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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
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 long 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. 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 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 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). The sb
structure contains the descriptor and a BerElement used for input
buffering. Only the sb_sd field is relevant to the ber_flush() routine.
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(). 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.
{ 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 enumberation 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.
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
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-types(3) ldap-async(3) ldap-sync(3)
ldap-parse(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.
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