LBER_ENCODE(3)

NAME
ber_alloc_t, ber_flush, ber_printf, ber_put_int, ber_put_enum, ber_put_ostring, ber_put_string, ber_put_null, ber_put_boolean, ber_put_bitstring, ber_start_seq, ber_start_set, ber_put_seq, ber_put_set - LBER simplified Basic Encoding Rules library routines for encoding

LIBRARY
OpenLDAP LBER (liblber, -llber)

SYNOPSIS
#include <lber.h>

BerElement *ber_alloc_t(int options);

int ber_flush(Sockbuf *sb, BerElement *ber, int freeit);

int ber_printf(BerElement *ber, const char *fmt, ...);

int ber_put_int(BerElement *ber, ber_int_t num, ber_tag_t tag);

int ber_put_enum(BerElement *ber, ber_int_t num, ber_tag_t tag);

int ber_put_ostring(BerElement *ber, const char *str, ber_len_t len, ber_tag_t tag);

int ber_put_string(BerElement *ber, const char *str, ber_tag_t tag);

int ber_put_null(BerElement *ber, ber_tag_t tag);

int ber_put_boolean(BerElement *ber, ber_int_t bool, ber_tag_t tag);

int ber_put_bitstring(BerElement *ber, const char *str, ber_len_t blen, ber_tag_t tag);

int ber_start_seq(BerElement *ber, ber_tag_t tag);

int ber_start_set(BerElement *ber, ber_tag_t tag);

int ber_put_seq(BerElement *ber);

int ber_put_set(BerElement *ber);

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_flush() 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_flush() 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 after its contents have been flushed.

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:

    b   Boolean. An ber_int_t parameter should be supplied. A boolean element is output.

    e   Enumeration. An ber_int_t parameter should be supplied. An enumeration element is output.

    i   Integer. An ber_int_t parameter should be supplied. An integer element is output.

    B   Bitstring. A char * pointer to the start of the bitstring is supplied, followed by the number of bits in the bitstring. A bitstring element is output.

    n   Null. No parameter is required. A null element is output.

    o   Octet string. A char * is supplied, followed by the length of the string pointed to. An octet string element is output.

    O   Octet string. A struct berval * is supplied. An octet string element is output.

    s   Octet string. A null-terminated string is supplied. An octet string element is output, not including the trailing NULL octet.

    t   Tag. A ber_tag_t specifying the tag to give the next element is provided. This works across calls.

    v   Several octet strings. A null-terminated array of char *'s is supplied. Note that a construct like '{v}' is required to get an actual SEQUENCE OF octet strings.

    V   Several octet strings. A null-terminated array of struct berval *'s is supplied. Note that a construct like '{V}' is required to get an actual SEQUENCE OF octet strings.

    W   Several octet strings. An array of struct berval's is supplied. The array is terminated by a struct berval with a NULL bv_val. Note that a construct like '{W}' is required to get an actual SEQUENCE OF octet strings.

    {   Begin sequence. No parameter is required.

    }   End sequence. No parameter is required.

    [   Begin set. No parameter is required.

    ]   End set. No parameter is required.

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