XDR(3) Linux Programmer's Manual XDR(3)NAME
xdr - library routines for external data representation
SYNOPSIS AND DESCRIPTION
These routines allow C programmers to describe arbitrary data struc‐
tures 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 suc‐
ceeds, 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 invok‐
ing 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 suc‐
ceeds, 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 desir‐
able feature of XDR streams is that simple arithmetic works with
this number, although the XDR stream instances need not guaran‐
tee 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 suc‐
ceeds, 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 rep‐
resent 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 send‐
size; a value of zero indicates the system should use a suitable
default. The stream's data is read from a buffer of size recv‐
size; 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, rea‐
dit 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: to read from an XDR stream created by this API, you'll
need to call xdrrec_skiprecord() first before calling any other
XDR APIs. This inserts additional bytes in the stream to pro‐
vide record boundary information. Also, XDR streams created
with different xdr*_create APIs are not compatible for the same
reason.
bool_t xdrrec_endofrecord(XDR *xdrs, int sendnow);
This routine can be invoked only on streams created by xdr‐
rec_create(). The data in the output buffer is marked as a com‐
pleted 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 xdr‐
rec_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 xdr‐
rec_create(). It tells the XDR implementation that the rest of
the current record in the stream's input buffer should be dis‐
carded. This routine returns one if it succeeds, zero other‐
wise.
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 pro‐
cedure that filters the structure between its C form and its
external representation. This routine returns one if it suc‐
ceeds, 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 other‐
wise.
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 inte‐
gers 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 suc‐
ceeds, zero otherwise.
bool_t xdr_void(void);
This routine always returns one. It may be passed to RPC rou‐
tines 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 inte‐
ger. 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.
ATTRIBUTES
For an explanation of the terms used in this section, see
attributes(7).
┌────────────────────────────────┬───────────────┬─────────┐
│Interface │ Attribute │ Value │
├────────────────────────────────┼───────────────┼─────────┤
│xdr_array(), xdr_bool(), │ Thread safety │ MT-Safe │
│xdr_bytes(), xdr_char(), │ │ │
│xdr_destroy(), xdr_double(), │ │ │
│xdr_enum(), xdr_float(), │ │ │
│xdr_free(), xdr_getpos(), │ │ │
│xdr_inline(), xdr_int(), │ │ │
│xdr_long(), xdrmem_create(), │ │ │
│xdr_opaque(), xdr_pointer(), │ │ │
│xdrrec_create(), xdrrec_eof(), │ │ │
│xdrrec_endofrecord(), │ │ │
│xdrrec_skiprecord(), │ │ │
│xdr_reference(), xdr_setpos(), │ │ │
│xdr_short(), xdrstdio_create(), │ │ │
│xdr_string(), xdr_u_char(), │ │ │
│xdr_u_int(), xdr_u_long(), │ │ │
│xdr_u_short(), xdr_union(), │ │ │
│xdr_vector(), xdr_void(), │ │ │
│xdr_wrapstring() │ │ │
└────────────────────────────────┴───────────────┴─────────┘
SEE ALSOrpc(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 4.14 of the Linux man-pages project. A
description of the project, information about reporting bugs, and the
latest version of this page, can be found at
https://www.kernel.org/doc/man-pages/.
2017-09-15 XDR(3)
