XDR
Section: Linux Programmer's Manual (3)
Updated: 2007-12-30
NAME
xdr - library routines for external data representation
SYNOPSIS AND DESCRIPTION
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.
The prototypes below are declared in
<rpc/xdr.h>
and make use of the following types:
typedef int bool_t;
typedef bool_t (*xdrproc_t) (XDR *, void *,...);
For the declaration of the
XDR
type, see
<rpc/xdr.h>.
bool_t xdr_array(XDR *xdrs, char **arrp, unsigned int *sizep,
unsigned int maxsize, unsigned int elsize,
xdrproc_t elproc);
-
A filter primitive that translates between variable-length arrays
and their corresponding external representations.
The argument
arrp
is the address of the pointer to the array, while
sizep
is the address of the element count of the array;
this element count cannot exceed
maxsize.
The argument
elsize
is the
sizeof
each of the array's elements, and
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.
bool_t xdr_bool(XDR *xdrs, bool_t *bp);
-
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.
bool_t xdr_bytes(XDR *xdrs, char **sp, unsigned int *sizep,
unsigned int maxsize);
-
A filter primitive that translates between counted byte
strings and their external representations.
The argument
sp
is the address of the string pointer.
The length of the
string is located at address
sizep;
strings cannot be longer than
maxsize.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_char(XDR *xdrs, char *cp);
-
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
xdr_bytes(),
xdr_opaque()
or
xdr_string().
void xdr_destroy(XDR *xdrs);
-
A macro that invokes the destroy routine associated with the XDR stream,
xdrs.
Destruction usually involves freeing private data structures
associated with the stream.
Using
xdrs
after invoking
xdr_destroy()
is undefined.
bool_t xdr_double(XDR *xdrs, double *dp);
-
A filter primitive that translates between C
double
precision numbers and their external representations.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_enum(XDR *xdrs, enum_t *ep);
-
A filter primitive that translates between C
enums
(actually integers) and their external representations.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_float(XDR *xdrs, float *fp);
-
A filter primitive that translates between C
floats
and their external representations.
This routine returns one if it succeeds, zero otherwise.
void xdr_free(xdrproc_t proc, char *objp);
-
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
not
freed, but what it points to
is
freed (recursively).
unsigned int xdr_getpos(XDR *xdrs);
-
A macro that invokes the get-position routine
associated with the XDR stream,
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.
long *xdr_inline(XDR *xdrs, int len);
-
A macro that invokes the inline routine associated with the XDR stream,
xdrs.
The routine returns a pointer
to a contiguous piece of the stream's buffer;
len
is the byte length of the desired buffer.
Note: pointer is cast to
long *.
-
Warning:
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.
bool_t xdr_int(XDR *xdrs, int *ip);
-
A filter primitive that translates between C integers
and their external representations.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_long(XDR *xdrs, long *lp);
-
A filter primitive that translates between C
long
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
void xdrmem_create(XDR *xdrs, char *addr, unsigned int size,
enum xdr_op op);
-
This routine initializes the XDR stream object pointed to by
xdrs.
The stream's data is written to, or read from,
a chunk of memory at location
addr
whose length is no more than
size
bytes long.
The
op
determines the direction of the XDR stream (either
XDR_ENCODE,
XDR_DECODE,
or
XDR_FREE).
bool_t xdr_opaque(XDR *xdrs, char *cp, unsigned int cnt);
-
A filter primitive that translates between fixed size opaque data
and its external representation.
The argument
cp
is the address of the opaque object, and
cnt
is its size in bytes.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_pointer(XDR *xdrs, char **objpp,
unsigned int objsize, xdrproc_t xdrobj);
-
Like
xdr_reference()
except that it serializes NULL pointers, whereas
xdr_reference()
does not.
Thus,
xdr_pointer()
can represent
recursive data structures, such as binary trees or
linked lists.
void xdrrec_create(XDR *xdrs, unsigned int sendsize,
unsigned int recvsize, char *handle,
int (*readit) (char *, char *, int),
int (*writeit) (char *, char *, int));
-
This routine initializes the XDR stream object pointed to by
xdrs.
The stream's data is written to a buffer of size
sendsize;
a value of zero indicates the system should use a suitable default.
The stream's data is read from a buffer of size
recvsize;
it too can be set to a suitable default by passing a zero value.
When a stream's output buffer is full,
writeit
is called.
Similarly, when a stream's input buffer is empty,
readit
is called.
The behavior of these two routines is similar to
the system calls
read(2)
and
write(2),
except that
handle
is passed to the former routines as the first argument.
Note: the XDR stream's
op
field must be set by the caller.
-
Warning: this XDR stream implements an intermediate record stream.
Therefore there are additional bytes in the stream
to provide record boundary information.
bool_t xdrrec_endofrecord(XDR *xdrs, int sendnow);
-
This routine can be invoked only on streams created by
xdrrec_create().
