Develop Reference

Server does not data from client

I'm implementing a basic UDP server and client.
the server and the client are running on a same computer.
Please, don't mind grammar or spelling error on the code because it's not copy & paste.
1 Client,
public void sendData() {
Bootstrap b = new Bootstrap();
b.option(ChannelOption.SO_BROADCAST, true);
b.channel(NioDatagramChannel.class);
b.handler(new LogSenderHandler());
Channel channel = b.bind(9002).sync.channel();
channel.writeAndFlush(new DatagramPacket(Unpooled.copiedBuffer("test", CharsetUtils.UTF_8), SocketUtils.socketAddress("localhost", 9001))).sync();
channel.closeFuture().await();
}
2 Server.
public void run(){
Bootstrap b = new Bootstrap();
b.channel(NioDatagramChannel.class);
b.option(ChannelOption.SO_BROADCAST, true);
b.handler(new LogServerHnalder());
Channel channel = b.bind(9001).sync.channel();
channel.closeFuture().await();
}
3 LogServerHandler
public class LogServerHandler extends SimpleChannelInboundHandler<DatagramPacket> {
#Override
protected void channelRead0(ChannelHandlerContext ctx, DatagramPacket msg) throws Exception {
/* some code...... */
}
}
I expect LogServerHandler.channelRead() to be excuted when I call Client.run().
However LogServerHandler.channelRead() never excuted.

Netty connect to unix domain socket failed

I am writing a small Java program that using Netty to connect to a unix domain socket to retrieve some information. I am using Netty 4.0.32.Final and using native epoll package. Here is the bootstrap code I wrote:
final Bootstrap bootstrap = new Bootstrap();
bootstrap
.group(new EpollEventLoopGroup())
.channel(EpollDomainSocketChannel.class)
.handler(
new ChannelInitializer<DomainSocketChannel>() {
#Override
protected void initChannel(
final DomainSocketChannel channel) throws Exception {
channel.pipeline().addLast(
new ChannelInboundHandlerAdapter() {
#Override
public void channelRead(
final ChannelHandlerContext ctx,
final Object msg) throws Exception {
final ByteBuf buff = (ByteBuf) msg;
try {
buff.readBytes(
DomainSocket.this.out,
buff.readableBytes()
);
} finally {
buff.release();
}
}
#Override
public void exceptionCaught(
final ChannelHandlerContext ctx,
final Throwable cause) throws Exception {
Logger.error(
"Error occur when reading from Unix domain socket: %s",
cause.getMessage()
);
ctx.close();
}
}
);
}
}
);
It looks fine to me but when I run
bootstrap.connect(new DomainSocketAddress("/tmp/test.sock"));
It always complains with the following errors:
java.net.ConnectException: connect() failed: Connection refused: /tmp/test.sock
at io.netty.channel.epoll.Native.newConnectException(Native.java:504)
at io.netty.channel.epoll.Native.connect(Native.java:481)
at io.netty.channel.epoll.AbstractEpollStreamChannel.doConnect(AbstractEpollStreamChannel.java:567)
at io.netty.channel.epoll.EpollDomainSocketChannel.doConnect(EpollDomainSocketChannel.java:81)
at io.netty.channel.epoll.AbstractEpollStreamChannel$EpollStreamUnsafe.connect(AbstractEpollStreamChannel.java:627)
at io.netty.channel.DefaultChannelPipeline$HeadContext.connect(DefaultChannelPipeline.java:1097)
May I know is there anything wrong with the bootstrap setup? Thanks.
Update
I wrote a simple server to test the code above in a unit test. Here are the server codes:
final ServerBootstrap bootstrap = new ServerBootstrap();
bootstrap
.group(new EpollEventLoopGroup(), new EpollEventLoopGroup())
.channel(EpollServerDomainSocketChannel.class)
.childHandler(
new ChannelInitializer<ServerDomainSocketChannel>() {
#Override
protected void initChannel(
final ServerDomainSocketChannel channel)
throws Exception {
channel.pipeline().addLast(
new ChannelInboundHandlerAdapter() {
#Override
public void channelActive(
final ChannelHandlerContext ctx)
throws Exception {
final ByteBuf buff = ctx.alloc().buffer();
buff.writeBytes("This is a test".getBytes());
ctx.writeAndFlush(buff)
.addListener(
ChannelFutureListener.CLOSE
);
}
}
);
}
}
);
final ChannelFuture future =
bootstrap.bind(new DomainSocketAddress(input)).sync();
future.channel().closeFuture().sync();
I started this server code in a separate thread using ExecutorService. Thanks.

