Re: Basic SocketServer & Thread Question

Lee Fesperman wrote:

shakah wrote:

john wrote:

How could I have a SocketServer accept connections from a handful of known
IP addresses, when the connections come and go in random order? Right now I
have one instance of ServerSocket accepting connections from all client IP
addresses:

ServerSocket ss = new ServerSocket(5000);  // listen on port 5000
while (true) {
 Socket s = serverSocket.accept();
 (new MyProcessor(s)).start();  // process stream in a new thread
}

But I want to bind to only specific IP addresses, something like this:

static final String[] validIP = {"100.200.300.1", "100.200.300.2",
"100.200.300.3"};
while (true) {
 for (int i=0; i<validIP.length; i++) {
   Socket s = serverSocket.bind(new InetSocketAddress(validIP[i], 5000));
   (new MyProcessor(s)).start();  // process stream in a new thread
 }
}

But this design requires the clients to connect in order. I could create a
thread that waits for a connection from each valid IP, but that would mean
having multiple instances of ServerSocket, and multiple ServerSocket
instances cannot listen to the same port number simultaneously. What can I
do?

Any hints or examples would be appreciated. I could just have MyProcessor
disconnect if it's not a valid address, but I was looking for a more elegant
solution.

Thanks.

-John 

Try extending your first example to use
Socket.getInetAddress().getHostAddress() on the accept'ed socket, e.g.
something like:

 ServerSocket ss = new ServerSocket(5000);  // listen on port 5000
 while (true) {
   Socket s = serverSocket.accept();
   String sIncomingHostAddress = s.getInetAddress().getHostAddress() ;
   if(/*sIncomingHostAddress is in list of acceptable hosts*/) {
     (new MyProcessor(s)).start();  // process stream in a new thread
   }
   else {
     s.close() ;
   }
 }


That's a reasonable solution depending on the circumstances. Alternatively, you can create a ServerSocket for each acceptable host and do accepts in separate threads.

I don't understand how this suggestion is supposed to work but you can also control the hosts which are accepted via a policy file SocketPermission/accept setting if you are prepared to let a SecurityManager loose.
.

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