Enable AUTO_CLOSE opton by default for backward compatibility / Deprecare AUTO_CLOSE option because it's gone in 5.0.

- Related #1952

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

@@ -189,15 +189,21 @@ public interface ChannelConfig {
     ChannelConfig setAutoRead(boolean autoRead);
 
     /**
+     * @deprecated From version 5.0, {@link Channel} will not be closed on write failure.
+     *
      * Returns {@code true} if and only if the {@link Channel} will be closed automatically and immediately on
      * write failure.  The default is {@code false}.
      */
+    @Deprecated
     boolean isAutoClose();
 
     /**
+     * @deprecated From version 5.0, {@link Channel} will not be closed on write failure.
+     *
      * Sets whether the {@link Channel} should be closed automatically and immediately on write faillure.
      * The default is {@code false}.
      */
+    @Deprecated
     ChannelConfig setAutoClose(boolean autoClose);
 
     /**

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

@@ -50,9 +50,12 @@ public class ChannelOption<T> extends UniqueName {
     public static final ChannelOption<Boolean> AUTO_READ = valueOf("AUTO_READ");
 
     /**
+     * @deprecated From version 5.0, {@link Channel} will not be closed on write failure.
+     *
      * {@code true} if and only if the {@link Channel} is closed automatically and immediately on write failure.
      * The default is {@code false}.
      */
+    @Deprecated
     public static final ChannelOption<Boolean> AUTO_CLOSE = valueOf("AUTO_CLOSE");
 
     public static final ChannelOption<Boolean> SO_BROADCAST = valueOf("SO_BROADCAST");

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

@@ -46,7 +46,7 @@ public class DefaultChannelConfig implements ChannelConfig {
     private volatile int maxMessagesPerRead;
     private volatile int writeSpinCount = 16;
     private volatile boolean autoRead = true;
-    private volatile boolean autoClose;
+    private volatile boolean autoClose = true;
     private volatile int writeBufferHighWaterMark = 64 * 1024;
     private volatile int writeBufferLowWaterMark = 32 * 1024;
 
@@ -65,6 +65,7 @@ public class DefaultChannelConfig implements ChannelConfig {
     }
 
     @Override
+    @SuppressWarnings("deprecation")
     public Map<ChannelOption<?>, Object> getOptions() {
         return getOptions(
                 null,
@@ -102,7 +103,7 @@ public class DefaultChannelConfig implements ChannelConfig {
     }
 
     @Override
-    @SuppressWarnings("unchecked")
+    @SuppressWarnings({ "unchecked", "deprecation" })
     public <T> T getOption(ChannelOption<T> option) {
         if (option == null) {
             throw new NullPointerException("option");
@@ -142,6 +143,7 @@ public class DefaultChannelConfig implements ChannelConfig {
     }
 
     @Override
+    @SuppressWarnings("deprecation")
     public <T> boolean setOption(ChannelOption<T> option, T value) {
         validate(option, value);