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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 - OpenLDAP  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().

	      A	 Octet	string.	  A  variant of "a".  A char ** should be sup‐
		 plied.	 Memory is allocated, filled with the contents of  the
		 octet string, null-terminated, and returned in the parameter,
		 unless a zero-length string would result; in that  case,  the
		 arg  is  set  to  NULL.   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 Software is developed and maintained by The  OpenLDAP  Project
       <http://www.openldap.org/>.   OpenLDAP Software is derived from Univer‐
       sity of Michigan LDAP 3.3 Release.

OpenLDAP 2.4.23			  2010/06/30			LBER_DECODE(3)
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