Add StreamToMessageDecoder.replace() (#332)

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

@@ -4,14 +4,19 @@ import static io.netty.handler.codec.MessageToMessageEncoder.*;
 import io.netty.buffer.ChannelBuffer;
 import io.netty.channel.ChannelBufferHolder;
 import io.netty.channel.ChannelBufferHolders;
+import io.netty.channel.ChannelInboundHandler;
 import io.netty.channel.ChannelInboundHandlerAdapter;
 import io.netty.channel.ChannelInboundHandlerContext;
+import io.netty.channel.ChannelPipeline;
 
 public abstract class StreamToMessageDecoder<O> extends ChannelInboundHandlerAdapter<Byte> {
 
+    private ChannelInboundHandlerContext<Byte> ctx;
+
     @Override
     public ChannelBufferHolder<Byte> newInboundBuffer(
             ChannelInboundHandlerContext<Byte> ctx) throws Exception {
+        this.ctx = ctx;
         return ChannelBufferHolders.byteBuffer();
     }
 
@@ -84,6 +89,31 @@ public abstract class StreamToMessageDecoder<O> extends ChannelInboundHandlerAda
         }
     }
 
+    /**
+     * Replace this decoder in the {@link ChannelPipeline} with the given handler.
+     * All remaining bytes in the inbound buffer will be forwarded to the new handler's
+     * inbound buffer.
+     */
+    public void replace(String newHandlerName, ChannelInboundHandler<Byte> newHandler) {
+        if (!ctx.channel().eventLoop().inEventLoop()) {
+            throw new IllegalStateException("not in event loop");
+        }
+
+        // We do not use ChannelPipeline.replace() here so that the current context points
+        // the new handler.
+        ctx.pipeline().addAfter(ctx.name(), newHandlerName, newHandler);
+
+        ChannelBuffer in = ctx.in().byteBuffer();
+        try {
+            if (in.readable()) {
+                ctx.nextIn().byteBuffer().writeBytes(ctx.in().byteBuffer());
+                ctx.fireInboundBufferUpdated();
+            }
+        } finally {
+            ctx.pipeline().remove(this);
+        }
+    }
+
     public abstract O decode(ChannelInboundHandlerContext<Byte> ctx, ChannelBuffer in) throws Exception;
 
     public O decodeLast(ChannelInboundHandlerContext<Byte> ctx, ChannelBuffer in) throws Exception {