alright well this is getting a bit more complicated. I can send plain text whenever I get a packet, but I can't print the message for whatever reason. I'm gonna try converting the text to whatever I can but I'm at a loss here. Here is all of my code, if you have any idea how to fix this I would be very much obliged.

I'm making a politically charged art piece for my senior year about the NSA and other domestic spying. The plan is to send the parsed data to a receipt printer, then allow the public to use black markers and highlighters on the unencrypted messages sent over Wi-Fi.

Code:

import org.rsg.carnivore.*;
import org.rsg.lib.Log;

String input;
String[] command;

void setup()
{
  size(800,600);
  CarnivoreP5 c = new CarnivoreP5(this);
  //the command is set up so that the text from the AIM message gets piped to the print job
  command = new String[3];
  command[0] = "/bin/bash";
  command[1] = "-c";
  command[2] = "echo test | lpr -P ReceiptPrinter -l";
  //this is some test text to check the printer connection
  sendToPrinter("Now we will start up and begin this entire process");
}

void draw () {
}

//triggered whenever a packet comes in
void packetEvent(CarnivorePacket p){
  String packetparsed = packetHtmlParser(p.ascii());
  if (packetparsed != "") {
    println(">> "+packetparsed);
    sendToPrinter(packetparsed.ascii);
  }
}

//a string function to grab the HTML string out of a packet (thanks fry)
String packetHtmlParser(String packetData) { 
  // StringBuffer is more efficient than String 
  StringBuffer plain = new StringBuffer(); 
  // better use lowercase 
  int start = packetData.toLowerCase().indexOf("<html"); 
  int stop = packetData.toLowerCase().indexOf("</html>"); 
  if (start == -1 || stop == -1) return ""; 
  // get the portion inside the html tags 
  String useful = packetData.substring(start, stop); 
  // split on each < or > 
  String[] pieces = split(useful, '<'); 
  // split each line into halves, and use the second half 
  for (int i = 1; i < pieces.length; i++) { 
    plain.append(pieces[i].substring(pieces[i].indexOf('>') + 1)); 
  } 
  return plain.toString(); 
} 

//function to send text to the printer
void sendToPrinter(String printText) {
  command[2] = "echo '"+printText+"' | lpr -P ReceiptPrinter -l";
  try {
    Process p = exec(command);
    BufferedReader in = new BufferedReader(new InputStreamReader(p.getInputStream()));
    String line = null;
    while ((line = in.readLine()) != null) {
      //print console errors and other output
      System.out.println(line);
    }
    //kill the process
    p.destroy();
  } 
  catch (IOException e) {
    e.printStackTrace();
  }
}
 

edit:
found the problem, the printer was waiting until the entire paragraph was written before it printed, I just need to add in some newlines and I'll be set. Feel free to modify and use non-commercially.