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The Bouncy Castle Java APIs for the TLS, including a JSSE provider. The APIs are designed primarily to be used in conjunction with the BC FIPS provider. The APIs may also be used with other providers although if being used in a FIPS context it is the responsibility of the user to ensure that any other providers used are FIPS certified and used appropriately.

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package org.bouncycastle.tls;

import java.io.IOException;
import java.net.DatagramPacket;
import java.net.DatagramSocket;

public class UDPTransport
    implements DatagramTransport
{
    protected final static int MIN_IP_OVERHEAD = 20;
    protected final static int MAX_IP_OVERHEAD = MIN_IP_OVERHEAD + 64;
    protected final static int UDP_OVERHEAD = 8;

    protected final DatagramSocket socket;
    protected final int receiveLimit, sendLimit;

    public UDPTransport(DatagramSocket socket, int mtu)
        throws IOException
    {
        if (!socket.isBound() || !socket.isConnected())
        {
            throw new IllegalArgumentException("'socket' must be bound and connected");
        }

        this.socket = socket;

        // NOTE: As of JDK 1.6, can use NetworkInterface.getMTU

        this.receiveLimit = mtu - MIN_IP_OVERHEAD - UDP_OVERHEAD;
        this.sendLimit = mtu - MAX_IP_OVERHEAD - UDP_OVERHEAD;
    }

    public int getReceiveLimit()
    {
        return receiveLimit;
    }

    public int getSendLimit()
    {
        // TODO[DTLS] Implement Path-MTU discovery?
        return sendLimit;
    }

    public int receive(byte[] buf, int off, int len, int waitMillis)
        throws IOException
    {
        socket.setSoTimeout(waitMillis);
        DatagramPacket packet = new DatagramPacket(buf, off, len);
        socket.receive(packet);
        return packet.getLength();
    }

    public void send(byte[] buf, int off, int len)
        throws IOException
    {
        if (len > getSendLimit())
        {
            /*
             * RFC 4347 4.1.1. "If the application attempts to send a record larger than the MTU,
             * the DTLS implementation SHOULD generate an error, thus avoiding sending a packet
             * which will be fragmented."
             */
            throw new TlsFatalAlert(AlertDescription.internal_error);
        }

        DatagramPacket packet = new DatagramPacket(buf, off, len);
        socket.send(packet);
    }

    public void close()
        throws IOException
    {
        socket.close();
    }
}