Padding added while converting from DatagramPacket to bye array

I'm trying to pass an RSA public key from a UDP Server to the client on Java.

For this, I generate a a public key at the Server, convert to a byte array and pass it as a DatagramPacket to the Client.

Unfortunately, at the Client side, while the packet received has the same size as the packet sent, after I save the packet data into a byte array, the size dramatically increases with some padding added after the received data.

How do I get rid of this padding?

Here's the code for the Server:

import java.net.*; import javax.crypto.Cipher; import java.io.*; import java.security.*; import java.security.spec.*; import java.util.*; import java.util.Base64.*;
class EchoServer 
{
public static void main( String args[] ) throws Exception 
{
System.out.println("Server running. Awaiting Connection Request...\n");
DatagramSocket socket = new DatagramSocket(1500);
//Receive Username
DatagramPacket packetU = new DatagramPacket(new byte[512],512);
socket.receive( packetU );
//Generate Key Pair
System.out.println("Generating Key Pair");
KeyPair pair = RSA.generateKeyPair();
byte[] encodedPrivateKey = pair.getPrivate().getEncoded();
byte[] encodedPublicKey = pair.getPublic().getEncoded();
System.out.println("\nPublic Key: " + Base64.getEncoder().encodeToString(encodedPublicKey));
//Sending Public Key
System.out.println("Sending Public Key");
DatagramPacket packetPK = new DatagramPacket(encodedPublicKey,encodedPublicKey.length,packetU.getAddress(),packetU.getPort());
socket.send( packetPK );
System.out.println("Packet length: " + packetPK.getLength());
}
}

And for the Client:

import java.net.*; import javax.crypto.Cipher; import java.io.*; import java.security.*; import java.security.spec.*; import java.util.*; import java.util.Base64.*;
class EchoClient 
{
public static void main( String args[] ) throws Exception 
{
Scanner sc = new Scanner (System.in);
DatagramSocket socket = new DatagramSocket();
socket.setSoTimeout(120000);
//Initiate Authentication
System.out.print("Enter username: ");
String username = sc.nextLine();			
byte[] uname = username.getBytes();
DatagramPacket packetU = new DatagramPacket(uname,uname.length,InetAddress.getByName(args[0]),1500);
socket.send( packetU );
//Recieving Public Key
System.out.println("Public Key Recieved");
DatagramPacket packetPK = new DatagramPacket(new byte[512],512);
socket.receive( packetPK );
byte[] publicKey = packetPK.getData();
System.out.println("Packet length: " + packetPK.getLength());
System.out.println("Byte[] length: " + publicKey.length);
System.out.println( "Alice at: "+new Date()+" "+packetPK.getAddress()+":"+packetPK.getPort()+"\nPublic Key: "+Base64.getEncoder().encodeToString(publicKey));
}
}

This is the output I receive at the Server terminal:

Server running. Awaiting Connection Request...

Generating Key Pair

Public Key: MIIBIjANBgkqhkiG9w0BAQEFAAOCAQ8AMIIBCgKCAQEAhYGTu7revdBCqdSm7ksM9qyagDirjsXtq52hPDdARoVbBNbZmZh4OoyNNorLqQqQzfF1oy9YtiDF4CLEip1t1T3oL2oRu1AQyIFlbbUyBoDh1jmvse0yAE2wcBumjZ1v8AvqV8tqzbn42uIaeBNjy3z5jLLx7NH80djSCHzkw1yCC+zs1uMJ8ZfuqPdDGqtOTskvw8qZ0LbhKcUFI1yLwkjlu1sVrZu1P86GTazEswV+B9f8255jyzS6AYR4+xosbvJpuyyQVahZ+LNRIAFFXnMe4BNX1WsT5hSlWOgtNy7NtKJSfXMts4RWJccZNznX8dRxZYPmZBEi7yI1WDHXkQIDAQAB
Sending Public Key
Packet length: 294

And the output at the Client terminal:

Enter username: Hello

Public Key Recieved

Packet length: 294

Byte[] length: 512

Alice at: Mon Jul 27 22:59:29 IST 2020 /127.0.0.1:1500

Public Key: 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

On the client side, you're getting the full buffer that you allocated, not just the data that was sent:

byte[] publicKey = packetPK.getData();

You need to also get the length of the data that was sent, and only print that portion of the data buffer:

int len = packetPK.getLength();

https://docs.oracle.com/en/java/javase/11/docs/api/java.base/java/net/DatagramPacket.html#getData()

When you convert your byte array to String, you will see that you are getting a proper response. Try:

        String x = new String(publicKey);
System.out.println(x);

So you see, it's the empty elements of the byteArray which are causing the issue.
Either conver publicKey to String and then use it or truncate your byte array to get rid of blank array elements. Both will work

I've figured it out. Thanks to the answers here I did some more research and found that instead of directly copying the packet to the byte array, I did the following:

byte[] publicKey = new byte[packetPK.getLength()];
System.arraycopy(packetPK.getData(), packetPK.getOffset(), publicKey, 0, packetPK.getLength());

I thought of using an ArrayList because of the byte array is initialized to a variable size, but as far as I know, the method above isn't wrong either since Java arrays are dynamic.