import java.io.*;
import java.net.*;

public class DatagramInputStream extends InputStream {
  byte[] buffer;
  int index, count;
  DatagramSocket socket;
  DatagramPacket packet;
  
  public DatagramInputStream (DatagramSocket socket) {
    this.socket = socket;
    buffer = new byte[65508];
    packet = new DatagramPacket (buffer, 0);
  }

  public synchronized int read () throws IOException {
    while (index >= count)
      receive ();
    return (int) buffer[index ++];
  }

  public synchronized int read (byte[] data, int offset, int length) throws IOException {
    if (length <= 0)
      return 0;
    while (index >= count)
      receive ();
    if (count - index < length)
      length = count - index;
    System.arraycopy (buffer, index, data, offset, length);
    index += length;
    return length;
  }

  public synchronized long skip (long amount) throws IOException {
    if (amount <= 0)
      return 0;
    while (index >= count)
      receive ();
    if (count - index < amount)
      amount = count - index;
    index += amount;
    return amount;
  }

  public synchronized int available () throws IOException {
    return count - index;
  }

  void receive () throws IOException {
    packet.setLength (buffer.length);
    socket.receive (packet);
    index = 0;
    count = packet.getLength ();
  }
}