xdr(NS)                        6 January 1993                        xdr(NS)


 Name

    xdr - library routines for external data representation

 Syntax 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.


    xdr_array(xdrs, arrp, sizep, maxsize, elsize, elproc)
    XDR *xdrs;
    char **arrp;
    uint *sizep, maxsize, elsize;
    xdrproc_t elproc;

    a filter primitive that translates between variable-length arrays and
    their corresponding external representations.  The parameter 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 parameter 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.


    xdr_bool(xdrs, bp)
    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.


    xdr_bytes(xdrs, sp, sizep, maxsize)
    XDR *xdrs;
    char **sp;
    uint *sizep, maxsize;

    a filter primitive that translates between counted byte strings and their
    external representations.  The parameter 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.


    xdr_char(xdrs, cp)
    XDR *xdrs;
    char *cp;

    a filter primitive that translates between C characters and their exter-
    nal representations.  This routine returns one if it succeeds; zero oth-
    erwise.

    _________________________________________________________________________
       NOTE  Encoded characters are not packed and occupy 4 bytes each.
       For arrays of characters, it is worthwhile to consider xdrbytes,
       xdropaque, or xdrstring.
    _________________________________________________________________________


    void
    xdr_destroy(xdrs)
    XDR *xdrs;

    a macro that invokes the destroy routine associated with the XDR stream,
    xdrs.  Destruction usually involves freeing private data structures asso-
    ciated with the stream.  Using xdrs after invoking xdrdestroy is unde-
    fined.


    xdr_double(xdrs, dp)
    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.


    xdr_enum(xdrs, ep)
    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.


    xdr_float(xdrs, fp)
    XDR *xdrs;
    float *fp;

    a filter primitive that translates between C floats and their external
    representations.  This routine returns one if it succeeds; zero other-
    wise.


    void
    xdr_free(proc, objp)
    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).
    _________________________________________________________________________


    uint
    xdr_getpos(xdrs)
    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(xdrs, len)
    XDR *xdrs;
    int len;

    a macro that invokes the in-line 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 that
    pointer is cast to long *.

    _________________________________________________________________________
       WARNING  xdrinline 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.
    _________________________________________________________________________


    xdr_int(xdrs, ip)
    XDR *xdrs;
    int *ip;

    a filter primitive that translates between C integers and their external
    representations.  This routine returns one if it succeeds; zero other-
    wise.


    xdr_long(xdrs, lp)
    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(xdrs, addr, size, op)
    XDR *xdrs;
    char *addr;
    uint size;
    enum xdr_op op;

    This routine initializes the XDR stream object to which xdrs points.  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 XDRENCODE, XDRDECODE, or XDRFREE).


    xdr_opaque(xdrs, cp, cnt)
    XDR *xdrs;
    char *cp;
    uint cnt;

    a filter primitive that translates between fixed size opaque data and its
    external representation.  The parameter, cp, is the address of the opaque
    object and cnt is its size in bytes.  This routine returns one if it
    succeeds; zero otherwise.


    xdr_pointer(xdrs, objpp, objsize, xdrobj)
    XDR *xdrs;
    char **objpp;
    uint objsize;
    xdrproc_t xdrobj;

    like xdrreference in that it XDR's pointers, but the difference is that
    xdrpointer serializes NULL pointers, whereas xdrreference does not.
    Thus xdrpointer can XDR recursive data structures, such as binary trees
    or linked lists, correctly, whereas xdrreference will fail.


    void
    xdrrec_create(xdrs, sendsize, recvsize, handle, readit, writeit)
    XDR *xdrs;
    uint sendsize, recvsize;
    char *handle;
    int (*readit)(), (*writeit)();

    This routine initializes the XDR stream object to which xdrs points.  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
    UNIX system calls read and write, except that handle is passed to the
    former routines as the first parameter.  Note that the XDR stream's op
    field must be set by the caller.

