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LBER_DECODE(3)                                 Library Functions Manual                                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
       decoding

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.


                 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, fol‐
                 lowed 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

              {  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  allo‐
       cated 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_element(), 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)
                 },

       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)