SmartFoxServer provides build-in NPC features. The mechanism behind the NPC features from SmartFoxServer is to connect a new player to the server internally. In other words, SmartFoxServer creates a new socket connect for the NPC. The server treats the NPC as a normal user that connects from localhost.

We can enable the NPC feature in the config.xml configuration file.

<EnableNPC>true</EnableNPC>

The NPCs will be controlled in the server-side extension. We have created a server-side extension to handle the players' request. Now we will create an extension dedicated to control the NPC logic.

<Extensions>
<extension name="virtualWorld" className="virtualworld.as" type="script" />
<extension name="VirtualWorld" className="VirtualWorld" type="java" />
<extension name="npc" className="virtualworld_npc.as" type="script" />
</Extensions>

The createNPC server-side API call will let us create the NPC and "connect" it to the server. It needs four parameters to create the NPC.

As the NPC creation is a real socket connection to the server, it is just like connecting a player to the server that requires both server IP address and port number. The NPC connection will receive server messages and events the same as players. In order to get the best performance, most of the time we should connect the NPC with the IP address set to 127.0.0.1.

_server.createNPC("NPC name", "127.0.0.1", 9339, _server. getCurrentZone().getName());

It is because the server is not ready yet when the init function is executed. We have to wait till the whole server initializes to create our NPC. The server will dispatch a serverReady internal event after the initialization. We will create our NPC at that time and join the room island1.

function handleInternalEvent(e){
if (e.name == "serverReady") {
theNpcUser = _server.createNPC("TestNPC", "127.0.0.1", 9339, _server.getCurrentZone().getName());
var ok = _server.joinRoom(theNpcUser, -1, true, _server. getCurrentZone().getRoomByName('island1').getId());
}
}

After players connect to the server, they have to choose our style before logging in to the server, and so does the NPC. In our virtual world, the NPCs need to set their appearances in user variables so that other players can draw them. We will assign the styles and position user variables to the NPC.

function handleInternalEvent(e){
if (e.name == "serverReady") {
theNpcUser = _server.createNPC("TestNPC", "127.0.0.1", 9339, _server.getCurrentZone().getName());
var ok = _server.joinRoom(theNpcUser, -1, true, _server. getCurrentZone().getRoomByName('island1').getId());
var uVars = {}
uVars.avatarColor = 0xccffcc;
uVars.isoPosX = 8;
uVars.isoPosY = 16;
uVars.fistTime = 1;
uVars.style = 1;
// Set the variables for this client
_server.setUserVariables(theNpcUser, uVars)
}
}

After restarting the server and logging in to the virtual world, we will see our NPC. However, if we wait for approximate five minutes in the virtual world, we will find that the NPC is disconnected by the server because of the excess of the maximum user idle time. It is because that NPC connection is same as the player's in the view of the server.

The disconnect message will be shown in the server prompt.

[ INFO ] > Disconneting idle user: TestNPC

In order to keep the NPC alive in the virtual world, we can schedule a loop for the NPC to update the server. We create an interval to execute the loop in a certain period. The time of the period can be of any value as long as it is shorter than the MaxUserIdleTime in the configuration file.

function init(){
myInterval = setInterval("npcLoop", 8000)
}

Inside the loop, we will call the updateMessageTime server-side API. This function will refresh the timestamp of the last message of the user to current time. That is to let the server know that the user is still alive in the world and not idling.

theNpcUser.updateMessageTime()

Besides updating the message time, we will also dispatch a public message by the NPC. It is useful for us to test the code and check if the loop is executing correctly.

function npcLoop() {
if (theNpcUser != null) {
theNpcUser.updateMessageTime()
var rooms = theNpcUser.getRoomsConnected();
_server.dispatchPublicMessage("|chat|Hello Virtual World", _server.getCurrentZone().getRoom(rooms[0]), theNpcUser)
}
}

In SmartFoxServer 1.6.5, there is a known issue with the NPC feature. According to the documentation from SmartFoxServer, all NPC connections will not be closed completely after the NPC disconnects. The connections remain in a CLOSE_WAIT state in TCP layer.

This problem will not affect the NPCs that are created once and last for the whole server life cycle. That is because the shut down process can remove all NPC connections.

However, if the NPCs are being created or destroyed repeatedly, the remaining incomplete and closed connections will eventually exhaust the number of sockets available in the operating system.

We can avoid this problem by writing an external application to connect to the server and act as the NPC.

We will create a basic NPC by using the Java API. It creates the NPC instance and holds the process until the terminate command. Create a new file anywhere on the server-side and name it NPC.java. We will implement a basic NPC within this file.

public class NPC implements ISFSEventListener{
public static void main (String[] args) {
NPC npc = new NPC();
try{
System.in.read(); // Wait until ctrl-C
}
catch(Exception e){}
}
...
}

The NPC client reads a configuration XML with the server IP, port, and the zone to connect.

private SmartFoxClient sfs;
public NPC() {
sfs = new SmartFoxClient(true);
sfs.addEventListener(SFSEvent.onConfigLoadSuccess, this);
sfs.addEventListener(SFSEvent.onConfigLoadFailure, this);
sfs.addEventListener(SFSEvent.onConnection, this);
sfs.addEventListener(SFSEvent.onLogin, this);
sfs.addEventListener(SFSEvent.onRoomListUpdate, this);
sfs.addEventListener(SFSEvent.onJoinRoom, this);
// Load the config file
sfs.loadConfig("config.xml", false);
}

Similar to the ActionScript SmartFoxClient, there are different events to indicate the state changes of the application. We will log in the NPC to the server step-by-step and finally set the user variables.

public void handleEvent(final SFSEvent event){
if(event.getName().equals(SFSEvent.onConfigLoadSuccess)) {
sfs.connect(sfs.ipAddress, sfs.port);
}
else if(event.getName().equals(SFSEvent.onConfigLoadFailure)) {
System.out.println("ERROR: Connect Failed.");
}
else if(event.getName().equals(SFSEvent.onConnection)) {
sfs.login(sfs.defaultZone, "JavaNPC", "");
}
else if(event.getName().equals(SFSEvent.onLogin)) {
}
else if(event.getName().equals(SFSEvent.onRoomListUpdate)) {
System.out.println("Login Successful");
// join the island1 room
sfs.joinRoom("island1","",false);
}
else if(event.getName().equals(SFSEvent.onJoinRoom)) {
Map<String, SFSVariable> uVars = new HashMap<String, SFSVariable>();
uVars.put("isoPosX", new SFSVariable("4", SFSVariable.TYPE_ NUMBER));
uVars.put("isoPosY", new SFSVariable("4", SFSVariable.TYPE_ NUMBER));
uVars.put("firstTime", new SFSVariable("true", SFSVariable. TYPE_BOOLEAN));
uVars.put("avatarColor", new SFSVariable("0xff0000", SFSVariable.TYPE_NUMBER));
uVars.put("style", new SFSVariable("2", SFSVariable.TYPE_ NUMBER));
sfs.setUserVariables(uVars);
}
}

To compile and run the code, we need the SmartFoxClient Java API library and some related utilities. These libraries are packed in the download file of the API.

After installing the required libraries, we can type the following command in the terminal to compile the Java NPC code.

javac -cp "lib/*" NPC.java

After successful compilation, we can run the NPC Java client within the same machine of SmartFoxServer.

java -cp "lib/*:./" NPC

The NPC will appear in the virtual world after running the NPC Java client.