Remove the distinction of inbound handlers and outbound handlers

- Fixes #1808
- Move all methods in ChannelInboundHandler and ChannelOutboundHandler up to ChannelHandler
- Remove ChannelInboundHandler and ChannelOutboundHandler
- Deprecate ChannelInboundHandlerAdapter, ChannelOutboundHandlerAdapter, and ChannelDuplexHandler
- Replace CombinedChannelDuplexHandler with ChannelHandlerAppender
  because it's not possible to combine two handlers into one easily now
- Introduce 'Skip' annotation to pass events through efficiently
- Remove all references to the deprecated types and update Javadoc

buffer/src/main/java/io/netty/buffer/package-info.java

@@ -75,13 +75,13 @@
  * type.
  * <pre>
  * // The composite type is compatible with the component type.
- * {@link ByteBuf} message = {@link Unpooled}.wrappedBuffer(header, body);
+ * {@link io.netty.buffer.ByteBuf} message = {@link io.netty.buffer.Unpooled}.wrappedBuffer(header, body);
  *
  * // Therefore, you can even create a composite by mixing a composite and an
  * // ordinary buffer.
- * {@link ByteBuf} messageWithFooter = {@link Unpooled}.wrappedBuffer(message, footer);
+ * {@link io.netty.buffer.ByteBuf} messageWithFooter = {@link io.netty.buffer.Unpooled}.wrappedBuffer(message, footer);
  *
- * // Because the composite is still a {@link ByteBuf}, you can access its content
+ * // Because the composite is still a {@link io.netty.buffer.ByteBuf}, you can access its content
  * // easily, and the accessor method will behave just like it's a single buffer
  * // even if the region you want to access spans over multiple components.  The
  * // unsigned integer being read here is located across body and footer.
@@ -100,7 +100,7 @@
  * <pre>
  * // A new dynamic buffer is created.  Internally, the actual buffer is created
  * // lazily to avoid potentially wasted memory space.
- * {@link ByteBuf} b = {@link Unpooled}.buffer(4);
+ * {@link io.netty.buffer.ByteBuf} b = {@link io.netty.buffer.Unpooled}.buffer(4);
  *
  * // When the first write attempt is made, the internal buffer is created with
  * // the specified initial capacity (4).

codec-http/src/main/java/io/netty/handler/codec/http/HttpClientCodec.java

@@ -18,7 +18,7 @@
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.Channel;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.CombinedChannelDuplexHandler;
+import io.netty.channel.ChannelHandlerAppender;
 import io.netty.handler.codec.PrematureChannelClosureException;
 
 import java.util.ArrayDeque;
@@ -40,8 +40,7 @@
  *
  * @see HttpServerCodec
  */
-public final class HttpClientCodec
-        extends CombinedChannelDuplexHandler<HttpResponseDecoder, HttpRequestEncoder> {
+public final class HttpClientCodec extends ChannelHandlerAppender {
 
     /** A queue that is used for correlating a request and a response. */
     private final Queue<HttpMethod> queue = new ArrayDeque<HttpMethod>();
@@ -61,14 +60,6 @@ public HttpClientCodec() {
         this(4096, 8192, 8192, false);
     }
 
-    public void setSingleDecode(boolean singleDecode) {
-        inboundHandler().setSingleDecode(singleDecode);
-    }
-
-    public boolean isSingleDecode() {
-        return inboundHandler().isSingleDecode();
-    }
-
     /**
      * Creates a new instance with the specified decoder options.
      */
@@ -90,10 +81,22 @@ public HttpClientCodec(
     public HttpClientCodec(
             int maxInitialLineLength, int maxHeaderSize, int maxChunkSize, boolean failOnMissingResponse,
             boolean validateHeaders) {
-        init(new Decoder(maxInitialLineLength, maxHeaderSize, maxChunkSize, validateHeaders), new Encoder());
+        add(new Decoder(maxInitialLineLength, maxHeaderSize, maxChunkSize, validateHeaders), new Encoder());
         this.failOnMissingResponse = failOnMissingResponse;
     }
 
+    private Decoder decoder() {
+        return handlerAt(0);
+    }
+
+    public void setSingleDecode(boolean singleDecode) {
+        decoder().setSingleDecode(singleDecode);
+    }
+
+    public boolean isSingleDecode() {
+        return decoder().isSingleDecode();
+    }
+
     private final class Encoder extends HttpRequestEncoder {
 
