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


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


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);


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(4) 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

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

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.

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

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

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:


The specific actions of each option follow.

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.

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.

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.

Used to take a ``local address'' such as a 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

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,
and the call is successful m_uaddr is set to an
address such as 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.


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.


See attributes(5) for descriptions of the following attributes:

|MT-Level | Safe |


gethostname(3C), getnetconfig(3NSL), getnetpath(3NSL), netconfig(4),

February 14, 2015 NETDIR(3NSL)