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>INET6_OPTION_SPACE(3) System Library Functions Manual INET6_OPTION_SPACE(3)
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NAME
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inet6_option_space, inet6_option_init, inet6_option_append,
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inet6_option_alloc, inet6_option_next, inet6_option_find - IPv6 Hop-by-
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Hop and Destination Options manipulation
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SYNOPSIS
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#include <netinet/in.h>
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int
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inet6_option_space(int nbytes);
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int
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inet6_option_init(void *bp, struct cmsghdr **cmsgp, int type);
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int
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inet6_option_append(struct cmsghdr *cmsg, const u_int8_t *typep,
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int multx, int plusy);
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u_int8_t *
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inet6_option_alloc(struct cmsghdr *cmsg, int datalen, int multx,
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int plusy);;
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int
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inet6_option_next(const struct cmsghdr *cmsg, u_int8_t **tptrp);
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int
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inet6_option_find(const struct cmsghdr *cmsg, u_int8_t **tptrp,
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int type);
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DESCRIPTION
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Building and parsing the Hop-by-Hop and Destination options is compli-
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cated due to alignment constranints, padding and ancillary data manipula-
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tion. RFC2292 defines a set of functions to help the application. The
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function prototypes for these functions are all in the <netinet/in.h>
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header.
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inet6_option_space
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inet6_option_space() returns the number of bytes required to hold an
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option when it is stored as ancillary data, including the cmsghdr struc-
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ture at the beginning, and any padding at the end (to make its size a
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multiple of 8 bytes). The argument is the size of the structure defining
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the option, which must include any pad bytes at the beginning (the value
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y in the alignment term ``xn + y''), the type byte, the length byte, and
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the option data.
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Note: If multiple options are stored in a single ancillary data object,
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which is the recommended technique, this function overestimates the
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amount of space required by the size of N-1 cmsghdr structures, where N
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is the number of options to be stored in the object. This is of little
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consequence, since it is assumed that most Hop-by-Hop option headers and
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Destination option headers carry only one option (appendix B of
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[RFC-2460]).
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inet6_option_init
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inet6_option_init() is called once per ancillary data object that will
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contain either Hop-by-Hop or Destination options. It returns 0 on suc-
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cess or -1 on an error.
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bp is a pointer to previously allocated space that will contain the
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ancillary data object. It must be large enough to contain all the indi-
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vidual options to be added by later calls to inet6_option_append() and
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inet6_option_alloc().
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cmsgp is a pointer to a pointer to a cmsghdr structure. *cmsgp is ini-
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tialized by this function to point to the cmsghdr structure constructed
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by this function in the buffer pointed to by bp.
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type is either IPV6_HOPOPTS or IPV6_DSTOPTS. This type is stored in the
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cmsg_type member of the cmsghdr structure pointed to by *cmsgp.
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inet6_option_append
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This function appends a Hop-by-Hop option or a Destination option into an
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ancillary data object that has been initialized by inet6_option_init().
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This function returns 0 if it succeeds or -1 on an error.
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cmsg is a pointer to the cmsghdr structure that must have been initial-
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ized by inet6_option_init().
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typep is a pointer to the 8-bit option type. It is assumed that this
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field is immediately followed by the 8-bit option data length field,
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which is then followed immediately by the option data. The caller ini-
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tializes these three fields (the type-length-value, or TLV) before call-
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ing this function.
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The option type must have a value from 2 to 255, inclusive. (0 and 1 are
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reserved for the Pad1 and PadN options, respectively.)
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The option data length must have a value between 0 and 255, inclusive,
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and is the length of the option data that follows.
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multx is the value x in the alignment term ``xn + y''. It must have a
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value of 1, 2, 4, or 8.
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plusy is the value y in the alignment term ``xn + y''. It must have a
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value between 0 and 7, inclusive.
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inet6_option_alloc
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This function appends a Hop-by-Hop option or a Destination option into an
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ancillary data object that has been initialized by inet6_option_init().
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This function returns a pointer to the 8-bit option type field that
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starts the option on success, or NULL on an error.