         @Override

codec-http/src/main/java/io/netty/handler/codec/http/HttpResponseEncoder.java

@@ -16,7 +16,6 @@
 package io.netty.handler.codec.http;
 
 import io.netty.buffer.ByteBuf;
-import io.netty.util.CharsetUtil;
 
 import static io.netty.handler.codec.http.HttpConstants.*;
 

codec-http/src/main/java/io/netty/handler/codec/http/HttpServerCodec.java

@@ -15,7 +15,7 @@
  */
 package io.netty.handler.codec.http;
 
-import io.netty.channel.CombinedChannelDuplexHandler;
+import io.netty.channel.ChannelHandlerAppender;
 
 
 /**
@@ -24,8 +24,7 @@
  *
  * @see HttpClientCodec
  */
-public final class HttpServerCodec
-        extends CombinedChannelDuplexHandler<HttpRequestDecoder, HttpResponseEncoder> {
+public final class HttpServerCodec extends ChannelHandlerAppender {
 
     /**
      * Creates a new instance with the default decoder options

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientProtocolHandler.java

@@ -15,8 +15,8 @@
  */
 package io.netty.handler.codec.http.websocketx;
 
+import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandler;
 import io.netty.channel.ChannelPipeline;
 import io.netty.handler.codec.http.HttpHeaders;
 
@@ -34,7 +34,7 @@
  * This implementation will establish the websocket connection once the connection to the remote server was complete.
  *
  * To know once a handshake was done you can intercept the
- * {@link ChannelInboundHandler#userEventTriggered(ChannelHandlerContext, Object)} and check if the event was of type
+ * {@link ChannelHandler#userEventTriggered(ChannelHandlerContext, Object)} and check if the event was of type
  * {@link ClientHandshakeStateEvent#HANDSHAKE_ISSUED} or {@link ClientHandshakeStateEvent#HANDSHAKE_COMPLETE}.
  */
 public class WebSocketClientProtocolHandler extends WebSocketProtocolHandler {

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketClientProtocolHandshakeHandler.java

@@ -17,11 +17,11 @@
 
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.handler.codec.http.FullHttpResponse;
 
-class WebSocketClientProtocolHandshakeHandler extends ChannelInboundHandlerAdapter {
+class WebSocketClientProtocolHandshakeHandler extends ChannelHandlerAdapter {
     private final WebSocketClientHandshaker handshaker;
 
     public WebSocketClientProtocolHandshakeHandler(WebSocketClientHandshaker handshaker) {

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketFrameDecoder.java

@@ -15,13 +15,12 @@
  */
 package io.netty.handler.codec.http.websocketx;
 
-import io.netty.channel.ChannelInboundHandler;
+import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelPipeline;
 
 /**
  * Marker interface which all WebSocketFrame decoders need to implement.
  *
  * This makes it easier to access the added encoder later in the {@link ChannelPipeline}.
  */
-public interface WebSocketFrameDecoder extends ChannelInboundHandler {
-}
+public interface WebSocketFrameDecoder extends ChannelHandler { }

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketFrameEncoder.java

@@ -15,13 +15,13 @@
  */
 package io.netty.handler.codec.http.websocketx;
 
-import io.netty.channel.ChannelOutboundHandler;
+import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelPipeline;
 
 /**
  * Marker interface which all WebSocketFrame encoders need to implement.
  *
  * This makes it easier to access the added encoder later in the {@link ChannelPipeline}.
  */
-public interface WebSocketFrameEncoder extends ChannelOutboundHandler {
+public interface WebSocketFrameEncoder extends ChannelHandler {
 }

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketServerProtocolHandler.java

@@ -18,9 +18,8 @@
 import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelFutureListener;
 import io.netty.channel.ChannelHandler;
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandler;
-import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.ChannelPipeline;
 import io.netty.handler.codec.http.DefaultFullHttpResponse;
 import io.netty.handler.codec.http.FullHttpRequest;
@@ -45,7 +44,7 @@
  * to the <tt>io.netty.example.http.websocketx.server.WebSocketServer</tt> example.
  *
  * To know once a handshake was done you can intercept the
- * {@link ChannelInboundHandler#userEventTriggered(ChannelHandlerContext, Object)} and check if the event was of type
+ * {@link ChannelHandler#userEventTriggered(ChannelHandlerContext, Object)} and check if the event was of type
  * {@link ServerHandshakeStateEvent#HANDSHAKE_COMPLETE}.
  */
 public class WebSocketServerProtocolHandler extends WebSocketProtocolHandler {
@@ -122,7 +121,7 @@ static void setHandshaker(ChannelHandlerContext ctx, WebSocketServerHandshaker h
     }
 
     static ChannelHandler forbiddenHttpRequestResponder() {
-        return new ChannelInboundHandlerAdapter() {
+        return new ChannelHandlerAdapter() {
             @Override
             public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
                 if (msg instanceof FullHttpRequest) {

codec-http/src/main/java/io/netty/handler/codec/http/websocketx/WebSocketServerProtocolHandshakeHandler.java