It looks like nothing is listening on that socket. Did you run any server listening there? Can you check:
netstat -na | grep /tmp/test.sock

Netty 4 read/write in handler multiple times

I'm new in Netty, and I decided to start with 4.0.0, because I thought it should be better, because it's newer. My server application should receive data from gps devices, and the process is like this - at first I'm receiving 2 bytes, which are length of device imei, and then I'm receiving imei with that length, then I should send 0x01 to device if I want to accept data from it. After my answer device sends me gps data with AVL protocol. Now my server is working without Netty, and I want to change it to work with netty.
This is what I have done:
I have created server class like this
public class BusDataReceiverServer {
private final int port;
private final Logger LOG = LoggerFactory.getLogger(BusDataReceiverServer.class);
public BusDataReceiverServer(int port) {
this.port = port;
}
public void run() throws Exception {
LOG.info("running thread");
EventLoopGroup bossGroup = new NioEventLoopGroup();
EventLoopGroup workerGroup = new NioEventLoopGroup();
try{
ServerBootstrap b = new ServerBootstrap();
b.group(bossGroup, workerGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new BusDataReceiverInitializer());
b.bind(port).sync().channel().closeFuture().sync();
}catch (Exception ex){
LOG.info(ex.getMessage());
}
finally {
LOG.info("thread closed");
bossGroup.shutdownGracefully();
workerGroup.shutdownGracefully();
}
}
public static void main(String[] args) throws Exception {
new BusDataReceiverServer(3129).run();
}
}
and created initializer class
public class BusDataReceiverInitializer extends ChannelInitializer<SocketChannel> {
#Override
protected void initChannel(SocketChannel socketChannel) throws Exception {
ChannelPipeline pipeline = socketChannel.pipeline();
pipeline.addLast("imeiDecoder", new ImeiDecoder());
pipeline.addLast("busDataDecoder", new BusDataDecoder());
pipeline.addLast("encoder", new ResponceEncoder());
pipeline.addLast("imeiHandler", new ImeiReceiverServerHandler());
pipeline.addLast("busDataHandler", new BusDataReceiverServerHandler());
}
}
then I have created decoders and encoder and 2 handlers. My imeiDecoder and encoder, and ImeiReceiverServerHandler are working. This is my ImeiReceiverServerHandler
public class ImeiReceiverServerHandler extends ChannelInboundHandlerAdapter {
private final Logger LOG = LoggerFactory.getLogger(ImeiReceiverServerHandler.class);
#Override
public void messageReceived(ChannelHandlerContext ctx, MessageList<Object> msgs) throws Exception {
MessageList<String> imeis = msgs.cast();
String imei = imeis.get(0);
ctx.write(Constants.BUS_DATA_ACCEPT);
ctx.fireMessageReceived(msgs);
}
#Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
super.channelInactive(ctx); //To change body of overridden methods use File | Settings | File Templates.
}
#Override
public void exceptionCaught(ChannelHandlerContext ctx, Throwable cause) throws Exception {
super.exceptionCaught(ctx, cause); //To change body of overridden methods use File | Settings | File Templates.
}
}
Now, after accepting I don't understand how to continue receive gps data and forward it to handler BusDataReceiverServerHandler.
If anyone could help me with this or could offer me useful documentation, I will be very grateful. Or if it is possible to do this with Netty 3, for this I will also be thankful.

I have not used Netty 4, so I am not sure if my answer will be 100% accurate or the best way to do things in Netty 4, but what you need to do is track the state of your connection / client session in order to know when to forward messages to your second handler.
E.g.
private enum HandlerState { INITIAL, IMEI_RECEIVED; }
private HandlerState state = HandlerState.INITIAL;
#Override
public void messageReceived(ChannelHandlerContext ctx, MessageList<Object> msgs) throws Exception
{
if (state == HandlerState.INITIAL)
{
MessageList<String> imeis = msgs.cast();
String imei = imeis.get(0);
ctx.write(Constants.BUS_DATA_ACCEPT);
state = HandlerState.IMEI_RECEIVED;
} else
{
// Forward message to next handler...
// Not sure exactly how this is done in Netty 4
// Maybe: ctx.fireMessageReceived(msgs);
// Or maybe it is:
// ctx.nextInboundMessageBuffer().add(msg);
// ctx.fireInboundBufferUpdated();
// I believe you could also remove the IMEI handler from the
// pipeline instead of having it keep state, if it is not going to do anything
// further.
}
}
So either track state in the handler, or remove the handler from the pipeline once it has finished if it will not be used further. When tracking state, you can either keep the state in the handler itself (as shown above), or keep the state variables in the context / attribute map (however that is done in netty 4).
The reason to not keep the state in the handler itself would be if you were going to make the handler shareable (one instance used across multiple channels). It is not necessary to do this, but there could be some resource savings if you have a large number of concurrent channels.

