CODEWITHSUNDEEP
javabukkit
Mark Irvine
Mark Irvine

Reputation: 1369

TCP connection from Bukkit plugin

I am attempting to create a bukkit plugin that will connect to a tcp server and send messages when triggered by an event.

I have the basics in place but I'm missing something and I don't understand where to go from here. I can see that the plugin makes a connection to the server, but then throws an error and no message gets sent.

I am trying to understand how I send a string to a tcp client when an event occurs. For testing, I'm using the player move event.

When I start up I see the following in the craftbukkit server log:

Loading libraries, please wait...
[19:53:25 INFO]: Starting minecraft server version 1.7.10
[19:53:25 INFO]: Loading properties
[19:53:25 INFO]: Default game type: SURVIVAL
[19:53:25 INFO]: Generating keypair
[19:53:26 INFO]: Starting Minecraft server on *:25565
[19:53:26 INFO]: This server is running CraftBukkit version git-Bukkit-1.7.9-R0.2-20-g0b2ed13-b3108jnks (MC: 1.7.10) (Implementing API version 1.7.10-R0.1-SNAPSHOT)
[19:53:27 INFO]: [Compass] Loading Compass v0.1
[19:53:27 INFO]: Preparing level "world"
[19:53:27 INFO]: Preparing start region for level 0 (Seed: 7985848474339719790)
[19:53:27 WARN]: Could not get information about this CraftBukkit version; perhaps you are running a custom one?: FileNotFoundException
[19:53:28 INFO]: Preparing spawn area: 66%
[19:53:28 WARN]: Could not get latest artifact information: FileNotFoundException
[19:53:28 INFO]: Preparing start region for level 1 (Seed: 524789769407484853)
[19:53:29 INFO]: Preparing spawn area: 70%
[19:53:30 INFO]: Preparing start region for level 2 (Seed: 524789769407484853)
[19:53:30 INFO]: [Compass] Enabling Compass v0.1
[19:53:30 INFO]: [Compass] Start up.
[19:53:30 INFO]: [Compass] trying connect0
[19:53:30 INFO]: [Compass] getOutputStream()
[19:53:30 INFO]: [Compass] getInputStream()
[19:53:30 INFO]: Server permissions file permissions.yml is empty, ignoring it
[19:53:30 INFO]: Done (3.312s)! For help, type "help" or "?"
[19:54:25 INFO]: UUID of player MagicPixelPunk is 0322446d-6b92-4b63-af77-98d6739ec53b
[19:54:25 INFO]: MagicPixelPunk[/127.0.0.1:55376] logged in with entity id 206 at ([world] -164.16068813003193, 65.0, -141.0983355740641)

When I connect with a minecraft client and move the player, I see the following error in the craftbukkit server log:

21:52:01 INFO]: outToServer is null
21:52:01 INFO]: [CompassTask] writing to outToServer
21:52:01 INFO]: [CompassTask] Send failed: exception:
21:52:01 WARN]: java.lang.NullPointerException
21:52:01 WARN]:        at compass.Compass.onMove(Compass.java:61)

The java class Compass.java is below:

package compass;

import java.util.logging.Logger;
import org.bukkit.command.Command;
import org.bukkit.command.CommandSender;
import org.bukkit.command.CommandException;
import org.bukkit.entity.Player;
import org.bukkit.plugin.Plugin;
import org.bukkit.plugin.java.JavaPlugin;
import org.bukkit.event.EventHandler;
import org.bukkit.event.Listener;
import org.bukkit.event.player.PlayerMoveEvent;
import org.bukkit.scheduler.BukkitRunnable;
import java.io.IOException;
import java.util.concurrent.TimeoutException;
import java.lang.Exception;
import java.lang.Error;
import java.io.*; 
import java.net.*; 

public class Compass extends JavaPlugin implements Listener{
  public static Logger log = Logger.getLogger("Minecraft");
  public DataOutputStream outToServer;

  public void onEnable() {
    log.info("[Compass] Start up.");
    String sentence;   
    String modifiedSentence;   
    BufferedReader inFromUser = new BufferedReader( new InputStreamReader(System.in));  
    log.info("[Compass] trying connect0"); 
    try{
      Socket clientSocket = new Socket("localhost", 6789);  
      log.info("[Compass] getOutputStream()");
      DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());   
      log.info("[Compass] getInputStream()");
      BufferedReader inFromServer = new BufferedReader(new InputStreamReader(clientSocket.getInputStream()));
    }
    catch (Exception e){
      log.info("[Compass] Send failed: Exception: ");
      e.printStackTrace();
    }

    getServer().getPluginManager().registerEvents(this, this);
  }
  public void onReload() {
    log.info("[Compass] Server reloaded.");
  }
  public void onDisable() {
    log.info("[Compass] Server stopping.");
  }

    @EventHandler
    public void onMove(PlayerMoveEvent event) {
        try{
          if (outToServer == null) {
            log.info("outToServer is null");
          }
          log.info("[CompassTask] writing to outToServer");
          outToServer.writeBytes("test"+"\n");
          log.info(" [x] Sent '" + "test" + "'");
        }
        catch (Exception e){
          log.info("[CompassTask] Send failed: exception:");
          e.printStackTrace();
        }
        catch (Error e){
          log.info("[CompassTask] Send failed: error:");
          e.printStackTrace();
        }
    }

}

Any ideas on why outToServer is null when I try to write to it?

Upvotes: 0

Views: 462

Answers (2)

Mark Irvine
Mark Irvine

Reputation: 1369

It appears the problem was with the line:

DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream());

I guess this was creating a local variable, and so outToServer was null when I tried to use it outside of onEnable()

I changed to: 

outToServer = new DataOutputStream(clientSocket.getOutputStream());

works fine now.

Upvotes: 2

trinityalps
trinityalps

Reputation: 397

Given that the error says 

[19:53:30 INFO]: [Compass] Enabling Compass v0.1
[19:53:30 INFO]: [Compass] Start up.
[19:53:30 INFO]: [Compass] trying connect0
[19:53:30 INFO]: [Compass] getOutputStream()
[19:53:30 INFO]: [Compass] getInputStream()

Then says 

error: [Errno 10054] An existing connection was forcibly closed by the remote host

I am going to say that your error lies with runnable.runTaskTimer(this, 20, 100); So most likely you are not giving the server enough time.

Upvotes: 1

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