// Definitions for a simple UDP file transfer server.
            // The protocol is modelled on the Trivial File Transfer
            // Protocol (TFTP) described in RFC 1350.
            // Only sending of a file is implemented, and the
            // transfer mode is binary (i.e. octet).

public interface UDPFileTransfer {
    // The (arbitrary) port of the file transfer service.
    public static final int ServerPort = 20069;
    // Opcode numbers.
    public static final int RRQ = 1, DATA = 3, ACK = 4, ERROR = 5;
    // Error values.
    public static final int FileNotFound = 1, AccessViolation = 2,
                        IllegalOperation = 4, UnknownPort = 5;
    // The size (in bytes) of the Opcode and block number.
    public static int opcodeSize = 2, blockNumberSize = 2;
    // The maximum size of any data that may be transferred.
    public static int MaxDataPacket = 512;
    // Define the length of a DATA header.
    public static int dataHeaderLength = opcodeSize+blockNumberSize;
    // Define the length of a full data packet.
    public static int fullDataPacket = dataHeaderLength+MaxDataPacket;
}