Netty allows same port to be bound multiple times by different programs
I'm a noob to Sockets Programming.Maybe am asking a fundamental question. Please bear with me. I wrote a sample netty server and started it from console. It runs fine. The problem i have is that when i run the same server from two console windows, i'd expect one of them to throw 'Address already in use' exception. It does not do that and I dont understand why. Please help.
public static void main(String[] args) {
ChannelFactory cf = new NioServerSocketChannelFactory(Executors.newFixedThreadPool(100), new MemoryAwareThreadPoolExecutor(1000,2048,25096,2,TimeUnit.SECONDS));
//ChannelFactory cf = new OioServerSocketChannelFactory(Executors.newFixedThreadPool(100), Executors.newCachedThreadPool());
ServerBootstrap bootstrap = new ServerBootstrap(cf);
bootstrap.setPipelineFactory(new ChannelPipelineFactory() {
@Override
public ChannelPipeline getPipeline() throws Exception {
return Channels.pipeline(new ChannelHandler("test"));
}
});
bootstrap.setOption("child.keepAlive", true);
bootstrap.setOption("child.tcpNoDelay", true);
bootstrap.setOption("child.reuseAddress", true);
bootstrap.setOption("child.connectTimeoutMillis", 30000);
//NEVER bootstrap.setOption("child.readWriteFair", true);
//bootstrap.setOption("disconnect", true);
bootstrap.setOption("tcpNoDelay", true);
bootstrap.setOption("reuseAddress", true);
bootstrap.setOption("connectTimeoutMillis", 30000);
bootstrap.setOption("readWriteFair", true);
bootstrap.bind(new InetSocketAddress(9998));
}
To sum up the many comments above:
The bootstrap.setOption("reuseAddress", true); option will allow binding to an already bound ip:port combination. This is usually used to be able to restart a server if it crashed/got killed (so while the socket is still in the TIME_WAIT state).
In Windows it is possible to have two completely different programs bind the exact same ip:port . So even if in your app you have bootstrap.setOption("reuseAddress", false); it is still possible for another app (ie malicious) that enables SO_REUSEADDR to succesfully bind on your ip:port .
See here for more details: http://msdn.microsoft.com/en-us/library/windows/desktop/ms740621(v=vs.85).aspx
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