Netty 5.0 swallowing exceptions

[Qix-]

Perhaps this is user error, but this is completely unintuitive in my opinion. Just sat here debugging something for a few hours; turns out Netty has been swallowing a bunch of exceptions, even when exceptionCaught was overridden.

The following code produces no output, and the server being connected to gets no data (it does, however, receive a connection).

package com.boltery.bouncer;

import io.netty.bootstrap.Bootstrap;
import io.netty.buffer.ByteBuf;
import io.netty.buffer.Unpooled;
import io.netty.channel.Channel;
import io.netty.channel.ChannelHandlerAdapter;
import io.netty.channel.ChannelHandlerContext;
import io.netty.channel.ChannelInitializer;
import io.netty.channel.ChannelOption;
import io.netty.channel.EventLoopGroup;
import io.netty.channel.nio.NioEventLoopGroup;
import io.netty.channel.socket.SocketChannel;
import io.netty.channel.socket.nio.NioSocketChannel;
import io.netty.handler.codec.MessageToMessageEncoder;

import java.nio.charset.Charset;
import java.util.List;
import java.util.concurrent.TimeUnit;

public class Maine2 {
    public static void main(String[] args) throws Exception {
        final EventLoopGroup loopGroup = new NioEventLoopGroup();
        final Bootstrap bootstrap = new Bootstrap()
                .group(loopGroup)
                .channel(NioSocketChannel.class)
                .handler(new ChannelInitializer<SocketChannel>() {
                    @Override
                    protected void initChannel(final SocketChannel socketChannel) throws Exception {
                        socketChannel.pipeline().addLast(new MessageToMessageEncoder<Object>() {
                            @Override
                            protected void encode(final ChannelHandlerContext channelHandlerContext, final Object o, final List<Object> list) throws Exception {
                                throw new Exception();
                            }

                            @Override
                            public void exceptionCaught(final ChannelHandlerContext ctx, final Throwable cause) throws Exception {
                                // never hit...
                                cause.printStackTrace();
                            }
                        });
                    }
                })
                .option(ChannelOption.SO_KEEPALIVE, true);

        final Channel ch = bootstrap.connect("127.0.0.1", 11792).await().channel();

        final ByteBuf buf = Unpooled.buffer();
        buf.retain();
        buf.writeBytes("Hello".getBytes(Charset.forName("UTF-8")));
        ch.writeAndFlush(buf);

        loopGroup.awaitTermination(2, TimeUnit.SECONDS);
    }
}

Am I missing something here? Adding a future listener and checking .isSuccess() works as expected...

ch.writeAndFlush(buf).addListener((future) -> {
    if (future.isSuccess()) {
        System.out.println("Success");
    } else {
        System.err.println("FAILED"); // correctly prints "FAILED" when run
    }
});

However if there isn't a listener, things should crash or exceptionCaught should be called. This is particularly useful in cases where a step shouldn't fail. What if a listener hasn't been added? This makes debugging an absolute nightmare to the point I would never want to use Netty in production.

[normanmaurer]

exceptionCaught(...) is only called for inbound exceptions. All outbound exceptions must by handled in a listener by design. If you always want to have exceptions handled in exceptionCaught(...) just add a ChannelOutboundHandler that will an listener for every outbound operation

[Qix-]

@normanmaurer ChannelOutboundHandler was deprecated in 5.0 I thought.

[normanmaurer]

And 5.0 was deprecated completly atm. Use 4.1 in which ChannelOutboundHandler was not deprecated. (In 5.0 you would have used ChannelHandler directly)

Am 17.01.2016 um 16:36 schrieb Josh Junon notifications@github.com:

@normanmaurer ChannelOutboundHandler was deprecated in 5.0.

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[Qix-]

How is 5.0 "deprecated completely"? Is it not the next Alpha version?

[normanmaurer]

No we not plan to work on 5.0 any time soon but concentrate on 4.0 and 4.1. All none breaking changes were backported to 4.1

Am 17.01.2016 um 17:37 schrieb Josh Junon notifications@github.com:

How is 5.0 "deprecated completely"? Is it not the next Alpha version?

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[Qix-]

Sad, I liked the changes that occurred in 5.0.

[normanmaurer]

Can you list which ones and for what reason?

Am 17.01.2016 um 18:05 schrieb Josh Junon notifications@github.com:

Sad, I liked the changes that occurred in 5.0.

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[Qix-]

The refactoring to use Java's Executor APIs a little more. Allows better interoperability between different libraries. That was a big one.

Call me crazy, but pipeline nodes should be agnostic to whether the data they're working on is inbound/outbound. Netty 5.0 started to move towards that I feel like.

One step further would be to explicitly specify which part of the duplex stream a pipeline handler should be put on (a simple approach to this would be two pipelines). Having two streams (inbound/outbound) in the same "stack" (pipeline) gets confusing, and doing automagic determination as to which handlers should be called for inbound/outbound data makes the API a bit messier.

I imagine it would reduce under-the-hood code as well, and thus even performance (I speculate) since you don't have to determine which handlers should be fired for each message.