Building a Future API on top of Netty - java-8

Question

I want to build an API based on Futures (from java.util.concurrent) that is powered by a custom protocol on top of Netty (version 4). Basic idea is to write a simple library that would abstract the underlying Netty implementation and make it easier to make requests.
Using this library, one should be able to write something like this:
Request req = new Request(...);
Future<Response> responseFuture = new ServerIFace(host, port).call(req);
// For example, let's block until this future is resolved
Reponse res = responseFuture.get().getResult();
Underneath this code, a Netty client is connected
public class ServerIFace {
private Bootstrap bootstrap;
private EventLoopGroup workerGroup;
private String host;
private int port;
public ServerIFace(String host, int port) {
this.host = host;
this.port = port;
this.workerGroup = new NioEventLoopGroup();
bootstrap();
}
private void bootstrap() {
bootstrap = new Bootstrap();
bootstrap.group(workerGroup);
bootstrap.channel(NioSocketChannel.class);
bootstrap.handler(new ChannelInitializer<SocketChannel>() {
#Override
protected void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new ObjectEncoder());
ch.pipeline().addLast(new ObjectDecoder(ClassResolvers.cacheDisabled(Response.class.getClassLoader())));
ch.pipeline().addLast("response", new ResponseReceiverChannelHandler());
}
});
}
public Future<Response> call(final Request request) throws InterruptedException {
CompletableFuture<Response> responseFuture = new CompletableFuture<>();
Channel ch = bootstrap.connect(host, port).sync().channel();
ch.writeAndFlush(request).addListener((f) -> {
if (f.isSuccess()) {
System.out.println("Wrote successfully");
} else {
f.cause().printStackTrace();
}
});
ChannelFuture closeFuture = ch.closeFuture();
// Have to 'convert' ChannelFuture to java.util.concurrent.Future
closeFuture.addListener((f) -> {
if (f.isSuccess()) {
// How to get this response?
Response response = ((ResponseReceiverChannelHandler) ch.pipeline().get("response")).getResponse();
responseFuture.complete(response);
} else {
f.cause().printStackTrace();
responseFuture.cancel(true);
}
ch.close();
}).sync();
return responseFuture;
}
}
Now, as you can see, in order to abstract Netty's inner ChannelFuture, I have to 'convert' it to Java's Future (I'm aware that ChannelFuture is derived from Future, but that information doesn't seem useful at this point).
Right now, I'm capturing this Response object in the last handler of my inbound part of the client pipeline, the ResponseReceiverChannelHandler.
public class ResponseReceiverChannelHandler extends ChannelInboundHandlerAdapter {
private Response response = null;
#Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
this.response = (Response)msg;
ctx.close();
}
public Response getResponse() {
return response;
}
}
Since I'm new to Netty and these things in general, I'm looking for a cleaner, thread-safe way of delivering this object to the API user.
Correct me if I'm wrong, but none of the Netty examples show how to achieve this, and most of the Client examples just print out whatever they get from Server.
Please note that my main goal here is to learn more about Netty, and that this code has no production purposes.
For the reference (although I don't think it's that relevant) here's the Server code.
public class Server {
public static class RequestProcessorHandler extends ChannelInboundHandlerAdapter {
#Override
public void channelRead(ChannelHandlerContext ctx, Object msg) throws Exception {
ChannelFuture future;
if (msg instanceof Request) {
Request req = (Request)msg;
Response res = some function of req
future = ctx.writeAndFlush(res);
} else {
future = ctx.writeAndFlush("Error, not a request!");
}
future.addListener((f) -> {
if (f.isSuccess()) {
System.out.println("Response sent!");
} else {
System.out.println("Response not sent!");
f.cause().printStackTrace();
}
});
}
}
public int port;
public Server(int port) {
this.port = port;
}
public void run() throws Exception {
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try {
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitializer<SocketChannel>() {
#Override
public void initChannel(SocketChannel ch) throws Exception {
ch.pipeline().addLast(new ObjectDecoder(ClassResolvers.cacheDisabled(Request.class.getClassLoader())));
ch.pipeline().addLast(new ObjectEncoder());
// Not really shutting down this threadpool but it's ok for now
ch.pipeline().addLast(new DefaultEventExecutorGroup(2), new RequestProcessorHandler());
}
})
.option(ChannelOption.SO_BACKLOG, 128)
.childOption(ChannelOption.SO_KEEPALIVE, true);
ChannelFuture f = b.bind(port).sync();
f.channel().closeFuture().sync();
} finally {
workerGroup.shutdownGracefully();
bossGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
int port;
if (args.length > 0) {
port = Integer.parseInt(args[0]);
} else {
port = 8080;
}
new Server(port).run();
}
}