ber_decode(3LDAP) LDAP Library Functions ber_decode(3LDAP)NAME
ber_decode, ber_alloc_t, ber_free, ber_bvdup, ber_init, ber_flatten,
ber_get_next, ber_skip_tag, ber_peek_tag, ber_scanf, ber_get_int,
ber_get_stringa, ber_get_stringal, ber_get_stringb, ber_get_null,
ber_get_boolean, ber_get_bitstring, ber_first_element, ber_next_ele‐
ment, ber_bvfree, ber_bvecfree - Basic Encoding Rules library decoding
functions
SYNOPSIS
cc[ flag... ] file... -lldap[ library... ]
#include <lber.h>
BerElement *ber_alloc_t(int options);
struct berval *ber_bvdup(struct berval *bv);
void ber_free(BerElement *ber, int freebuf);
BerElement *ber_init(struct berval *bv);
int ber_flatten(BerElement *ber, struct berval **bvPtr);
ber_get_next(Sockbuf *sb, unsigned long *len, char *bv_val);
ber_skip_tag(BerElement **ber, unsigned long **len);
ber_peek_tag(BerElement **ber, unsigned long **len);
ber_get_int(BerElement **ber, long **num);
ber_get_stringb(BerElement **ber, char **buf, unsigned long **len);
ber_get_stringa(BerElement **ber, char ***buf);
ber_get_stringal(BerElement **ber, struct berval ***bv);
ber_get_null(BerElement **ber);
ber_get_boolean(BerElement **ber, int **bool);
ber_get_bitstringa(BerElement **ber, char ***buf, unsigned long
**blen);
ber_first_element(BerElement **ber, unsigned long **len, char
***cookie);
ber_next_element(BerElement **ber, unsigned long **len, char **cookie);
ber_scanf(BerElement **ber, char **fmt [, arg...]);
ber_bvfree(struct berval **bv );
ber_bvecfree(struct berval ***bvec);
DESCRIPTION
These functions provide a subfunction interface to a simplified imple‐
mentation 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 descrip‐
tions below, it refers to the tag, class, and primitive or constructed
bit in the first octet of the encoding. This man page describes the
decoding functions in the lber library. See ber_encode(3LDAP) for
details on the corresponding encoding functions.
Normally, the only functions that need 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 functions are provided for those
applications that need more control than ber_scanf() provides. In
general, these functions return the tag of the element decoded, or −1
if an error occurred.
The ber_get_next() function is used to read the next BER element from
the given Sockbuf, sb. A Sockbuf consists of the descriptor (usually
socket, but a file descriptor works just as well) from which to read,
and a BerElement structure used to maintain a buffer. On the first
call, the sb_ber struct should be zeroed. It strips off and returns
the leading tag byte, strips off and returns the length of the entire
element in len, and sets up ber for subsequent calls to ber_scanf(),
and all to decode the element.
The ber_scanf() function is used to decode a BER element in much the
same way that scanf(3C) 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 addi‐
tional 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.
-s Octet string. A char * buffer should be supplied, fol‐
lowed by a pointer to an integer initialized to the
size of the buffer. Upon return, the null-terminated
octet string is put into the buffer, and the integer 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 memory allocated struct
berval containing the octet string and its length.
ber_bvfree() can be called to free the allocated mem‐
ory.
-b Boolean. A pointer to an integer should be supplied.
-i Integer. A pointer to an integer should be supplied.
-B Bitstring. A char ** should be supplied which will
point to the memory allocated bits, followed by an
unsigned long *, 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 sup‐
plied, which upon return points to a memory allocated
null-terminated array of char *'s containing the octet
strings. NULL is returned if the sequence is empty.
-V Sequence of octet strings with lengths. A struct berval
*** should be supplied, which upon return points to a
memory allocated, null-terminated array of struct
berval *'s containing the octet strings and their
lengths. NULL is returned if the sequence is empty.
ber_bvecfree() can be called to free the allocated mem‐
ory.
-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() function tries to interpret the next element as an
integer, returning the result in num. The tag of whatever it finds is
returned on success, -1 on failure.
The ber_get_stringb() function 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() function is used to allocate memory space into
which an octet string is read.
The ber_get_stringal() function is used to allocate memory space into
which an octet string and its length are read. It takes a struct
berval **, and returns the result in this parameter.
The ber_get_null() function is used to read a NULL element. It
returns the tag of the element it skips over.
The ber_get_boolean() function is used to read a boolean value. It is
called the same way that ber_get_int() is called.
The ber_get_bitstringa() function is used to read a bitstring value.
It takes a char ** which will hold the allocated memory bits, followed
by an unsigned long *, which will point to the length (in bits) of the
bitstring returned.
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.
ber_alloc_t() constructs and returns BerElement. A null pointer is
returned on error. The options field contains a bitwise-or of options
which are to be used when generating the encoding of this BerElement.
One option is defined and must always be supplied:
#define LBER_USE_DER 0x01
When this option is present, lengths will always be encoded in the min‐
imum number of octets. Note that this option does not cause values of
sets and sequences to be rearranged in tag and byte order, so these
functions are not suitable for generating DER output as defined in
X.509 and X.680
The ber_init function constructs a BerElement and returns a new
BerElement containing a copy of the data in the bv argument. ber_init
returns the null pointer on error.
ber_free() frees a BerElement which is returned from the API calls
ber_alloc_t() or ber_init(). Each BerElement must be freed by the
caller. The second argument freebuf should always be set to 1 to
ensure that the internal buffer used by the BER functions is freed as
well as the BerElement container itself.
ber_bvdup() returns a copy of a berval. The bv_val field in the
returned berval points to a different area of memory as the bv_val
field in the argument berval. The null pointer is returned on error
(that is, is out of memory).
The ber_flatten routine allocates a struct berval whose contents are
BER encoding taken from the ber argument. The bvPtr pointer points to
the returned berval, which must be freed using ber_bvfree(). This
routine returns 0 on success and −1 on error.
EXAMPLES
Example 1: 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 (3N)
},
sizelimit INTEGER (0 .. 65535),
timelimit INTEGER (0 .. 65535),
attrsOnly BOOLEAN,
attributes SEQUENCE OF AttributeType
}
Example 2: The element can be decoded using ber_scanf() as follows.
int scope, ali, size, time, attrsonly;
char *dn, **attrs;
if ( ber_scanf( ber, "{aiiiib{v}}", &dn, &scope, &ali,
&size, &time, &attrsonly, &attrs ) == -1 )
/* error */
else
/* success */
ERRORS
If an error occurs during decoding, generally these functions return
−1.
NOTES
The return values for all of these functions are declared in the
<lber.h> header file. Some functions may allocate memory which must be
freed by the calling application.
ATTRIBUTES
See attributes(5) for a description of the following attributes:
┌─────────────────────────────┬─────────────────────────────┐
│ ATTRIBUTE TYPE │ ATTRIBUTE VALUE │
│Availability │SUNWcsl (32-bit) │
│ │SUNWcslx (64-bit) │
│Interface Stability │Evolving │
└─────────────────────────────┴─────────────────────────────┘
SEE ALSOber_encode(3LDAP)
Yeong, W., Howes, T., and Hardcastle-Kille, S., "Lightweight Directory
Access Protocol", OSI-DS-26, April 1992.
Information Processing - Open Systems Interconnection - Model and Nota‐
tion - Service Definition - Specification of Basic Encoding Rules for
Abstract Syntax Notation One, International Organization for Standard‐
ization, International Standard 8825.
SunOS 5.10 27 Jan 2002 ber_decode(3LDAP)
