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LBER_DECODE(3)                                                  LBER_DECODE(3)



NAME
       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 decod-
       ing

LIBRARY
       OpenLDAP LBER (liblber, -llber)

SYNOPSIS
       #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
       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 termi-
                 nated 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  bit-
       string 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_ele-
       ment(), which returns similar information.

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


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

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



OpenLDAP 2.4.40                   2014/09/20                    LBER_DECODE(3)