man-pages/man3/xdr.3

.\" This page was taken from the 4.4BSD-Lite CDROM (BSD license)
.\"
.\" @(#)xdr.3n	2.2 88/08/03 4.0 RPCSRC; from 1.16 88/03/14 SMI
.\" FIXME -- change this page to use modern C prototypes
.TH XDR 3 2007-05-18 "" "Linux Programmer's Manual"
.SH NAME
xdr \- library routines for external data representation
.SH "SYNOPSIS AND DESCRIPTION"
.LP
These routines allow C programmers to describe
arbitrary data structures in a machine-independent fashion.
Data for remote procedure calls are transmitted using these
routines.
.LP
.ft B
.nf
.sp .5
xdr_array(xdrs, arrp, sizep, maxsize, elsize, elproc)
XDR *xdrs;
char **arrp;
unsigned int *sizep, maxsize, elsize;
xdrproc_t elproc;
.fi
.ft R
.IP
A filter primitive that translates between variable-length
arrays
and their corresponding external representations.
The parameter
.I arrp
is the address of the pointer to the array, while
.I sizep
is the address of the element count of the array;
this element count cannot exceed
.IR maxsize .
The parameter
.I elsize
is the
.I sizeof
each of the array's elements, and
.I elproc
is an
XDR
filter that translates between
the array elements' C form, and their external
representation.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 8
.LP
.ft B
.nf
.sp .5
xdr_bool(xdrs, bp)
XDR *xdrs;
bool_t *bp;
.fi
.ft R
.IP
A filter primitive that translates between booleans (C
integers)
and their external representations.
When encoding data, this
filter produces values of either one or zero.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 10
.LP
.ft B
.nf
.sp .5
xdr_bytes(xdrs, sp, sizep, maxsize)
XDR *xdrs;
char **sp;
unsigned int *sizep, maxsize;
.fi
.ft R
.IP
A filter primitive that translates between counted byte
strings and their external representations.
The parameter
.I sp
is the address of the string pointer.
The length of the
string is located at address
.IR sizep ;
strings cannot be longer than
.IR maxsize .
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 7
.LP
.ft B
.nf
.sp .5
xdr_char(xdrs, cp)
XDR *xdrs;
char *cp;
.fi
.ft R
.IP
A filter primitive that translates between C characters
and their external representations.
This routine returns one if it succeeds, zero otherwise.
Note: encoded characters are not packed, and occupy 4 bytes each.
For arrays of characters, it is worthwhile to
consider
.BR xdr_bytes (),
.BR xdr_opaque ()
or
.BR xdr_string ().
.br
.if t .ne 8
.LP
.ft B
.nf
.sp .5
void
xdr_destroy(xdrs)
XDR *xdrs;
.fi
.ft R
.IP
A macro that invokes the destroy routine associated with the
XDR
stream,
.IR xdrs .
Destruction usually involves freeing private data structures
associated with the stream.
Using
.I xdrs
after invoking
.BR xdr_destroy ()
is undefined.
.br
.if t .ne 7
.LP
.ft B
.nf
.sp .5
xdr_double(xdrs, dp)
XDR *xdrs;
double *dp;
.fi
.ft R
.IP
A filter primitive that translates between C
.I double
precision numbers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 7
.LP
.ft B
.nf
.sp .5
xdr_enum(xdrs, ep)
XDR *xdrs;
enum_t *ep;
.fi
.ft R
.IP
A filter primitive that translates between C
.IR enum s
(actually integers) and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 8
.LP
.ft B
.nf
.sp .5
xdr_float(xdrs, fp)
XDR *xdrs;
float *fp;
.fi
.ft R
.IP
A filter primitive that translates between C
.IR float s
and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 9
.LP
.ft B
.nf
.sp .5
void
xdr_free(proc, objp)
xdrproc_t proc;
char *objp;
.fi
.ft R
.IP
Generic freeing routine.
The first argument is the
XDR
routine for the object being freed.
The second argument
is a pointer to the object itself.
