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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:  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 *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

       For an explanation of the terms used in this section, see attributes(7).

       ┌────────────────────────────────┬───────────────┬─────────┐
       │InterfaceAttributeValue   │
       ├────────────────────────────────┼───────────────┼─────────┤
       │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

       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

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       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)