@@ -17,8 +17,8 @@
 
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.ChannelPipeline;
 import io.netty.handler.codec.http.DefaultFullHttpResponse;
 import io.netty.handler.codec.http.FullHttpRequest;
@@ -35,8 +35,7 @@
 /**
  * Handles the HTTP handshake (the HTTP Upgrade request) for {@link WebSocketServerProtocolHandler}.
  */
-class WebSocketServerProtocolHandshakeHandler
-        extends ChannelInboundHandlerAdapter {
+class WebSocketServerProtocolHandshakeHandler extends ChannelHandlerAdapter {
 
     private final String websocketPath;
     private final String subprotocols;

codec-http/src/main/java/io/netty/handler/codec/spdy/SpdyCodecUtil.java

@@ -16,7 +16,6 @@
 package io.netty.handler.codec.spdy;
 
 import io.netty.buffer.ByteBuf;
-import io.netty.util.CharsetUtil;
 
 final class SpdyCodecUtil {
 

codec-http/src/main/java/io/netty/handler/codec/spdy/SpdyFrameCodec.java

@@ -15,12 +15,12 @@
  */
 package io.netty.handler.codec.spdy;
 
-import io.netty.channel.CombinedChannelDuplexHandler;
+import io.netty.channel.ChannelHandlerAppender;
 
 /**
  * A combination of {@link SpdyFrameDecoder} and {@link SpdyFrameEncoder}.
  */
-public final class SpdyFrameCodec extends CombinedChannelDuplexHandler<SpdyFrameDecoder, SpdyFrameEncoder> {
+public final class SpdyFrameCodec extends ChannelHandlerAppender {
     /**
      * Creates a new instance with the specified {@code version} and
      * the default decoder and encoder options

codec-http/src/main/java/io/netty/handler/codec/spdy/SpdyHttpCodec.java

@@ -15,13 +15,12 @@
  */
 package io.netty.handler.codec.spdy;
 
-import io.netty.channel.CombinedChannelDuplexHandler;
+import io.netty.channel.ChannelHandlerAppender;
 
 /**
  * A combination of {@link SpdyHttpDecoder} and {@link SpdyHttpEncoder}
  */
-public final class SpdyHttpCodec
-        extends CombinedChannelDuplexHandler<SpdyHttpDecoder, SpdyHttpEncoder> {
+public final class SpdyHttpCodec extends ChannelHandlerAppender {
     /**
      * Creates a new instance with the specified decoder options.
      */

codec-http/src/main/java/io/netty/handler/codec/spdy/SpdyOrHttpChooser.java

@@ -18,7 +18,6 @@
 import io.netty.buffer.ByteBuf;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandler;
 import io.netty.channel.ChannelPipeline;
 import io.netty.handler.codec.ByteToMessageDecoder;
 import io.netty.handler.codec.http.HttpObjectAggregator;
@@ -30,7 +29,7 @@
 import java.util.List;
 
 /**
- * {@link ChannelInboundHandler} which is responsible to setup the {@link ChannelPipeline} either for
+ * {@link ChannelHandler} which is responsible to setup the {@link ChannelPipeline} either for
  * HTTP or SPDY. This offers an easy way for users to support both at the same time while not care to
  * much about the low-level details.
  */
@@ -125,21 +124,21 @@ protected void addHttpHandlers(ChannelHandlerContext ctx) {
     }
 
     /**
-     * Create the {@link ChannelInboundHandler} that is responsible for handling the http requests
+     * Create the {@link ChannelHandler} that is responsible for handling the http requests
      * when the {@link SelectedProtocol} was {@link SelectedProtocol#HTTP_1_0} or
      * {@link SelectedProtocol#HTTP_1_1}
      */
-    protected abstract ChannelInboundHandler createHttpRequestHandlerForHttp();
+    protected abstract ChannelHandler createHttpRequestHandlerForHttp();
 
