openldap/doc/man/man3/lber-encode.3

.TH LBER_ENCODE 3 "22 September 1998" "OpenLDAP LDVERSION"
.SH NAME
ber_alloc, ber_flush, ber_printf, ber_put_int, ber_put_ostring, ber_put_string, ber_put_null, ber_put_boolean, ber_put_bitstring, ber_start_seq, ber_start_set, ber_put_seq, ber_put_set \- LBER simplified Basic Encoding Rules library routines for encoding
.SH SYNOPSIS
.nf
.ft B
#include <lber.h>
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.fi
.LP
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typedef struct berelement BerElement;
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.fi
.LP
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typedef struct sockbuf Sockbuf;
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.fi
.LP
.nf
.ft B
BerElement *ber_alloc()
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.fi
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.nf
.ft B
ber_flush(sb, ber, freeit)
Sockbuf *sb;
BerElement *ber;
int freeit;
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.fi
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.nf
.ft B
ber_printf(ber, fmt [, arg... ] )
BerElement *ber;
char \(**fmt;
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ber_put_int(ber, num, tag)
BerElement *ber;
long num;
char tag;
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.ft B
ber_put_ostring(ber, str, len, tag)
BerElement *ber;
char \(**str;
unsigned long len;
char tag;
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.nf
.ft B
ber_put_string(ber, str, tag)
BerElement *ber;
char \(**str;
char tag;
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.ft B
ber_put_null(ber, tag)
BerElement *ber;
char tag;
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.ft B
ber_put_boolean(ber, bool, tag)
BerElement *ber;
int bool;
char tag;
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.ft B
ber_put_bitstring(ber, str, blen, tag)
BerElement *ber;
char *str;
int blen;
char tag;
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.ft B
ber_start_seq(ber, tag)
BerElement *ber;
char tag;
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ber_start_set(ber, tag)
BerElement *ber;
char tag;
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ber_put_seq(ber)
BerElement *ber;
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.ft B
ber_put_set(ber)
BerElement *ber;
.SH DESCRIPTION
.LP
These routines provide a subroutine interface to a simplified
implementation of the Basic Encoding Rules of ASN.1.  The version
of BER these routines support is the one defined for the LDAP
protocol.  The encoding rules are the same as BER, except that 
only definite form lengths are used, and bitstrings and octet strings
are always encoded in primitive form.  In addition, these lightweight
BER routines restrict tags and class to fit in a single octet (this
means the actual tag must be less than 31).  When a "tag" is specified
in the descriptions below, it refers to the tag, class, and primitive
or constructed bit in the first octet of the encoding.  This
man page describes the encoding routines in the lber library.  See
lber-decode(3) for details on the corresponding decoding routines.
.LP
Normally, the only routines that need be called by an application
are ber_alloc() to allocate a BER element for encoding, ber_printf()
to do the actual encoding, and ber_flush() to actually write the
element.  The other routines are provided for those
applications that need more control than ber_printf() provides.  In
general, these routines return the length of the element encoded, or
-1 if an error occurred.
.LP
The ber_alloc() routine is used to allocate a new BER element.  The
ber_flush() routine is used to actually write the element to a socket
(or file) descriptor, once it has been fully encoded (using ber_printf()
and friends).  The \fIsb\fP structure contains the descriptor and a
BerElement used for input buffering.  Only the \fIsb_sd\fP field is relevant
to the ber_flush() routine.
.LP
The ber_printf() routine is used to encode a BER element in much the
same way that sprintf(3) works.  One important difference, though, is
that some state information is kept with the \fIber\fP parameter so
that multiple calls can be made to ber_printf() to append things to
the end of the BER element.  Ber_printf() writes to \fIber\fP, a pointer to a
BerElement such as returned by ber_alloc().  It interprets and
formats its arguments according to the format string \fIfmt\fP.
The format string can contain the following characters:
.RS
.LP
.TP 3
.SM b
Boolean.  An integer parameter should be supplied.  A boolean element
is output.
.TP
.SM i
Integer.  An integer parameter should be supplied.  An integer element
is output.
.TP
.SM B
Bitstring.  A char * pointer to the start of the bitstring is supplied,
followed by the number of bits in the bitstring.  A bitstring element
is output.
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.SM n
Null.  No parameter is required.  A null element is output.
.TP
.SM o
Octet string.  A char * is supplied, followed by the length of the
string pointed to.  An octet string element is output.
.TP
.SM s
Octet string.  A null-terminated string is supplied.  An octet string
element is output, not including the trailing NULL octet.
.TP
.SM t
Tag.  An int specifying the tag to give the next element is provided.
This works across calls.
.TP
.SM v
Several octet strings.  A null-terminated array of char *'s is
supplied.  Note that a construct like '{v}' is required to get
an actual SEQUENCE OF octet strings.
.TP
.SM {
Begin sequence.  No parameter is required.
.TP
.SM }
End sequence.  No parameter is required.
.TP
.SM [
Begin set.  No parameter is required.
.TP
.SM ]
End set.  No parameter is required.
.RE
.LP
The ber_put_int() routine writes the integer element \fInum\fP to
the BER element \fIber\fP.
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The ber_put_boolean() routine writes the boolean value given by
\fIbool\fP to the BER element.
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The ber_put_bitstring() routine writes \fIblen\fP bits starting
at \fIstr\fP as a bitstring value to the given BER element.  Note
that \fIblen\fP is the length \fIin bits\fP of the bitstring.
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The ber_put_ostring() routine writes \fIlen\fP bytes starting at
\fIstr\fP to the BER element as an octet string.
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The ber_put_string() routine writes the null-terminated string (minus
the terminating '\0') to the BER element as an octet string.
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The ber_put_null() routine writes a NULL element to the BER element.
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The ber_start_seq() routine is used to start a sequence in the BER
element.  The ber_start_set() routine works similarly.
The end of the sequence or set is marked by the nearest matching
call to ber_put_seq() or ber_put_set(), respectively.
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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 \fIcookie\fP
a magic cookie parameter that should be passed to subsequent calls to
ber_next_element(), which returns similar information.
.SH EXAMPLES
Assuming the following variable declarations, and that the variables
have been assigned appropriately, an lber encoding of
the following ASN.1 object:
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.nf
      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
      }
.fi
.LP
can be achieved like so:
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.nf
      int    scope, ali, size, time, attrsonly;
      char   *dn, **attrs;

      /* ... fill in values ... */
      if ( (ber = ber_alloc()) == NULLBER )
		/* error */

      if ( ber_printf( ber, "{siiiib{v}}", dn, scope, ali,
          size, time, attrsonly, attrs ) == -1 )
              /* error */
      else
              /* success */
.fi
.SH ERRORS
If an error occurs during encoding, generally these routines return -1.
.LP
.SH NOTES
.LP
The return values for all of these functions are declared in the
<lber.h> header file.
.SH SEE ALSO
.BR ldap-async (3)
.BR ldap-sync (3)
.BR ldap-parse (3)
.BR lber-decode (3)
.LP
Yeong, W., Howes, T., and Hardcastle-Kille, S., "Lightweight Directory Access
Protocol", OSI-DS-26, April 1992.
.LP
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.
.SH AUTHOR
Tim Howes, University of Michigan
.SH ACKNOWLEDGEMENTS
.B	OpenLDAP
is developed and maintained by The OpenLDAP Project (http://www.openldap.org/).
.B	OpenLDAP
is derived from University of Michigan LDAP 3.3 Release.