty.bootstrap.Bootstrap;
+import io.netty.bootstrap.ServerBootstrap;
+import io.netty.channel.local.LocalAddress;
+import io.netty.channel.local.LocalChannel;
+import io.netty.channel.local.LocalServerChannel;
+import org.junit.After;
+import org.junit.Before;
+import org.junit.Test;
+
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+
+import static org.junit.Assert.assertEquals;
+
+public class ChannelInitializerTest {
+    private static final int TIMEOUT_MILLIS = 1000;
+    private static final LocalAddress SERVER_ADDRESS = new LocalAddress("addr");
+    private EventLoopGroup group;
+    private ServerBootstrap server;
+    private Bootstrap client;
+    private InspectableHandler testHandler;
+
+    @Before
+    public void setUp() {
+        group = new DefaultEventLoopGroup(1);
+        server = new ServerBootstrap()
+                .group(group)
+                .channel(LocalServerChannel.class)
+                .localAddress(SERVER_ADDRESS);
+        client = new Bootstrap()
+                .group(group)
+                .channel(LocalChannel.class)
+                .handler(new ChannelInboundHandlerAdapter());
+        testHandler = new InspectableHandler();
+    }
+
+    @After
+    public void tearDown() {
+        group.shutdownGracefully(0, TIMEOUT_MILLIS, TimeUnit.MILLISECONDS).syncUninterruptibly();
+    }
+
+    @Test(timeout = TIMEOUT_MILLIS)
+    public void firstHandlerInPipelineShouldReceiveChannelRegisteredEvent() {
+        testChannelRegisteredEventPropagation(new ChannelInitializer<LocalChannel>() {
+            @Override
+            public void initChannel(LocalChannel channel) {
+                channel.pipeline().addFirst(testHandler);
+            }
+        });
+    }
+
+    @Test(timeout = TIMEOUT_MILLIS)
+    public void lastHandlerInPipelineShouldReceiveChannelRegisteredEvent() {
+        testChannelRegisteredEventPropagation(new ChannelInitializer<LocalChannel>() {
+            @Override
+            public void initChannel(LocalChannel channel) {
+                channel.pipeline().addLast(testHandler);
+            }
+        });
+    }
+
+    private void testChannelRegisteredEventPropagation(ChannelInitializer<LocalChannel> init) {
+        Channel clientChannel = null, serverChannel = null;
+        try {
+            server.childHandler(init);
+            serverChannel = server.bind().syncUninterruptibly().channel();
+            clientChannel = client.connect(SERVER_ADDRESS).syncUninterruptibly().channel();
+            assertEquals(1, testHandler.channelRegisteredCount.get());
+        } finally {
+            closeChannel(clientChannel);
+            closeChannel(serverChannel);
+        }
+    }
+
+    private static void closeChannel(Channel c) {
+        if (c != null) {
+            c.close().syncUninterruptibly();
+        }
+    }
+
+    private static final class InspectableHandler extends ChannelDuplexHandler {
+        final AtomicInteger channelRegisteredCount = new AtomicInteger(0);
+
+        @Override
+        public void channelRegistered(ChannelHandlerContext ctx) {
+            channelRegisteredCount.incrementAndGet();
+            ctx.fireChannelRegistered();
+        }
+    }
+}