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 
       ⟨git://git.openldap.org/openldap.git⟩ on 2017-03-13.  If you discover
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       COLOPHON (which is not part of the original manual page), send a mail
       to man-pages@man7.org

OpenLDAP LDVERSION               RELEASEDATE                  LBER_DECODE(3)