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.TH LIBPSAP 3 "15 APR 1986"
.\" $header: /f/iso/psap/rcs/libpsap.3,v 4.4 88/05/31 15:19:26 mrose exp $
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.SH NAME
libpsap \- asn.1 presentation services library
.SH SYNOPSIS
.B "#include <isode/psap.h>"
.sp
\fIcc\fR\0...\0\fB\-lpsap\fR
.SH DESCRIPTION
the \filibpsap\fr library contains a set of routines which implement
presentation syntax abstractions.
two primary objects are manipulated:
presentation \fielements\fr and presentation \fistreams\fr.
.SH "PRESENTATION STREAMS"
a stream is an object, similar to a \fbfile*\fr object in \fistdio\fr\0(3),
which is used to read and write elements.
a stream is created by calling \fbps_alloc\fr with the address of an
integer\-valued routine that will initialize certain stream\-dependent
variables (presently, the read and write routines).
two standard initialization routines are available:
\fbstd_open\fr,
which is used for presentation streams connected to \fistdio\fr objects;
and,
\fbstr_open\fr,
which is used for presentation streams connected to \fistring\fr objects.
after \fbps_alloc\fr successfully returns,
final initialization is performed,
usually by calling either
\fbstd_setup\fr with the \fistdio\fr object to be bound;
or,
\fbstr_setup\fr with the string object to be bound.
after the setup routine successfully returns,
the presentation stream is ready for reading or writing.
.PP
currently streams which have been initialized by these routines are
uni-directional.
This might change in a future distribution.
Streams which have been initialized by \fBstd_open\fR and \fBstr_open\fR
will automatically allocate additional resources when necessary,
to the limits allowed by the operating system
(e.g., repeated calls to a stream connected to a \fIstring\fR object will
result in additional memory being allocated from UNIX).
.PP
Low\-level I/O is done from/to the stream by the macros \fBps_read\fR and
\fBps_write\fR.
These both call an internal routine which switches to the object\-specific
read or write routine as appropriate.
This internal routine, \fBps_io\fR, implements the consistent presentation
stream abstraction.
.PP
Finally,
when a stream has been exhausted, 
it can be closed and de\-allocated with \fBps_free\fR.
.PP
The user may implement additional stream objects.
Examine the source to the \fBstd_\fR and \fBstr_\fR routines
to understand the internal protocol and uniform interface.
.SH TRANSLATION
The routine \fBps2pe\fR can be used to read the next presentation element
from a stream.
This routine returns a pointer to the element or \fBNULLPE\fR on error.
Similarly, \fBpe2ps\fR can be used to write a presentation element at the end
of the stream.
This returns returns \fBOK\fR if all went well, \fBNOTOK\fR otherwise.
On errors with either routine,
the \fBps_errno\fR field of the stream can be consulted to see what happened.
.PP
When writing to a presentation stream,
the variable \fBps_len_strategy\fR controls how long CONStructor types are
represented.
If this variable is equal to \fBPS_LEN_SPAG\fR (the default),
then the indefinite form is used whenever the length field of the element can
not be represented in one octet.
If \fBPS_LEN_INDF\fR,
then the indefinite form is used regardless of the length of the element.
Otherwise,
if \fBPS_LEN_LONG\fR,
then the indefinite form is never used.
.PP
For debugging purposes,
instead of treating a presentation stream as a binary object,
the routines \fBpl2pe\fR and \fBpe2pl\fR can be used.
These translate between presentation \fIlists\fR and presentation elements.
A list is an ASCII text representation,
with a simple LISP\-like syntax which contains semantic information
identical to its presentation stream counterpart.
.SH "PRESENTATION ELEMENTS"
Once a presentation stream has been initialized and elements are being read,
there are several routines that can be used to translate between the
machine\-independent representation of the element and machine\-specific
objects such as integers, strings, and the like.
It is extremely important that programs use these routines to perform the
translation between objects.
They have been carefully coded to present a simple, uniform interface between
machine\-specifics and the machine\-independent presentation protocol.
.PP
A new element can be created with \fBpe_alloc\fR,
and de\-allocated with \fBpe_free\fR
(see the warning in the \fBBUGS\fR section below).
Two elements can be compared with \fBpe_cmp\fR,
and an element can be copied with \fBpe_cpy\fR.
.PP
A \fIboolean\fR is an integer taking on the values \fB0\fR or \fB1\fR.
The routine \fBprim2bool\fR takes an element and returns the boolean value
encoded therein.
Similarly, \fBbool2prim\fR takes a boolean and returns an element which
encodes that value.
