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+.\" @(#)xdr.3n 2.2 88/08/03 4.0 RPCSRC; from 1.16 88/03/14 SMI
+.\" $FreeBSD: src/lib/libc/xdr/xdr.3,v 1.8 2000/03/02 09:14:05 sheldonh Exp $
+.\"
+.TH XDR 3 "16 February 1988"
+.SH NAME
+xdr \- library routines for external data representation
+.SH SYNOPSIS AND DESCRIPTION
+.LP
+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.
+.LP
+.ft B
+.nf
+.sp .5
+xdr_array(xdrs, arrp, sizep, maxsize, elsize, elproc)
+\s-1XDR\s0 *xdrs;
+char **arrp;
+u_int *sizep, maxsize, elsize;
+xdrproc_t elproc;
+.fi
+.ft R
+.IP
+A filter primitive that translates between variable-length
+arrays
+and their corresponding external representations.
+The
+parameter
+.I arrp
+is the address of the pointer to the array, while
+.I sizep
+is the address of the element count of the array;
+this element count cannot exceed
+.IR maxsize .
+The parameter
+.I elsize
+is the
+.I sizeof
+each of the array's elements, and
+.I elproc
+is an
+.SM XDR
+filter that translates between
+the array elements' C form, and their external
+representation.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 8
+.LP
+.ft B
+.nf
+.sp .5
+xdr_bool(xdrs, bp)
+\s-1XDR\s0 *xdrs;
+bool_t *bp;
+.fi
+.ft R
+.IP
+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.
+.br
+.if t .ne 10
+.LP
+.ft B
+.nf
+.sp .5
+xdr_bytes(xdrs, sp, sizep, maxsize)
+\s-1XDR\s0 *xdrs;
+char **sp;
+u_int *sizep, maxsize;
+.fi
+.ft R
+.IP
+A filter primitive that translates between counted byte
+strings and their external representations.
+The parameter
+.I sp
+is the address of the string pointer.
+The length of the
+string is located at address
+.IR sizep ;
+strings cannot be longer than
+.IR maxsize .
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 7
+.LP
+.ft B
+.nf
+.sp .5
+xdr_char(xdrs, cp)
+\s-1XDR\s0 *xdrs;
+char *cp;
+.fi
+.ft R
+.IP
+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
+.BR xdr_bytes(\|) ,
+.B xdr_opaque(\|)
+or
+.BR xdr_string(\|) .
+.br
+.if t .ne 8
+.LP
+.ft B
+.nf
+.sp .5
+void
+xdr_destroy(xdrs)
+\s-1XDR\s0 *xdrs;
+.fi
+.ft R
+.IP
+A macro that invokes the destroy routine associated with the
+.SM XDR
+stream,
+.IR xdrs .
+Destruction usually involves freeing private data structures
+associated with the stream. Using
+.I xdrs
+after invoking
+.B xdr_destroy(\|)
+is undefined.
+.br
+.if t .ne 7
+.LP
+.ft B
+.nf
+.sp .5
+xdr_double(xdrs, dp)
+\s-1XDR\s0 *xdrs;
+double *dp;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.B double
+precision numbers and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 7
+.LP
+.ft B
+.nf
+.sp .5
+xdr_enum(xdrs, ep)
+\s-1XDR\s0 *xdrs;
+enum_t *ep;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.BR enum s
+(actually integers) and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 8
+.LP
+.ft B
+.nf
+.sp .5
+xdr_float(xdrs, fp)
+\s-1XDR\s0 *xdrs;
+float *fp;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.BR float s
+and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 9
+.LP
+.ft B
+.nf
+.sp .5
+void
+xdr_free(proc, objp)
+xdrproc_t proc;
+char *objp;
+.fi
+.ft R
+.IP
+Generic freeing routine.
+The first argument is the
+.SM 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
+.I not
+freed, but what it points to
+.I is
+freed (recursively).
+.br
+.if t .ne 8
+.LP
+.ft B
+.nf
+.sp .5
+u_int
+xdr_getpos(xdrs)
+\s-1XDR\s0 *xdrs;
+.fi
+.ft R
+.IP
+A macro that invokes the get-position routine
+associated with the
+.SM XDR
+stream,
+.IR xdrs .
+The routine returns an unsigned integer,
+which indicates the position of the
+.SM XDR
+byte stream.
