NAME

xdr, xdr_accepted_reply, xdr_array, xdr_authunix_parms, xdr_bool, xdr_bytes, xdr_callhdr, xdr_callmsg, xdr_char, xdr_destroy, xdr_double, xdr_enum, xdr_float, xdr_free, xdr_functions, xdr_getpos, xdr_hyper, xdr_inline, xdr_int, xdr_long, xdr_longlong_t, xdrmem_create, xdr_opaque, xdr_pointer, xdrrec_create, xdrrec_endofrecord, xdrrec_eof, xdrrec_skiprecord, xdr_reference, xdr_setpos, xdr_short, xdrstdio_create, xdr_string, xdr_u_char, xdr_u_hyper, xdr_u_int, xdr_u_long, xdr_u_longlong_t, xdr_u_short, xdr_union, xdr_vector, xdr_void, xdr_wrapstring − 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 ONC remote procedure calls are transmitted using these routines. 

#include <rpc/xdr.h>

xdr_array(xdrs, arrp, sizep, maxsize, elsize, elproc)
XDR ∗xdrs;
char ∗∗arrp;
u_int ∗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;
u_int ∗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 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(xdrs)
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. 

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 otherwise. 

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). 

u_int
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. 

xdr_hyper(xdrs, hp)
XDR ∗xdrs;
longlong_t ∗hp;

A filter primitive that translates between C long integers and their external representations. (The typedef longlong_t is defined as long in the file <rpc/types.h>, which is included from the file <rpc/xdr.h>.) This routine will translate all 8 bytes of data to the XDR stream. Note that this differentiates this routine from xdr_long in that they both take a pointer to a long as an argument, while xdr_long only translates 4 bytes of data to the XDR stream. This routine returns one if it succeeds, zero otherwise. 

The xdr_hyper routine is functionally equivalent to the xdr_longlong_t routine. 

See the following section that explains the differences between xdr_long and xdr_hyper. 

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: 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. 

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 otherwise. 

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. 

Note that the argument lp must be the C language type long. The amount of data encoded to the XDR stream is only 4 bytes (not the full 8 bytes of data represented by the C long type). This is because in the context of XDR streams a long type is considered to be 4 bytes. When data is encoded from the XDR stream, 4 bytes will be received from the XDR stream; the xdr_long interface then then sign extends the high order 4 bytes of the C long type. 

Prior to serializing the data on the ENCODE side the xdr_long performs a validity check to insure that the value represents a valid 32-bit signed number.  This involves determining that the signed value is no less than the most negative 32-bit signed quantity (which is the hexadecimal value 0x80000000) and no greater than the most positive 32-bit signed quantity (which is the hexadecimal value 0x7fffffff).  If the value pointed to by the argument lp is not within this range the xdr_long interface returns an error. 

To translate the full 8 bytes of a C long, use the xdr_hyper interface. 

See the following section that explains the differences between xdr_long and xdr_hyper. 

xdr_longlong_t(xdrs, hp)
XDR ∗xdrs;
longlong_t ∗hp;

A filter primitive that translates between C long integers and their external representations. (The typedef longlong_t is defined as long in the file <rpc/types.h>, which is included from the file <rpc/xdr.h>.) This routine will translate all 8 bytes of data to the XDR stream. Note that this differentiates this routine from xdr_long in that they both take a pointer to a long as an argument, while xdr_long only translates 4 bytes of data to the XDR stream. This routine returns one if it succeeds, zero otherwise. 

The xdr_longlong_t routine is functionally equivalent to the xdr_hyper routine. 

See the following section that explains the differences between xdr_long and xdr_hyper. 

void
xdrmem_create(xdrs, addr, size, op)
XDR ∗xdrs;
char ∗addr;
u_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). 

xdr_opaque(xdrs, cp, cnt)
XDR ∗xdrs;
char ∗cp;
u_int 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;
u_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(xdrs, sendsize, recvsize, handle, readit, writeit)
XDR ∗xdrs;
u_int sendsize, recvsize;
char ∗handle;
int (∗readit) (), (∗writeit) ();

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 and write, except that handle is passed to the former routines as the first parameter.  The XDR stream’s op field must be set by the caller.  sendsize and recvsize should be multiples of 4. 

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 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 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 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. 

xdrrec_skiprecord(xdrs)
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. 

xdr_reference(xdrs, pp, size, proc)
XDR ∗xdrs;
char ∗∗pp;
u_int size;
xdrproc_t proc;

A primitive that provides pointer chasing within structures.  The parameter 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(xdrs, pos)
XDR ∗xdrs;
u_int pos;

A macro that invokes the set position routine associated with the XDR stream xdrs. The parameter 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. 

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 pointed to by xdrs. 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 XDR_ENCODE, XDR_DECODE, or XDR_FREE). 

