Opaque Data

In some protocols, handles are passed from a server to client. The client passes the handle back to the server at some later time. Handles are never inspected by clients; they are obtained and submitted. That is to say, handles are opaque. The xdr_opaque() primitive is used for describing fixed sized, opaque bytes.

bool_t
xdr_opaque(xdrs, p, len)
   XDR *xdrs;
   char *p;
   u_int len;

The parameter p is the location of the bytes; len is the number of bytes in the opaque object. By definition, the actual data contained in the opaque object are not machine portable.

In SunOS/SVR4 there is another routine for manipulating opaque data. This routine, xdr_netobj sends counted opaque data, much like xdr_opaque(). Example A-10 illustrates the syntax of xdr_netobj().

Example A-10 xdr_netobj Routine

struct netobj {
	u_int   n_len;
	char    *n_bytes;
};
typedef struct netobj netobj;

bool_t
xdr_netobj(xdrs, np)
	XDR *xdrs;
	struct netobj *np;

The xdr_netobj() routine is a filter primitive that translates between variable length opaque data and its external representation. The parameter np is the address of the netobj structure containing both a length and a pointer to the opaque data. The length may be no more than MAX_NETOBJ_SZ bytes. This routine returns TRUE if it succeeds, FALSE otherwise.