Mysterious exception (NullPointerException)

SimJ

Hi,

I am trying to get to work a simple server-client communication using Processing's Network library.

I want that my server refuses new clients past a certain amount of already connected clients.

Here is my serverEvent method :

void serverEvent(Server _S, Client _C) // is run when a client connects
{
  if(idCount > maxClients)
  {
    _S.disconnect(_C);
    println("Client "+idCount+" refused.");
    idCount ++;
  }
  else {
    S.write(_C.ip()+" "+Integer.toString(idCount));
    println("Client "+idCount+" connected.");
    idCount ++;
  }
}

The else part works fine. But when the program executes the if part, it throws this exception :

java.lang.NullPointerException
    at processing.net.Client.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)

However the exception is thrown outside the if brackets : I can print something after the if/else statement before the exception is thrown.

Any hint to solve this ?

KevinWorkman

What do you mean by "certain amount of already connected clients"? What is the number?

SimJ

I've set maxClients = 10. I don't intend to set it to a much larger value.

KevinWorkman

Can you please post a more complete example? It's pretty hard to help you without seeing what's going on. Try narrowing your problem down to a MCVE.

SimJ

Sure !

To reproduce the problem :
- Create one sketch for the server and one for the client
- Run the server, then the client
- The server throws the exception

/*
    Server
*/

import processing.net.*;

Server S;

int idCount;
int maxClients;

void setup()
{
  size(100, 100);

  idCount = 11;
  maxClients = 10;
  S = new Server(this, 5204);
}

void draw(){}

void serverEvent(Server _S, Client _C) // is run when a client connects
{
  if(idCount > maxClients)
  {
    _S.disconnect(_C);
    println("Client "+idCount+" refused.");
    idCount ++;
  }
  else {
    println("Client "+idCount+" connected.");
    idCount ++;
  }
  println("End of serverEvent method.");
}

.

/*
    Client
*/

import processing.net.*;

Client C;

void setup()
{
  size(100, 100);

  C = new Client(this, "127.0.0.1", 5204);
}

void draw(){}

koogs

println(_S, _C);

after line 24

SimJ

I ran it a first time. The server didn't throw the exception when I ran the client sketch. I closed the client and ran it again, and then the server threw the exception :

processing.net.Server@6be9bac5 processing.net.Client@144e887f
Client 11 refused.
End of serverEvent method.
Client SocketException: Socket closed
processing.net.Server@6be9bac5 processing.net.Client@5674b403
Client 12 refused.
End of serverEvent method.
java.lang.NullPointerException
    at processing.net.Client.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)

I closed the server and started it again and this time it threw the exception on the first client connection.

processing.net.Server@3e0642fd processing.net.Client@6243d79
Client 11 refused.
End of serverEvent method.
java.lang.NullPointerException
    at processing.net.Client.run(Unknown Source)
    at java.lang.Thread.run(Thread.java:748)