.PP
An \fIinteger\fR is a signed\-quantity, whose precision is specific to a
particular host.
The routine \fBprim2int\fR takes an element and returns the integer value
encoded therein (if the value is \fBNOTOK\fR, check the \fBpe_errno\fR field
of the element to see if there was an error).
The routine \fBint2prim\fR performs the inverse operation.
.PP
An \fIoctetstring\fR is a pair of values,
a character pointer and an integer length.
The pointer addresses the first octet in the string
(which need not be null\-terminated),
the length indicates how many octets are in the string.
The routine \fBprim2oct\fR takes an element and allocates a new string
containing the value encoded therein.
The routine \fBoct2prim\fR performs the inverse operation,
copying the original string (and not de\-allocating it).
.PP
A \fIbitvector\fR is an arbitrarily long string of bits with three operations:
\fBbit_on\fR which turns the indicated bit on,
\fBbit_off\fR which turns the indicated bit off,
and,
\fBbit_test\fR which returns a boolean value telling if the indicated bit was
on.
The routine \fBprim2bit\fR takes an element and builds such an abstraction
containing the value encoded therein.
The routine \fBbit2prim\fR performs the inverse operation.
.PP
A \fItimestring\fR represents a date/time in many forms.
Consult \fB<isode/psap.h>\fR for the elements in this structure.
The routines \fBprim2utc\fR and \fButc2prim\fR are used to translate between
a machine\-specific internal form and the machine\-independent form.
.PP
Two list disciplines are implemented:
\fIsets\fR, in which each member is distinguished by a unique identifier;
and,
\fIsequences\fR, in which each element is distinguished by its offset from
the head of the list.
On both types of lists,
the macro \fBfirst_member\fR returns the first member in the list,
while \fBnext_member\fR returns the next member.
.PP
The routines \fBprim2set\fR and \fBset2prim\fR are used to translate between
presentation elements and the set list;
\fBset_add\fR may be called to add a new member to the set;
\fBset_del\fR may be called to remove the identified member from the set;
and,
\fBset_find\fR may be called to locate the identified member.
.PP
The routines \fBprim2seq\fR and \fBseq2prim\fR are used to translate between
presentation elements and the sequence list;
\fBseq_add\fR may be called to add a new element to the sequence;
\fBseq_del\fR may be called to remove the identified element from the sequence;
and,
\fBseq_find\fR may be called to locate the identified element.
.PP
With both lists,
a convenient way of stepping through all the members is:
.sp
.in +.5i
.nf
.B "for (p = first_member (pe); p; p = next_member (pe, p))"
.B "\0\0\0\0switch (\fIdiscriminator\fR) {"
.B "\0\0\0\0\0\0\0\0...."
.B "\0\0\0\0}"
.fi
.in -.5i
.sp
where \fIdiscriminator\fR is:
.sp
.in +.5i
.B "PE_ID (p \-> pe_class, p \-> pe_id)"
.in -.5i
.sp
for sets,
and:
.sp
.in +.5i
.B "p \-> pe_offset"
.in -.5i
.sp
for sequences.
.SH FILES
None
.SH "SEE ALSO"
pepy(1),
.br
\fIThe ISO Development Environment: User's Manual\fR,
.br
ISO 8825:
\fIInformation Processing \-\- Open Systems
Interconnection \-\- Specification of basic encoding rules for Abstract Syntax
Notation One (ASN.1)\fR,
.br
CCITT Recommendation X.409:
\fIMessage Handling Systems:
Presentation Transfer Syntax and Notation\fR
.SH DIAGNOSTICS
Most routines either return the manifest constant \fBNULL\fR (0) or
\fBNOTOK\fR (\-1) on error.
In addition,
routines called with a pointer to a presentation stream also update the
\fBps_errno\fR field of the stream on error.
The routine \fBps_error\fR returns a null\-termianted diagnostic string when
given the value of this field.
Similarly,
routines called with a pointer to a presentation element also update the
\fBpe_errno\fR field of the stream on error.
The routine \fBpe_error\fR returns a null\-termianted diagnostic string when
given the value of this field.
.SH AUTHOR
Marshall T. Rose
.SH BUGS
A \*(lqvirtual\*(rq presentation element option should be available to avoid
reading everything in\-core during parsing.
.PP
When using \fBpe_free\fR on an element,
care must be taken to remove any references to that element in other
structures.
For example,
if you have a sequence containing a sequence,
and you free the child sequence,
be sure to zero\-out the parent's pointer to the child,
otherwise subsequent calls using the parent will go romping through
hyperspace.
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