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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | EXAMPLES | ERRORS | NOTES | SEE ALSO | ACKNOWLEDGEMENTS | COLOPHON |
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LBER_DECODE(3) Library Functions Manual LBER_DECODE(3)
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_stringal,
ber_get_stringbv, ber_get_null, ber_get_boolean,
ber_get_bitstring, ber_first_element, ber_next_element - OpenLDAP
LBER simplified Basic Encoding Rules library routines for decoding
OpenLDAP LBER (liblber, -llber)
#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 *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_stringbv(BerElement *ber, struct berval *bv, int
alloc);
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);
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 decoding routines in the lber library. See
lber-encode(3) for details on the corresponding encoding 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_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 general, these routines
return the tag of the element decoded, or LBER_ERROR if an error
occurred.
The ber_get_next() routine is used to read the next BER element
from the given Sockbuf, sb. It strips off and returns the leading
tag, 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. See lber-sockbuf(3) for details of the Sockbuf
implementation of the sb parameter.
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 additional 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
allocated, filled with the contents of the octet string,
null-terminated, and returned in the parameter. The
caller should free the returned string using
ber_memfree().
A Octet string. A variant of "a". A char ** should be
supplied. Memory is allocated, filled with the contents
of the octet string, null-terminated, and returned in
the parameter, unless a zero-length string would result;
in that case, the arg is set to NULL. The caller should
free the returned string 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 ber_len_t
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 contains the dynamically allocated
octet string and its length. The caller should free the
returned octet string using ber_memfree().
m Octet string. A struct ber_val * should be supplied,
which upon return contains the octet string and its
length. The string resides in memory assigned to the
BerElement, and must not be freed by the caller.
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 a
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-terminated 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 containing the octet strings and their
lengths. NULL is returned if the sequence is empty.
The caller should free the returned structures using
ber_bvecfree().
W Sequence of octet strings with lengths. A BerVarray *
should be supplied, which upon return points to a
dynamically allocated array of struct berval's
containing the octet strings and their lengths. The
array is terminated by a struct berval with a NULL
bv_val string pointer. NULL is returned if the sequence
is empty. The caller should free the returned
structures using ber_bvarray_free().
M Sequence of octet strings with lengths. This is a
generalized form of the previous three formats. A void
** (ptr) should be supplied, followed by a ber_len_t *
(len) and a ber_len_t (off). Upon return (ptr) will
point to a dynamically allocated array whose elements
are all of size (*len). A struct berval will be filled
starting at offset (off) in each element. The strings
in each struct berval reside in memory assigned to the
BerElement and must not be freed by the caller. The
array is terminated by a struct berval with a NULL
bv_val string pointer. NULL is returned if the sequence
is empty. The number of elements in the array is also
stored in (*len) on return. The caller should free the
returned array using ber_memfree().
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_stringbv() routine is used to read an octet string and
its length into the provided struct berval *. If the alloc
parameter is zero, the string will reside in memory assigned to
the BerElement, and must not be freed by the caller. If the alloc
parameter is non-zero, the string will be copied into dynamically
allocated space which should be returned using ber_memfree().
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, followed 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.
Assume the variable ber contains a lightweight 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 (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 );
If an error occurs during decoding, generally these routines
return LBER_ERROR ((ber_tag_t)-1).
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.
lber-encode(3), lber-memory(3), lber-sockbuf(3), lber-types(3)
OpenLDAP Software is developed and maintained by The OpenLDAP
Project <http://www.openldap.org/>. OpenLDAP Software is derived
from the University of Michigan LDAP 3.3 Release.
This page is part of the OpenLDAP (an open source implementation
of the Lightweight Directory Access Protocol) project.
Information about the project can be found at
⟨http://www.openldap.org/⟩. If you have a bug report for this
manual page, see ⟨http://www.openldap.org/its/⟩. This page was
obtained from the project's upstream Git repository
⟨https://git.openldap.org/openldap/openldap.git⟩ on 2025-08-11.
(At that time, the date of the most recent commit that was found
in the repository was 2025-08-05.) If you discover any rendering
problems in this HTML version of the page, or you believe there is
a better or more up-to-date source for the page, or you have
corrections or improvements to the information in this COLOPHON
(which is not part of the original manual page), send a mail to
man-pages@man7.org
OpenLDAP LDVERSION RELEASEDATE LBER_DECODE(3)
Pages that refer to this page: lber-encode(3), lber-memory(3), lber-sockbuf(3), lber-types(3), ldap(3)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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