Transport Interfaces Programming Guide

Using the Name-to-Address Mapping Routines

This section provides an overview of what routines are available to use. The routines return or convert the network names to their respective network addresses. Note that netdir_getbyname(), netdir_getbyaddr(), and taddr2uaddr() return pointers to data that must be freed by calls to netdir_free().

 int netdir_getbyname(struct netconfig *nconf,
   struct nd_hostserv *service,
   struct nd_addrlist **addrs);

netdir_getbyname() maps the host and service name specified in service to a set of addresses consistent with the transport identified in nconf. The nd_hostserv and nd_addrlist structures are defined in the netdir(3N) man page. A pointer to the addresses is returned in addrs.

To find all addresses of a host and service (on all available transports), call netdir_getbyname() with each netconfig structure returned by either getnetpath() or getnetconfig().

int netdir_getbyaddr(struct netconfig *nconf,
	   struct nd_hostservlist **service,
	   struct netbuf *netaddr);

netdir_getbyaddr() maps addresses into host and service names. The function is called with an address in netaddr and returns a list of host-name and service-name pairs in service. The nd_hostservlist structure is defined in netdir(3N).

void netdir_free(void *ptr, int struct_type);

The netdir_free() routine frees structures allocated by the name-to-address translation routines. The parameters can take the values shown in Table 4-3.

Table 4-3 netdir_free() Routines


struct_type	ptr
`ND_HOSTSERV`	Pointer to an `nd_hostserv` structure
`ND_HOSTSERVLIST`	Pointer to an `nd_hostservlist` structure
`ND_ADDR`	Pointer to a `netbuf` structure
`ND_ADDRLIST`	Pointer to an `nd_addrlist` structure

char *taddr2uaddr(struct netconfig *nconf, struct netbuf *addr);

taddr2uaddr() translates the address pointed to by addr and returns a transport-independent character representation of the address ("universal address"). nconf specifies the transport for which the address is valid. The universal address can be freed by free().

struct netbuf *uaddr2taddr(struct netconfig *nconf, char *uaddr);

The "universal address" pointed to by uaddr is translated into a netbuf structure; nconf specifies the transport for which the address is valid.

int netdir_options(struct netconfig *nconf, int option, int fd,

	char *point_to_args);

netdir_options() interfaces to transport-specific capabilities (such as the broadcast address and reserved port facilities of TCP and UDP). nconf specifies a transport. option specifies the transport-specific action to take. fd might or might not be used depending upon the value of option. The fourth argument points to operation-specific data.

Table 4-4 shows the values used for option:

Table 4-4 Values for netdir_options


Option	Description
`ND_SET_BROADCAST`	Sets the transport for broadcast (if the transport supports broadcast)
`ND_SET_RESERVEDPORT`	Lets the application bind to a reserved port (if allowed by the transport)
`ND_CHECK_RESERVEDPORT`	Verifies that an address corresponds to a reserved port (if the transport supports reserved ports)
`ND_MERGEADDR`	Transforms a locally meaningful address into an address to which client hosts can connect

netdir_perror() displays the message stating why one of the name-to-address mapping routines failed on stderr.

void netdir_perror(char *s);

netdir_sperror() returns a string containing the error message stating why one of the name-to-address mapping routines failed.

char *netdir_sperror(void);

Example 4-7 shows network selection and name-to-address mapping.

Example 4-7 Network Selection and Name-to-Address Mapping

#include <netconfig.h>
#include <netdir.h>
#include <sys/tiuser.h>

struct nd_hostserv nd_hostserv;   /* host and service information
*/
struct nd_addrlist *nd_addrlistp; /* addresses for the service */
struct netbuf *netbufp;           /* the address of the service */
struct netconfig *nconf;          /* transport information*/
int i;                            /* the number of addresses */
char *uaddr;                      /* service universal address */
void *handlep;                    /* a handle into network selection
/*
 * Set the host structure to reference the "date"
 * service on host "gandalf"
 */
nd_hostserv.h_host = "gandalf";
nd_hostserv.h_serv = "date";
/*
 * Initialize the network selection mechanism.
 */
if ((handlep = setnetpath()) == (void *)NULL) {
   nc_perror(argv[0]);
   exit(1);
}
/*
 * Loop through the transport providers.
 */
while ((nconf = getnetpath(handlep)) != (struct netconfig *)NULL)
{
   /*
    * Print out the information associated with the
    * transport provider described in the "netconfig"
    * structure.
    */
   printf("Transport provider name: %s\n", nconf->nc_netid);
   printf("Transport protocol family: %s\n", nconf->nc_protofmly);
   printf("The transport device file: %s\n", nconf->nc_device);
   printf("Transport provider semantics: ");
	   switch (nconf->nc_semantics) {
   case NC_TPI_COTS:
      printf("virtual circuit\n");
      break;
   case NC_TPI_COTS_ORD:
      printf("virtual circuit with orderly release\n");
      break;

   case NC_TPI_CLTS:
      printf("datagram\n");
      break;
   }
   /*
    * Get the address for service "date" on the host
    * named "gandalf" over the transport provider
    * specified in the netconfig structure.
    */
   if (netdir_getbyname(nconf, &nd_hostserv, &nd_addrlistp) != ND_OK) {
   printf("Cannot determine address for service\n");
      netdir_perror(argv[0]);
      continue;
   }
   printf("<%d> address of date service on gandalf:\n",
      nd_addrlistp->n_cnt);
   /*
    * Print out all addresses for service "date" on
    * host "gandalf" on current transport provider.
    */
   netbufp = nd_addrlistp->n_addrs;
   for (i = 0; i < nd_addrlistp->n_cnt; i++, netbufp++) {
   uaddr = taddr2uaddr(nconf,netbufp);
   printf("%s\n",uaddr);
   free(uaddr);
   }
   	netdir_free( nd_addrlistp, ND_ADDRLIST );

}
endnetconfig(handlep);