.\" $OpenBSD: inet6_opt_init.3,v 1.8 2022/03/31 17:27:16 naddy Exp $ .\" $KAME: inet6_opt_init.3,v 1.7 2004/12/27 05:08:23 itojun Exp $ .\" .\" Copyright (C) 2004 WIDE Project. .\" All rights reserved. .\" .\" Redistribution and use in source and binary forms, with or without .\" modification, are permitted provided that the following conditions .\" are met: .\" 1. Redistributions of source code must retain the above copyright .\" notice, this list of conditions and the following disclaimer. .\" 2. Redistributions in binary form must reproduce the above copyright .\" notice, this list of conditions and the following disclaimer in the .\" documentation and/or other materials provided with the distribution. .\" 3. Neither the name of the project nor the names of its contributors .\" may be used to endorse or promote products derived from this software .\" without specific prior written permission. .\" .\" THIS SOFTWARE IS PROVIDED BY THE PROJECT AND CONTRIBUTORS ``AS IS'' AND .\" ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE .\" IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE .\" ARE DISCLAIMED. IN NO EVENT SHALL THE PROJECT OR CONTRIBUTORS BE LIABLE .\" FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL .\" DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS .\" OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) .\" HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT .\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY .\" OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF .\" SUCH DAMAGE. .\" .Dd $Mdocdate: March 31 2022 $ .Dt INET6_OPT_INIT 3 .Os .\" .Sh NAME .Nm inet6_opt_init , .Nm inet6_opt_append , .Nm inet6_opt_finish , .Nm inet6_opt_set_val , .Nm inet6_opt_next , .Nm inet6_opt_find , .Nm inet6_opt_get_val .Nd IPv6 Hop-by-Hop and Destination Options manipulation .\" .Sh SYNOPSIS .In netinet/in.h .Ft "int" .Fn inet6_opt_init "void *extbuf" "socklen_t extlen" .Ft "int" .Fn inet6_opt_append "void *extbuf" "socklen_t extlen" "int offset" "u_int8_t type" "socklen_t len" "u_int8_t align" "void **databufp" .Ft "int" .Fn inet6_opt_finish "void *extbuf" "socklen_t extlen" "int offset" .Ft "int" .Fn inet6_opt_set_val "void *databuf" "int offset" "void *val" "socklen_t vallen" .Ft "int" .Fn inet6_opt_next "void *extbuf" "socklen_t extlen" "int offset" "u_int8_t *typep" "socklen_t *lenp" "void **databufp" .Ft "int" .Fn inet6_opt_find "void *extbuf" "socklen_t extlen" "int offset" "u_int8_t type" "socklen_t *lenp" "void **databufp" .Ft "int" .Fn inet6_opt_get_val "void *databuf" "socklen_t offset" "void *val" "socklen_t vallen" .\" .Sh 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-Hop and Destination options. These functions use the formatting rules specified in Appendix B in RFC 2460, i.e. that the largest field is placed last in the option. The function prototypes for these functions are all contained in the header file .In netinet/in.h . .\" .Ss inet6_opt_init The .Fn inet6_opt_init function returns the number of bytes needed for an empty extension header, one without any options. If the .Va extbuf argument points to a valid section of memory then the .Fn inet6_opt_init function also initializes the extension header's length field. When attempting to initialize an extension buffer passed in the .Va extbuf argument, .Fa extlen must be a positive multiple of 8 or else the function fails and returns \-1 to the caller. .\" .Ss inet6_opt_append The .Fn inet6_opt_append function can perform different jobs. When a valid .Fa 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 .Fa databufp . If the value of .Fa extbuf is .Dv NULL then the .Fn inet6_opt_append function only reports what the total length would be if the option were actually appended. The .Fa len and .Fa align arguments specify the length of the option and the required data alignment which must be used when appending the option. The .Fa offset argument should be the length returned by the .Fn inet6_opt_init function or a previous call to .Fn inet6_opt_append . .Pp The .Fa type argument is the 8-bit option type. .Pp After .Fn inet6_opt_append has been called, the application can use the buffer pointed to by .Fa databufp directly, or use .Fn inet6_opt_set_val to specify the data to be contained in the option. .Pp Option types of .Li 0 and .Li 1 are reserved for the .Li Pad1 and .Li PadN options. All other values from 2 through 255 may be used by applications. .Pp The length of the option data is contained in an 8-bit value and so may contain any value from 0 through 255. .Pp The .Fa align parameter must have a value of 1, 2, 4, or 8 and cannot exceed the value of .Fa len . The alignment values represent no alignment, 16-bit, 32-bit and 64-bit alignments respectively. .