.\"	$KAME: inet6_rth_space.3,v 1.7 2005/01/05 03:00:44 itojun Exp $
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.Dd December 24, 2004
.Dt INET6_RTH_SPACE 3
.Os
.\"
.Sh NAME
.Nm inet6_rth_space ,
.Nm inet6_rth_init ,
.Nm inet6_rth_add ,
.Nm inet6_rth_reverse ,
.Nm inet6_rth_segments ,
.Nm inet6_rth_getaddr
.Nd IPv6 Routing Header Options manipulation
.\"
.Sh SYNOPSIS
.In netinet/in.h
.Ft socklen_t
.Fn inet6_rth_space "int" "int"
.Ft "void *"
.Fn inet6_rth_init "void *" "socklen_t" "int" "int"
.Ft int
.Fn inet6_rth_add "void *" "const struct in6_addr *"
.Ft int
.Fn inet6_rth_reverse "const void *" "void *"
.Ft int
.Fn inet6_rth_segments "const void *"
.Ft "struct in6_addr *"
.Fn inet6_rth_getaddr "const void *" "int"
.\"
.Sh DESCRIPTION
The IPv6 Advanced API, RFC 3542, defines the functions that an
application calls to build and examine IPv6 Routing headers.
Routing headers are used to perform source routing in IPv6 networks.
The RFC uses the word 
.Dq segments
to describe addresses and that is the term used here as well.
All of the functions are defined in the
.In netinet/in.h
header file.
The functions described in this manual page all operate
on routing header structures which are defined in
.In netinet/ip6.h
but which should not need to be modified outside the use of this API.
The size and shape of the route header structures may change, so using
the APIs is a more portable, long term, solution.
.Pp
The functions in the API are split into two groups, those that build a
routing header and those that parse a received routing header.
We will describe the builder functions followed by the parser functions.
.Ss inet6_rth_space
The
.Fn inet6_rth_space
function returns the number of bytes required to hold a Routing Header
of the type, specified in the
.Fa type 
argument and containing the number of addresses specified in the
.Fa segments
argumment.
When the type is 
.Dv IPV6_RTHDR_TYPE_0
the number of segments must be from 0 through 127.
Routing headers of type 
.Dv IPV6_RTHDR_TYPE_2
contain only one segment, and are only used with Mobile IPv6.
The return value from this function is the number of bytes required to
store the routing header.
If the value 0 is returned then either the
route header type was not recognized or another error occurred.
.Ss inet6_rth_init
The
.Fn inet6_rth_init
function initializes the pre-allocated buffer pointed to by
.Fa bp
to contain a routing header of the specified type The
.Fa bp_len
argument is used to verify that the buffer is large enough.
The caller must allocate the buffer pointed to by bp.
The necessary buffer size should be determined by calling
.Fn inet6_rth_space
described in the previous sections.
.Pp
The
.Fn inet6_rth_init
function returns a pointer to
.Fa bp
on success and
.Dv NULL
when there is an error.
.Ss inet6_rth_add
The
.Fn inet6_rth_add
function adds the IPv6 address pointed to by
.Fa addr
to the end of the routing header being constructed.
.Pp
A successful addition results in the function returning 0, otherwise
\-1 is returned.
.Ss inet6_rth_reverse
The
.Fn inet6_rth_reverse
function takes a routing header, pointed to by the
argument
.Fa in ,
and writes a new routing header into the argument pointed to by
.Fa out .
The routing header at that sends datagrams along the reverse of that
route.
Both arguments are allowed to point to the same buffer meaning
that the reversal can occur in place.
.Pp
The return value of the function is 0 on success, or \-1 when
there is an error.
.\"
.Pp
The next set of functions operate on a routing header that the
application wants to parse.
In the usual case such a routing header
is received from the network, although these functions can also be
used with routing headers that the application itself created.
.Ss inet6_rth_segments
The
.Fn inet6_rth_segments
function returns the number of segments contained in the
routing header pointed to by
.Fa bp .
The return value is the number of segments contained in the routing
header, or \-1 if an error occurred.
It is not an error for 0 to be
returned as a routing header may contain 0 segments.
.\"
.Ss inet6_rth_getaddr
The
.Fn inet6_rth_getaddr
function is used to retrieve a single address from a routing header.
The
.Fa index
is the location in the routing header from which the application wants
to retrieve an address.
The 
.Fa index 
parameter must have a value between 0 and one less than the number of
segments present in the routing header.
The
.Fn inet6_rth_segments 
function, described in the last section, should be used to determine
the total number of segments in the routing header.
The
.Fn inet6_rth_getaddr
function returns a pointer to an IPv6 address on success or 
.Dv NULL
when an error has occurred.
.\"
.Sh DIAGNOSTICS
The
.Fn inet6_rth_space
and
.Fn inet6_rth_getaddr
functions return 0 on errors.
.Pp
The
.Fn inet6_rthdr_init
function returns
.Dv NULL
on error.
The
.Fn inet6_rth_add
and
.Fn inet6_rth_reverse
functions return 0 on success, or \-1 upon an error.
.\"
.Sh EXAMPLES
RFC 3542 gives extensive examples in Section 21, Appendix B.
.Pp
KAME also provides examples in the advapitest directory of its kit.
.\"
.Sh SEE ALSO
.Rs
.%A W. Stevens
.%A M. Thomas
.%A E. Nordmark
.%A T. Jinmei
.%T "Advanced Sockets API for IPv6"
.%N RFC 3542
.%D May 2003
.Re
.Rs
.%A S. Deering
.%A R. Hinden
.%T "Internet Protocol, Version 6 (IPv6) Specification"
.%N RFC2460
.%D December 1998
.Re
.Sh HISTORY
The implementation first appeared in KAME advanced networking kit.