Note: the pointer passed
to this routine is
.I not
freed, but what it points to
.I is
freed (recursively).
.br
.if t .ne 8
.LP
.ft B
.nf
.sp .5
unsigned int
xdr_getpos(xdrs)
XDR *xdrs;
.fi
.ft R
.IP
A macro that invokes the get-position routine
associated with the
XDR
stream,
.IR xdrs .
The routine returns an unsigned integer,
which indicates the position of the
XDR
byte stream.
A desirable feature of
XDR
streams is that simple arithmetic works with this number,
although the
XDR
stream instances need not guarantee this.
.br
.if t .ne 4
.LP
.ft B
.nf
.sp .5
.br
long *
xdr_inline(xdrs, len)
XDR *xdrs;
int len;
.fi
.ft R
.IP
A macro that invokes the in-line routine associated with the
XDR
stream,
.IR xdrs .
The routine returns a pointer
to a contiguous piece of the stream's buffer;
.I len
is the byte length of the desired buffer.
Note: pointer is cast to
.IR "long *" .
.IP
Warning:
.BR xdr_inline ()
may return
NULL
(0)
if it cannot allocate a contiguous piece of a buffer.
Therefore the behavior may vary among stream instances;
it exists for the sake of efficiency.
.br
.if t .ne 7
.LP
.ft B
.nf
.sp .5
xdr_int(xdrs, ip)
XDR *xdrs;
int *ip;
.fi
.ft R
.IP
A filter primitive that translates between C integers
and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 7
.LP
.ft B
.nf
.sp .5
xdr_long(xdrs, lp)
XDR *xdrs;
long *lp;
.fi
.ft R
.IP
A filter primitive that translates between C
.I long
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 12
.LP
.ft B
.nf
.sp .5
void
xdrmem_create(xdrs, addr, size, op)
XDR *xdrs;
char *addr;
unsigned int size;
enum xdr_op op;
.fi
.ft R
.IP
This routine initializes the
XDR
stream object pointed to by
.IR xdrs .
The stream's data is written to, or read from,
a chunk of memory at location
.I addr
whose length is no more than
.I size
bytes long.
The
.I op
determines the direction of the
XDR
stream
(either
.BR XDR_ENCODE ,
.BR XDR_DECODE ,
or
.BR XDR_FREE ).
.br
.if t .ne 10
.LP
.ft B
.nf
.sp .5
xdr_opaque(xdrs, cp, cnt)
XDR *xdrs;
char *cp;
unsigned int cnt;
.fi
.ft R
.IP
A filter primitive that translates between fixed size opaque data
and its external representation.
The parameter
.I cp
is the address of the opaque object, and
.I cnt
is its size in bytes.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 10
.LP
.ft B
.nf
.sp .5
xdr_pointer(xdrs, objpp, objsize, xdrobj)
XDR *xdrs;
char **objpp;
unsigned int objsize;
xdrproc_t xdrobj;
.fi
.ft R
.IP
Like
.BR xdr_reference ()
except that it serializes
NULL
pointers, whereas
.BR xdr_reference ()
does not.
Thus,
.BR xdr_pointer ()
can represent
recursive data structures, such as binary trees or
linked lists.
.br
.if t .ne 15
.LP
.ft B
.nf
.sp .5
void
xdrrec_create(xdrs, sendsize, recvsize, handle, readit, writeit)
XDR *xdrs;
unsigned int sendsize, recvsize;
char *handle;
int (*readit) (), (*writeit) ();
.fi
.ft R
.IP
This routine initializes the
XDR
stream object pointed to by
.IR xdrs .
The stream's data is written to a buffer of size
.IR sendsize ;
a value of zero indicates the system should use a suitable
default.
The stream's data is read from a buffer of size
.IR recvsize ;
it too can be set to a suitable default by passing a zero
value.
When a stream's output buffer is full,
.I writeit
is called.
Similarly, when a stream's input buffer is empty,
.I readit
is called.
