lber-decode(3) — Linux manual page

NAME | LIBRARY | SYNOPSIS | DESCRIPTION | EXAMPLES | ERRORS | NOTES | SEE ALSO | ACKNOWLEDGEMENTS | COLOPHON

LBER_DECODE(3)          Library Functions Manual          LBER_DECODE(3)

NAME         top

       ber_get_next, ber_skip_tag, ber_peek_tag, ber_scanf, ber_get_int,
       ber_get_enum, ber_get_stringb, ber_get_stringa, ber_get_stringal,
       ber_get_stringbv, ber_get_null, ber_get_boolean,
       ber_get_bitstring, ber_first_element, ber_next_element - OpenLDAP
       LBER simplified Basic Encoding Rules library routines for
       decoding

LIBRARY         top

       OpenLDAP LBER (liblber, -llber)

SYNOPSIS         top

       #include <lber.h>

       ber_tag_t ber_get_next(Sockbuf *sb, ber_len_t *len, BerElement
       *ber);

       ber_tag_t ber_skip_tag(BerElement *ber, ber_len_t *len);

       ber_tag_t ber_peek_tag(BerElement *ber, ber_len_t *len);

       ber_tag_t ber_scanf(BerElement *ber, const char *fmt, ...);

       ber_tag_t ber_get_int(BerElement *ber, ber_int_t *num);

       ber_tag_t ber_get_enum(BerElement *ber, ber_int_t *num);

       ber_tag_t ber_get_stringb(BerElement *ber, char *buf, ber_len_t
       *len);

       ber_tag_t ber_get_stringa(BerElement *ber, char **buf);

       ber_tag_t ber_get_stringal(BerElement *ber, struct berval **bv);

       ber_tag_t ber_get_stringbv(BerElement *ber, struct berval *bv,
       int alloc);

       ber_tag_t ber_get_null(BerElement *ber);

       ber_tag_t ber_get_boolean(BerElement *ber, ber_int_t *bool);

       ber_tag_t ber_get_bitstringa(BerElement *ber, char **buf,
       ber_len_t *blen);

       ber_tag_t ber_first_element(BerElement *ber, ber_len_t *len, char
       **cookie);

       ber_tag_t ber_next_element(BerElement *ber, ber_len_t *len, const
       char *cookie);

DESCRIPTION         top

       These routines provide a subroutine interface to a simplified
       implementation of the Basic Encoding Rules of ASN.1.  The version
       of BER these routines support is the one defined for the LDAP
       protocol.  The encoding rules are the same as BER, except that
       only definite form lengths are used, and bitstrings and octet
       strings are always encoded in primitive form.  This man page
       describes the decoding routines in the lber library.  See
       lber-encode(3) for details on the corresponding encoding
       routines.  Consult lber-types(3) for information about types,
       allocators, and deallocators.

       Normally, the only routines that need to be called by an
       application are ber_get_next() to get the next BER element and
       ber_scanf() to do the actual decoding.  In some cases,
       ber_peek_tag() may also need to be called in normal usage.  The
       other routines are provided for those applications that need more
       control than ber_scanf() provides.  In general, these routines
       return the tag of the element decoded, or LBER_ERROR if an error
       occurred.

       The ber_get_next() routine is used to read the next BER element
       from the given Sockbuf, sb.  It strips off and returns the
       leading tag, strips off and returns the length of the entire
       element in len, and sets up ber for subsequent calls to
       ber_scanf() et al to decode the element. See lber-sockbuf(3) for
       details of the Sockbuf implementation of the sb parameter.

       The ber_scanf() routine is used to decode a BER element in much
       the same way that scanf(3) works.  It reads from ber, a pointer
       to a BerElement such as returned by ber_get_next(), interprets
       the bytes according to the format string fmt, and stores the
       results in its additional arguments.  The format string contains
       conversion specifications which are used to direct the
       interpretation of the BER element.  The format string can contain
       the following characters.

              a  Octet string.  A char ** should be supplied.  Memory is
                 allocated, filled with the contents of the octet
                 string, null-terminated, and returned in the parameter.
                 The caller should free the returned string using
                 ber_memfree().

