1LBER_DECODE(3) Library Functions Manual LBER_DECODE(3)
2
6 ber_get_next, ber_skip_tag, ber_peek_tag, ber_scanf, ber_get_int,
7 ber_get_enum, ber_get_stringb, ber_get_stringa, ber_get_stringal,
8 ber_get_stringbv, ber_get_null, ber_get_boolean, ber_get_bitstring,
9 ber_first_element, ber_next_element - LBER simplified Basic Encoding
10 Rules library routines for decoding
11
13 OpenLDAP LBER (liblber, -llber)
14
16 #include <lber.h>
17 ber_tag_t ber_get_next(Sockbuf *sb, ber_len_t *len, BerElement *ber);
19 ber_tag_t ber_skip_tag(BerElement *ber, ber_len_t *len);
21 ber_tag_t ber_peek_tag(BerElement *ber, ber_len_t *len);
23 ber_tag_t ber_scanf(BerElement *ber, const char *fmt, ...);
25 ber_tag_t ber_get_int(BerElement *ber, ber_int_t *num);
27 ber_tag_t ber_get_enum(BerElement *ber, ber_int_t *num);
29 ber_tag_t ber_get_stringb(BerElement *ber, char *buf, ber_len_t *len);
31 ber_tag_t ber_get_stringa(BerElement *ber, char **buf);
33 ber_tag_t ber_get_stringal(BerElement *ber, struct berval **bv);
35 ber_tag_t ber_get_stringbv(BerElement *ber, struct berval *bv, int
37 alloc);
38 ber_tag_t ber_get_null(BerElement *ber);
40 ber_tag_t ber_get_boolean(BerElement *ber, ber_int_t *bool);
42 ber_tag_t ber_get_bitstringa(BerElement *ber, char **buf, ber_len_t
44 *blen);
45 ber_tag_t ber_first_element(BerElement *ber, ber_len_t *len, char
47 **cookie);
48 ber_tag_t ber_next_element(BerElement *ber, ber_len_t *len, const char
50 *cookie);
51
53 These routines provide a subroutine interface to a simplified implemen‐
54 tation of the Basic Encoding Rules of ASN.1. The version of BER these
55 routines support is the one defined for the LDAP protocol. The encod‐
56 ing rules are the same as BER, except that only definite form lengths
57 are used, and bitstrings and octet strings are always encoded in primi‐
58 tive form. This man page describes the decoding routines in the lber
59 library. See lber-encode(3) for details on the corresponding encoding
60 routines. Consult lber-types(3) for information about types, alloca‐
61 tors, and deallocators.
62 Normally, the only routines that need to be called by an application
64 are ber_get_next() to get the next BER element and ber_scanf() to do
65 the actual decoding. In some cases, ber_peek_tag() may also need to be
66 called in normal usage. The other routines are provided for those
67 applications that need more control than ber_scanf() provides. In gen‐
68 eral, these routines return the tag of the element decoded, or
69 LBER_ERROR if an error occurred.
70 The ber_get_next() routine is used to read the next BER element from
72 the given Sockbuf, sb. It strips off and returns the leading tag,
73 strips off and returns the length of the entire element in len, and
74 sets up ber for subsequent calls to ber_scanf() et al to decode the
75 element. See lber-sockbuf(3) for details of the Sockbuf implementation
76 of the sb parameter.
77 The ber_scanf() routine is used to decode a BER element in much the
79 same way that scanf(3) works. It reads from ber, a pointer to a
80 BerElement such as returned by ber_get_next(), interprets the bytes
81 according to the format string fmt, and stores the results in its addi‐
82 tional arguments. The format string contains conversion specifications
83 which are used to direct the interpretation of the BER element. The
84 format string can contain the following characters.
85 a Octet string. A char ** should be supplied. Memory is allo‐
87 cated, filled with the contents of the octet string, null-
88 terminated, and returned in the parameter. The caller should
89 free the returned string using ber_memfree().
90 s Octet string. A char * buffer should be supplied, followed
92 by a pointer to a ber_len_t initialized to the size of the
93 buffer. Upon return, the null-terminated octet string is put
94 into the buffer, and the ber_len_t is set to the actual size
95 of the octet string.
96 O Octet string. A struct ber_val ** should be supplied, which
98 upon return points to a dynamically allocated struct berval
99 containing the octet string and its length. The caller
100 should free the returned structure using ber_bvfree().
101 o Octet string. A struct ber_val * should be supplied, which
103 upon return contains the dynamically allocated octet string
104 and its length. The caller should free the returned octet
105 string using ber_memfree().
106 m Octet string. A struct ber_val * should be supplied, which
108 upon return contains the octet string and its length. The
109 string resides in memory assigned to the BerElement, and must
110 not be freed by the caller.
111 b Boolean. A pointer to a ber_int_t should be supplied.
113 e Enumeration. A pointer to a ber_int_t should be supplied.
115 i Integer. A pointer to a ber_int_t should be supplied.
117 B Bitstring. A char ** should be supplied which will point to
119 the dynamically allocated bits, followed by a ber_len_t *,
120 which will point to the length (in bits) of the bitstring
121 returned.
122 n Null. No parameter is required. The element is simply
124 skipped if it is recognized.
125 v Sequence of octet strings. A char *** should be supplied,
127 which upon return points to a dynamically allocated null-ter‐
128 minated array of char *'s containing the octet strings. NULL
129 is returned if the sequence is empty. The caller should free
130 the returned array and octet strings using ber_memvfree().
131 V Sequence of octet strings with lengths. A struct berval ***
133 should be supplied, which upon return points to a dynamically
134 allocated null-terminated array of struct berval *'s contain‐
135 ing the octet strings and their lengths. NULL is returned if
136 the sequence is empty. The caller should free the returned
137 structures using ber_bvecfree().