+A desirable feature of
+.SM XDR
+streams is that simple arithmetic works with this number,
+although the
+.SM XDR
+stream instances need not guarantee this.
+.br
+.if t .ne 4
+.LP
+.ft B
+.nf
+.sp .5
+.br
+long *
+xdr_inline(xdrs, len)
+\s-1XDR\s0 *xdrs;
+int len;
+.fi
+.ft R
+.IP
+A macro that invokes the in-line routine associated with the
+.SM XDR
+stream,
+.IR xdrs .
+The routine returns a pointer
+to a contiguous piece of the stream's buffer;
+.I len
+is the byte length of the desired buffer.
+Note: pointer is cast to
+.BR "long *" .
+.IP
+Warning:
+.B xdr_inline(\|)
+may return
+.SM 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.
+.br
+.if t .ne 7
+.LP
+.ft B
+.nf
+.sp .5
+xdr_int(xdrs, ip)
+\s-1XDR\s0 *xdrs;
+int *ip;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C integers
+and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 7
+.LP
+.ft B
+.nf
+.sp .5
+xdr_long(xdrs, lp)
+\s-1XDR\s0 *xdrs;
+long *lp;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.B long
+integers and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 12
+.LP
+.ft B
+.nf
+.sp .5
+void
+xdrmem_create(xdrs, addr, size, op)
+\s-1XDR\s0 *xdrs;
+char *addr;
+u_int size;
+enum xdr_op op;
+.fi
+.ft R
+.IP
+This routine initializes the
+.SM XDR
+stream object pointed to by
+.IR xdrs .
+The stream's data is written to, or read from,
+a chunk of memory at location
+.I addr
+whose length is no more than
+.I size
+bytes long. The
+.I op
+determines the direction of the
+.SM XDR
+stream
+(either
+.BR \s-1XDR_ENCODE\s0 ,
+.BR \s-1XDR_DECODE\s0 ,
+or
+.BR \s-1XDR_FREE\s0 ).
+.br
+.if t .ne 10
+.LP
+.ft B
+.nf
+.sp .5
+xdr_opaque(xdrs, cp, cnt)
+\s-1XDR\s0 *xdrs;
+char *cp;
+u_int cnt;
+.fi
+.ft R
+.IP
+A filter primitive that translates between fixed size opaque
+data
+and its external representation.
+The parameter
+.I cp
+is the address of the opaque object, and
+.I cnt
+is its size in bytes.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 10
+.LP
+.ft B
+.nf
+.sp .5
+xdr_pointer(xdrs, objpp, objsize, xdrobj)
+\s-1XDR\s0 *xdrs;
+char **objpp;
+u_int objsize;
+xdrproc_t xdrobj;
+.fi
+.ft R
+.IP
+Like
+.B xdr_reference(\|)
+execpt that it serializes
+.SM NULL
+pointers, whereas
+.B xdr_reference(\|)
+does not. Thus,
+.B xdr_pointer(\|)
+can represent
+recursive data structures, such as binary trees or
+linked lists.
+.br
+.if t .ne 15
+.LP
+.ft B
+.nf
+.sp .5
+void
+xdrrec_create(xdrs, sendsize, recvsize, handle, readit, writeit)
+\s-1XDR\s0 *xdrs;
+u_int sendsize, recvsize;
+char *handle;
+int (*readit) (\|), (*writeit) (\|);
+.fi
+.ft R
+.IP
+This routine initializes the
+.SM XDR
+stream object pointed to by
+.IR xdrs .
+The stream's data is written to a buffer of size
+.IR sendsize ;
+a value of zero indicates the system should use a suitable
+default.
+The stream's data is read from a buffer of size
+.IR recvsize ;
+it too can be set to a suitable default by passing a zero
+value.
+When a stream's output buffer is full,
+.I writeit
+is called. Similarly, when a stream's input buffer is empty,
+.I readit
+is called. The behavior of these two routines is similar to
+the
+system calls
+.B read
+and
+.BR write ,
+except that
+.I handle
+is passed to the former routines as the first parameter.
+Note: the
+.SM XDR
+stream's
+.I op
+field must be set by the caller.
+.IP
+Warning: this
+.SM XDR
+stream implements an intermediate record stream.
+Therefore there are additional bytes in the stream
+to provide record boundary information.
