netdir(3N)

NAME

netdir: netdir_getbyname(), netdir_getbyaddr(), netdir_free(), netdir_options(), taddr2uaddr(), uaddr2taddr(), netdir_perror(), netdir_sperror() — generic transport name-to-address translation

SYNOPSIS

#include <netdir.h>

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

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

void netdir_free(void *ptr, const int struct_type);

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

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

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

void netdir_perror(char *s);

char *netdir_sperror(void);

DESCRIPTION

These routines 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() routine 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 routine 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;

netdir_getbyname() 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() (see gethostname(2)), 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 will be 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() routine with each struct netconfig structure returned by getnetconfig(). (See getnetconfig(3N)).

The netdir_getbyaddr() routine maps addresses to service names. This routine returns service, a list of host and service pairs that would yield this address. If more than one tuple of host and service name is returned, then 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() function is used to free the structures allocated by the name to address translation routines. 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 universal address returned by taddr2uaddr() should be freed by free().

The netdir_options() routine 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() routine 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 taddr2uaddr() and uaddr2taddr() routines support translation between universal addresses and TLI type netbufs. The taddr2uaddr() routine 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 may not support a universal address form.

uaddr2taddr() is the reverse of taddr2uaddr(). It returns the struct netbuf data structure for the given universal address.

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 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 (i.e., the result of a t_open of /dev/udp). pointer_to_args is not used. If this completes, broadcast operations may 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 will be bound to a reserved port. If pointer_to_args is a pointer to a netbuf structure, an attempt will be 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 addr */

char c_uaddr; /* client's universal addr */

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.

MULTITHREAD USAGE

Thread Safe:: Yes
Cancel Safe:: Yes
Fork Safe:: No
Async-cancel Safe:: No
Async-signal Safe:: No

These functions can be called safely in a multithreaded environment. They may be cancellation points in that they call functions that are cancel points.

In a multithreaded environment, these functions are not safe to be called by a child process after fork() and before exec(). These functions should not be called by a multithreaded application that supports asynchronous cancellation or asynchronous signals.

RETURN VALUE

The netdir_perror() routine prints an error message on the standard output stating why one of the name-to-address mapping routines failed. The error message is preceded by the string given as an argument.

The netdir_sperror() returns a pointer to a buffer which contains an error message string stating why one of the name-to-address mapping routines failed. This buffer is overwritten on each call. In multithreaded applications, this buffer is implemented as thread-specific data.

The netdir_getbyaddr() function returns 0 on success and a non-zero value on failure.

netdir(3N)

Technical documentation

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NAME

SYNOPSIS

DESCRIPTION

MULTITHREAD USAGE

RETURN VALUE

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