How to pass application/user data to the ChannelHandler Netty

When you design an a client that is going to connect to a lot of servers, like a crawler.
You will code something like that :
// the pipeline
public class CrawlerPipelineFactory implements ChannelPipelineFactory {
public ChannelPipeline getPipeline() throws Exception {
return Channels.pipeline(new CrawlerHandler());
}
}
// the channel handler
public class CrawlerHandler extends SimpleChannelHandler {
#Override
public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
// ...
}
}
// the main :
public static void main(){
ChannelFactory factory = new NioClientSocketChannelFactory(Executors.newCachedThreadPool(),Executors.newCachedThreadPool());
ClientBootstrap scannerBootstrap = new ClientBootstrap(factory);
scannerBootstrap.setPipelineFactory(new CrawlerPipelineFactory());
while(true){
MyURL url = stack.pop();
ChannelFuture connect = scannerBootstrap.connect(url.getSocketAddress());
}
}
Now when you are in your ApplicationHandler, the stuff that implements your SimpleChannelHandler or WhatEverStreamHandler, (CrawlerHander in the example) the only piece of information you get is the socketAdress you are connecting to that you can recover in "public void channelConnected()" function.
Ok but what if I want to recover some user data, like the MyURL object you see in my code example ?
I use a dirty hack, I use a Map<"ip:port",MyURL> so I can retrieve the associated data in channelConnected because I know ip:port i'm connected on.
This hack is really dirty, it won't work if you are connecting simultaneously to the same server (or you'll have to bind to a local port and use a key like "localport:ip:remoteport" but it's so dirty).
So I'm seeking what is the good way to pass data the the CrawlerHander ?
It would be cool if we could pass this data via the connect() method of the bootstrap. I know I can pass argument in my ChannelPipelineFactory.getPipeline() because it's invoked via connect(). But now we can't, so here is another dirty hack I use :
EDIT:
// the main
while(!targets.isEmpty()){
client.connect("localhost",111); // we will never connect to localhost, it's a hack
}
// the pipleline
public ChannelPipeline getPipeline() throws Exception {
return Channels.pipeline(
new CrawlerHandler(targets.pop()) // I specify each new host to connect here
);
}
// in my channel handler
// Now I have the data I want in the constructor, so I m sure I get them before everything is called
public class CrawlerHandler extends SimpleChannelHandler {
ExtraParameter target;
public CrawlerHandler(ExtraParameter target) {
this.target = target;
// but, and it's the most dirty part, I have to abort the connection to localhost, and reinit a new connection to the real target
boolean bFirstConnect=true;
#Override
public void connectRequested(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
if(bFirstConnect){
bFirstConnect = false;
ctx.getChannel().connect(target.getSocketAddr());
}

You can pass variables to Channel via Bootstrap.
Netty.io 4.1 & SO - Adding an attribute to a Channel before creation
Update to this answer while very late.

You can pass the data to the newly connected channel/channel handler using ChannelLocal or in ChannelHandlerContext (or in the Channel it self in latest Netty 3.x) using a connect future listener. In below example, ChannelLocal is used.
public class ChannelDataHolder {
public final static ChannelLocal<String> CHANNEL_URL = new ChannelLocal<String>(true);
}
// for each url in bootstrap
MyURL url = ....;
ChannelFuture cf = scannerBootstrap.connect(url.getSocketAddress());
final String urlString = url.getUrl();
cf.addListener(new ChannelFutureListener() {
#Override
public void operationComplete(ChannelFuture future) throws Exception {
ChannelDataHolder.CHANNEL_URL.set(future.getChannel(), urlString);
}
});
//In the handler
public class CrawlerHandler extends SimpleChannelHandler {
#Override
public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
String urlString = ChannelDataHolder.CHANNEL_URL.get(ctx.getChannel());
// ...use the data here
}
}
Note: instead of ChannelLocal, you can set and get the data using
ChannelHandlerContext.setAttachment()/getAttachment()
Channel.setAttachment()/getAttachment() in latest 3.x version of Netty
but both approaches does not support type safety.

