Партнёры:
Хостинг:
NAME
ber_decode, ber_alloc_t, ber_free, ber_bvdup, ber_init,
ber_flatten, ber_get_next, ber_skiptag, 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_element,
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 simpli-
fied 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 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() pro-
vides. 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 additional argu-
ments. The format string contains conversion specifications
which are used to direct the interpretation of the BER ele-
ment. The format string can contain the following charac-
ters.
-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 parame-
ter.
-s Octet string. A char * buffer should be supplied,
followed 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
memory.
-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 sim-
ply 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 ber-
val *** 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
memory.
-x Skip element. The next element is skipped.
-{ Begin sequence. No parameter is required. The ini-
tial 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 ele-
ment 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 ele-
ment. 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 bit-
string value. It takes a char ** which will hold the allo-
cated 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 minimum 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 BerEle-
ment 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 suc-
cess 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 func-
tions 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 attri-
butes:
____________________________________________________________
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
| Availability | SUNWlldap (32-bit) |
| | SUNWldapx (64-bit) |
| Stability Level | Evolving |
|_____________________________|_____________________________|
SEE ALSO
ber_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 Notation - Service Definition - Specification of
Basic Encoding Rules for Abstract Syntax Notation One,
International Organization for Standardization, Interna-
tional Standard 8825.
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