lber-decode(3ldap)

Synopsis

#include <lber.h> 
 
typedef struct berelement { 
    char             ber_buf; 
    char             ber_ptr; 
    char             ber_end; 
    struct seqorset  ber_sos; 
    int              ber_tag; 
    int              ber_usertag; 
} BerElement; 
 
typedef struct sockbuf { 
    int              sb_sd; 
    BerElement       sb_ber; 
} Sockbuf; 
 
typedef struct berval { 
    unsigned long    bv_len; 
    char             bv_val; 
}; 
 
ber_get_next(Sockbuf sb, unsigned long len, BerElement ber); 
 
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...]); 
 
void ber_free(BerElement ber, int freebuf); 
 
ber_bvfree(struct berval bv); 
 
ber_bvecfree(struct berval bvec); 

Description

Normally, the only routines 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 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 -1 if an error occurred.

The ber_get_next routine 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, sb_ber 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 others) to decode the element.

The ber_scanf routine is used to decode a BER element in much the same way that scanf works (see the fscanf(3S) manual page for details). 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.

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 malloc'd struct berval containing the octet string and its length. ber_bvfree can be called to free the malloc'd 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 malloc'd 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 supplied, which upon return points to a malloc'd 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 malloc'd 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 malloc'd memory.

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_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 malloc space into which an octet string is read.

The ber_get_stringal routine is used to malloc 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 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_bitstringa routine is used to read a bitstring value. It takes a char which will hold the malloc'd bits, followed by an unsigned long , which will point to the length (in bits) of the bitstring returned.

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.

Return values

Warnings

Examples

   AlmostASearchRequest := SEQUENCE { 
       baseObject      DistinguishedName, 
       scope           ENUMERATED { 
           baseObject    (0), 
           singleLevel   (1), 
           wholeSubtree  (2) 
       }, 
       derefAliases    ENUMERATED { 
           neverDerefaliases   (0), 
           derefInSearching    (1), 
           derefFindingBaseObj (2), 
           alwaysDerefAliases   3ldap 
       }, 
       sizelimit       INTEGER (0 .. 65535), 
       timelimit       INTEGER (0 .. 65535), 
       attrsOnly       BOOLEAN, 
       attributes      SEQUENCE OF AttributeType 
   } 

   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 / 

References

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, International Standard 8825.