Function UdpAliasIn

freebsd/netinet/libalias/alias.c:727–819

}

static int
UdpAliasIn(struct libalias *la, struct ip *pip)
{
	struct udphdr *ud;
	struct alias_link *lnk;
	size_t dlen;

	LIBALIAS_LOCK_ASSERT(la);

	dlen = ntohs(pip->ip_len) - (pip->ip_hl << 2);
	if (dlen < sizeof(struct udphdr))
		return (PKT_ALIAS_IGNORED);

	ud = (struct udphdr *)ip_next(pip);
	if (dlen < ntohs(ud->uh_ulen))
		return (PKT_ALIAS_IGNORED);

	lnk = FindUdpTcpIn(la, pip->ip_src, pip->ip_dst,
	    ud->uh_sport, ud->uh_dport,
	    IPPROTO_UDP, !(la->packetAliasMode & PKT_ALIAS_PROXY_ONLY));
	if (lnk != NULL) {
		struct in_addr alias_address;
		struct in_addr original_address;
		struct in_addr proxy_address;
		u_short alias_port;
		u_short proxy_port;
		int accumulate;
		int error;
		struct alias_data ad = {
			.lnk = lnk, 
			.oaddr = &original_address, 
			.aaddr = &alias_address,
			.aport = &alias_port,
			.sport = &ud->uh_sport,
			.dport = &ud->uh_dport,
			.maxpktsize = 0
		};

		alias_address = GetAliasAddress(lnk);
		original_address = GetOriginalAddress(lnk);
		proxy_address = GetProxyAddress(lnk);
		alias_port = ud->uh_dport;
		ud->uh_dport = GetOriginalPort(lnk);
		proxy_port = GetProxyPort(lnk);

		/* Walk out chain. */		
		error = find_handler(IN, UDP, la, pip, &ad);
		/* If we cannot figure out the packet, ignore it. */
		if (error < 0)
			return (PKT_ALIAS_IGNORED);

/* If UDP checksum is not zero, then adjust since destination port */
/* is being unaliased and destination address is being altered.    */
		if (ud->uh_sum != 0) {
			accumulate = alias_port;
			accumulate -= ud->uh_dport;
			accumulate += twowords(&alias_address);
			accumulate -= twowords(&original_address);