How to add Channel Handler to TCPServer on Channel initialization - project-reactor

Question

I have the following code snipped that creates a TCPServer, and attaches a ChannelHandler to the channel in the doOnChannelInit() function. The server is to process byte data from an embedded device.
#Component
#RequiredArgsConstructor
public class NettyServer {
Logger log = LoggerFactory.getLogger(NettyServer.class);
private final NettyProperties nettyProperties;
private final NettyServerHandler nettyServerHandler;
private TcpServer server;
public void run() {
server = TcpServer
.create()
.host("localhost")
.port(nettyProperties.getTcpPort())
.doOnChannelInit((connectionObserver, channel, remoteAddress) -> {
log.info("Connection from " + remoteAddress);
channel.pipeline()
.addLast("idleStateHandler", new IdleStateHandler(0, 0, 4, TimeUnit.MINUTES))
.addLast(new ByteArrayDecoder())
.addLast(new ByteArrayEncoder())
.addLast(nettyServerHandler);
});
server.bindNow();
log.info("Server running");
}
}
Channel handler
#Component
#RequiredArgsConstructor
#ChannelHandler.Sharable
public class NettyServerHandler extends SimpleChannelInboundHandler<byte[]> {
Logger log = LoggerFactory.getLogger(NettyServerHandler.class);
private final AttributeKey<byte[]> dataKey = AttributeKey.valueOf("dataBuf");
private final AttributeKey<Integer> dataLen = AttributeKey.valueOf("dataBufLen");
#Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
log.info("New Meter connection from : " + ctx.channel());
}
#Override
public void channelInactive(ChannelHandlerContext ctx) throws Exception {
if (ctx.channel() != null) {
log.info(String.format("Meter/Client Disconnected. No: %s ; Channel : %s", meterNo, ctx.channel()));
}
ctx.close();
}
#Override
protected void channelRead0(ChannelHandlerContext ctx, byte[] msg) throws Exception {
log.info("Message received: " + new String(msg);
ctx.channel().read();
}
}
I'm able to connect to the server, but when i send a message, nothing happens, the log statements are not triggered.
I'm not sure what I'm missing here, would appreciate some help.
Thanks

Answer 1

There is no need to add custom handlers to the Netty pipeline. The example above can be written like this:
#Component
#RequiredArgsConstructor
public class NettyServer {
Logger log = LoggerFactory.getLogger(NettyServer.class);
private final NettyProperties nettyProperties;
private TcpServer server;
public void run() {
server = TcpServer
.create()
.host("localhost")
.port(nettyProperties.getTcpPort())
.doOnChannelInit((connectionObserver, channel, remoteAddress) -> {
log.info("Connection from " + remoteAddress);
channel.pipeline()
.addLast("idleStateHandler", new IdleStateHandler(0, 0, 4, TimeUnit.MINUTES));
})
.handle((in, out) ->
in.receive()
.asString()
.doOnNext(s -> log.info("Message received: " + s))
.then());
server.bindNow();
log.info("Server running");
}
}
Consider checking the Reference Documentation
The incoming data can be transformed to String with (asString), to byte[] with (asByteArray) etc. If there is no suitable transformation you can use map(byteBuf -> ...) and transform the ByteBuf to the needed abstraction.