The behavior of these two routines is similar to
the system calls
.BR read (2)
and
.BR write (2),
except that
.I handle
is passed to the former routines as the first parameter.
Note: the
XDR
stream's
.I op
field must be set by the caller.
.IP
Warning: this
XDR
stream implements an intermediate record stream.
Therefore there are additional bytes in the stream
to provide record boundary information.
.br
.if t .ne 9
.LP
.ft B
.nf
.sp .5
xdrrec_endofrecord(xdrs, sendnow)
XDR *xdrs;
int sendnow;
.fi
.ft R
.IP
This routine can be invoked only on
streams created by
.BR xdrrec_create ().
The data in the output buffer is marked as a completed
record,
and the output buffer is optionally written out if
.I sendnow
is nonzero.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 8
.LP
.ft B
.nf
.sp .5
xdrrec_eof(xdrs)
XDR *xdrs;
int empty;
.fi
.ft R
.IP
This routine can be invoked only on
streams created by
.BR xdrrec_create ().
After consuming the rest of the current record in the stream,
this routine returns one if the stream has no more input,
zero otherwise.
.br
.if t .ne 3
.LP
.ft B
.nf
.sp .5
xdrrec_skiprecord(xdrs)
XDR *xdrs;
.fi
.ft R
.IP
This routine can be invoked only on
streams created by
.BR xdrrec_create ().
It tells the
XDR
implementation that the rest of the current record
in the stream's input buffer should be discarded.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 11
.LP
.ft B
.nf
.sp .5
xdr_reference(xdrs, pp, size, proc)
XDR *xdrs;
char **pp;
unsigned int size;
xdrproc_t proc;
.fi
.ft R
.IP
A primitive that provides pointer chasing within structures.
The parameter
.I pp
is the address of the pointer;
.I size
is the
.I sizeof
the structure that
.I *pp
points to; and
.I proc
is an
XDR
procedure that filters the structure
between its C form and its external representation.
This routine returns one if it succeeds, zero otherwise.
.IP
Warning: this routine does not understand
NULL
pointers.
Use
.BR xdr_pointer ()
instead.
.br
.if t .ne 10
.LP
.ft B
.nf
.sp .5
xdr_setpos(xdrs, pos)
XDR *xdrs;
unsigned int pos;
.fi
.ft R
.IP
A macro that invokes the set position routine associated with
the
XDR
stream
.IR xdrs .
The parameter
.I pos
is a position value obtained from
.BR xdr_getpos ().
This routine returns one if the
XDR
stream could be repositioned,
and zero otherwise.
.IP
Warning: it is difficult to reposition some types of
XDR
streams, so this routine may fail with one
type of stream and succeed with another.
.br
.if t .ne 8
.LP
.ft B
.nf
.sp .5
xdr_short(xdrs, sp)
XDR *xdrs;
short *sp;
.fi
.ft R
.IP
A filter primitive that translates between C
.I short
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 10
.LP
.ft B
.nf
.sp .5
void
xdrstdio_create(xdrs, file, op)
XDR *xdrs;
FILE *file;
enum xdr_op op;
.fi
.ft R
.IP
This routine initializes the
XDR
stream object pointed to by
.IR xdrs .
The
XDR
stream data is written to, or read from, the
.I stdio
stream
.IR file .
The parameter
.I op
determines the direction of the
XDR
stream (either
.BR XDR_ENCODE ,
.BR XDR_DECODE ,
or
.BR XDR_FREE ).
.IP
Warning: the destroy routine associated with such
XDR
streams calls
.BR fflush (3)
on the
.I file
stream, but never
.BR fclose (3).
.br
.if t .ne 9
.LP
.ft B
.nf
.sp .5
xdr_string(xdrs, sp, maxsize)
XDR
*xdrs;
char **sp;
unsigned int maxsize;
.fi
.ft R
.IP
A filter primitive that translates between C strings and
their
corresponding external representations.
Strings cannot be longer than
.IR maxsize .
