Netty Client Connect with Server, but server does not fire channelActive/Registered - server

Question

I have the following architecture in use:
- [Client] - The enduser connecting to our service.
- [GameServer] - The game server on which the game is running.
- [GameLobby] - A server that is responsible for matching Clients with a GameServer.
If we have for example 4 Clients that want to play a game and get matched to a GameLobby, then the first time all these connection succeeds properly.
However when they decide to rematch, then one of the Clients will not properly connect.
The connection between all the Clients and the GameServer happens simultaneously.
Clients that rematch first removes their current connection with the GameServer and head into the lobby again.
This connection will succeed, no errors are thrown. Even using a ChannelFuture it shows that the client connection was made properly, the following values are retrieved to show that the client thinks the connection was correct:
- ChannelFuture.isSuccess() = True
- ChannelFuture.isDone() = True
- ChannelFuture.cause() = Null
- ChannelFuture.isCancelled() = False
- Channel.isOpen() = True
- Channel.isActive() = True
- Channel.isRegistered() = True
- Channel.isWritable() = True
Thus the connection was properly made according to the Client. However on the GameServer at the SimpleChannelInboundHandler, the method ChannelRegistered/ChannelActive is never called for that specific Client. Only for the other 3 Clients.
All the 4 Clients, the GameServer, and the Lobby are running on the same IPAddress.
Since it only happens when (re)connecting again to the GameServer, I thought that is had to do with not properly closing the connection. Currently this is done through:
try {
group.shutdownGracefully();
channel.closeFuture().sync();
} catch (InterruptedException e) {
e.printStackTrace();
}
On the GameServer the ChannelUnregister is called thus this is working, and the connection is destroyed.
I have tried adding listeners to the ChannelFuture of the malfunctioning channel connection, however according to the channelFuture everything works, which is not the case.
I tried adding ChannelOptions to allow for more Clients queued to the server.
GameServer
The GameServer server is initialized as follow:
// Create the bootstrap to make this act like a server.
ServerBootstrap serverBootstrap = new ServerBootstrap();
serverBootstrap.group(bossGroup)
.channel(NioServerSocketChannel.class)
.childHandler(new ChannelInitialisation(new ClientInputReader(gameThread)))
.option(ChannelOption.SO_BACKLOG, 1000)
.childOption(ChannelOption.SO_KEEPALIVE, true)
.childOption(ChannelOption.TCP_NODELAY, true);
bossGroup.execute(gameThread); // Executing the thread that handles all games on this GameServer.
// Launch the server with the specific port.
serverBootstrap.bind(port).sync();
The GameServer ClientInputReader
#ChannelHandler.Sharable
public class ClientInputReader extends SimpleChannelInboundHandler<Packet> {
private ServerMainThread serverMainThread;
public ClientInputReader(ServerMainThread serverMainThread) {
this.serverMainThread = serverMainThread;
}
#Override
public void channelRegistered(ChannelHandlerContext ctx) throws Exception {
System.out.println("[Connection: " + ctx.channel().id() + "] Channel registered");
super.channelRegistered(ctx);
}
#Override
protected void channelRead0(ChannelHandlerContext ctx, Packet packet) {
// Packet handling
}
}
The malfunction connection is not calling anything of the SimpleChannelInboundHandler. Not even ExceptionCaught.
The GameServer ChannelInitialisation
public class ChannelInitialisation extends ChannelInitializer<SocketChannel> {
private SimpleChannelInboundHandler channelInputReader;
public ChannelInitialisation(SimpleChannelInboundHandler channelInputReader) {
this.channelInputReader = channelInputReader;
}
#Override
protected void initChannel(SocketChannel ch) throws Exception {
ChannelPipeline pipeline = ch.pipeline();
// every packet is prefixed with the amount of bytes that will follow
pipeline.addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
pipeline.addLast(new LengthFieldPrepender(4));
pipeline.addLast(new PacketEncoder(), new PacketDecoder(), channelInputReader);
}
}
Client
Client creating a GameServer connection:
// Configure the client.
group = new NioEventLoopGroup();
Bootstrap b = new Bootstrap();
b.group(group)
.channel(NioSocketChannel.class)
.option(ChannelOption.TCP_NODELAY, true)
.handler(new ChannelInitialisation(channelHandler));
// Start the client.
channel = b.connect(address, port).await().channel();
/* At this point, the client thinks that the connection was succesfully, as the channel is active, open, registered and writable...*/
ClientInitialisation:
public class ChannelInitialisation extends ChannelInitializer<SocketChannel> {
private SimpleChannelInboundHandler<Packet> channelHandler;
ChannelInitialisation(SimpleChannelInboundHandler<Packet> channelHandler) {
this.channelHandler = channelHandler;
}
#Override
public void initChannel(SocketChannel ch) throws Exception {
// prefix messages by the length
ch.pipeline().addLast(new LengthFieldBasedFrameDecoder(Integer.MAX_VALUE, 0, 4, 0, 4));
ch.pipeline().addLast(new LengthFieldPrepender(4));
// our encoder, decoder and handler
ch.pipeline().addLast(new PacketEncoder(), new PacketDecoder(), channelHandler);
}
}
ClientHandler:
public class ClientPacketHandler extends SimpleChannelInboundHandler<Packet> {
#Override
public void channelActive(ChannelHandlerContext ctx) throws Exception {
super.channelActive(ctx);
System.out.println("Channel active: " + ctx.channel().id());
ctx.channel().writeAndFlush(new PacketSetupClientToGameServer());
System.out.println("Sending setup packet to the GameServer: " + ctx.channel().id());
// This is successfully called, as the client thinks the connection was properly made.
}
#Override
protected void channelRead0(ChannelHandlerContext ctx, Packet packet) {
// Reading packets.
}
}
I expect that the Client could connect properly to the server. Since the other Clients are properly connecting and the client could previously connect just fine.
TL;DR: When multiple Clients try to create a new match, there is a possibility that one, possibly more, Client(s) will not connect properly with the server, after the previous connection was closed.

Answer 1

For some that struggle with this issue in some way or another.
I did a workaround that allows me to continue even tho there is still a bug inside the Netty framework (as far as I am concerned). The workaround is quite simple just create a connection pool.
My solution uses a maximum of five connections inside the connection pool. If one of the connection gets no reply from the GameServer, then it is not that big of a deal, since there are four others that will have a high chance of succeeding. I know this is a bad workaround, but I could not find any information on this issue. It works and only gives a maximum delay of 5 seconds (each retry takes a second)