+.br
+.if t .ne 9
+.LP
+.ft B
+.nf
+.sp .5
+xdrrec_endofrecord(xdrs, sendnow)
+\s-1XDR\s0 *xdrs;
+int sendnow;
+.fi
+.ft R
+.IP
+This routine can be invoked only on
+streams created by
+.BR xdrrec_create(\|) .
+The data in the output buffer is marked as a completed
+record,
+and the output buffer is optionally written out if
+.I sendnow
+is non-zero.
+This routine returns one if it succeeds, zero
+otherwise.
+.br
+.if t .ne 8
+.LP
+.ft B
+.nf
+.sp .5
+xdrrec_eof(xdrs)
+\s-1XDR\s0 *xdrs;
+int empty;
+.fi
+.ft R
+.IP
+This routine can be invoked only on
+streams created by
+.BR 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.
+.br
+.if t .ne 3
+.LP
+.ft B
+.nf
+.sp .5
+xdrrec_skiprecord(xdrs)
+\s-1XDR\s0 *xdrs;
+.fi
+.ft R
+.IP
+This routine can be invoked only on
+streams created by
+.BR xdrrec_create(\|) .
+It tells the
+.SM 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.
+.br
+.if t .ne 11
+.LP
+.ft B
+.nf
+.sp .5
+xdr_reference(xdrs, pp, size, proc)
+\s-1XDR\s0 *xdrs;
+char **pp;
+u_int size;
+xdrproc_t proc;
+.fi
+.ft R
+.IP
+A primitive that provides pointer chasing within structures.
+The parameter
+.I pp
+is the address of the pointer;
+.I size
+is the
+.I sizeof
+the structure that
+.I *pp
+points to; and
+.I proc
+is an
+.SM XDR
+procedure that filters the structure
+between its C form and its external representation.
+This routine returns one if it succeeds, zero otherwise.
+.IP
+Warning: this routine does not understand
+.SM NULL
+pointers.
+Use
+.B xdr_pointer(\|)
+instead.
+.br
+.if t .ne 10
+.LP
+.ft B
+.nf
+.sp .5
+xdr_setpos(xdrs, pos)
+\s-1XDR\s0 *xdrs;
+u_int pos;
+.fi
+.ft R
+.IP
+A macro that invokes the set position routine associated with
+the
+.SM XDR
+stream
+.IR xdrs .
+The parameter
+.I pos
+is a position value obtained from
+.BR xdr_getpos(\|) .
+This routine returns one if the
+.SM XDR
+stream could be repositioned,
+and zero otherwise.
+.IP
+Warning: it is difficult to reposition some types of
+.SM XDR
+streams, so this routine may fail with one
+type of stream and succeed with another.
+.br
+.if t .ne 8
+.LP
+.ft B
+.nf
+.sp .5
+xdr_short(xdrs, sp)
+\s-1XDR\s0 *xdrs;
+short *sp;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.B short
+integers and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 10
+.LP
+.ft B
+.nf
+.sp .5
+void
+xdrstdio_create(xdrs, file, op)
+\s-1XDR\s0 *xdrs;
+\s-1FILE\s0 *file;
+enum xdr_op op;
+.fi
+.ft R
+.IP
+This routine initializes the
+.SM XDR
+stream object pointed to by
+.IR xdrs .
+The
+.SM XDR
+stream data is written to, or read from, the Standard
+.B I/O
+stream
+.IR file .
+The parameter
+.I op
+determines the direction of the
+.SM XDR
+stream (either
+.BR \s-1XDR_ENCODE\s0 ,
+.BR \s-1XDR_DECODE\s0 ,
+or
+.BR \s-1XDR_FREE\s0 ).
+.IP
+Warning: the destroy routine associated with such
+.SM XDR
+streams calls
+.B fflush(\|)
+on the
+.I file
+stream, but never
+.BR fclose(\|) .
+.br
+.if t .ne 9
+.LP
+.ft B
+.nf
+.sp .5
+xdr_string(xdrs, sp, maxsize)
+\s-1XDR\s0
+*xdrs;
+char **sp;
+u_int maxsize;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C strings and
+their
+corresponding external representations.
+Strings cannot be longer than
+.IR maxsize .
