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NAME

       xdr - library routines for external data representation

LIBRARY

       Standard C library (libc, -lc)

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 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, enum_t *dscmp, char *unp,
                        const 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(), xdr_bytes(), xdr_char(),              │ Thread safety │ MT-Safe │
       │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.