Cleanup ChannelId handling of basic methods

Motiviation:

Simplify implementation of compareTo/equals/hashCode for ChannelIds.

Modifications:

We simplfy the hashCode implementation for DefaultChannelId by not
making it random, but making it based on the underlying data. We fix the
compareTo implementation for DefaultChannelId by using lexicographic
comparison of the underlying data array. We fix the compareTo
implementation for CustomChannelId to avoid the possibility of overflow.

Result:

Cleaner code that is easier to maintain.

common/src/main/java/io/netty/util/internal/MathUtil.java

@@ -64,6 +64,20 @@ public final class MathUtil {
         return (index | length | (index + length) | (capacity - (index + length))) < 0;
     }
 
+    /**
+     * Compares two {@code int} values.
+     *
+     * @param  x the first {@code int} to compare
+     * @param  y the second {@code int} to compare
+     * @return the value {@code 0} if {@code x == y};
+     *         {@code -1} if {@code x < y}; and
+     *         {@code 1} if {@code x > y}
+     */
+    public static int compare(final int x, final int y) {
+        // do not subtract for comparison, it could overflow
+        return x < y ? -1 : (x > y ? 1 : 0);
+    }
+
     /**
      * Compare two {@code long} values.
      * @param x the first {@code long} to compare.

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

@@ -178,10 +178,10 @@ public final class DefaultChannelId implements ChannelId {
 
         // random
         int random = ThreadLocalRandom.current().nextInt();
-        hashCode = random;
         i = writeInt(i, random);
-
         assert i == data.length;
+
+        hashCode = Arrays.hashCode(data);
     }
 
     private int writeInt(int i, int value) {
@@ -247,21 +247,35 @@ public final class DefaultChannelId implements ChannelId {
     }
 
     @Override
-    public int compareTo(ChannelId o) {
-        return 0;
+    public int compareTo(final ChannelId o) {
+        if (o instanceof DefaultChannelId) {
+            final byte[] otherData = ((DefaultChannelId)o).data;
+            if (this == o) {
+                // short circuit
+                return 0;
+            }
+            // lexicographic comparison
+            int len1 = data.length;
+            int len2 = otherData.length;
+            int len = Math.min(len1, len2);
+
+            for (int k = 0; k < len; k++) {
+                byte x = data[k];
+                byte y = otherData[k];
+                if (x != y) {
+                    // treat these as unsigned bytes for comparison
+                    return (x & 0xff) - (y & 0xff);
+                }
+            }
+            return len1 - len2;
+        }
+
+        return asLongText().compareTo(o.asLongText());
     }
 
     @Override
     public boolean equals(Object obj) {
-        if (obj == this) {
-            return true;
-        }
-
-        if (!(obj instanceof DefaultChannelId)) {
-            return false;
-        }
-
-        return Arrays.equals(data, ((DefaultChannelId) obj).data);
+        return this == obj || (obj instanceof DefaultChannelId && Arrays.equals(data, ((DefaultChannelId) obj).data));
     }
 
     @Override

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

@@ -40,7 +40,7 @@ final class EmbeddedChannelId implements ChannelId {
     }
 
     @Override
-    public int compareTo(ChannelId o) {
+    public int compareTo(final ChannelId o) {
         if (o instanceof EmbeddedChannelId) {
             return 0;
         }

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

@@ -16,22 +16,25 @@
 package io.netty.channel.embedded;
 
 import io.netty.channel.ChannelId;
+import io.netty.util.internal.MathUtil;
 
 public class CustomChannelId implements ChannelId {
+
     private static final long serialVersionUID = 1L;
 
     private int id;
 
-    public CustomChannelId(int id) {
+    CustomChannelId(int id) {
         this.id = id;
     }
 
     @Override
-    public int compareTo(ChannelId o) {
+    public int compareTo(final ChannelId o) {
         if (o instanceof CustomChannelId) {
-            return id - ((CustomChannelId) o).id;
+            return MathUtil.compare(id, ((CustomChannelId)o).id);
         }
-        return -1;
+
+        return asLongText().compareTo(o.asLongText());
     }
 
     @Override
@@ -41,10 +44,7 @@ public class CustomChannelId implements ChannelId {
 
     @Override
     public boolean equals(Object obj) {
-        if (obj instanceof CustomChannelId) {
-            return id == ((CustomChannelId) obj).id;
-        }
-        return false;
+        return obj instanceof CustomChannelId && id == ((CustomChannelId) obj).id;
     }
 
     @Override