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The difference between this function and inet6_option_append() is that
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the latter copies the contents of a previously built option into the
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ancillary data object while the current function returns a pointer to the
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space in the data object where the option's TLV must then be built by the
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caller.
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cmsg is a pointer to the cmsghdr structure that must have been initial-
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ized by inet6_option_init().
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datalen is the value of the option data length byte for this option.
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This value is required as an argument to allow the function to determine
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if padding must be appended at the end of the option. (The
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inet6_option_append() function does not need a data length argument since
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the option data length must already be stored by the caller.)
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multx is the value x in the alignment term ``xn + y''. It must have a
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value of 1, 2, 4, or 8.
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plusy is the value y in the alignment term ``xn + y''. It must have a
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value between 0 and 7, inclusive.
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inet6_option_next
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This function processes the next Hop-by-Hop option or Destination option
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in an ancillary data object. If another option remains to be processed,
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the return value of the function is 0 and *tptrp points to the 8-bit
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option type field (which is followed by the 8-bit option data length,
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followed by the option data). If no more options remain to be processed,
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the return value is -1 and *tptrp is NULL. If an error occurs, the
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return value is -1 and *tptrp is not NULL.
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cmsg is a pointer to cmsghdr structure of which cmsg_level equals
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IPPROTO_IPV6 and cmsg_type equals either IPV6_HOPOPTS or IPV6_DSTOPTS.
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tptrp is a pointer to a pointer to an 8-bit byte and *tptrp is used by
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the function to remember its place in the ancillary data object each time
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the function is called. The first time this function is called for a
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given ancillary data object, *tptrp must be set to NULL.
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Each time this function returns success, *tptrp points to the 8-bit
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option type field for the next option to be processed.
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inet6_option_find
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This function is similar to the previously described inet6_option_next()
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function, except this function lets the caller specify the option type to
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be searched for, instead of always returning the next option in the
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ancillary data object. cmsg is a pointer to cmsghdr structure of which
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cmsg_level equals IPPROTO_IPV6 and cmsg_type equals either IPV6_HOPOPTS
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or IPV6_DSTOPTS.
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tptrp is a pointer to a pointer to an 8-bit byte and *tptrp is used by
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the function to remember its place in the ancillary data object each time
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the function is called. The first time this function is called for a
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given ancillary data object, *tptrp must be set to NULL. ~ This function
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starts searching for an option of the specified type beginning after the
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value of *tptrp. If an option of the specified type is located, this
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function returns 0 and *tptrp points to the 8- bit option type field for
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the option of the specified type. If an option of the specified type is
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not located, the return value is -1 and *tptrp is NULL. If an error
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occurs, the return value is -1 and *tptrp is not NULL.
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DIAGNOSTICS
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inet6_option_init() and inet6_option_append() return 0 on success or -1
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on an error.
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inet6_option_alloc() returns NULL on an error.
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| 263 |
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On errors, inet6_option_next() and inet6_option_find() return -1 setting
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| 265 |
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*tptrp to non NULL value.
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EXAMPLES
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| 268 |
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RFC2292 gives comprehensive examples in chapter 6.
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SEE ALSO
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| 271 |
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W. Stevens and M. Thomas, Advanced Sockets API for IPv6, RFC2292,
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| 272 |
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February 1998.
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| 274 |
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S. Deering and R. Hinden, Internet Protocol, Version 6 (IPv6)
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| 275 |
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Specification, RFC2460, December 1998.
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HISTORY
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| 278 |
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The implementation first appeared in KAME advanced networking kit.
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| 280 |
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STANDARDS
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| 281 |
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The functions are documented in ``Advanced Sockets API for IPv6''
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| 282 |
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(RFC2292).
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BUGS
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| 285 |
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The text was shamelessly copied from RFC2292.
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| 287 |
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BSD December 10, 1999 BSD
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</PRE
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>inet</TD
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WIDTH="34%"
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ALIGN="center"
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><A
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HREF="tcpip-library-reference.html"
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ACCESSKEY="U"
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>Up</A
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></TD
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WIDTH="33%"
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VALIGN="top"
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>inet6_rthdr_space</TD
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></TR
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></TABLE
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></DIV
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></BODY
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></HTML
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>
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