Netty Camel samples

I'm a newbie to Netty.
I'm looking for some samples. (Preferably but not necessarity using Camel Netty Component and Spring)
Specifically a sample Netty app that consumes TCP messages.
Also how can I write a JUnit test that can test this netty app?
Thanks,
Dar

I assume you still want to integrate with Camel. I would first look at the camel documentation . After that frustrates you, you will need to start experimenting. I have one example where I created a Camel Processor as a Netty Server. The Netty components work such that a From endpoint is a server which consumes and a To endpoint is a client which produces. I needed a To endpoint that was a server and the component did not support that. I simply implemented a Camel Processor as a spring bean that started a Netty Server when it was initialized. The JBoss Netty documentation and samples are very good though. It is worthwhile to step through them.
Here is my slimmed down example. It is a server that sends a message to all the clients that are connected. If you are new to Netty I highly suggest going through the samples I linked to above:
public class NettyServer implements Processor {
private final ChannelGroup channelGroup = new DefaultChannelGroup();
private NioServerSocketChannelFactory serverSocketChannelFactory = null;
private final ExecutorService executor = Executors.newCachedThreadPool();
private String listenAddress = "0.0.0.0"; // overridden by spring-osgi value
private int listenPort = 51501; // overridden by spring-osgi value
#Override
public void process(Exchange exchange) throws Exception {
byte[] bytes = (byte[]) exchange.getIn().getBody();
// send over the wire
sendMessage(bytes);
}
public synchronized void sendMessage(byte[] message) {
ChannelBuffer cb = ChannelBuffers.copiedBuffer(message);
//writes to all clients connected.
this.channelGroup.write(cb);
}
private class NettyServerHandler extends SimpleChannelUpstreamHandler {
#Override
public void channelOpen(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
super.channelOpen(ctx, e);
//add client to the group.
NettyServer.this.channelGroup.add(e.getChannel());
}
// Perform an automatic recon.
#Override
public void channelConnected(ChannelHandlerContext ctx, ChannelStateEvent e) throws Exception {
super.channelConnected(ctx, e);
// do something here when a clien connects.
}
#Override
public void messageReceived(ChannelHandlerContext ctx, MessageEvent e) {
// Do something when a message is received...
}
#Override
public void exceptionCaught(ChannelHandlerContext ctx, ExceptionEvent e) {
// Log the exception/
}
}
private class PublishSocketServerPipelineFactory implements ChannelPipelineFactory {
#Override
public ChannelPipeline getPipeline() throws Exception {
// need to set the handler.
return Channels.pipeline(new NettyServerHandler());
}
}
// called by spring to start the server
public void init() {
try {
this.serverSocketChannelFactory = new NioServerSocketChannelFactory(this.executor, this.executor);
final ServerBootstrap serverBootstrap = new ServerBootstrap(this.serverSocketChannelFactory);
serverBootstrap.setPipelineFactory(new PublishSocketServerPipelineFactory());
serverBootstrap.setOption("reuseAddress", true);
final InetSocketAddress listenSocketAddress = new InetSocketAddress(this.listenAddress, this.listenPort);
this.channelGroup.add(serverBootstrap.bind(listenSocketAddress));
} catch (Exception e) {
}
}
// called by spring to shut down the server.
public void destroy() {
try {
this.channelGroup.close();
this.serverSocketChannelFactory.releaseExternalResources();
this.executor.shutdown();
} catch (Exception e) {
}
}
// injected by spring
public void setListenAddress(String listenAddress) {
this.listenAddress = listenAddress;
}
// injected by spring
public void setListenPort(int listenPort) {
this.listenPort = listenPort;
}
}

The camel release has a lot of examples but without a simple one for netty component.
Netty component can be use to setup a socket server to consume message and produce response back to the client. After some time of search on the web, I create my own tutorial using netty component in camel as a simple Camel-Netty hello world example to show:
Using netty component in camel to receive TCP message
Using POJO class to process the received message and create response
Sending response back to client.