/*
 * natd - Network Address Translation Daemon for FreeBSD.
 *
 * This software is provided free of charge, with no 
 * warranty of any kind, either expressed or implied.
 * Use at your own risk.
 * 
 * You may copy, modify and distribute this software (icmp.c) freely.
 *
 * Ari Suutari <suutari@iki.fi>
 */

#include <stdlib.h>
#include <stdio.h>
#include <unistd.h>
#include <string.h>
#include <ctype.h>

#include <sys/types.h>
#include <sys/socket.h>
#include <sys/time.h>
#include <errno.h>
#include <signal.h>

#include <netdb.h>

#include <netinet/in.h>
#include <netinet/in_systm.h>
#include <netinet/ip.h>
#include <netinet/ip_icmp.h>

#include <alias.h>

#include "natd.h"

int SendNeedFragIcmp (int sock, struct ip* failedDgram, int mtu)
{
        char                    icmpBuf[IP_MAXPACKET];
        struct ip*              ip;
        struct icmp*            icmp;
        int                     icmpLen;
        int                     failBytes;
        int                     failHdrLen;
        struct sockaddr_in      addr;
        int                     wrote;
        struct in_addr          swap;
/*
 * Don't send error if packet is
 * not the first fragment.
 */
        if (ntohs (failedDgram->ip_off) & ~(IP_MF | IP_DF))
                return 0;
/*
 * Dont respond if failed datagram is ICMP.
 */
        if (failedDgram->ip_p == IPPROTO_ICMP)
                return 0;
/*
 * Start building the message.
 */
        ip   = (struct ip*) icmpBuf;
        icmp = (struct icmp*) (icmpBuf + sizeof (struct ip));
/*
 * Complete ICMP part.
 */
        icmp->icmp_type         = ICMP_UNREACH;
        icmp->icmp_code         = ICMP_UNREACH_NEEDFRAG;
        icmp->icmp_cksum        = 0;
        icmp->icmp_void         = 0;
        icmp->icmp_nextmtu      = htons (mtu);
/*
 * Copy header + 64 bits of original datagram.
 */
        failHdrLen = (failedDgram->ip_hl << 2);
        failBytes  = failedDgram->ip_len - failHdrLen;
        if (failBytes > 8)
                failBytes = 8;

        failBytes += failHdrLen;
        icmpLen    = ICMP_MINLEN + failBytes;

        memcpy (&icmp->icmp_ip, failedDgram, failBytes);
/*
 * Calculate checksum.
 */
        icmp->icmp_cksum = LibAliasInternetChecksum (mla, (u_short*) icmp,
                                                        icmpLen);
/*
 * Add IP header using old IP header as template.
 */
        memcpy (ip, failedDgram, sizeof (struct ip));

        ip->ip_v        = 4;
        ip->ip_hl       = 5;
        ip->ip_len      = htons (sizeof (struct ip) + icmpLen);
        ip->ip_p        = IPPROTO_ICMP;
        ip->ip_tos      = 0;

        swap = ip->ip_dst;
        ip->ip_dst = ip->ip_src;
        ip->ip_src = swap;

        LibAliasIn (mla, (char*) ip, IP_MAXPACKET);

        addr.sin_family         = AF_INET;
        addr.sin_addr           = ip->ip_dst;
        addr.sin_port           = 0;
/*
 * Put packet into processing queue.
 */
        wrote = sendto (sock, 
                        icmp,
                        icmpLen,
                        0,
                        (struct sockaddr*) &addr,
                        sizeof addr);
        
        if (wrote != icmpLen)
                Warn ("Cannot send ICMP message.");

        return 1;
}