BER_ENCODE(3LDAP) LDAP Library Functions BER_ENCODE(3LDAP)


NAME


ber_encode, ber_alloc, ber_printf, ber_put_int, 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 - simplified Basic
Encoding Rules library encoding functions

SYNOPSIS


cc[ flag... ] file... -lldap[ library... ]
#include <lber.h>

BerElement *ber_alloc();


ber_printf(BerElement *ber, char **fmt[, arg... ]);


ber_put_int(BerElement *ber, long num, char tag);


ber_put_ostring(BerElement *ber, char **str, unsigned long len,
char tag);


ber_put_string(BerElement *ber, char **str, char tag);


ber_put_null(BerElement *ber, char tag);


ber_put_boolean(BerElement *ber, int bool, char tag);


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


ber_start_seq(BerElement *ber, char tag);


ber_start_set(BerElement *ber, char tag);


ber_put_seq(BerElement *ber);


ber_put_set(BerElement *ber);


DESCRIPTION


These functions provide a subfunction interface to a simplified
implementation of the Basic Encoding Rules of ASN.1. The version of BER
these functions 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. In addition, these lightweight BER functions 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 encoding functions in
the lber library. See ber_decode(3LDAP) for details on the corresponding
decoding functions.


Normally, the only functions that need be called by an application are
ber_alloc(), to allocate a BER element, and ber_printf() to do the actual
encoding. The other functions are provided for those applications that
need more control than ber_printf() provides. In general, these
functions return the length of the element encoded, or -1 if an error
occurred.


The ber_alloc() function is used to allocate a new BER element.


The ber_printf() function is used to encode a BER element in much the
same way that sprintf(3C) 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(). It interprets and formats
its arguments according to the format string fmt. The format string can
contain the following characters:

b
Boolean. An integer parameter should be supplied. A boolean
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.


i
Integer. An integer parameter should be supplied. An integer
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. An int specifying the tag to give the next element is
provided. This works across calls.


v
Several octet strings. A null-terminated array of char * is
supplied. Note that a construct like '{v}' 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() function writes the integer element num to the BER
element ber.


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


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


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


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


The ber_start_seq() function is used to start a sequence in the BER
element. The ber_start_set() function 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.


The ber_first_element() function 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


Example 1: Assuming the following variable declarations, and that the


variables have been assigned appropriately, an 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 (3N)
},
sizelimit INTEGER (0 .. 65535),
timelimit INTEGER (0 .. 65535),
attrsOnly BOOLEAN,
attributes SEQUENCE OF AttributeType
}


can be achieved like so:

int scope, ali, size, time, attrsonly;
char *dn, **attrs;

/* ... fill in values ... */
if ( (ber = ber_alloc()) == NULLBER )
/* error */

if ( ber_printf( ber, "{siiiib{v}}", dn, scope, ali,
size, time, attrsonly, attrs ) == -1 )
/* error */
else
/* success */


RETURN VALUES


If an error occurs during encoding, ber_alloc() returns NULL; other
functions generally return -1.

ATTRIBUTES


See attributes(5) for a description of the following attributes:


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Committed |
+--------------------+-----------------+

SEE ALSO


ber_decode(3LDAP), attributes(5)


Yeong, W., Howes, T., and Hardcastle-Kille, S., "Lightweight Directory
Access Protocol", OSI-DS-26, April 1992.


Information Processing - Open Systems Interconnection - Model and
Notation - Service Definition - Specification of Basic Encoding Rules for
Abstract Syntax Notation One, International Organization for
Standardization, International Standard 8825.

NOTES


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


October 6, 2008 BER_ENCODE(3LDAP)