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.