Expose eventloop on Stream

[ianopolous]

The use for the EventLoop is a p2p http proxy. It accepts incoming libp2p connections and proxies it to a fixed http endpoint or http handler. We needed access to the eventloop to add the new http handlers when receiving a new connection: https://github.com/Peergos/nabu/blob/master/src/main/java/org/peergos/protocol/http/HttpProtocol.java#L103

It is basically HTTP over libp2p. The entire implementation is in the single file linked above. We explain the use case a bit more in the "Decentralization" section of https://peergos.org/posts/dev-update

[Nashatyrev]

    public static void proxyRequest(Stream stream,
                                    HttpRequest msg,
                                    SocketAddress proxyTarget,
                                    Consumer<HttpObject> replyHandler) {
        Bootstrap b = new Bootstrap();
        b.group(stream.eventLoop())
                .channel(NioSocketChannel.class)
                .handler(new LoggingHandler(LogLevel.TRACE));

        ChannelFuture fut = b.connect(proxyTarget);
        Channel ch = fut.channel();
        ch.pipeline().addLast(new HttpRequestEncoder());
        ch.pipeline().addLast(new HttpResponseDecoder());
        ch.pipeline().addLast(new ResponseWriter(replyHandler));

        fut.addListener(x -> ch.writeAndFlush(msg));
    }

I'm not sure why do you need stream's eventLoop to create an independent connection?
Why not create a new NioEventLoopGroup or create and cache a single instance if it's performance critical?

[ianopolous]

I wanted to reuse the same thread. We were originally using a new pool, but this was 1000X faster. However I've just benchmarked using a static instance and that doesn't seem any slower than the same thread. So I think you're right, we don't need this.

[Nashatyrev]

Good, thanks for sorting this out 👍

A couple of notes on Netty code:

• It's not safe adding handlers after connect() - it could be the case when data arrives earlier than handlers added and it would just be discarded
• Need to double check if it's safe to invoke write() when connect() ChannelFuture completes. Basically the channel is ready for writing on channelActive event (see ChannelInboundHandler)

[Nashatyrev]

Sorry, accidentally posted incomplete comment. Some edit updates to previous comment

[Nashatyrev]

Was part of #272