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Name

xdr_complex, xdr_array, xdr_bytes, xdr_opaque, xdr_pointer, xdr_reference, xdr_string, xdr_union, xdr_vector, xdr_wrapstring - library routines for external data representation

MT-Level

Safe

Description

XDR library routines allow C programmers to describe complex data structures in a machine-independent fashion. Protocols such as remote procedure calls (RPC ) use these routines to describe the format of the data. These routines are the XDR library routines for complex data structures. They require the creation of XDR stream (see xdr_create(3N) ).

Routines

See rpc(3N) for the definition of the XDR data structure. Note that any buffers passed to the XDR routines must be properly aligned. It is suggested that malloc() be used to allocate these buffers or that the programmer insure that the buffer address is divisible evenly by four.

#include <rpc/xdr.h>

bool_t xdr_array(XDR *xdrs, caddr_t *arrp, u_int *sizep, const u_int maxsize, const u_int elsize, const xdrproc_t elproc);

xdr_array()
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 size of each of the array’s elements, and elproc is an XDR routine that translates between the array elements’ C form and their external representation. If *aarp is null when decoding, xdr_array() allocates memory and *aarp points to it. This routine returns TRUE if it succeeds, FALSE otherwise.

bool_t xdr_bytes(XDR *xdrs, char **sp, u_int *sizep, const u_int maxsize);

xdr_bytes()
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. If *sp is null when decoding, xdr_bytes() allocates memory and *sp points to it. This routine returns TRUE if it succeeds, FALSE otherwise.

bool_t xdr_opaque(XDR *xdrs, caddr_t cp, const u_int cnt);

xdr_opaque()
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 TRUE if it succeeds, FALSE otherwise.

bool_t xdr_pointer(XDR *xdrs, char **objpp, u_int objsize, const 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. If *objpp is null when decoding, xdr_pointer() allocates memory and *objpp points to it.

bool_t xdr_reference(XDR *xdrs, caddr_t *pp, u_int size, const xdrproc_t proc);

xdr_reference()
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 translates the structure between its C form and its external representation. If *pp is null when decoding, xdr_reference() allocates memory and *pp points to it. This routine returns 1 if it succeeds, 0 otherwise.
Warning:
this routine does not understand NULL pointers. Use xdr_pointer() instead.

bool_t xdr_string(XDR *xdrs, char **sp, const u_int maxsize);

xdr_string()
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. If *sp is null when decoding, xdr_string() allocates memory and *sp points to it. This routine returns TRUE if it succeeds, FALSE otherwise. Note: xdr_string() can be used to send an empty string (""), but not a NULL string.

bool_t xdr_union(XDR *xdrs, enum_t *dscmp, char *unp, const struct xdr_discrim *choices, const xdrproc_t (*defaultarm);

xdr_union()
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 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 TRUE if it succeeds, FALSE otherwise.

bool_t xdr_vector(XDR *xdrs, char *arrp, const u_int size, const u_int elsize, const xdrproc_t elproc);

xdr_vector()
translates between fixed-length arrays and their corresponding external representations. The parameter arrp is the address of the pointer to 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 routine that translates between the array elements’ C form and their external representation. This routine returns TRUE if it succeeds, FALSE otherwise.

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

A routine that calls
xdr_string(xdrs, sp, maxuint); where maxuint is the maximum value of an unsigned integer.
Many routines,
such as xdr_array(), xdr_pointer(), and xdr_vector() take a function pointer of type xdrproc_t(), which takes two arguments. xdr_string(), one of the most frequently used routines, requires three arguments, while xdr_wrapstring() only requires two. For these routines, xdr_wrapstring() is desirable. This routine returns TRUE if it succeeds, FALSE otherwise.

See Also

rpc(3N) , xdr_admin(3N) , xdr_create(3N) , xdr_simple(3N)

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