The data in the output buffer is marked as a completed record,
and the output buffer is optionally written out if
sendnow
is nonzero.
This routine returns one if it succeeds, zero otherwise.
bool_t xdrrec_eof(XDR *xdrs);
-
This routine can be invoked only on streams created by
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.
bool_t xdrrec_skiprecord(XDR *xdrs);
-
This routine can be invoked only on
streams created by
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.
bool_t xdr_reference(XDR *xdrs, char **pp, unsigned int size,
xdrproc_t proc);
-
A primitive that provides pointer chasing within structures.
The argument
pp
is the address of the pointer;
size
is the
sizeof
the structure that
*pp
points to; and
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.
-
Warning: this routine does not understand NULL pointers.
Use
xdr_pointer()
instead.
xdr_setpos(XDR *xdrs, unsigned int pos);
-
A macro that invokes the set position routine associated with
the XDR stream
xdrs.
The argument
pos
is a position value obtained from
xdr_getpos().
This routine returns one if the XDR stream could be repositioned,
and zero otherwise.
-
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.
bool_t xdr_short(XDR *xdrs, short *sp);
-
A filter primitive that translates between C
short
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
void xdrstdio_create(XDR *xdrs, FILE *file, enum xdr_op op);
-
This routine initializes the XDR stream object pointed to by
xdrs.
The XDR stream data is written to, or read from, the
stdio
stream
file.
The argument
op
determines the direction of the XDR stream (either
XDR_ENCODE,
XDR_DECODE,
or
XDR_FREE).
-
Warning: the destroy routine associated with such XDR streams calls
fflush(3)
on the
file
stream, but never
fclose(3).
bool_t xdr_string(XDR *xdrs, char **sp, unsigned int maxsize);
-
A filter primitive that translates between C strings and
their corresponding external representations.
Strings cannot be longer than
maxsize.
Note:
sp
is the address of the string's pointer.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_u_char(XDR *xdrs, unsigned char *ucp);
-
A filter primitive that translates between
unsigned
C characters and their external representations.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_u_int(XDR *xdrs, unsigned *up);
-
A filter primitive that translates between C
unsigned
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_u_long(XDR *xdrs, unsigned long *ulp);
-
A filter primitive that translates between C
unsigned long
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_u_short(XDR *xdrs, unsigned short *usp);
-
A filter primitive that translates between C
unsigned short
integers and their external representations.
This routine returns one if it succeeds, zero otherwise.
bool_t xdr_union(XDR *xdrs, int *dscmp, char *unp,
struct xdr_discrim *choices,
xdrproc_t defaultarm); /* may equal NULL */
-
A filter primitive that translates between a discriminated C
union
and its corresponding external representation.
It first
translates the discriminant of the union located at
dscmp.
This discriminant is always an
enum_t.
Next the union located at
unp
is translated.
The argument
choices
is a pointer to an array of
xdr_discrim()
structures.
Each structure contains an ordered pair of
[value,proc].
If the union's discriminant is equal to the associated
value,
then the
proc
is called to translate the union.
The end of the
xdr_discrim()
structure array is denoted by a routine of value NULL.
If the discriminant is not found in the
choices
array, then the
defaultarm
procedure is called (if it is not NULL).
Returns one if it succeeds, zero otherwise.
bool_t xdr_vector(XDR *xdrs, char *arrp, unsigned int size,
unsigned int elsize, xdrproc_t elproc);
-
A filter primitive that translates between fixed-length arrays
and their corresponding external representations.
The argument
arrp
is the address of the pointer to the array, while
size
is the element count of the array.
The argument
elsize
is the
sizeof
each of the array's elements, and
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.
bool_t xdr_void(void);
-
This routine always returns one.
It may be passed to RPC routines that require a function argument,
where nothing is to be done.
bool_t xdr_wrapstring(XDR *xdrs, char **sp);
-
A primitive that calls
xdr_string(xdrs, sp,MAXUN.UNSIGNED );
where
MAXUN.UNSIGNED
is the maximum value of an unsigned integer.
xdr_wrapstring()
is handy because the RPC package passes a maximum of two XDR
routines as arguments, and
xdr_string(),
one of the most frequently used primitives, requires three.
Returns one if it succeeds, zero otherwise.
SEE ALSO
rpc(3)
The following manuals:
-
eXternal Data Representation Standard: Protocol Specification
eXternal Data Representation: Sun Technical Notes
XDR: External Data Representation Standard,
RFC 1014, Sun Microsystems, Inc.,
USC-ISI.
COLOPHON
This page is part of release 3.27 of the Linux
man-pages
project.
A description of the project,
and information about reporting bugs,
can be found at
http://www.kernel.org/doc/man-pages/.
Index
- NAME
-
- SYNOPSIS AND DESCRIPTION
-
- SEE ALSO
-
- COLOPHON
-
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