INET6_OPT_INIT(3)

NAME
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

SYNOPSIS
#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, socklen_t offset, void *val, socklen_t vallen);

DESCRIPTION
Building and parsing the Hop-by-Hop and Destination options is complicated. The advanced API therefore defines a set of functions to help applications. These functions assume 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 in the <netinet/in.h> header.

  inet6_opt_init
inet6_opt_init() returns the number of bytes needed for the empty extension header i.e. without any options. If extbuf is not NULL it also initializes the extension header to have the correct length field. In that case if the extlen value is not a positive ( i.e., non-zero) multiple of 8 the function fails and returns -1.

  inet6_opt_append
inet6_opt_append() returns the updated total length taking into account adding an option with length len and alignment align. Offset should be the length returned by inet6_opt_init() or a previous inet6_opt_append(). If extbuf is not NULL then, in addition to returning the length, the function inserts any needed pad option, initializes the option ( setting the type and length fields) and returns a pointer to the location for the option content in databufp.

type is the 8-bit option type. len is the length of the option data ( i.e. excluding the option type and option length fields.)

Once inet6_opt_append() has been called the application can use the databuf directly, or use inet6_opt_set_val() to specify the content of the option.

The option type must have a value from 2 to 255, inclusive. ( 0 and 1 are reserved for the Pad1 and PadN options, respectively.)

The option data length must have a value between 0 and 255, inclusive, and is the length of the option data that follows.

The align parameter must have a value of 1, 2, 4, or 8. The align value can not exceed the value of len.

  inet6_opt_finish
inet6_opt_finish() returns the updated total length taking into account the final padding of the extension header to make it a multiple of 8 bytes. Offset should be the length returned by inet6_opt_init() or inet6_opt_append(). If extbuf is not NULL the function also initializes the option by inserting a Pad1 or PadN option of the proper length.

If the necessary pad does not fit in the extension header buffer the function returns -1.

  inet6_opt_set_val
inet6_opt_set_val() inserts data items of various sizes in the data portion of the option. Databuf should be a pointer returned by inet6_opt_append(). val should point to the data to be inserted. Offset specifies where in the data portion of the option the value should be inserted; the first byte after the option type and length is accessed by specifying an offset of zero.

The caller should ensure that each field is aligned on its natural boundaries as described in Appendix B of RFC2460, but the function must not rely on the caller's behavior. Even when the alignment requirement is not satisfied, the function should just copy the data as required.

The function returns the offset for the next field ( i.e., offset + vallen) which can be used when composing option content with multiple fields.

  inet6_opt_next
inet6_opt_next() parses received extension headers returning the next option. Extbuf and extlen specifies the extension header. Offset should either be zero (for the first option) or the length returned by a previous call to inet6_opt_next() or inet6_opt_find(). It specifies the position where to continue scanning the extension buffer. The next option is returned by updating typep, lenp, and databufp. This function returns the updated “previous” length computed by advancing past the option that was returned. This returned “previous” length can then be passed to subsequent calls to inet6_opt_next(). This function does not return any PAD1 or PADN options. When there are no more options the return value is -1.

  inet6_opt_get_val
inet6_opt_get_val() This function extracts data items of various sizes in the data portion of the option. Databuf should be a pointer returned by inet6_opt_next() or inet6_opt_find(). Val should point to the destination for the extracted data. Offset specifies from where in the data portion of the option the value should be extracted; the first byte after the option type and length is accessed by specifying an offset of zero.

It is expected that each field is aligned on its natural boundaries as described in Appendix B of RFC2460, but the function must not rely on the alignment.

The function returns the offset for the next field ( i.e., offset + vallen) which can be used when extracting option content with multiple fields. Robust receivers might want to verify alignment before calling this function.

DIAGNOSTICS
All the functions return -1 on an error.

EXAMPLES
draft-ietf-ipngwg-rfc2292bis-08.txt gives comprehensive examples in Section 23.

KAME also provides examples in the advapitest directory of its kit.

SEE ALSO
W. Stevens, M. Thomas, E. Nordmark, T. Jinmei, Advanced Sockets API for IPv6, draft-ietf-ipngwg-rfc2292bis-08, October 2002. S. Deering, R. Hinden, Internet Protocol, Version 6 (IPv6) Specification, RFC2460, December 1998.

HISTORY
The implementation first appeared in KAME advanced networking kit.

STANDARDS
The functions are documented in “Advanced Sockets API for IPv6” (draft-ietf-ipngwg-rfc2292bis-08.txt).

BUGS
The text was shamelessly copied from internet-drafts for RFC2292bis.