1LBER_DECODE(3) Library Functions Manual LBER_DECODE(3)
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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 - OpenLDAP LBER simplified Basic
10 Encoding Rules library routines for decoding
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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 al‐
37 loc);
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 ap‐
67 plications that need more control than ber_scanf() provides. In gen‐
68 eral, these routines return the tag of the element decoded, or LBER_ER‐
69 ROR 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 el‐
75 ement. See lber-sockbuf(3) for details of the Sockbuf implementation of
76 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 ac‐
81 cording 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 A Octet string. A variant of "a". A char ** should be sup‐
92 plied. Memory is allocated, filled with the contents of the
93 octet string, null-terminated, and returned in the parameter,
94 unless a zero-length string would result; in that case, the
95 arg is set to NULL. The caller should free the returned
96 string using ber_memfree().
97 s Octet string. A char * buffer should be supplied, followed
99 by a pointer to a ber_len_t initialized to the size of the
100 buffer. Upon return, the null-terminated octet string is put
101 into the buffer, and the ber_len_t is set to the actual size
102 of the octet string.
103 O Octet string. A struct ber_val ** should be supplied, which
105 upon return points to a dynamically allocated struct berval
106 containing the octet string and its length. The caller
107 should free the returned structure using ber_bvfree().
108 o Octet string. A struct ber_val * should be supplied, which
110 upon return contains the dynamically allocated octet string
111 and its length. The caller should free the returned octet
112 string using ber_memfree().
113 m Octet string. A struct ber_val * should be supplied, which
115 upon return contains the octet string and its length. The
116 string resides in memory assigned to the BerElement, and must
117 not be freed by the caller.
118 b Boolean. A pointer to a ber_int_t should be supplied.
120 e Enumeration. A pointer to a ber_int_t should be supplied.
122 i Integer. A pointer to a ber_int_t should be supplied.
124 B Bitstring. A char ** should be supplied which will point to
126 the dynamically allocated bits, followed by a ber_len_t *,
127 which will point to the length (in bits) of the bitstring re‐
128 turned.
129 n Null. No parameter is required. The element is simply
131 skipped if it is recognized.
132 v Sequence of octet strings. A char *** should be supplied,
134 which upon return points to a dynamically allocated null-ter‐
135 minated array of char *'s containing the octet strings. NULL
136 is returned if the sequence is empty. The caller should free
137 the returned array and octet strings using ber_memvfree().
138 V Sequence of octet strings with lengths. A struct berval ***
140 should be supplied, which upon return points to a dynamically
141 allocated null-terminated array of struct berval *'s contain‐
142 ing the octet strings and their lengths. NULL is returned if
143 the sequence is empty. The caller should free the returned
144 structures using ber_bvecfree().
145 W Sequence of octet strings with lengths. A BerVarray * should
147 be supplied, which upon return points to a dynamically allo‐
148 cated array of struct berval's containing the octet strings
149 and their lengths. The array is terminated by a struct berval
150 with a NULL bv_val string pointer. NULL is returned if the
151 sequence is empty. The caller should free the returned
152 structures using ber_bvarray_free().
153 M Sequence of octet strings with lengths. This is a general‐
155 ized form of the previous three formats. A void ** (ptr)
156 should be supplied, followed by a ber_len_t * (len) and a
157 ber_len_t (off). Upon return (ptr) will point to a dynami‐
158 cally allocated array whose elements are all of size (*len).
159 A struct berval will be filled starting at offset (off) in
160 each element. The strings in each struct berval reside in
161 memory assigned to the BerElement and must not be freed by
162 the caller. The array is terminated by a struct berval with
163 a NULL bv_val string pointer. NULL is returned if the se‐
164 quence is empty. The number of elements in the array is also
165 stored in (*len) on return. The caller should free the re‐
166 turned array using ber_memfree().
167 l Length of the next element. A pointer to a ber_len_t should
169 be supplied.
170 t Tag of the next element. A pointer to a ber_tag_t should be
172 supplied.
173 T Skip element and return its tag. A pointer to a ber_tag_t
175 should be supplied.
176 x Skip element. The next element is skipped.
178 { Begin sequence. No parameter is required. The initial se‐
180 quence tag and length are skipped.