Note:
.I sp
is the address of the string's pointer.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 8
.LP
.ft B
.nf
.sp .5
xdr_u_char(xdrs, ucp)
XDR *xdrs;
unsigned char *ucp;
.fi
.ft R
.IP
A filter primitive that translates between
.I unsigned
C characters and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 9
.LP
.ft B
.nf
.sp .5
xdr_u_int(xdrs, up)
XDR *xdrs;
unsigned *up;
.fi
.ft R
.IP
A filter primitive that translates between C
.I unsigned
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 7
.LP
.ft B
.nf
.sp .5
xdr_u_long(xdrs, ulp)
XDR *xdrs;
unsigned long *ulp;
.fi
.ft R
.IP
A filter primitive that translates between C
.I "unsigned long"
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 7
.LP
.ft B
.nf
.sp .5
xdr_u_short(xdrs, usp)
XDR *xdrs;
unsigned short *usp;
.fi
.ft R
.IP
A filter primitive that translates between C
.I "unsigned short"
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 16
.LP
.ft B
.nf
.sp .5
xdr_union(xdrs, dscmp, unp, choices, dfault)
XDR *xdrs;
int *dscmp;
char *unp;
struct xdr_discrim *choices;
bool_t (*defaultarm) ();  /* may equal NULL */
.fi
.ft R
.IP
A filter primitive that translates between a discriminated C
.I union
and its corresponding external representation.
It first
translates the discriminant of the union located at
.IR dscmp .
This discriminant is always an
.IR enum_t .
Next the union located at
.I unp
is translated.
The parameter
.I choices
is a pointer to an array of
.BR xdr_discrim ()
structures.
Each structure contains an ordered pair of
.RI [ value , proc ].
If the union's discriminant is equal to the associated
.IR value ,
then the
.I proc
is called to translate the union.
The end of the
.BR xdr_discrim ()
structure array is denoted by a routine of value
NULL.
If the discriminant is not found in the
.I choices
array, then the
.I defaultarm
procedure is called (if it is not
NULL).
Returns one if it succeeds, zero otherwise.
.br
.if t .ne 6
.LP
.ft B
.nf
.sp .5
xdr_vector(xdrs, arrp, size, elsize, elproc)
XDR *xdrs;
char *arrp;
unsigned int size, elsize;
xdrproc_t elproc;
.fi
.ft R
.IP
A filter primitive that translates between fixed-length
arrays
and their corresponding external representations.
The parameter
.I arrp
is the address of the pointer to the array, while
.I size
is the element count of the array.
The parameter
.I elsize
is the
.I sizeof
each of the array's elements, and
.I elproc
is an
XDR
filter that translates between
the array elements' C form, and their external
representation.
This routine returns one if it succeeds, zero otherwise.
.br
.if t .ne 5
.LP
.ft B
.nf
.sp .5
xdr_void()
.fi
.ft R
.IP
This routine always returns one.
It may be passed to
RPC
routines that require a function parameter,
where nothing is to be done.
.br
.if t .ne 10
.LP
.ft B
.nf
.sp .5
xdr_wrapstring(xdrs, sp)
XDR *xdrs;
char **sp;
.fi
.ft R
.IP
A primitive that calls
.B "xdr_string(xdrs, sp,MAXUN.UNSIGNED );"
where
.B
.B MAXUN.UNSIGNED
is the maximum value of an unsigned integer.
.BR xdr_wrapstring ()
is handy because the
RPC
package passes a maximum of two
XDR
routines as parameters, and
.BR xdr_string (),
one of the most frequently used primitives, requires three.
Returns one if it succeeds, zero otherwise.
.SH "SEE ALSO"
.BR rpc (3)
.LP
The following manuals:
.RS
.ft I
eXternal Data Representation Standard: Protocol Specification
.br
eXternal Data Representation: Sun Technical Notes
.ft R
.br
.IR "XDR: External Data Representation Standard" ,
RFC\ 1014, Sun Microsystems, Inc.,
USC-ISI.
.RE