Function ip6_nexthdr

freebsd/netinet6/ip6_input.c:1627–1697

* get next header offset. m will be retained. */

 * get next header offset.  m will be retained.
 */
int
ip6_nexthdr(const struct mbuf *m, int off, int proto, int *nxtp)
{
	struct ip6_hdr ip6;
	struct ip6_ext ip6e;
	struct ip6_frag fh;

	/* just in case */
	if (m == NULL)
		panic("ip6_nexthdr: m == NULL");
	if ((m->m_flags & M_PKTHDR) == 0 || m->m_pkthdr.len < off)
		return -1;

	switch (proto) {
	case IPPROTO_IPV6:
		if (m->m_pkthdr.len < off + sizeof(ip6))
			return -1;
		m_copydata(m, off, sizeof(ip6), (caddr_t)&ip6);
		if (nxtp)
			*nxtp = ip6.ip6_nxt;
		off += sizeof(ip6);
		return off;

	case IPPROTO_FRAGMENT:
		/*
		 * terminate parsing if it is not the first fragment,
		 * it does not make sense to parse through it.
		 */
		if (m->m_pkthdr.len < off + sizeof(fh))
			return -1;
		m_copydata(m, off, sizeof(fh), (caddr_t)&fh);
		/* IP6F_OFF_MASK = 0xfff8(BigEndian), 0xf8ff(LittleEndian) */
		if (fh.ip6f_offlg & IP6F_OFF_MASK)
			return -1;
		if (nxtp)
			*nxtp = fh.ip6f_nxt;
		off += sizeof(struct ip6_frag);
		return off;

	case IPPROTO_AH:
		if (m->m_pkthdr.len < off + sizeof(ip6e))
			return -1;
		m_copydata(m, off, sizeof(ip6e), (caddr_t)&ip6e);
		if (nxtp)
			*nxtp = ip6e.ip6e_nxt;
		off += (ip6e.ip6e_len + 2) << 2;
		return off;

	case IPPROTO_HOPOPTS:
	case IPPROTO_ROUTING:
	case IPPROTO_DSTOPTS:
		if (m->m_pkthdr.len < off + sizeof(ip6e))
			return -1;
		m_copydata(m, off, sizeof(ip6e), (caddr_t)&ip6e);
		if (nxtp)
			*nxtp = ip6e.ip6e_nxt;
		off += (ip6e.ip6e_len + 1) << 3;
		return off;