/*
 * $Id$
 *
 * Copyright (C) 2003-2015 JNode.org
 *
 * This library is free software; you can redistribute it and/or modify it
 * under the terms of the GNU Lesser General Public License as published
 * by the Free Software Foundation; either version 2.1 of the License, or
 * (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful, but 
 * WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
 * or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public 
 * License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public License
 * along with this library; If not, write to the Free Software Foundation, Inc., 
 * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
 */
 
package org.jnode.net.ipv4.icmp;

import java.net.SocketException;

import org.jnode.net.SocketBuffer;
import org.jnode.net.ipv4.IPv4Address;
import org.jnode.net.ipv4.IPv4Constants;
import org.jnode.net.ipv4.IPv4Header;
import org.jnode.net.ipv4.IPv4Service;

/**
 * Utility class for other IP protocols, to allow them to call simple methods
 * for generating ICMP messages.
 * 
 * @author epr
 */
public class ICMPUtils {

    private final IPv4Service ipService;

    /**
     * Create a new instance
     * 
     * @param ipService
     */
    public ICMPUtils(IPv4Service ipService) {
        this.ipService = ipService;
    }

    /**
     * Send an ICMP port unreachable message in response to the given buffer.
     * The IP header and the Transport layer header must be set as attributes in
     * srcBuf, and must be removed from the head of the buffer.
     * 
     * @param srcBuf
     */
    public void sendPortUnreachable(SocketBuffer srcBuf) throws SocketException {
        sendUnreachable(srcBuf, 3);
    }

    /**
     * Send an ICMP unreachable message in response to the given buffer. The IP
     * header and the Transport layer header must be set as attributes in
     * srcBuf, and must be removed from the head of the buffer.
     * 
     * @param srcBuf
     */
    private final void sendUnreachable(SocketBuffer srcBuf, int code) throws SocketException {
        // Do not respond to linklayer broadcast messages
        if (srcBuf.getLinkLayerHeader().getDestinationAddress().isBroadcast()) {
            return;
        }

        // Gets the original IP header
        final IPv4Header origIpHdr = (IPv4Header) srcBuf.getNetworkLayerHeader();

        // Do not respond to networklayer broadcast/multicast messages
        if (origIpHdr.getDestination().isBroadcast() || origIpHdr.getDestination().isMulticast()) {
            return;
        }

        final int tos = 0;
        final int ttl = 0xFF;
        final IPv4Address dstAddr = origIpHdr.getSource();

        // Build the response ICMP header
        final ICMPHeader icmpHdr = new ICMPUnreachableHeader(code);
        // Build the response IP header
        final IPv4Header ipHdr = new IPv4Header(tos, ttl, IPv4Constants.IPPROTO_ICMP, dstAddr, 0);

        // Unpull the original transportlayer header
        srcBuf.unpull(srcBuf.getTransportLayerHeader().getLength());

        // Unpull the original IP header
        srcBuf.unpull(origIpHdr.getLength());

        // Create a response buffer
        final SocketBuffer skbuf = new SocketBuffer();
        // Prefix the ICMP header to the response buffer
        icmpHdr.prefixTo(skbuf);
        // Append the original message to the response buffer
        skbuf.append(srcBuf);
        // / RFC says return as much as we can without exceeding 576 bytes.
        skbuf.trim(576);

        ipService.transmit(ipHdr, skbuf);
    }
}