Function UdpAliasOut

freebsd/netinet/libalias/alias.c:821–928

}

static int
UdpAliasOut(struct libalias *la, struct ip *pip, int maxpacketsize, int create)
{
	struct udphdr *ud;
	struct alias_link *lnk;
	struct in_addr dest_address;
	struct in_addr proxy_server_address;
	u_short dest_port;
	u_short proxy_server_port;
	int proxy_type;
	int error;
	size_t dlen;

	LIBALIAS_LOCK_ASSERT(la);

/* Return if proxy-only mode is enabled and not proxyrule found.*/
	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);

	proxy_type = ProxyCheck(la, &proxy_server_address, 
		&proxy_server_port, pip->ip_src, pip->ip_dst, 
		ud->uh_dport, pip->ip_p);
	if (proxy_type == 0 && (la->packetAliasMode & PKT_ALIAS_PROXY_ONLY))
		return (PKT_ALIAS_OK);

/* If this is a transparent proxy, save original destination,
 * then alter the destination and adjust checksums */
	dest_port = ud->uh_dport;
	dest_address = pip->ip_dst;

	if (proxy_type != 0) {
	        int accumulate;

		accumulate = twowords(&pip->ip_dst);
		accumulate -= twowords(&proxy_server_address);

	        ADJUST_CHECKSUM(accumulate, pip->ip_sum);

		if (ud->uh_sum != 0) {
			accumulate = twowords(&pip->ip_dst);
			accumulate -= twowords(&proxy_server_address);
    			accumulate += ud->uh_dport;
	        	accumulate -= proxy_server_port;
	    		ADJUST_CHECKSUM(accumulate, ud->uh_sum);
		}
	        pip->ip_dst = proxy_server_address;
	        ud->uh_dport = proxy_server_port;
	}
	lnk = FindUdpTcpOut(la, pip->ip_src, pip->ip_dst,
	    ud->uh_sport, ud->uh_dport,
	    IPPROTO_UDP, create);
	if (lnk != NULL) {
		u_short alias_port;