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LBER_DECODE(3)							LBER_DECODE(3)

NAME
       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 - LBER  simplified  Basic  Encoding
       Rules library routines for decoding

LIBRARY
       OpenLDAP LBER (liblber, -llber)

SYNOPSIS
       #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);

DESCRIPTION
       These routines provide a subroutine interface to a simplified implemen‐
       tation of the Basic Encoding Rules of ASN.1.  The version of BER	 these
       routines	 support is the one defined for the LDAP protocol.  The encod‐
       ing rules are the same as BER, except that only definite	 form  lengths
       are used, and bitstrings and octet strings are always encoded in primi‐
       tive 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,  alloca‐
       tors, 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 gen‐
       eral, 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 addi‐
       tional 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 allo‐
		 cated,	 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().

	      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-ter‐
		 minated 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 contain‐
		 ing 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	 allo‐
		 cated	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 general‐
		 ized 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  dynami‐
		 cally	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, fol‐
       lowed 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.

EXAMPLES
       Assume the variable ber contains a lightweight BER encoding of the fol‐
       lowing 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 );

ERRORS
       If an error occurs during decoding,  generally  these  routines	return
       LBER_ERROR ((ber_tag_t)-1).

NOTES
       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.

SEE ALSO
       lber-encode(3), lber-memory(3), lber-sockbuf(3), lber-types(3)

ACKNOWLEDGEMENTS
       OpenLDAP	  is   developed   and	maintained  by	The  OpenLDAP  Project
       (http://www.openldap.org/).  OpenLDAP is	 derived  from	University  of
       Michigan LDAP 3.3 Release.

OpenLDAP 2.3.24			  2006/05/30			LBER_DECODE(3)
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