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INET6_OPT_INIT(3)		   BSD Library Functions Manual 		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
     sockets API defines a set of functions to help applications create and manipulate Hop-by-
     Hope and Destination options.  These functions use the formatting rules specified in Appen-
     dix 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.

   inet6_opt_init
     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.

   inet6_opt_append
     The inet6_opt_append() function can perform to 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 pre-
     vious 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 respec-
     tively.

   inet6_opt_finish
     The inet6_opt_finish() 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.

   inet6_opt_set_val
     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.

   inet6_opt_next
     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 pre-
     vious 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.  typep, lenp, and databufp 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.

   inet6_opt_find
     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.  extbuf and
     extlen 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.

   inet6_opt_get_val
     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.

DIAGNOSTICS
     All the functions return -1 on an error.

EXAMPLES
     RFC3542 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, 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.

HISTORY
     The implementation first appeared in KAME advanced networking kit.

STANDARDS
     The functions are documented in ``Advanced Sockets API for IPv6'' (RFC3542).

BSD					December 23, 2004				      BSD
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