INET6_OPT_INIT(3) | Library Functions Manual | INET6_OPT_INIT(3) |
inet6_opt_init
,
inet6_opt_append
,
inet6_opt_finish
,
inet6_opt_set_val
,
inet6_opt_next
,
inet6_opt_find
,
inet6_opt_get_val
— IPv6
Hop-by-Hop and Destination Options manipulation
#include
<netinet/in.h>
int
inet6_opt_init
(void
*extbuf, socklen_t
extlen);
int
inet6_opt_append
(void
*extbuf, socklen_t
extlen, int offset,
u_int8_t type,
socklen_t len,
u_int8_t align,
void **databufp);
int
inet6_opt_finish
(void
*extbuf, socklen_t
extlen, int
offset);
int
inet6_opt_set_val
(void
*databuf, int
offset, void *val,
socklen_t vallen);
int
inet6_opt_next
(void
*extbuf, socklen_t
extlen, int offset,
u_int8_t *typep,
socklen_t *lenp,
void **databufp);
int
inet6_opt_find
(void
*extbuf, socklen_t
extlen, int offset,
u_int8_t type,
socklen_t *lenp,
void **databufp);
int
inet6_opt_get_val
(void
*databuf, int
offset, void *val,
socklen_t vallen);
Building and parsing the Hop-by-Hop and Destination options is
complicated. The advanced sockets API defines a set of functions to help
applications create and manipulate Hop-by-Hop and Destination options. This
man page describes the functions specified in IETF Draft RFC3542. These
functions use the formatting rules specified in Appendix B in RFC2460, i.e.,
that the largest field is placed last in the option. The function prototypes
for these functions are all contained in the
<netinet/in.h>
header
file.
The
inet6_opt_init
()
function returns the number of bytes needed for an empty extension header,
one without any options. If the extbuf argument points
to a valid section of memory then the
inet6_opt_init
() function also initializes the
extension header's length field. When attempting to initialize an extension
buffer passed in the extbuf argument,
extlen must be a positive multiple of 8 or else the
function fails and returns -1 to the caller.
The inet6_opt_append
() function can
perform two different jobs. When a valid extbuf
argument is supplied it appends an option to the extension buffer and
returns the updated total length as well as a pointer to the newly created
option in databufp. If the value of
extbuf is NULL
then the
inet6_opt_append
() function only reports what the
total length would be if the option were actually appended. The
len and align arguments specify
the length of the option and the required data alignment which must be used
when appending the option. The offset argument should
be the length returned by the inet6_opt_init
()
function or a previous call to
inet6_opt_append
().
The type argument is the 8-bit option type.
After
inet6_opt_append
()
has been called, the application can use the buffer pointed to by
databufp directly, or use
inet6_opt_set_val
() to specify the data to be
contained in the option.
Option types of 0
and
1
are reserved for the Pad1
and PadN
options. All other values from 2 through
255 may be used by applications.
The length of the option data is contained in an 8-bit value and so may contain any value from 0 through 255.
The align parameter must have a value of 1, 2, 4, or 8 and cannot exceed the value of len. The alignment values represent no alignment, 16 bit, 32 bit and 64 bit alignments, respectively.
The
inet6_opt_finish
()
function calculates the final padding necessary to make the extension header
a multiple of 8 bytes, as required by the IPv6 extension header
specification, and returns the extension header's updated total length. The
offset argument should be the length returned by
inet6_opt_init
() or
inet6_opt_append
(). When
extbuf is not NULL
the
function also sets up the appropriate padding bytes by inserting a Pad1 or
PadN option of the proper length.
If the extension header is too small to contain the proper padding then an error of -1 is returned to the caller.
The
inet6_opt_set_val
()
function inserts data items of various sizes into the data portion of the
option. The databuf argument is a pointer to memory
that was returned by the inet6_opt_append
() call and
the offset argument specifies where the option should
be placed in the data buffer. The val argument points
to an area of memory containing the data to be inserted into the extension
header, and the vallen argument indicates how much
data to copy.
The caller should ensure that each field is aligned on its natural boundaries as described in Appendix B of RFC2460.
The function returns the offset for the next field which is calculated as offset + vallen and is used when composing options with multiple fields.
The
inet6_opt_next
()
function parses received extension headers. The extbuf
and extlen arguments specify the location and length
of the extension header being parsed. The offset
argument should either be zero, for the first option, or the length value
returned by a previous call to inet6_opt_next
() or
inet6_opt_find
(). The return value specifies the
position where to continue scanning the extension buffer. The option is
returned in the arguments typep,
lenp, and databufp, which point
to the 8-bit option type, the 8-bit option length and the option data,
respectively. This function does not return any PAD1 or PADN options. When
an error occurs or there are no more options, the return value is -1.
The inet6_opt_find
() function searches the
extension buffer for a particular option type, passed in through the
type argument. If the option is found then the
lenp and databufp arguments are
updated to point to the option's length and data, respectively. The
extbuf and extlen arguments must
point to a valid extension buffer and give its length. The
offset argument can be used to search from a location
anywhere in the extension header.
The inet6_opt_get_val
() function extracts
data items of various sizes in the data portion of the option. The
databuf is a pointer returned by the
inet6_opt_next
() or
inet6_opt_find
() functions. The
val argument points where the data will be extracted.
The offset argument specifies from where in the data
portion of the option the value should be extracted; the first byte of
option data is specified by an offset of zero.
It is expected that each field is aligned on its natural boundaries as described in Appendix B of RFC2460.
The function returns the offset for the next field by calculating offset + vallen which can be used when extracting option content with multiple fields. Robust receivers must verify alignment before calling this function.
All the functions return -1 on an error.
RFC3542 gives comprehensive examples in Section 23.
KAME also provides examples in the advapitest directory of its kit.
W. Stevens, M. Thomas, E. Nordmark, and T. Jinmei, Advanced Sockets API for IPv6, RFC3542, October 2002.
S. Deering and R. Hinden, Internet Protocol, Version 6 (IPv6) Specification, RFC2460, December 1998.
The functions are documented in “Advanced Sockets API for IPv6” (RFC3542).
The implementation first appeared in KAME advanced networking kit.
December 23, 2004 | macOS 14.6 |