DefaultChannelHandlerContext write leak

Motivation:
DefaultChannelHandlerContext calls a utility method validatePromise which may throw if the arguments are not valid. If this method throws then the message will not be released.

Modifications:
- If an exception is thrown the message should be released

Result:
No more leak in DefaultChannelHandlerContext.write

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

@@ -599,11 +599,16 @@ abstract class AbstractChannelHandlerContext extends DefaultAttributeMap impleme
             throw new NullPointerException("msg");
         }
 
+        try {
             if (!validatePromise(promise, true)) {
                 ReferenceCountUtil.release(msg);
                 // cancelled
                 return promise;
             }
+        } catch (RuntimeException e) {
+            ReferenceCountUtil.release(msg);
+            throw e;
+        }
         write(msg, false, promise);
 
         return promise;

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

@@ -0,0 +1,75 @@
+/*
+ * 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.channel.local.LocalChannel;
+import io.netty.util.ReferenceCounted;
+import io.netty.util.concurrent.ImmediateEventExecutor;
+import org.junit.Before;
+import org.junit.Test;
+import org.mockito.Mock;
+import org.mockito.MockitoAnnotations;
+
+import static org.junit.Assert.*;
+import static org.mockito.Mockito.verify;
+import static org.mockito.Mockito.when;
+
+public class DefaultChannelHandlerContextTest {
+    @Mock
+    private ReferenceCounted msg;
+    @Mock
+    private ChannelHandlerContext ctx;
+    @Mock
+    private ChannelPromise promise;
+    @Mock
+    private ChannelHandler handler;
+
+    @Before
+    public void setup() {
+        MockitoAnnotations.initMocks(this);
+    }
+
+    private DefaultChannelHandlerContext newContext() {
+        return new DefaultChannelHandlerContext(new DefaultChannelPipeline(new LocalChannel()),
+                ImmediateEventExecutor.INSTANCE, "test_context", handler);
+    }
+
+    @Test
+    public void writeWithInvalidPromiseStillReleasesMessage() {
+        when(promise.isDone()).thenReturn(true);
+        DefaultChannelHandlerContext ctx = newContext();
+        try {
+            ctx.write(msg, promise);
+        } catch (IllegalArgumentException e) {
+            verify(msg).release();
+            return;
+        }
+        fail();
+    }
+
+    @Test
+    public void writeWithNullPromiseStillReleasesMessage() {
+        when(promise.isDone()).thenReturn(true);
+        DefaultChannelHandlerContext ctx = newContext();
+        try {
+            ctx.write(msg, null);
+        } catch (NullPointerException e) {
+            verify(msg).release();
+            return;
+        }
+        fail();
+    }
+}