NETDIR(3NSL) Networking Services Library Functions NETDIR(3NSL)

NAME

netdir, netdir_getbyname, netdir_getbyaddr, netdir_free,
netdir_options, taddr2uaddr, uaddr2taddr, netdir_perror,
netdir_sperror, netdir_mergeaddr - generic transport name-to-address
translation

SYNOPSIS

cc [ flag... ] file... -lnsl [ library...]
#include <netdir.h>

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


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


void netdir_free(void *ptr, int struct_type);


int netdir_options(struct netconfig *config, int option, int fildes,
char *pointer_to_args);


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


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


void netdir_perror(char *s);


char *netdir_sperror(void);

DESCRIPTION

The netdir functions provide a generic interface for name-to-address
mapping that will work with all transport protocols. This interface
provides a generic way for programs to convert transport specific
addresses into common structures and back again. The netconfig
structure, described on the netconfig(5) manual page, identifies the
transport.


The netdir_getbyname() function maps the machine name and service
name in the nd_hostserv structure to a collection of addresses of the
type understood by the transport identified in the netconfig
structure. This function returns all addresses that are valid for
that transport in the nd_addrlist structure. The nd_hostserv
structure contains the following members:

char *h_host; /* host name */
char *h_serv; /* service name */


The nd_addrlist structure contains the following members:

int n_cnt; /* number of addresses */
struct netbuf *n_addrs;


The netdir_getbyname() function accepts some special-case host names.
The host names are defined in <netdir.h>. The currently defined host
names are:

HOST_SELF
Represents the address to which local programs
will bind their endpoints. HOST_SELF differs
from the host name provided by gethostname(3C),
which represents the address to which remote
programs will bind their endpoints.


HOST_ANY
Represents any host accessible by this transport
provider. HOST_ANY allows applications to
specify a required service without specifying a
particular host name.


HOST_SELF_CONNECT
Represents the host address that can be used to
connect to the local host.


HOST_BROADCAST
Represents the address for all hosts accessible
by this transport provider. Network requests to
this address are received by all machines.


All fields of the nd_hostserv structure must be initialized.


To find the address of a given host and service on all available
transports, call the netdir_getbyname() function with each struct
netconfig structure returned by getnetconfig(3NSL).


The netdir_getbyaddr() function maps addresses to service names. The
function returns service, a list of host and service pairs that yield
these addresses. If more than one tuple of host and service name is
returned, the first tuple contains the preferred host and service
names:

struct nd_hostservlist {
int *h_cnt; /* number of hostservs found */
struct hostserv *h_hostservs;
}


The netdir_free() structure is used to free the structures allocated
by the name to address translation functions. The ptr parameter
points to the structure that has to be freed. The parameter
struct_type identifies the structure:

struct netbuf ND_ADDR
struct nd_addrlist ND_ADDRLIST
struct hostserv ND_HOSTSERV
struct nd_hostservlist ND_HOSTSERVLIST


The netdir_options() function is used to do all transport-specific
setups and option management. fildes is the associated file
descriptor. option, fildes, and pointer_to_args are passed to the
netdir_options() function for the transport specified in config.
Currently four values are defined for option:

ND_SET_BROADCAST
ND_SET_RESERVEDPORT
ND_CHECK_RESERVEDPORT
ND_MERGEADDR


The specific actions of each option follow.

ND_SET_BROADCAST
Sets the transport provider up to allow
broadcast if the transport supports
broadcast. fildes is a file descriptor into
the transport, that is, the result of a
t_open of /dev/udp. pointer_to_args is not
used. If this completes, broadcast
operations can be performed on file
descriptor fildes.


ND_SET_RESERVEDPORT
Allows the application to bind to a reserved
port if that concept exists for the
transport provider. fildes is an unbound
file descriptor into the transport. If
pointer_to_args is NULL, fildes is bound to
a reserved port. If pointer_to_args is a
pointer to a netbuf structure, an attempt is
made to bind to any reserved port on the
specified address.


ND_CHECK_RESERVEDPORT
Used to verify that the address corresponds
to a reserved port if that concept exists
for the transport provider. fildes is not
used. pointer_to_args is a pointer to a
netbuf structure that contains the address.
This option returns 0 only if the address
specified in pointer_to_args is reserved.


ND_MERGEADDR
Used to take a ``local address'' such as a
0.0.0.0 TCP address and return a ``real
address'' to which client machines can
connect. fildes is not used. pointer_to_args
is a pointer to a struct nd_mergearg which
has the following members:

char s_uaddr; /* server's universal address */
char c_uaddr; /* client's universal address */
char m_uaddr; /* the result */

If s_uaddr is an address such as
0.0.0.0.1.12, and the call is successful
m_uaddr is set to an address such as
192.11.109.89.1.12. For most transports,
m_uaddr is identical to s_uaddr.


If a transport provider does not support an option, netdir_options
returns -1 and the error message can be printed through
netdir_perror() or netdir_sperror().


The taddr2uaddr() and uaddr2taddr() functions support translation
between universal addresses and TLI type netbufs. The taddr2uaddr()
function takes a struct netbuf data structure and returns a pointer
to a string that contains the universal address. It returns NULL if
the conversion is not possible. This is not a fatal condition as some
transports do not support a universal address form.


The free() function is used to free the universal address returned by
the taddr2uaddr() function.


The uaddr2taddr() function is the reverse of the taddr2uaddr()
function. It returns the struct netbuf data structure for the given
universal address and NULL on failure.


The netdir_perror() function prints an error message in standard
output that states the cause of a name-to-address mapping failure.
The error message is preceded by the string given as an argument.


The netdir_sperror() function returns a string with an error message
that states the cause of a name-to-address mapping failure.

RETURN VALUES

The netdir_sperror() function returns a pointer to a buffer which
contains the error message string. The buffer is overwritten on each
call. In multithreaded applications, this buffer is implemented as
thread-specific data.


The netdir_getbyname(), netdir_getbyaddr(), and netdir_options()
functions return 0 on success and a non-zero value on failure.

ATTRIBUTES

See attributes(7) for descriptions of the following attributes:


+---------------+-----------------+
|ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+---------------+-----------------+
|MT-Level | Safe |
+---------------+-----------------+

SEE ALSO

gethostname(3C), getnetconfig(3NSL), getnetpath(3NSL), netconfig(5),
attributes(7)

February 14, 2015 NETDIR(3NSL)