              A  Octet string.  A variant of "a".  A char ** should be
                 supplied.  Memory is allocated, filled with the
                 contents of the octet string, null-terminated, and
                 returned in the parameter, unless a zero-length string
                 would result; in that case, the arg is set to NULL.
                 The caller should free the returned string using
                 ber_memfree().

              s  Octet string.  A char * buffer should be supplied,
                 followed by a pointer to a ber_len_t initialized to the
                 size of the buffer.  Upon return, the null-terminated
                 octet string is put into the buffer, and the ber_len_t
                 is set to the actual size of the octet string.

              O  Octet string.  A struct ber_val ** should be supplied,
                 which upon return points to a dynamically allocated
                 struct berval containing the octet string and its
                 length.  The caller should free the returned structure
                 using ber_bvfree().

              o  Octet string.  A struct ber_val * should be supplied,
                 which upon return contains the dynamically allocated
                 octet string and its length.  The caller should free
                 the returned octet string using ber_memfree().

              m  Octet string.  A struct ber_val * should be supplied,
                 which upon return contains the octet string and its
                 length.  The string resides in memory assigned to the
                 BerElement, and must not be freed by the caller.

              b  Boolean.  A pointer to a ber_int_t should be supplied.

              e  Enumeration.  A pointer to a ber_int_t should be
                 supplied.

              i  Integer.  A pointer to a ber_int_t should be supplied.

              B  Bitstring.  A char ** should be supplied which will
                 point to the dynamically allocated bits, followed by a
                 ber_len_t *, which will point to the length (in bits)
                 of the bitstring returned.

              n  Null.  No parameter is required.  The element is simply
                 skipped if it is recognized.

              v  Sequence of octet strings.  A char *** should be
                 supplied, which upon return points to a dynamically
                 allocated null-terminated array of char *'s containing
                 the octet strings.  NULL is returned if the sequence is
                 empty.  The caller should free the returned array and
                 octet strings using ber_memvfree().

              V  Sequence of octet strings with lengths.  A struct
                 berval *** should be supplied, which upon return points
                 to a dynamically allocated null-terminated array of
                 struct berval *'s containing the octet strings and
                 their lengths.  NULL is returned if the sequence is
                 empty.  The caller should free the returned structures
                 using ber_bvecfree().

              W  Sequence of octet strings with lengths.  A BerVarray *
                 should be supplied, which upon return points to a
                 dynamically allocated array of struct berval's
                 containing the octet strings and their lengths. The
                 array is terminated by a struct berval with a NULL
                 bv_val string pointer.  NULL is returned if the
                 sequence is empty.  The caller should free the returned
                 structures using ber_bvarray_free().

              M  Sequence of octet strings with lengths.  This is a
                 generalized form of the previous three formats.  A void
                 ** (ptr) should be supplied, followed by a ber_len_t *
                 (len) and a ber_len_t (off).  Upon return (ptr) will
                 point to a dynamically allocated array whose elements
                 are all of size (*len).  A struct berval will be filled
                 starting at offset (off) in each element.  The strings
                 in each struct berval reside in memory assigned to the
                 BerElement and must not be freed by the caller.  The
                 array is terminated by a struct berval with a NULL
                 bv_val string pointer.  NULL is returned if the
                 sequence is empty.  The number of elements in the array
                 is also stored in (*len) on return.  The caller should
                 free the returned array using ber_memfree().

              l  Length of the next element.  A pointer to a ber_len_t
                 should be supplied.

              t  Tag of the next element.  A pointer to a ber_tag_t
                 should be supplied.

              T  Skip element and return its tag.  A pointer to a
                 ber_tag_t should be supplied.

              x  Skip element.  The next element is skipped.

              {  Begin sequence.  No parameter is required.  The initial
                 sequence tag and length are skipped.

              }  End sequence.  No parameter is required and no action
                 is taken.

              [  Begin set.  No parameter is required.  The initial set
                 tag and length are skipped.

              ]  End set.  No parameter is required and no action is
                 taken.

       The ber_get_int() routine tries to interpret the next element as
       an integer, returning the result in num.  The tag of whatever it
       finds is returned on success, LBER_ERROR (-1) on failure.

       The ber_get_stringb() routine is used to read an octet string
       into a preallocated buffer.  The len parameter should be
       initialized to the size of the buffer, and will contain the
       length of the octet string read upon return.  The buffer should
       be big enough to take the octet string value plus a terminating
       NULL byte.

