xdr(3) — Linux manual page

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() 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 int *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(), xdr_bytes(), │ Thread safety │ MT-Safe │
       │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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       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/.

                               2021-03-22                         XDR(3)

Pages that refer to this page: rpc(3)