Name-to-Address Mapping

Name-to-address mapping enables an application to obtain the address of a service on a specified host independent of the transport used. Name-to-address mapping consists of the following interfaces:

netdir_getbyname(3NSL)

Maps the host and service name to a set of addresses

netdir_getbyaddr(3NSL)

Maps addresses into host and service names

netdir_free(3NSL)

Frees structures allocated by the name-to-address translation routines

taddr2uaddr(3NSL)

Translates an address and returns a transport-independent character representation of the address

uaddr2taddr(3NSL)

The universal address is translated into a netbuf structure

netdir_options(3NSL)

Interfaces to transport-specific capabilities such as the broadcast address and reserved port facilities of TCP and UDP

netdir_perror(3NSL)

Displays a message stating why one of the routines that map name-to-address failed on stderr.

netdir_sperror(3NSL)

Returns a string containing the error message stating why one of the routines that map name-to-address failed.

The first argument of each routine points to a netconfig(4) structure that describes a transport. The routine uses the array of directory-lookup library paths in the netconfig(4) structure to call each path until the translation succeeds.

The name-to-address libraries are described in Table 10-1. The routines that are described in Using the Name-to-Address Mapping Routines are defined in the netdir(3NSL) man page.

Table 10-1 Name-to-Address Libraries

straddr.so Library

Name–to–address translation files for the straddr.so library are created by the system administrator. The system administrator also maintains these translation files. The straddr.so files are /etc/net/transport-name/hosts and /etc/net/transport-name/services. transport-name is the local name of the transport that accepts string addresses, which is specified in the network ID field of the /etc/netconfig file. For example, the host file for ticlts would be /etc/net/ticlts/hosts, and the service file for ticlts would be /etc/net/ticlts/services.

Most string addresses do not distinguish between host and service. However, separating the string into a host part and a service part is consistent with other transports. The /etc/net/transport-name/hosts file contains a text string that is assumed to be the host address, followed by the host name:

joyluckaddr

joyluck

carpediemaddr

carpediem

thehopaddr

thehop

pongoaddr

pongo

The /etc/net/transport-name/services file contains service names followed by strings that identify the service address:

rpcbind    rpc
listen    serve

The routines create the full-string address by concatenating the host address, a period (.), and the service address. For example, the address of the listen service on pongo is pongoaddr.serve.

When an application requests the address of a service on a particular host on a transport that uses this library, the host name must be in /etc/net/transport/hosts. The service name must be in /etc/net/transport/services. If either name is missing, the name-to-address translation fails.

Using the Name-to-Address Mapping Routines

This section is an overview of the mapping routines that are available for use. The routines return or convert the network names to their respective network addresses. Note that netdir_getbyname(3NSL), netdir_getbyaddr(3NSL), and taddr2uaddr(3NSL) return pointers to data that must be freed by calls to netdir_free(3NSL).

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

netdir_getbyname(3NSL) maps the host and service name specified in service to a set of addresses that are consistent with the transport identified in nconf. The nd_hostserv and nd_addrlist structures are defined in the netdir(3NSL) 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(3NSL) with each netconfig(4) structure returned by either getnetpath(3NSL) or getnetconfig(3NSL).

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

netdir_getbyaddr(3NSL) maps addresses into host and service names. The interface 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(3NSL).

void netdir_free(void *ptr, int struct_type);

The netdir_free(3NSL) routine frees structures allocated by the name-to-address translation routines. The parameters can take the values that are shown in the following table.

Table 10-2 netdir_free(3NSL) Routines

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

taddr2uaddr(3NSL) translates the address pointed to by addr and returns a transport-independent character representation of the address. This character representation is called a universal address. The value that is given in nconf specifies the transport for which the address is valid. The universal address can be freed by free(3C).

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(const struct netconfig *config,
          const int option, const int fildes, char *point_to_args);

netdir_options(3NSL) provides interfaces to transport-specific capabilities, such as the broadcast address and reserved port facilities of TCP and UDP. The value of nconf specifies a transport, while option specifies the transport-specific action to take. The value in option might disable consideration of the value in fd. The fourth argument points to operation-specific data.

The following table shows the values used for option.

Table 10-3 Values for netdir_options

The netdir_perror(3NSL) routine displays a message stating why one of the routines that map name-to-address failed on stderr.

void netdir_perror(char *s);

The netdir_sperror(3NSL) routine returns a string containing the error message stating why one of the routines that map name-to-address failed.

char *netdir_sperror(void);

The following example shows network selection and name-to-address mapping.

Example 10-1 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> addresses 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);