NAME | SYNOPSIS AND DESCRIPTION | ATTRIBUTES | SEE ALSO | COLOPHON

XDR(3)                    Linux Programmer's Manual                   XDR(3)

NAME         top

       xdr - library routines for external data representation

SYNOPSIS AND DESCRIPTION         top

       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: To read from an XDR stream created by this API,
              you'll need to call xdrrec_skiprecord(3) first before calling
              any other XDR APIs.  This inserts additional bytes in the
              stream to provide 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
              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.

ATTRIBUTES         top

       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 ALSO         top

       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         top

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       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/.

                                 2015-07-23                           XDR(3)