Improve flexibility of EmbeddedChannel ID

Motivation:

EmbeddedChannelId#hashCode() and equals() do not behave correctly if an
instance is serialized and then deserialized. Additionally,
EmbeddedChannel does not allow use of any other type of ChannelId, and
EmbeddedChannelId is (mostly) a singleton instance. This creates a
problem for unit tests that construct multiple EmbeddedChannels and
expect each channel to have a unique ID.

Modifications:

EmbeddedChannelId is modified so equals() will return true and
hashCode() will return the same value for any instance of the class.
EmbeddedChannel is modified to allow a ChannelId to be specified when
the channel is constructed. Tests added for both changes.

Result:

EmbeddedChannelId now behaves correctly when deserialized, and
EmbeddedChannels can now have unique IDs.

transport/src/main/java/io/netty/channel/embedded/EmbeddedChannel.java

@@ -21,6 +21,7 @@ import io.netty.channel.ChannelConfig;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.ChannelId;
 import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.ChannelMetadata;
@@ -64,19 +65,39 @@ public class EmbeddedChannel extends AbstractChannel {
     private State state;
 
     /**
-     * Create a new instance with an empty pipeline.
+     * Create a new instance with an {@link EmbeddedChannelId} and an empty pipeline.
      */
     public EmbeddedChannel() {
         this(EMPTY_HANDLERS);
     }
 
+    /**
+     * Create a new instance with the specified ID and an empty pipeline.
+     *
+     * @param channelId the {@link ChannelId} that will be used to identify this channel
+     */
+    public EmbeddedChannel(ChannelId channelId) {
+        this(channelId, EMPTY_HANDLERS);
+    }
+
     /**
      * Create a new instance with the pipeline initialized with the specified handlers.
      *
-     * @param handlers the @link ChannelHandler}s which will be add in the {@link ChannelPipeline}
+     * @param handlers the {@link ChannelHandler}s which will be add in the {@link ChannelPipeline}
      */
     public EmbeddedChannel(final ChannelHandler... handlers) {
-        super(null, EmbeddedChannelId.INSTANCE);
+        this(EmbeddedChannelId.INSTANCE, handlers);
+    }
+
+    /**
+     * Create a new instance with the channel ID set to the given ID and the pipeline
+     * initialized with the specified handlers.
+     *
+     * @param channelId the {@link ChannelId} that will be used to identify this channel
+     * @param handlers the {@link ChannelHandler}s which will be add in the {@link ChannelPipeline}
+     */
+    public EmbeddedChannel(ChannelId channelId, final ChannelHandler... handlers) {
+        super(null, channelId);
 
         if (handlers == null) {
             throw new NullPointerException("handlers");

transport/src/main/java/io/netty/channel/embedded/EmbeddedChannelId.java

@@ -41,7 +41,7 @@ final class EmbeddedChannelId implements ChannelId {
 
     @Override
     public int compareTo(ChannelId o) {
-        if (o == INSTANCE) {
+        if (o instanceof EmbeddedChannelId) {
             return 0;
         }
 
@@ -50,12 +50,12 @@ final class EmbeddedChannelId implements ChannelId {
 
     @Override
     public int hashCode() {
-        return super.hashCode();
+        return 0;
     }
 
     @Override
     public boolean equals(Object obj) {
-        return super.equals(obj);
+        return obj instanceof EmbeddedChannelId;
     }
 
     @Override

transport/src/test/java/io/netty/channel/embedded/CustomChannelId.java

@@ -0,0 +1,65 @@
+/*
+ * Copyright 2015 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.embedded;
+
+import io.netty.channel.ChannelId;
+
+public class CustomChannelId implements ChannelId {
+    private static final long serialVersionUID = 1L;
+
+    private int id;
+
+    public CustomChannelId(int id) {
+        this.id = id;
+    }
+
+    @Override
+    public int compareTo(ChannelId o) {
+        if (o instanceof CustomChannelId) {
+            return id - ((CustomChannelId) o).id;
+        }
+        return -1;
+    }
+
+    @Override
+    public int hashCode() {
+        return id;
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj instanceof CustomChannelId) {
+            return id == ((CustomChannelId) obj).id;
+        }
+        return false;
+    }
+
+    @Override
+    public String toString() {
+        return "CustomChannelId " + id;
+    }
+
+    @Override
+    public String asShortText() {
+        return toString();
+    }
+
+    @Override
+    public String asLongText() {
+        return toString();
+    }
+
+}

transport/src/test/java/io/netty/channel/embedded/EmbeddedChannelIdTest.java

@@ -0,0 +1,51 @@
+/*
+ * Copyright 2015 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.embedded;
+
+import java.io.IOException;
+import java.io.ObjectInputStream;
+import java.io.ObjectOutputStream;
+
+import org.junit.Assert;
+import org.junit.Test;
+
+import io.netty.buffer.ByteBufInputStream;
+import io.netty.buffer.ByteBufOutputStream;
+import io.netty.buffer.Unpooled;
+import io.netty.channel.ChannelId;
+
+public class EmbeddedChannelIdTest {
+
+    @Test
+    public void testSerialization() throws IOException, ClassNotFoundException {
+        // test that a deserialized instance works the same as a normal instance (issue #2869)
+        ChannelId normalInstance = EmbeddedChannelId.INSTANCE;
+
+        ByteBufOutputStream buffer = new ByteBufOutputStream(Unpooled.buffer());
+        ObjectOutputStream outStream = new ObjectOutputStream(buffer);
+        outStream.writeObject(normalInstance);
+        outStream.close();
+
+        ObjectInputStream inStream = new ObjectInputStream(new ByteBufInputStream(buffer.buffer()));
+        ChannelId deserializedInstance = (ChannelId) inStream.readObject();
+        inStream.close();
+
+        Assert.assertEquals(normalInstance, deserializedInstance);
+        Assert.assertEquals(normalInstance.hashCode(), deserializedInstance.hashCode());
+        Assert.assertEquals(0, normalInstance.compareTo(deserializedInstance));
+    }
+
+}

transport/src/test/java/io/netty/channel/embedded/EmbeddedChannelTest.java

@@ -20,6 +20,7 @@ import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.ChannelId;
 import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.ChannelPipeline;
@@ -136,6 +137,13 @@ public class EmbeddedChannelTest {
         Assert.assertNull(channel.readOutbound());
     }
 
+    @Test
+    public void testConstructWithChannelId() {
+        ChannelId channelId = new CustomChannelId(1);
+        EmbeddedChannel channel = new EmbeddedChannel(channelId);
+        Assert.assertSame(channelId, channel.id());
+    }
+
     // See https://github.com/netty/netty/issues/4316.
     @Test(timeout = 2000)
     public void testFireChannelInactiveAndUnregisteredOnClose() throws InterruptedException {