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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.

       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

       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.