    _________________________________________________________________________
       WARNING  This XDR stream implements an intermediate record stream.
       Therefore, there are additional bytes in the stream to provide
       record boundary information.
    _________________________________________________________________________


    xdrrec_endofrecord(xdrs, sendnow)
    XDR *xdrs;
    int sendnow;

    This routine can be invoked only on streams created by xdrreccreate.
    The data in the output buffer is marked as a completed record, and the
    output buffer is optionally written out if sendnow is non-zero.  This
    routine returns one if it succeeds; zero otherwise.


    xdrrec_eof(xdrs)
    XDR *xdrs;
    int empty;

    This routine can be invoked only on streams created by xdrreccreate.
    After consuming the rest of the current record in the stream, this rou-
    tine returns one if the stream has no more input; zero otherwise.


    xdrrec_skiprecord(xdrs)
    XDR *xdrs;

    This routine can be invoked only on streams created by xdrreccreate.  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.


    xdr_reference(xdrs, pp, size, proc)
    XDR *xdrs;
    char **pp;
    uint size;
    xdrproc_t proc;

    a primitive that provides pointer-chasing within structures.  The parame-
    ter pp is the address of the pointer; size is the sizeof the structure to
    which *pp points, 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
       xdrpointer instead.
    _________________________________________________________________________


    xdr_setpos(xdrs, pos)
    XDR *xdrs;
    uint pos;

    a macro that invokes the set position routine associated with the XDR
    stream, xdrs.  The parameter pos is a position value obtained from
    xdrgetpos.  This routine returns one if the XDR stream could be reposi-
    tioned; 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.
    _________________________________________________________________________


    xdr_short(xdrs, sp)
    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(xdrs, file, op)
    XDR *xdrs;
    FILE *file;
    enum xdr_op op;

    This routine initializes the XDR stream object to which xdrs points.  The
    XDR stream data is written to or read from the standard I/O stream, file.
    The parameter op determines the direction of the XDR stream (either
    XDRENCODE, XDRDECODE, or XDRFREE).

    _________________________________________________________________________
       WARNING  the destroy routine associated with such XDR streams calls
       fflush on the file stream, but never fclose.
    _________________________________________________________________________


    xdr_string(xdrs, sp, maxsize)
    XDR *xdrs;
    char **sp;
    uint maxsize;

    a filter primitive that translates between C strings and their corre-
    sponding external representations.  Strings cannot be longer than max-
    size.  Note that sp is the address of the string's pointer.  This routine
    returns one if it succeeds; zero otherwise.


    xdr_u_char(xdrs, ucp)
    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.


    xdr_u_int(xdrs, up)
    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.


    xdr_u_long(xdrs, ulp)
    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.


    xdr_u_short(xdrs, usp)
    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.


    xdr_union(xdrs, dscmp, unp, choices, dfault)
    XDR *xdrs;
    int *dscmp;
    char *unp;
    struct xdr_discrim *choices;
    bool_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 enumt.  Next the union located at unp is translated.  The parameter,
    choices, is a pointer to an array of xdrdiscrim structures.  Each struc-
    ture contains an ordered pair of [value, proc].  If the union's discrim-
    inant is equal to the associated value, then the proc is called to
    translate the union.  The end of the xdrdiscrim 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).  This routine returns one if it succeeds; zero otherwise.


    xdr_vector(xdrs, arrp, size, elsize, elproc)
    XDR *xdrs;
    char *arrp;
    uint size, elsize;
    xdrproc_t elproc;

    a filter primitive that translates between fixed-length arrays and their
    corresponding external representations.  The parameter arrp is the
    address of the pointer to the array and size is is the element count of
    the array.  The parameter, elsize, is the sizeof each of the array's ele-
    ments and elproc is an XDR filter that translates between the array ele-
    ments' C form and their external representation.  This routine returns
    one if it succeeds; zero otherwise.


    xdr_void()

    This routine always returns one.  It may be passed to RPC routines that
    require a function parameter, where nothing is to be done.


    xdr_wrapstring(xdrs, sp)
    XDR *xdrs;
    char **sp;

    a primitive that calls xdrstring(xdrs, sp, LASTUNSIGNED); where LASTUN-
    SIGNED is the maximum value of an unsigned integer.  xdrwrapstring is
    useful because the RPC package passes a maximum of two XDR routines as
    parameters, and xdrstring, one of the most frequently used primitives,
    requires three.  This routine returns one if it succeeds; zero otherwise.

 See also

    rpc(NS)