Logs in invokeExceptionCaught have been made consistent and full

Motivation:

In case of exception in invokeExceptionCaught() only original exception passed to invokeExceptionCaught() will be logged on any log level.
+ AbstractChannelHandlerContext and CombinedChannelDuplexHandler log different exceptions.

Modifications:

Fix inconsistent logging code and add ability to see both stacktraces on DEBUG level.

Result:

Both handlers log now both original exception and thrown from invokeExceptionCaught. To see full stacktrace of exception thrown from invokeExceptionCaught DEBUG log level must be enabled.

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

@@ -0,0 +1,48 @@
+/*
+ * 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.util.internal;
+
+import java.io.ByteArrayOutputStream;
+import java.io.IOException;
+import java.io.PrintStream;
+
+public final class ThrowableUtils {
+
+    /**
+     * <p>Gets the stack trace from a Throwable as a String.</p>
+     *
+     * @param throwable the <code>Throwable</code> to be examined
+     * @return the stack trace as generated by the exception's
+     *  <code>printStackTrace(PrintWriter)</code> method
+     */
+    public static String stackTraceToString(Throwable cause) {
+        ByteArrayOutputStream out = new ByteArrayOutputStream();
+        PrintStream pout = new PrintStream(out);
+        cause.printStackTrace(pout);
+        pout.flush();
+        try {
+            return new String(out.toByteArray());
+        } finally {
+            try {
+                out.close();
+            } catch (IOException ignore) {
+                // ignore as should never happen
+            }
+        }
+    }
+
+    private ThrowableUtils() { }
+}

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

@@ -16,13 +16,14 @@
 package io.netty.channel;
 
 import io.netty.buffer.ByteBufAllocator;
-import io.netty.util.DefaultAttributeMap;
-import io.netty.util.ResourceLeakHint;
 import io.netty.util.Attribute;
 import io.netty.util.AttributeKey;
+import io.netty.util.DefaultAttributeMap;
 import io.netty.util.Recycler;
 import io.netty.util.ReferenceCountUtil;
+import io.netty.util.ResourceLeakHint;
 import io.netty.util.concurrent.EventExecutor;
+import io.netty.util.internal.ThrowableUtils;
 import io.netty.util.internal.ObjectUtil;
 import io.netty.util.internal.StringUtil;
 import io.netty.util.internal.SystemPropertyUtil;
@@ -274,11 +275,18 @@ abstract class AbstractChannelHandlerContext extends DefaultAttributeMap
         if (isAdded()) {
             try {
                 handler().exceptionCaught(this, cause);
-            } catch (Throwable t) {
+            } catch (Throwable error) {
-                if (logger.isWarnEnabled()) {
+                if (logger.isDebugEnabled()) {
+                    logger.debug(
+                        "An exception {}" +
+                        "was thrown by a user handler's exceptionCaught() " +
+                        "method while handling the following exception:",
+                        ThrowableUtils.stackTraceToString(error), cause);
+                } else if (logger.isWarnEnabled()) {
                     logger.warn(
-                            "An exception was thrown by a user handler's " +
+                        "An exception '{}' [enable DEBUG level for full stacktrace] " +
-                                    "exceptionCaught() method while handling the following exception:", cause);
+                        "was thrown by a user handler's exceptionCaught() " +
+                        "method while handling the following exception:", error, cause);
                 }
             }
         } else {

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

@@ -25,12 +25,10 @@ import io.netty.util.ReferenceCountUtil;
 import io.netty.util.concurrent.FastThreadLocal;
 import io.netty.util.internal.InternalThreadLocalMap;
 import io.netty.util.internal.PlatformDependent;
+import io.netty.util.internal.ThrowableUtils;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
-import java.io.ByteArrayOutputStream;
-import java.io.IOException;
-import java.io.PrintStream;
 import java.nio.ByteBuffer;
 import java.nio.channels.ClosedChannelException;
 import java.util.Arrays;
@@ -679,7 +677,7 @@ public final class ChannelOutboundBuffer {
             } else {
                 logger.warn(
                         "Failed to mark a promise as success because it has failed already: {}, unnotified cause {}",
-                        promise, stackTraceToString(err));
+                        promise, ThrowableUtils.stackTraceToString(err));
             }
         }
     }
@@ -692,23 +690,7 @@ public final class ChannelOutboundBuffer {
             } else {
                 logger.warn(
                         "Failed to mark a promise as failure because it hass failed already: {}, unnotified cause {}",
-                        promise, stackTraceToString(err), cause);
+                        promise, ThrowableUtils.stackTraceToString(err), cause);
-            }
-        }
-    }
-
-    private static String stackTraceToString(Throwable cause) {
-        ByteArrayOutputStream out = new ByteArrayOutputStream();
-        PrintStream pout = new PrintStream(out);
-        cause.printStackTrace(pout);
-        pout.flush();
-        try {
-            return new String(out.toByteArray());
-        } finally {
-            try {
-                out.close();
-            } catch (IOException ignore) {
-                // ignore as should never happen
             }
         }
     }

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

@@ -19,6 +19,7 @@ import io.netty.buffer.ByteBufAllocator;
 import io.netty.util.Attribute;
 import io.netty.util.AttributeKey;
 import io.netty.util.concurrent.EventExecutor;
+import io.netty.util.internal.ThrowableUtils;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
 
@@ -142,10 +143,17 @@ public class CombinedChannelDuplexHandler<I extends ChannelInboundHandler, O ext
                         // as well
                         outboundHandler.exceptionCaught(outboundCtx, cause);
                     } catch (Throwable error) {
-                        if (logger.isWarnEnabled()) {
+                        if (logger.isDebugEnabled()) {
+                            logger.debug(
+                                    "An exception {}" +
+                                    "was thrown by a user handler's exceptionCaught() " +
+                                    "method while handling the following exception:",
+                                    ThrowableUtils.stackTraceToString(error), cause);
+                        } else if (logger.isWarnEnabled()) {
                             logger.warn(
-                                    "An exception was thrown by a user handler's " +
+                                    "An exception '{}' [enable DEBUG level for full stacktrace] " +
-                                            "exceptionCaught() method while handling the following exception:", error);
+                                    "was thrown by a user handler's exceptionCaught() " +
+                                    "method while handling the following exception:", error, cause);
                         }
                     }
                 } else {