\" .Ss inet6_opt_finish The .Fn 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 .Fa offset argument should be the length returned by .Fn inet6_opt_init or .Fn inet6_opt_append . When .Fa extbuf is not .Dv NULL , the function also sets up the appropriate padding bytes by inserting a Pad1 or PadN option of the proper length. .Pp If the extension header is too small to contain the proper padding then an error of \-1 is returned to the caller. .\" .Ss inet6_opt_set_val The .Fn inet6_opt_set_val function inserts data items of various sizes into the data portion of the option. The .Fa databuf argument is a pointer to memory that was returned by the .Fn inet6_opt_append call and the .Fa offset argument specifies where the option should be placed in the data buffer. The .Fa val argument points to an area of memory containing the data to be inserted into the extension header, and the .Fa vallen argument indicates how much data to copy. .Pp The caller should ensure that each field is aligned on its natural boundaries as described in Appendix B of RFC 2460. .Pp The function returns the offset for the next field which is calculated as .Fa offset + .Fa vallen and is used when composing options with multiple fields. .\" .Ss inet6_opt_next The .Fn inet6_opt_next function parses received extension headers. The .Fa extbuf and .Fa extlen arguments specify the location and length of the extension header being parsed. The .Fa offset argument should either be zero, for the first option, or the length value returned by a previous call to .Fn inet6_opt_next or .Fn inet6_opt_find . The return value specifies the position where to continue scanning the extension buffer. The option is returned in the arguments .Fa typep , lenp , and .Fa databufp . .Fa typep , lenp , and .Fa 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. .\" .Ss inet6_opt_find The .Fn inet6_opt_find function searches the extension buffer for a particular option type, passed in through the .Fa type argument. If the option is found then the .Fa lenp and .Fa databufp arguments are updated to point to the option's length and data respectively. .Fa extbuf and .Fa extlen must point to a valid extension buffer and give its length. The .Fa offset argument can be used to search from a location anywhere in the extension header. .Ss inet6_opt_get_val The .Fn inet6_opt_get_val function extracts data items of various sizes in the data portion of the option. The .Fa databuf is a pointer returned by the .Fn inet6_opt_next or .Fn inet6_opt_find functions. The .Fa val argument points to where the data will be extracted. The .Fa 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. .Pp It is expected that each field is aligned on its natural boundaries as described in Appendix B of RFC 2460. .Pp The function returns the offset for the next field by calculating .Fa offset + .Fa vallen which can be used when extracting option content with multiple fields. Robust receivers must verify alignment before calling this function. .\" .Sh EXAMPLES RFC 3542 gives comprehensive examples in Section 23. KAME also provides examples in the .Pa advapitest directory of its kit. .\" .Sh DIAGNOSTICS All the functions return \-1 on an error. .\" .Sh STANDARDS .Rs .%A S. Deering .%A R. Hinden .%D December 1998 .%R RFC 2460 .%T Internet Protocol, Version 6 (IPv6) Specification .Re .Pp .Rs .%A W. Stevens .%A M. Thomas .%A E. Nordmark .%A T. Jinmei .%D May 2003 .%R RFC 3542 .%T Advanced Sockets Application Program Interface (API) for IPv6 .Re .Sh HISTORY The implementation first appeared in KAME advanced networking kit. .\"