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 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 implemen-
       tation of the Basic Encoding Rules of ASN.1.  The version of BER  these
       routines  support is the one defined for the LDAP protocol.  The encod-
       ing rules are the same as BER, except that only definite  form  lengths
       are used, and bitstrings and octet strings are always encoded in primi-
       tive 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,  alloca-
       tors, 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 gen-
       eral, 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 addi-
       tional 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 allo-
                 cated,  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 sup-
                 plied.  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-ter-
                 minated 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 contain-
                 ing 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 allo-
                 cated 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  general-
                 ized  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 dynami-
                 cally 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,  fol-
       lowed  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
       Assume the variable ber contains a lightweight BER encoding of the fol-
       lowing 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  Univer-
       sity of Michigan LDAP 3.3 Release.



OpenLDAP 2.4.11                   2008/07/16                    LBER_DECODE(3)