       The ber_get_stringa() routine is used to dynamically allocate
       space into which an octet string is read.  The caller should free
       the returned string using ber_memfree().

       The ber_get_stringal() routine is used to dynamically allocate
       space into which an octet string and its length are read.  It
       takes a struct berval **, and returns the result in this
       parameter.  The caller should free the returned structure using
       ber_bvfree().

       The ber_get_stringbv() routine is used to read an octet string
       and its length into the provided struct berval *. If the alloc
       parameter is zero, the string will reside in memory assigned to
       the BerElement, and must not be freed by the caller. If the alloc
       parameter is non-zero, the string will be copied into dynamically
       allocated space which should be returned using ber_memfree().

       The ber_get_null() routine is used to read a NULL element.  It
       returns the tag of the element it skips over.

       The ber_get_boolean() routine is used to read a boolean value.
       It is called the same way that ber_get_int() is called.

       The ber_get_enum() routine is used to read a enumeration value.
       It is called the same way that ber_get_int() is called.

       The ber_get_bitstringa() routine is used to read a bitstring
       value.  It takes a char ** which will hold the dynamically
       allocated bits, followed by an ber_len_t *, which will point to
       the length (in bits) of the bitstring returned.  The caller
       should free the returned string using ber_memfree().

       The ber_first_element() routine is used to return the tag and
       length of the first element in a set or sequence.  It also
       returns in cookie a magic cookie parameter that should be passed
       to subsequent calls to ber_next_element(), which returns similar
       information.

EXAMPLES         top

       Assume the variable ber contains a lightweight BER encoding of
       the following ASN.1 object:

             AlmostASearchRequest := SEQUENCE {
                 baseObject      DistinguishedName,
                 scope           ENUMERATED {
                     baseObject    (0),
                     singleLevel   (1),
                     wholeSubtree  (2)
                 },
                 derefAliases    ENUMERATED {
                     neverDerefaliases   (0),
                     derefInSearching    (1),
                     derefFindingBaseObj (2),
                     alwaysDerefAliases  (3)
                 },
                 sizelimit       INTEGER (0 .. 65535),
                 timelimit       INTEGER (0 .. 65535),
                 attrsOnly       BOOLEAN,
                 attributes      SEQUENCE OF AttributeType
             }

       The element can be decoded using ber_scanf() as follows.

             ber_int_t    scope, deref, size, time, attrsonly;
             char   *dn, **attrs;
             ber_tag_t tag;

             tag = ber_scanf( ber, "{aeeiib{v}}",
                 &dn, &scope, &deref,
                 &size, &time, &attrsonly, &attrs );

             if( tag == LBER_ERROR ) {
                     /* error */
             } else {
                     /* success */
             }

             ber_memfree( dn );
             ber_memvfree( attrs );

ERRORS         top

       If an error occurs during decoding, generally these routines
       return LBER_ERROR ((ber_tag_t)-1).

NOTES         top

       The return values for all of these functions are declared in the
       <lber.h> header file.  Some routines may dynamically allocate
       memory which must be freed by the caller using supplied
       deallocation routines.

SEE ALSO         top

       lber-encode(3), lber-memory(3), lber-sockbuf(3), lber-types(3)

ACKNOWLEDGEMENTS         top

       OpenLDAP Software is developed and maintained by The OpenLDAP
       Project <http://www.openldap.org/>.  OpenLDAP Software is derived
       from the University of Michigan LDAP 3.3 Release.

COLOPHON         top

       This page is part of the OpenLDAP (an open source implementation
       of the Lightweight Directory Access Protocol) project.
       Information about the project can be found at 
       ⟨http://www.openldap.org/⟩.  If you have a bug report for this
       manual page, see ⟨http://www.openldap.org/its/⟩.  This page was
       obtained from the project's upstream Git repository
       ⟨https://git.openldap.org/openldap/openldap.git⟩ on 2020-12-18.
       (At that time, the date of the most recent commit that was found
       in the repository was 2020-12-16.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
       is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to
       man-pages@man7.org

OpenLDAP LDVERSION             RELEASEDATE                LBER_DECODE(3)

Pages that refer to this page: lber-encode(3)lber-memory(3)lber-sockbuf(3)lber-types(3)ldap(3)