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ber_get_null

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_null,
       ber_get_boolean, ber_get_bitstring, ber_first_element, ber_next_element
       - LBER simplified Basic Encoding Rules library routines for decoding

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 long *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_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.   In addition, these lightweight BER routines restrict tags
       and class to fit in a single octet (this means the actual tag  must  be
       less than 31).  When a "tag" is specified in the descriptions below, it
       refers to the tag, class, and primitive or constructed bit in the first
       octet  of  the encoding.  This man page describes the decoding routines
       in the lber library.  See lber-encode(3) for details on the correspond-
       ing  encoding  routines.   Consult  lber-types(3) for information about
       types, allocators, and deallocators.

       Normally, the only routines that need 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 -1 if an
       error occurred.

       The ber_get_next() routine is used to read the next  BER  element  from
       the  given  Sockbuf, sb.  A Sockbuf consists of the descriptor (usually
       socket, but a file descriptor works just as well) from which  to  read,
       and  a  BerElement  structure  used to maintain a buffer.  On the first
       call, the sb_ber struct should be zeroed.  It strips  off  and  returns
       the  leading  tag byte, 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.

       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 ber_val 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 integer 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 points containing the dynamically allocated octet
                 string  and  its length.  The caller should free the returned
                 octet string using ber_memfree().

              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 an 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().

              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_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 (-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-types(3) ldap-parse(3) ldap-sync(3)
       ldap-async(3)

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



OpenLDAP 2.0.27-Release          12 July 2000                   LBER_DECODE(3)