GETNAMEINFO(3XNET) X/Open Networking Services Library Functions

NAME

getnameinfo - get name information

SYNOPSIS

cc [ flag ... ] file ... -lxnet [ library ... ]
#include <sys/socket.h>
#include <netdb.h>

int getnameinfo(const struct sockaddr *restrict sa, socklen_t salen,
char *restrict node, socklen_t nodelen, char *restrict service,
socklen_t servicelen, unsigned flags);

DESCRIPTION

The getnameinfo() function translates a socket address to a node name
and service location, all of which are defined as in
getaddrinfo(3XNET).


The sa argument points to a socket address structure to be
translated. If the socket address structure contains an IPv4-mapped
IPv6 address or an IPv4-compatible IPv6 address, the implementation
extracts the embedded IPv4 address and lookup the node name for that
IPv4 address.


If the node argument is non-NULL and the nodelen argument is non-
zero, then the node argument points to a buffer able to contain up to
nodelen characters that receives the node name as a null-terminated
string. If the node argument is NULL or the nodelen argument is zero,
the node name is not returned. If the node's name cannot be located,
the numeric form of the node's address is returned instead of its
name.


If the service argument is non-NULL and the servicelen argument is
non-zero, then the service argument points to a buffer able to
contain up to servicelen bytes that receives the service name as a
null-terminated string. If the service argument is NULL or the
servicelen argument is zero, the service name is not returned. If the
service's name cannot be located, the numeric form of the service
address (for example, its port number) is returned instead of its
name.


The flags argument is a flag that changes the default actions of the
function. By default the fully-qualified domain name (FQDN) for the
host is returned, but:

o If the flag bit NI_NOFQDN is set, only the node name
portion of the FQDN is returned for local hosts.

o If the flag bit NI_NUMERICHOST is set, the numeric form of
the host's address is returned instead of its name, under
all circumstances.

o If the flag bit NI_NAMEREQD is set, an error is returned
if the host's name cannot be located.

o If the flag bit NI_NUMERICSERV is set, the numeric form of
the service address is returned (for example, its port
number) instead of its name, under all circumstances.

o If the flag bit NI_DGRAM is set, this indicates that the
service is a datagram service (SOCK_DGRAM). The default
behavior assumes that the service is a stream service
(SOCK_STREAM).

RETURN VALUES

A 0 return value for getnameinfo() indicates successful completion; a
non-zero return value indicates failure. The possible values for the
failures are listed in the ERRORS section.


Upon successful completion, getnameinfo() returns the node and
service names, if requested, in the buffers provided. The returned
names are always null-terminated strings.

ERRORS

The getnameinfo() function will fail if:

EAI_AGAIN
The name could not be resolved at this time. Future
attempts might succeed.


EAI_BADFLAGS
The flags argument had an invalid value.


EAI_FAIL
A non-recoverable error occurred.


EAI_FAMILY
The address family was not recognized or the address
length was invalid for the specified family.


EAI_MEMORY
There was a memory allocation failure.


EAI_NONAME
The name does not resolve for the supplied
parameters. NI_NAMEREQD is set and the host's
name cannot be located, or both nodename and servname
were NULL.


EAI_SYSTEM
A system error occurred. The error code can be found
in errno.

USAGE

If the returned values are to be used as part of any further name
resolution (for example, passed to getaddrinfo()), applications
should provide buffers large enough to store any result possible on
the system.


Given the IPv4-mapped IPv6 address "::ffff:1.2.3.4", the
implementation performs a lookup as if the socket address structure
contains the IPv4 address "1.2.3.4".

ATTRIBUTES

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


+--------------------+-----------------+
| ATTRIBUTE TYPE | ATTRIBUTE VALUE |
+--------------------+-----------------+
|Interface Stability | Standard |
+--------------------+-----------------+
|MT-Level | MT-Safe |
+--------------------+-----------------+

SEE ALSO

sockaddr(3SOCKET), gai_strerror(3XNET), getaddrinfo(3XNET),
getservbyname(3XNET), socket(3XNET), attributes(7), standards(7)

NOTES

The IPv6 unspecified address ("::") and the IPv6 loopback address
("::1") are not IPv4-compatible addresses. If the address is the IPv6
unspecified address ("::"), a lookup is not performed, and the
EAI_NONAME error is returned.


The two NI_NUMERICxxx flags are required to support the -n flag that
many commands provide.


The NI_DGRAM flag is required for the few AF_INET and AF_INET6 port
numbers (for example, [512,514]) that represent different services
for UDP and TCP.

November 1, 2003 GETNAMEINFO(3XNET)