Zpl printer receive fragmented data from Java application

Question

Background

I am trying to create a java application to send ZPL command to a ZPL printer and get a label printed. I set up a ZPL emulator(https://chrome.google.com/webstore/detail/zpl-printer/phoidlklenidapnijkabnfdgmadlcmjo) by following this post : Emulate ZPL printer

Issue

1. After setting the emulator up and add it as zpl printer via mac Printer&Scanner ,

I try to use lp command to print it. it is stable the reliable:

lp -o "raw" -q1 -d zpl <<< "^XA\n^FO50,60^A0,40^FDWorld Best Griddle^FS\n^FO60,120^BY3^BCN,60,,,,A^FD1234ABC^FS\n^FO25,25^GB380,200,2^FS\n^XZ"

2. However, my use case is send the command to a printer remotely on the network, Therefore I need to create a java application to send the Zpl command to the printer. It succeeds initially, then it randomly get splitted:
   java code:

import java.io.*;
import java.net.*;
class TCPClient
{
    public static void main (String argv[]) throws Exception
    {

        Socket clientSocket=new Socket("127.0.0.1",9100);

        DataOutputStream outToServer = new DataOutputStream(clientSocket.getOutputStream() );
        try {
            outToServer.writeBytes("^XA\n^FO50,60^A0,40^FDWorld Best Griddle^FS\n^FO60,120^BY3^BCN,60,,,,A^FD1234ABC^FS\n^FO25,25^GB380,200,2^FS\n^XZ");
                
        } catch (Throwable e) {
            System.out.println(e);
        }

        outToServer.flush();
        outToServer.close();
        clientSocket.close();
//        outToServer.flush();

    }
}

Result:

So quite often, it succeeds once and then following 2 or 3 printing get fragmented or failed. I suspect it might be the socket TCP fragmentation issue. or there any socket option I can configure? But not sure how to solve it. Can anyone help here?

Update:

I try to use wireshark. The issue resides in the TCP package size:

For lp command, everything is sent as one single pack:

As for java app, it is broken down into smaller packs for some reason.

But I still don't know how to configure the pack size. Also it confuses me a lot why Java app will break the data packet to like 1 byte or two byte sized?

Answer 1

I think you are using a wrong method to send printing job. I'm not sure lp command uses Socket connection. Try calling lp from Java using Runtime.getRuntime().exec:

String cmd = "lp -o \"raw\" -q1 -d zpl <<< \"^XA\n^FO50,60^A0,40^FDWorld Best Griddle^FS\n^FO60,120^BY3^BCN,60,,,,A^FD1234ABC^FS\n^FO25,25^GB380,200,2^FS\n^XZ\"";
Runtime.getRuntime().exec(String.format(cmd));