readBytes always empty byte-array

[Bizarrus]

The method <serialPort>.readBytes​(byte[] buffer, int bytesToRead) wont fill the byte array.

Version: 2.11.0

Sample

import com.fazecast.jSerialComm.SerialPort;

public class Main {
	private static final char[] HEX_ARRAY = "0123456789ABCDEF".toCharArray();
	public static String bytesToHex(byte[] bytes) {
	    char[] hexChars = new char[bytes.length * 2];
	    for (int j = 0; j < bytes.length; j++) {
	        int v = bytes[j] & 0xFF;
	        hexChars[j * 2] = HEX_ARRAY[v >>> 4];
	        hexChars[j * 2 + 1] = HEX_ARRAY[v & 0x0F];
	    }
	    return new String(hexChars);
	}
	
	public static void main(String[] args) {
		String target = "COM3";
		SerialPort connection = null;		
		SerialPort[] ports = SerialPort.getCommPorts();
		
		System.out.println("+++++ List Serial Devices +++++");
		
		for(SerialPort port : ports) {
			System.out.println("Name: " + port.toString() + ", BaudRate=" +  port.getBaudRate() + ", Port=" + port.getSystemPortName());
			
			if(target.equals(port.getSystemPortName())) {
				connection = port;
				break;
			}
		}
		
		System.out.println("");
		
		connection.setComPortParameters(56700, 8, SerialPort.TWO_STOP_BITS, SerialPort.NO_PARITY, false);
		//connection.setBaudRate(56700);
		//connection.setFlowControl(SerialPort.FLOW_CONTROL_DISABLED);
		//connection.setNumDataBits(8);
		//connection.setNumStopBits(SerialPort.ONE_STOP_BIT);
		//connection.setParity(SerialPort.NO_PARITY);
		connection.setComPortTimeouts(SerialPort.TIMEOUT_NONBLOCKING, 0, 0);
		if(!connection.openPort()) {
			System.err.println("Port already used/blocked!");
			System.exit(-1);
		}
		
		try {
			   while (true)
			   {
			      while (connection.bytesAvailable() == 0)
			         Thread.sleep(20);

			      byte[] readBuffer = new byte[connection.bytesAvailable()];
			      int numRead = connection.readBytes(readBuffer, readBuffer.length, 0);
			      System.out.println("[" + numRead + " bytes] " + bytesToHex(readBuffer));
			   }
			} catch (Exception e) { e.printStackTrace(); }
		
		
		connection.closePort();
		
	}

}

Output

+++++ List Serial Devices +++++
Name: Kommunikationsanschluss (COM1), BaudRate=9600, Port=COM1
Name: com0com - serial port emulator, BaudRate=9600, Port=COM6
Name: com0com - serial port emulator, BaudRate=9600, Port=COM5
Name: Prolific USB-to-Serial Comm Port (COM3), BaudRate=9600, Port=COM3

[13 bytes] 00000000000000000000000000
[1 bytes] 00
[1 bytes] FC
[372 bytes] 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
[132 bytes] 000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000
[200 bytes] 0000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000

[NorbertSandor]

You should check using another tool (with the same serial port settings) that the device really doesn't send zeros, just to be sure (especially because a non-zero byte 0xFC has been received as well).
This readBytes() method is a very "core" one, I use it in my app without problems (although with TIMEOUT_READ_SEMI_BLOCKING mode, using an older library version 2.10.2).
(Otherwise, I see no problem in your code, the reading loop is almost the same as in the offical example.)