138 W Sequence of octet strings with lengths. A BerVarray * should
140 be supplied, which upon return points to a dynamically allo‐
141 cated array of struct berval's containing the octet strings
142 and their lengths. The array is terminated by a struct berval
143 with a NULL bv_val string pointer. NULL is returned if the
144 sequence is empty. The caller should free the returned
145 structures using ber_bvarray_free().
146 M Sequence of octet strings with lengths. This is a general‐
148 ized form of the previous three formats. A void ** (ptr)
149 should be supplied, followed by a ber_len_t * (len) and a
150 ber_len_t (off). Upon return (ptr) will point to a dynami‐
151 cally allocated array whose elements are all of size (*len).
152 A struct berval will be filled starting at offset (off) in
153 each element. The strings in each struct berval reside in
154 memory assigned to the BerElement and must not be freed by
155 the caller. The array is terminated by a struct berval with
156 a NULL bv_val string pointer. NULL is returned if the
157 sequence is empty. The number of elements in the array is
158 also stored in (*len) on return. The caller should free the
159 returned array using ber_memfree().
160 l Length of the next element. A pointer to a ber_len_t should
162 be supplied.
163 t Tag of the next element. A pointer to a ber_tag_t should be
165 supplied.
166 T Skip element and return its tag. A pointer to a ber_tag_t
168 should be supplied.
169 x Skip element. The next element is skipped.
171 { Begin sequence. No parameter is required. The initial
173 sequence tag and length are skipped.
174 } End sequence. No parameter is required and no action is
176 taken.
177 [ Begin set. No parameter is required. The initial set tag
179 and length are skipped.
180 ] End set. No parameter is required and no action is taken.
182 The ber_get_int() routine tries to interpret the next element as an
184 integer, returning the result in num. The tag of whatever it finds is
185 returned on success, LBER_ERROR (-1) on failure.
186 The ber_get_stringb() routine is used to read an octet string into a
188 preallocated buffer. The len parameter should be initialized to the
189 size of the buffer, and will contain the length of the octet string
190 read upon return. The buffer should be big enough to take the octet
191 string value plus a terminating NULL byte.
192 The ber_get_stringa() routine is used to dynamically allocate space
194 into which an octet string is read. The caller should free the
195 returned string using ber_memfree().
196 The ber_get_stringal() routine is used to dynamically allocate space
198 into which an octet string and its length are read. It takes a struct
199 berval **, and returns the result in this parameter. The caller should
200 free the returned structure using ber_bvfree().
201 The ber_get_stringbv() routine is used to read an octet string and its
203 length into the provided struct berval *. If the alloc parameter is
204 zero, the string will reside in memory assigned to the BerElement, and
205 must not be freed by the caller. If the alloc parameter is non-zero,
206 the string will be copied into dynamically allocated space which should
207 be returned using ber_memfree().
208 The ber_get_null() routine is used to read a NULL element. It returns
210 the tag of the element it skips over.
211 The ber_get_boolean() routine is used to read a boolean value. It is
213 called the same way that ber_get_int() is called.
214 The ber_get_enum() routine is used to read a enumeration value. It is
216 called the same way that ber_get_int() is called.
217 The ber_get_bitstringa() routine is used to read a bitstring value. It
219 takes a char ** which will hold the dynamically allocated bits, fol‐
220 lowed by an ber_len_t *, which will point to the length (in bits) of
221 the bitstring returned. The caller should free the returned string
222 using ber_memfree().
223 The ber_first_element() routine is used to return the tag and length of
225 the first element in a set or sequence. It also returns in cookie a
226 magic cookie parameter that should be passed to subsequent calls to
227 ber_next_element(), which returns similar information.
228
230 Assume the variable ber contains a lightweight BER encoding of the fol‐
231 lowing ASN.1 object:
232 AlmostASearchRequest := SEQUENCE {
234 baseObject DistinguishedName,
235 scope ENUMERATED {
236 baseObject (0),
237 singleLevel (1),
238 wholeSubtree (2)
239 },
240 derefAliases ENUMERATED {
241 neverDerefaliases (0),
242 derefInSearching (1),
243 derefFindingBaseObj (2),
244 alwaysDerefAliases (3)
245 },
246 sizelimit INTEGER (0 .. 65535),
247 timelimit INTEGER (0 .. 65535),
248 attrsOnly BOOLEAN,
249 attributes SEQUENCE OF AttributeType
250 }
251 The element can be decoded using ber_scanf() as follows.
253 ber_int_t scope, deref, size, time, attrsonly;
255 char *dn, **attrs;
256 ber_tag_t tag;
257 tag = ber_scanf( ber, "{aeeiib{v}}",
259 &dn, &scope, &deref,
260 &size, &time, &attrsonly, &attrs );
261 if( tag == LBER_ERROR ) {
263 /* error */
264 } else {
265 /* success */
266 }
267 ber_memfree( dn );
269 ber_memvfree( attrs );
270
272 If an error occurs during decoding, generally these routines return
273 LBER_ERROR ((ber_tag_t)-1).
274
276 The return values for all of these functions are declared in the
277 <lber.h> header file. Some routines may dynamically allocate memory
278 which must be freed by the caller using supplied deallocation routines.
279
281 lber-encode(3), lber-memory(3), lber-sockbuf(3), lber-types(3)
282
284 OpenLDAP is developed and maintained by The OpenLDAP Project
285 (http://www.openldap.org/). OpenLDAP is derived from University of
286 Michigan LDAP 3.3 Release.
287OpenLDAP 2.3.34 2007/2/16 LBER_DECODE(3)