[#4087] Correctly forward bytes when remove codec and handle channelInactive / channelReadComplete(...)

Motivation:

We missed to correctly implement the handlerRemoved(...) / channelInactive(...) and channelReadComplete(...) method, this leaded to multiple problems:

 - Missed to forward bytes when the codec is removed from the pipeline
 - Missed to call decodeLast(...) once the Channel goes in active
 - No correct handling of channelReadComplete that could lead to grow of cumulation buffer.

Modifications:

- Correctly implement methods and forward to the internal ByteToMessageDecoder
- Add unit test.

Result:

Correct behaviour

codec/src/main/java/io/netty/handler/codec/ByteToMessageCodec.java

@@ -108,6 +108,34 @@ public abstract class ByteToMessageCodec<I> extends ChannelDuplexHandler {
         encoder.write(ctx, msg, promise);
     }
 
+    @Override
+    public void channelReadComplete(ChannelHandlerContext ctx) throws Exception {
+        decoder.channelReadComplete(ctx);
+    }
+
+    @Override
+    public void channelInactive(ChannelHandlerContext ctx) throws Exception {
+        decoder.channelInactive(ctx);
+    }
+
+    @Override
+    public void handlerAdded(ChannelHandlerContext ctx) throws Exception {
+        try {
+            decoder.handlerAdded(ctx);
+        } finally {
+            encoder.handlerAdded(ctx);
+        }
+    }
+
+    @Override
+    public void handlerRemoved(ChannelHandlerContext ctx) throws Exception {
+        try {
+            decoder.handlerRemoved(ctx);
+        } finally {
+            encoder.handlerRemoved(ctx);
+        }
+    }
+
     /**
      * @see MessageToByteEncoder#encode(ChannelHandlerContext, Object, ByteBuf)
      */

codec/src/test/java/io/netty/handler/codec/ByteToMessageCodecTest.java

@@ -16,12 +16,16 @@
 package io.netty.handler.codec;
 
 import io.netty.buffer.ByteBuf;
+import io.netty.buffer.Unpooled;
 import io.netty.channel.ChannelHandler;
 import io.netty.channel.ChannelHandlerContext;
+import io.netty.channel.embedded.EmbeddedChannel;
 import org.junit.Test;
 
 import java.util.List;
 
+import static org.junit.Assert.*;
+
 public class ByteToMessageCodecTest {
 
     @Test(expected = IllegalStateException.class)
@@ -34,6 +38,39 @@ public class ByteToMessageCodecTest {
         new InvalidByteToMessageCodec2();
     }
 
+    @Test
+    public void testForwardPendingData() {
+        ByteToMessageCodec<Integer> codec = new ByteToMessageCodec<Integer>() {
+            @Override
+            protected void encode(ChannelHandlerContext ctx, Integer msg, ByteBuf out) throws Exception {
+                out.writeInt(msg);
+            }
+
+            @Override
+            protected void decode(ChannelHandlerContext ctx, ByteBuf in, List<Object> out) throws Exception {
+                if (in.readableBytes() >= 4) {
+                    out.add(in.readInt());
+                }
+            }
+        };
+
+        ByteBuf buffer = Unpooled.buffer();
+        buffer.writeInt(1);
+        buffer.writeByte('0');
+
+        EmbeddedChannel ch = new EmbeddedChannel(codec);
+        assertTrue(ch.writeInbound(buffer));
+        ch.pipeline().remove(codec);
+        assertTrue(ch.finish());
+        assertEquals(1, ch.readInbound());
+
+        ByteBuf buf = (ByteBuf) ch.readInbound();
+        assertEquals(Unpooled.wrappedBuffer(new byte[]{'0'}), buf);
+        buf.release();
+        assertNull(ch.readInbound());
+        assertNull(ch.readOutbound());
+    }
+
     @ChannelHandler.Sharable
     private static final class InvalidByteToMessageCodec extends ByteToMessageCodec<Integer> {
         InvalidByteToMessageCodec() {