How do I send data to only one client (using the network library)? [SOLVED!]

Core Library Questions

Pacifist ..

How do I send data to only one client (using the network library)? [SOLVED!]

in Core Library Questions • 1 month ago

When I use serverName.write() it sends out data to every client. I want to only send data to one client even when connected to multiple clients. I've tried creating an array of servers so that the client would only connect to one of them, but that didn't work; when it called serverName[serverNumber].write() it still wrote to all clients connected to the entire server program. If its relevant, the two client programs and one server program were all running on my computer. This was my attempt:

The server:

import processing.net.*;
Server littleServer[] = new Server[0];
Server mainServer;
int val[] = new int[0];
void setup() {
size(200, 200);
mainServer = new Server(this, 5204);
noStroke();
val = expand(val, val.length+1);
}
void draw() {
background(0);
textAlign(CENTER);
text(littleServer.length, width/2., height/2.);
for (int i = 0; i < littleServer.length; i++)
{
val[i] = (val[i]+i+1)%255;
littleServer[i].write(byte(val[i]));
text(val[i], width/2., height/2.+15*(i+1));
//println(i+"'s value is: "+val[i]);
}
}
void serverEvent(Server srvr, Client clnt) {
littleServer = (Server[]) expand(littleServer, littleServer.length+1);
littleServer[littleServer.length-1] = srvr;
doStuff();
}
void doStuff()
{
val = expand(val, val.length+1);
if (val.length>1)
val[val.length-1] = val[val.length-2];
}

The client was essentially the same as the processing example for Client, but displays the text "MULTIPLE INPUT" to the program's screen if it gets 2 bytes or more in its buffer (which I don't think is a perfect test, but with other tests it seems to confirm that it is indeed getting two different values from the two different litttleServers).
The client:

import processing.net.*;
Client myClient;
int dataIn;
void setup() {
size(200, 200);
myClient = new Client(this, "127.0.0.1", 5204);
}
void draw() {
textAlign(CENTER);
background(0);
for(int i = 0; true; i++)
{
if (myClient.available() > 0) {
dataIn = myClient.read();
//text("Client 2 data: "+int(dataIn), width/2., height/2.);
//background(dataIn);
if(i >= 1)
{
text("MULTIPLE INPUT", width/2., height/2.);
}
}
else
break;
}
}

Also, I think I posted something similar to this over a year ago but IIIRC nobody else ever replied, so sorry if I'm spamming.

Replies(5)

tfguy44

Re: How do I send data to only one client (using the network library)?

1 month ago

My understanding - and I may very well be wrong about this - is that you don't. You send the message to all the clients, and those clients that the message is not intended for should simply ignore it. You'll probably want the message itself to include which client(s) it is intended for, so a client can determine if it should ignore it or not.

Pacifist ..

Re: How do I send data to only one client (using the network library)?

1 month ago

I thought about that and I really don't like that solution. Besides wasting bandwidth (since the data sent would grow by N^2 (N = number of clients) instead of N since every new client would mean everyone would get one more chunk of useless data), I'm afraid of malicious users taking data that isn't intended for them (especially since the project may be open source and therefore relatively easy to modify the code to not ignore any data). I suppose you could encrypt data so that only the intended client could understand it, but then you'd have spend a bunch of development time integrating some encryption scheme that could have its own averse effects and you'd still be wasting a bunch of bandwidth. Thanks for the input, though.

PhiLho

Re: How do I send data to only one client (using the network library)?

1 month ago

In this case, you probably need to go down to Java itself. Study the source code of Server and Client, look at the Java reference of the classes and methods they use, and see if this can modified to more targeted communication. More work, but perhaps less than going the encryption way.

Note that messages are still broadcast on the network, but the client listening will be done at a lower level, reducing the risk of interception. If you use a tool like Wireshark, you can see you can observe most of the communications done on a LAN.

dimkir

Re: How do I send data to only one client (using the network library)?

1 month ago

If you look at implementation of the write() method, you will see that all it does, just forwards the data to the Client.write().

So in order to write to specific client, all you have to do is to save your clients when your sketch is notified via serverEvent()

http://processing.org/reference/libraries/net/serverEvent_.html

and then just do simple mySavedClient.write("My data"); here's short snippet

Client myLastClient;

void serverEvent(Server someServer, Client someClient) {
  println("We have a new client: " + someClient.ip());

  myLastClient = someClient;
}

void draw(){
  if ( myLastClient != null ){
         println("We only write to the last connected client with ip: "+ myLastClient.ip());
         myLastClient.write("You're still our last client");
   }
}

This is code from Server.write(String) method:

               
                  
                public 
                void 
                write
                (
                String 
                data
                ) 
                {
               
               
                    
                int 
                index 
                = 
                0
                ;
               
               
                    
                while 
                (
                index 
                < 
                clientCount
                ) 
                {
               
               
                      
                clients
                [
                index
                ].
                write
                (
                data
                );
               
               
                      
                if 
                (
                clients
                [
                index
                ].
                active
                ()) 
                {
               
               
                        
                index
                ++;
               
               
                      
                } 
                else 
                {
               
               
                        
                removeIndex
                (
                index
                );
               
               
                      
                }
               
               
                    
                }
               
               
                  
                }
               
               
                

               
               
                Could be found on github here
               
               
                https://github.com/processing/processing/blob/master/java/libraries/net/src/processing/net/Server.java#L303

Pacifist ..

Re: Re: How do I send data to only one client (using the network library)?

1 month ago

Wow! Thank you so much dimkir, it works perfectly! You're the best! I thought for sure I was screwed, I had no idea you could do clientName.write() in the server program!
Also thanks for contributing and mentioning Wireshark, PhiLho, I still have a lot to learn about networking, so any information like that is really helpful.

If anyone wants to see my implementation (which, warning, is just an example, and could probably be improved upon), here it is:

Server:

//Example code for a server with multiple clients communicating to only one at a time.
import processing.net.*;
Server mainServer;
int val[] = new int[0];
Client c[] = new Client[0];//the array of clients
void setup() {
size(200, 200);
mainServer = new Server(this, 5204);
noStroke();
val = expand(val, val.length+1);
}
void draw() {
background(0);
textAlign(CENTER);
text(c.length, width/2., height/2.);//Displays how many clients have connected to the server
for (int i = 0; i < c.length; i++)
{
val[i] = (val[i]+i+1)%255;//changes the value based on which client number it has (the higher client number, the fast it changes).
c[i].write(byte(val[i]));//writes to the right client (using the byte type is not necessary)
text(val[i], width/2., height/2.+15*(i+1));
}
}
void serverEvent(Server srvr, Client clnt)//Called when a client connects.
{
c = (Client[]) expand(c, c.length+1);//expand the array of clients
c[c.length-1] = clnt;//sets the last client to be the newly connected client
doStuff();
}
void doStuff()//this is extra stuff that can be done,
{//in this case expanding a value array to have a value for each client.
val = expand(val, val.length+1);
}

And it will work for any client. My particular client code is basically just a copy of the example (which helps demonstrate that each client is indeed getting its own data):

import processing.net.*;
Client myClient;
int dataIn;
void setup() {
size(200, 200);
myClient = new Client(this, "127.0.0.1", 5204);
}
void draw() {
textAlign(CENTER);
background(0);
background(dataIn);
text("Client #clientNumber data: "+int(dataIn), width/2., height/2.);// you can replace clientNumber with whatever number you wish
fill(255,0,0);
for(int i = 0; true; i++)
{
if (myClient.available() > 0) {
dataIn = myClient.read();
}
else
break;
}
}

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