Function ProxyEncodeTcpStream

freebsd/netinet/libalias/alias_proxy.c:285–376

}

static void
ProxyEncodeTcpStream(struct alias_link *lnk,
    struct ip *pip,
    int maxpacketsize)
{
	int slen;
	char buffer[40];
	struct tcphdr *tc;
	char addrbuf[INET_ADDRSTRLEN];

/* Compute pointer to tcp header */
	tc = (struct tcphdr *)ip_next(pip);

/* Don't modify if once already modified */

	if (GetAckModified(lnk))
		return;

/* Translate destination address and port to string form */
	snprintf(buffer, sizeof(buffer) - 2, "[DEST %s %d]",
	    inet_ntoa_r(GetProxyAddress(lnk), INET_NTOA_BUF(addrbuf)),
	    (u_int) ntohs(GetProxyPort(lnk)));

/* Pad string out to a multiple of two in length */
	slen = strlen(buffer);
	switch (slen % 2) {
	case 0:
		strcat(buffer, " \n");
		slen += 2;
		break;
	case 1:
		strcat(buffer, "\n");
		slen += 1;
	}

/* Check for packet overflow */
	if ((int)(ntohs(pip->ip_len) + strlen(buffer)) > maxpacketsize)
		return;

/* Shift existing TCP data and insert destination string */
	{
		int dlen;
		int hlen;
		char *p;

		hlen = (pip->ip_hl + tc->th_off) << 2;
		dlen = ntohs(pip->ip_len) - hlen;

/* Modify first packet that has data in it */

		if (dlen == 0)
			return;

		p = (char *)pip;
		p += hlen;

		bcopy(p, p + slen, dlen);
		memcpy(p, buffer, slen);