181 } End sequence. No parameter is required and no action is
183 taken.
184 [ Begin set. No parameter is required. The initial set tag
186 and length are skipped.
187 ] End set. No parameter is required and no action is taken.
189 The ber_get_int() routine tries to interpret the next element as an in‐
191 teger, returning the result in num. The tag of whatever it finds is
192 returned on success, LBER_ERROR (-1) on failure.
193 The ber_get_stringb() routine is used to read an octet string into a
195 preallocated buffer. The len parameter should be initialized to the
196 size of the buffer, and will contain the length of the octet string
197 read upon return. The buffer should be big enough to take the octet
198 string value plus a terminating NULL byte.
199 The ber_get_stringa() routine is used to dynamically allocate space
201 into which an octet string is read. The caller should free the re‐
202 turned string using ber_memfree().
203 The ber_get_stringal() routine is used to dynamically allocate space
205 into which an octet string and its length are read. It takes a struct
206 berval **, and returns the result in this parameter. The caller should
207 free the returned structure using ber_bvfree().
208 The ber_get_stringbv() routine is used to read an octet string and its
210 length into the provided struct berval *. If the alloc parameter is
211 zero, the string will reside in memory assigned to the BerElement, and
212 must not be freed by the caller. If the alloc parameter is non-zero,
213 the string will be copied into dynamically allocated space which should
214 be returned using ber_memfree().
215 The ber_get_null() routine is used to read a NULL element. It returns
217 the tag of the element it skips over.
218 The ber_get_boolean() routine is used to read a boolean value. It is
220 called the same way that ber_get_int() is called.
221 The ber_get_enum() routine is used to read a enumeration value. It is
223 called the same way that ber_get_int() is called.
224 The ber_get_bitstringa() routine is used to read a bitstring value. It
226 takes a char ** which will hold the dynamically allocated bits, fol‐
227 lowed by an ber_len_t *, which will point to the length (in bits) of
228 the bitstring returned. The caller should free the returned string us‐
229 ing ber_memfree().
230 The ber_first_element() routine is used to return the tag and length of
232 the first element in a set or sequence. It also returns in cookie a
233 magic cookie parameter that should be passed to subsequent calls to
234 ber_next_element(), which returns similar information.
235
237 Assume the variable ber contains a lightweight BER encoding of the fol‐
238 lowing ASN.1 object:
239 AlmostASearchRequest := SEQUENCE {
241 baseObject DistinguishedName,
242 scope ENUMERATED {
243 baseObject (0),
244 singleLevel (1),
245 wholeSubtree (2)
246 },
247 derefAliases ENUMERATED {
248 neverDerefaliases (0),
249 derefInSearching (1),
250 derefFindingBaseObj (2),
251 alwaysDerefAliases (3)
252 },
253 sizelimit INTEGER (0 .. 65535),
254 timelimit INTEGER (0 .. 65535),
255 attrsOnly BOOLEAN,
256 attributes SEQUENCE OF AttributeType
257 }
258 The element can be decoded using ber_scanf() as follows.
260 ber_int_t scope, deref, size, time, attrsonly;
262 char *dn, **attrs;
263 ber_tag_t tag;
264 tag = ber_scanf( ber, "{aeeiib{v}}",
266 &dn, &scope, &deref,
267 &size, &time, &attrsonly, &attrs );
268 if( tag == LBER_ERROR ) {
270 /* error */
271 } else {
272 /* success */
273 }
274 ber_memfree( dn );
276 ber_memvfree( attrs );
277
279 If an error occurs during decoding, generally these routines return
280 LBER_ERROR ((ber_tag_t)-1).
281
283 The return values for all of these functions are declared in the
284 <lber.h> header file. Some routines may dynamically allocate memory
285 which must be freed by the caller using supplied deallocation routines.
286
288 lber-encode(3), lber-memory(3), lber-sockbuf(3), lber-types(3)
289
291 OpenLDAP Software is developed and maintained by The OpenLDAP Project
292 <http://www.openldap.org/>. OpenLDAP Software is derived from the Uni‐
293 versity of Michigan LDAP 3.3 Release.
294OpenLDAP 2.4.57 2021/01/18 LBER_DECODE(3)