LIBRARY

OpenLDAP LBER (liblber, -llber)

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 encoding routines in the lber library. See lber-decode(3) for details on the corresponding decoding 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_alloc_t() to allocate a BER element for encoding, ber_printf() to do the actual encoding, and ber_flush2() to actually write the element. The other routines are provided for those applications that need more control than ber_printf() provides. In general, these routines return the length of the element encoded, or -1 if an error occurred.

The ber_alloc_t() routine is used to allocate a new BER element. It should be called with an argument of LBER_USE_DER.

The ber_flush2() routine is used to actually write the element to a socket (or file) descriptor, once it has been fully encoded (using ber_printf() and friends). See lber-sockbuf(3) for more details on the Sockbuf implementation of the sb parameter. If the freeit parameter is non-zero, the supplied ber will be freed. If LBER_FLUSH_FREE_ON_SUCCESS is used, the ber is only freed when successfully flushed, otherwise it is left intact; if LBER_FLUSH_FREE_ON_ERROR is used, the ber is only freed when an error occurs, otherwise it is left intact; if LBER_FLUSH_FREE_ALWAYS is used, the ber is freed anyway. This function differs from the original ber_flush(3) function, whose behavior corresponds to that indicated for LBER_FLUSH_FREE_ON_SUCCESS. Note that in the future, the behavior of ber_flush(3) with freeit non-zero might change into that of ber_flush2(3) with freeit set to LBER_FLUSH_FREE_ALWAYS.

The ber_printf() routine is used to encode a BER element in much the same way that sprintf(3) works. One important difference, though, is that some state information is kept with the ber parameter so that multiple calls can be made to ber_printf() to append things to the end of the BER element. Ber_printf() writes to ber, a pointer to a BerElement such as returned by ber_alloc_t(). It interprets and formats its arguments according to the format string fmt. The format string can contain the following characters:

The ber_put_int() routine writes the integer element num to the BER element ber.

The ber_put_enum() routine writes the enumeration element num to the BER element ber.

The ber_put_boolean() routine writes the boolean value given by bool to the BER element.

The ber_put_bitstring() routine writes blen bits starting at str as a bitstring value to the given BER element. Note that blen is the length in bits of the bitstring.

The ber_put_ostring() routine writes len bytes starting at str to the BER element as an octet string.

The ber_put_string() routine writes the null-terminated string (minus the terminating ' ') to the BER element as an octet string.

The ber_put_null() routine writes a NULL element to the BER element.

The ber_start_seq() routine is used to start a sequence in the BER element. The ber_start_set() routine works similarly. The end of the sequence or set is marked by the nearest matching call to ber_put_seq() or ber_put_set(), respectively.

EXAMPLES

Assuming the following variable declarations, and that the variables have been assigned appropriately, an lber 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
      }

can be achieved like so:

      int rc;
      ber_int_t    scope, ali, size, time, attrsonly;
      char   *dn, **attrs;
      BerElement *ber;

      /* ... fill in values ... */

      ber = ber_alloc_t( LBER_USE_DER );

      if ( ber == NULL ) {
              /* error */
      }

      rc = ber_printf( ber, "{siiiib{v}}", dn, scope, ali,
          size, time, attrsonly, attrs );

      if( rc == -1 ) {
              /* error */
      } else {
              /* success */
      }

ERRORS

If an error occurs during encoding, generally these routines return -1.

NOTES

The return values for all of these functions are declared in the <lber.h> header file.

SEE ALSO

lber-decode(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.