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;
u_int maxsize;

A filter primitive that translates between C strings and their corresponding external representations.  Strings cannot be longer than maxsize. sp is the address of the string’s pointer. While decoding if ∗sp is NULL , the necessary storage is allocated to hold this null−terminated string and ∗sp is set to point to this. This storage can be freed by using xdr_free() (see xdr_simple(3) ). 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_hyper(xdrs, uhp)
XDR ∗xdrs;
u_longlong_t ∗uhp;

A filter primitive that translates between C unsigned long integers and their external representations.  (The typedef u_longlong_t is defined as unsigned long in the file <rpc/types.h>, which is included from the file <rpc/xdr.h>.) This routine will translate all 8 bytes of data to the XDR stream. Note that this differentiates this routine from xdr_u_long in that they both take a pointer to an unsigned long as an argument, while xdr_u_long only translates 4 bytes of data to the XDR stream. This routine returns one if it succeeds, zero otherwise. 

The xdr_u_hyper routine is functionally equivalent to the xdr_u_longlong_t routine. 

See the following section that explains the differences between xdr_long and xdr_hyper. 

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. 

Prior to serializing the data on the ENCODE side the xdr_u_long performs a validity check to insure that the value represents a valid 32-bit unsigned number.  This involves determining that the unsigned value is no greater than the largest 32-bit unsigned quantity (which is the hexadecimal value 0xffffffff).  If the value pointed to by the argument ulp is not within this range, the xdr_u_long interface returns an error. 

For DECODE operations, the 32-bit unsigned value is sign extended into the 64-bit unsigned long referred to by the argument ulp. 

Note that this routine actually translates 4 bytes of the data to or from the XDR stream. Refer to the description of xdr_long for a more detailed explanation. 

xdr_u_longlong_t(xdrs, uhp)
XDR ∗xdrs;
u_longlong_t ∗uhp;

A filter primitive that translates between C unsigned long integers and their external representations.  (The typedef u_longlong_t is defined as unsigned long in the file <rpc/types.h>, which is included from the file <rpc/xdr.h>.) This routine will translate all 8 bytes of data to the XDR stream. Note that this differentiates this routine from xdr_u_long in that they both take a pointer to an unsigned long as an argument, while xdr_u_long only translates 4 bytes of data to the XDR stream. This routine returns one if it succeeds, zero otherwise. 

The xdr_u_longlong routine is functionally equivalent to the xdr_u_hyper routine. 

See the following section that explains the differences between xdr_long and xdr_hyper. 

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 enum_t.  Next the union located at unp is translated.  The parameter 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 any of the values, the associated proc is called to translate the union.  The end of the xdr_discrim() structure array is denoted by a NULL pointer. 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. 

xdr_vector(xdrs, arrp, size, elsize, elproc)
XDR ∗xdrs;
char ∗arrp;
u_int 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 array, while size is the element count of the array.  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_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 xdr_string(xdrs, sp,MAXUNSIGNED ); where MAXUNSIGNED is the maximum value of an unsigned integer.  xdr_wrapstring() is handy because the RPC package passes a maximum of two XDR routines as parameters, and xdr_string(), one of the most frequently used primitives, requires three.  sp is the address of the pointer to the string. While decoding if ∗sp is NULL , the necessary storage is allocated to hold the null −terminated string and ∗sp is set to point to this. This storage can be freed by using xdr_free() (see xdr_simple(3) ). Returns one if it succeeds, zero otherwise. 

Differences Between xdr_long and xdr_hyper Routines

On DEC OSF/1 platforms, the C programming language and the XDR routines apply different conventions to the definitions of the long data type. 

On DEC OSF/1 platforms, the C programming language applies the following conventions for int and long data types:

Data Type	bits	bytes
int	32	4 bytes
long	64	8 bytes

The XDR routines apply the following conventions:

Data Type	bits	bytes
int	32	4 bytes
long	32	4 bytes
hyper	64	8 bytes

The xdr_long() and xdr_u_long() interfaces serialize 4 bytes of data. The xdr_hyper() and xdr_u_hyper() serialize 8 bytes of data. 

On DEC OSF/1 systems, the second argument to both xdr_long and xdr_hyper must be either a pointer or of the C language type long (8 bytes).  When xdr_hyper is called with a parameter that points to a long all 8-bytes are serialized.  In contrast, when xdr_long is called with a parameter that points to a long only the low order 4-bytes are serialized. 

When calling xdr_long on the DECODE operation, the upper 4-bytes of the long are sign extended in accordance with the high order bit of the lower 4-byte quantity. This is necessary to maintain the XDR convention of xdr_long serializing 4-bytes. 

If you want all 8-bytes to be serialized, use the xdr_hyper interface. 

The xdr_longlong_t and the xdr_u_longlong_t perform the same function as the xdr_hyper and the xdr_u_hyper interfaces respectively. 

RELATED INFORMATION

rpc(3)