+Note:
+.I sp
+is the address of the string's pointer.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 8
+.LP
+.ft B
+.nf
+.sp .5
+xdr_u_char(xdrs, ucp)
+\s-1XDR\s0 *xdrs;
+unsigned char *ucp;
+.fi
+.ft R
+.IP
+A filter primitive that translates between
+.B unsigned
+C characters and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 9
+.LP
+.ft B
+.nf
+.sp .5
+xdr_u_int(xdrs, up)
+\s-1XDR\s0 *xdrs;
+unsigned *up;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.B unsigned
+integers and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 7
+.LP
+.ft B
+.nf
+.sp .5
+xdr_u_long(xdrs, ulp)
+\s-1XDR\s0 *xdrs;
+unsigned long *ulp;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.B "unsigned long"
+integers and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 7
+.LP
+.ft B
+.nf
+.sp .5
+xdr_u_short(xdrs, usp)
+\s-1XDR\s0 *xdrs;
+unsigned short *usp;
+.fi
+.ft R
+.IP
+A filter primitive that translates between C
+.B "unsigned short"
+integers and their external representations.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 16
+.LP
+.ft B
+.nf
+.sp .5
+xdr_union(xdrs, dscmp, unp, choices, dfault)
+\s-1XDR\s0 *xdrs;
+int *dscmp;
+char *unp;
+struct xdr_discrim *choices;
+bool_t (*defaultarm) (\|); /* may equal \s-1NULL\s0 */
+.fi
+.ft R
+.IP
+A filter primitive that translates between a discriminated C
+.B union
+and its corresponding external representation.
+It first
+translates the discriminant of the union located at
+.IR dscmp .
+This discriminant is always an
+.BR enum_t .
+Next the union located at
+.I unp
+is translated. The parameter
+.I choices
+is a pointer to an array of
+.B xdr_discrim(\|)
+structures.
+Each structure contains an ordered pair of
+.RI [ value , proc ].
+If the union's discriminant is equal to the associated
+.IR value ,
+then the
+.I proc
+is called to translate the union. The end of the
+.B xdr_discrim(\|)
+structure array is denoted by a routine of value
+.SM NULL\s0.
+If the discriminant is not found in the
+.I choices
+array, then the
+.I defaultarm
+procedure is called (if it is not
+.SM NULL\s0).
+Returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 6
+.LP
+.ft B
+.nf
+.sp .5
+xdr_vector(xdrs, arrp, size, elsize, elproc)
+\s-1XDR\s0 *xdrs;
+char *arrp;
+u_int size, elsize;
+xdrproc_t elproc;
+.fi
+.ft R
+.IP
+A filter primitive that translates between fixed-length
+arrays
+and their corresponding external representations. The
+parameter
+.I arrp
+is the address of the pointer to the array, while
+.I size
+is the element count of the array. The parameter
+.I elsize
+is the
+.I sizeof
+each of the array's elements, and
+.I elproc
+is an
+.SM XDR
+filter that translates between
+the array elements' C form, and their external
+representation.
+This routine returns one if it succeeds, zero otherwise.
+.br
+.if t .ne 5
+.LP
+.ft B
+.nf
+.sp .5
+xdr_void(\|)
+.fi
+.ft R
+.IP
+This routine always returns one.
+It may be passed to
+.SM RPC
+routines that require a function parameter,
+where nothing is to be done.
+.br
+.if t .ne 10
+.LP
+.ft B
+.nf
+.sp .5
+xdr_wrapstring(xdrs, sp)
+\s-1XDR\s0 *xdrs;
+char **sp;
+.fi
+.ft R
+.IP
+A primitive that calls
+.B "xdr_string(xdrs, sp,\s-1MAXUN.UNSIGNED\s0 );"
+where
+.B
+.SM MAXUN.UNSIGNED
+is the maximum value of an unsigned integer.
+.B xdr_wrapstring(\|)
+is handy because the
+.SM RPC
+package passes a maximum of two
+.SM XDR
+routines as parameters, and
+.BR xdr_string(\|) ,
+one of the most frequently used primitives, requires three.
+Returns one if it succeeds, zero otherwise.
+.SH SEE ALSO
+.BR rpc (3)
+.LP
+The following manuals:
+.RS
+.ft I
+eXternal Data Representation Standard: Protocol Specification
+.br
+eXternal Data Representation: Sun Technical Notes
+.ft R
+.br
+.IR "\s-1XDR\s0: External Data Representation Standard" ,
+.SM RFC1014, Sun Microsystems, Inc.,
+.SM USC-ISI\s0.