     /**
-     * Create the {@link ChannelInboundHandler} that is responsible for handling the http responses
+     * Create the {@link ChannelHandler} that is responsible for handling the http responses
      * when the {@link SelectedProtocol} was {@link SelectedProtocol#SPDY_3} or
      * {@link SelectedProtocol#SPDY_3_1}.
      *
      * By default this getMethod will just delecate to {@link #createHttpRequestHandlerForHttp()}, but
      * sub-classes may override this to change the behaviour.
      */
-    protected ChannelInboundHandler createHttpRequestHandlerForSpdy() {
+    protected ChannelHandler createHttpRequestHandlerForSpdy() {
         return createHttpRequestHandlerForHttp();
     }
 }

codec-http/src/main/java/io/netty/handler/codec/spdy/SpdySessionHandler.java

@@ -15,22 +15,21 @@
  */
 package io.netty.handler.codec.spdy;
 
-import io.netty.channel.ChannelDuplexHandler;
 import io.netty.channel.ChannelFuture;
 import io.netty.channel.ChannelFutureListener;
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
 import io.netty.channel.ChannelPromise;
 import io.netty.util.internal.EmptyArrays;
 
 import java.util.concurrent.atomic.AtomicInteger;
 
-import static io.netty.handler.codec.spdy.SpdyCodecUtil.SPDY_SESSION_STREAM_ID;
+import static io.netty.handler.codec.spdy.SpdyCodecUtil.*;
 
 /**
  * Manages streams within a SPDY session.
  */
-public class SpdySessionHandler
-        extends ChannelDuplexHandler {
+public class SpdySessionHandler extends ChannelHandlerAdapter {
 
     private static final SpdyProtocolException PROTOCOL_EXCEPTION = new SpdyProtocolException();
     private static final SpdyProtocolException STREAM_CLOSED = new SpdyProtocolException("Stream closed");

codec-http/src/test/java/io/netty/handler/codec/http/websocketx/WebSocketServerProtocolHandlerTest.java

@@ -16,9 +16,8 @@
 package io.netty.handler.codec.http.websocketx;
 
 import io.netty.channel.ChannelHandler;
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandlerAdapter;
-import io.netty.channel.ChannelOutboundHandlerAdapter;
 import io.netty.channel.ChannelPromise;
 import io.netty.channel.embedded.EmbeddedChannel;
 import io.netty.handler.codec.http.DefaultFullHttpRequest;
@@ -143,7 +142,7 @@ private static String getResponseMessage(FullHttpResponse response) {
         return new String(response.content().array());
     }
 
-    private class MockOutboundHandler extends ChannelOutboundHandlerAdapter {
+    private class MockOutboundHandler extends ChannelHandlerAdapter {
 
         @Override
         public void write(ChannelHandlerContext ctx, Object msg, ChannelPromise promise) throws Exception {
@@ -156,7 +155,7 @@ public void flush(ChannelHandlerContext ctx) throws Exception {
         }
     }
 
-    private static class CustomTextFrameHandler extends ChannelInboundHandlerAdapter {
+    private static class CustomTextFrameHandler extends ChannelHandlerAdapter {
         private String content;
 
         @Override

codec-http/src/test/java/io/netty/handler/codec/spdy/SpdyFrameDecoderTest.java

@@ -18,8 +18,8 @@
 import io.netty.bootstrap.Bootstrap;
 import io.netty.bootstrap.ServerBootstrap;
 import io.netty.channel.Channel;
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.ChannelInitializer;
 import io.netty.channel.EventLoopGroup;
 import io.netty.channel.nio.NioEventLoopGroup;
@@ -128,7 +128,7 @@ private static void addHeader(SpdyHeadersFrame frame, int headerNameSize, int he
         frame.headers().add(headerName.toString(), headerValue.toString());
     }
 
-    private static class CaptureHandler extends ChannelInboundHandlerAdapter {
+    private static class CaptureHandler extends ChannelHandlerAdapter {
         public volatile Object message;
 
         @Override

codec-http/src/test/java/io/netty/handler/codec/spdy/SpdySessionHandlerTest.java

@@ -15,8 +15,8 @@
  */
 package io.netty.handler.codec.spdy;
 
+import io.netty.channel.ChannelHandlerAdapter;
 import io.netty.channel.ChannelHandlerContext;
-import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.embedded.EmbeddedChannel;
 import io.netty.util.internal.logging.InternalLogger;
 import io.netty.util.internal.logging.InternalLoggerFactory;
@@ -330,7 +330,7 @@ public void testSpdyServerSessionHandlerGoAway() {
 
     // Echo Handler opens 4 half-closed streams on session connection
     // and then sets the number of concurrent streams to 1
-    private static class EchoHandler extends ChannelInboundHandlerAdapter {
+    private static class EchoHandler extends ChannelHandlerAdapter {
         private final int closeSignal;
         private final boolean server;